Brake Service Philosophy

Brake Service Philosophy

When someone gets a brake service done, the last thing they want is to come back pre-maturely. Many mechanics complete a job, only to have a customer return a few days later with a complaints. The good news is, there are a few simple ground rules that can help prevent this from ever happening. Whether you are a full time mechanic or a newbie, holding to just a few rules can help ensure that any of your work is done well.

Service Philosophies

As with most jobs, there are several ways to ensure a quality brake service is provided. We strongly suggest abiding by these 2 specific philosophies.

1: Take your time and do it right

2: Do what you can to prevent pre-mature re-visits.

Mechanic working on tire

Doing the Brake Service Right

But it is absolutely essential that you know what you are doing. Always make sure you have the necessary knowledge to complete the job, then take the time to do it right. Try to think of it this way: If you take an extra 10 minutes to do it correctly, you’ll save yourself the time and headache of having to redo the entire brake service later. By ensuring a job well done, you also ensure the happiness of customers and the trust you build with them will remain strong.

One way to ensure you know all necessary steps to complete your brake service, is to do research. All across the internet you can find tutorials for specific car models and issues. By taking advantage of these resources, you will not only do the job right, but you’ll be able to complete it more quickly as well. Some common websites/mechanics to learn from are Eric the Car Guy, various Youtube channels or check out our videos. You can even social media groups like Mechanic Mafia to interact with more experienced Mechanics. Always remember, when in doubt, search it out.

Smiling Mechanic

Preventing a Re-do

As you work on a vehicle, try to think of everything you can do to help keep it out of the shop. This is why taking the time to do job right is so important. As you keep a sharp eye for detail and refrain from rushing, you are more likely to catch other issues. Don’t be afraid to bring up any new issues with the customer. Doing so will benefit you by providing more work, and further building a bridge of trust between you and your customer. By always striving to keep cars out of the shop, you can provide the best service possible.


Brake System Troubleshooting Tips THINK SAFETY!! Don’t attempt working on your brakes if you aren’t experienced with brake systems. These troubleshooting tips assume a person is familiar and equipped with jacking and supporting safety stands, brake tools, seal and...

Effective Slider Service – Fighting the Elements

Problem: Corrosion causing premature pad wear Cause: Moisture intrusion causing caliper housing to corrode Solution: It is a common belief that if the caliper hardware looks like the caliper pictured in Figure 35.1 that no service is necessary. In other words, if...

Hub Removal on Late Model Honda Trapped Rotors

Problem: Removal of hub assembly on late model Honda vehicles. Cause: Rust and corrosion form between the hub assembly and the steering knuckle. This corrosion bonds the two parts together. Solution: NOTE: While it is possible to perform the following steps on the...

Can You Reduce Automotive Comebacks To Just 1%?

Does your shop have too many comebacks?    Common reasons for comebacks  All auto shops have had exceptions to the rule, but generally comebacks can fall into one of three categories.  Miscommunication between Techs, Service Advisors and Customers  Inadequate...

Rotor & Drum Specification Accuracy

Problem: Not all of the specifications provided are 100% accurate. Cause: Consolidated specification sources often make mistakes when compiling the information from the various manufacturers. Solution: Verifying accuracy of rotor and drum specifications. A close look...

What is Friction Break In and How To Do It

Problem: Brake noise complaints or lack of stopping power shortly after brake job Cause: Not performing a proper break-in after performing brake service Solution: Once the job has been completed, a test drive should be performed. The test drive has two goals. The...

Removing Broken Bleeder Screws

Problem: Broken Bleeder Screw Cause: Failure to follow proper loosening procedures Solution: Every good technician has to bail themselves or someone else out of a jam once in a while. In brake service an example of this would be how to deal with a broken bleeder. It’s...

How to Determine Intermittent Low Brake Pedal on Vehicles equipped with Delco VI ABS

Figure 46.1 Problem: Intermittent low brake pedal on vehicles equipped with Delco VI ABS (see figure 46.1) Cause: EMB (electromagnetic brake) or ESB (expansion spring brake) not holding motor in homed position. See more info section Solution: This condition is usually...

How to Diagnose Excessive Disc Thickness Variation (DTV)

Problem: Determining if one or more rotors has excessive DTV Cause: The average specification for disc thickness variation (DTV) is .0005” (See Figure 24.1). The maximum allowable variation in thickness on a rotor is 5 ten thousandths of an inch. This dimension is too...

How to Diagnose Premature Pad Wear on RWD and FWD

We are continuing our discussion on premature pad wear. This week we will be discussing pad wear on rear wheel drive and front wheel drive vehicles. Here is a link to our post from last week on premature inboard pad wear. Problem: One or more brake pads are wearing...
Copper Check Press Release

Copper Check Press Release

Copper check

Lower Pricing

The same industry standard brake fluid copper test you are used to from Phoenix Systems, but now at a lower price.

Finds Broken Brake Fluid

No other brake fluid test finds broken brake fluid faster than Copper Check. Copper Check is reliable, repeatable and 100% accurate.

revolutionary copper check finds broken brake fluid fast

Copper Check, a revolutionary diagnostic test strip used to determine when to change a vehicle’s brake fluid, is soon to be available to the automotive aftermarket. This test strip helps automotive service technicians quickly find and replace corrosive brake fluid.   

(PRWEB) August 26, 2020 – Automotive diagnostic technology has come far in past decades, but even the modern technician is still left to guess on when brake fluid should or should not be changed. Copper Check puts a stop to this guessing by providing an industry standard copper corrosion test strip that reveals the age and condition of DOT 3, 4 and 5.1 brake fluid. With the introduction of Copper Check to the automotive aftermarket, technicians can now find broken brake fluid in less than 60 seconds.  

Copper Check uses medical grade colorimetric test strip technology to discover the copper ion contamination within brake fluid. Nearly 50% of the used vehicles on the road today have enough copper corrosion contamination to no longer pass a DOT corrosion test. Copper corrosion within brake fluid is created when oxygen and heat are introduced through the master cylinder cap, rubber hoses, and overheated calipers. Brake lines are coated with copper inside to make them seamless, problem is, copper is the first metal to corrode. Once copper ion levels reach 200 ppm they begin to attack iron components and cause frozen calipers, malfunctioning ABS units, and leaking master cylinders.

Copper Check is ideal for service centers who want to utilize the most up to date technology when diagnosing a vehicle brake system. This test is repeatable, reliable and 100% accurate. In today’s ever changing environment it is vital to provide accurate proof for the services a shop recommends. 

Copper Check will be available to purchase early Q4 of 2020. Please contact Jeremiah at to obtain more information about pricing and availability.


About Copper Check 

Copper Check is owned by the leading authority in brake fluid testing, Phoenix Systems. Phoenix Systems pioneered the technology of using copper ions to determine when to change brake fluid. Copper corrosion testing brake fluid is included in the MAP/AMRA EUICS service codes and trusted by the majority of all large chain service centers and owner operated shops in the United States and Canada.


download press release

CLICK HERE to download Copper Check press release and 300dpi images.

Are you selling a “Phony Flush?”

Are you selling a “Phony Flush?”

Are you selling a “Phony Flush?”

Changing Brake Fluid is an important service for the safety and longevity of our vehicles. However, it can be difficult to determine when the right time is to change the fluid. Many service centers offer a “Phony Flush” by recommending an un-needed service.  Or they send customers home without properly diagnosing worn out brake fluid which does need to be changed.

Common unethical methods used to validate a need for changing brake fluid:

Looks Dirty

Rubber brake lines and fittings will often discolor brake fluid in a brand new vehicle. Changing brake fluid based upon color is too subjective and unethical. This includes using bottles, trays and paper to show the color of the brake fluid.

Smells Bad

I don’t believe many of us know what brake fluid should or should’nt smell like. The smell is surely not a good reason to change brake fluid.

Has Moisture

Moisture does not equal boiling point. Most brake fluid with up to 3% moisture will Not fail a boiling point test. There is No standard for changing brake fluid based upon moisture content. Moisture pens are known to fail brand new brake fluid.

Because I Say So

We realize there are master mechanics with an unlimited amount of knowledge, however science can now take the subjectivity out of a recommendation. It is time to get up to speed with today’s testing technology and make a proper recommendation.

Valid and ethical reasons to change brake fluid:


Different vehicle manufacturers have different intervals for changing brake fluid. Most Ford, Chrysler and GM models have No interval for brake fluid, while most European and many Asian manufacturers have an interval of somewhere between 15K to 24K miles. Making a recommendation to change brake fluid based upon an OEM service interval is a valid reason for service.

Boiling Point

Moisture does not equal boiling point. The best method for testing the boiling point of brake fluid is to use a boiling point analyzer. The DOT FMVSS standards state that DOT 3 brake fluid should not boil below 284° F. On average less than 4 % of vehicles on the road will have a boiling point below 284° F.

Copper Testing

Using copper testing technology to determine when to change brake fluid has become the most used and recognized standard to determine when to change brake fluid. Up to 50% of vehicles on the road today have enough copper corrosion in their brake fluid to keep them from passing the DOT FMVSS corrosion test. Testing brake fluid copper levels is part of the AMRA EUICS standards and helps a shop comply with the Automotive Repair Act of California. Copper testing brake fluid is also part of the inspection process for Firestone, GoodYear, Monro, Tire Kingdom, Jiffy Lube, Pep Boys, AAA and many other service centers.

Recommending a brake fluid service based upon copper content in brake fluid will:

 #1 Deliver the most ethical and legal method to determine when to change brake fluid.

#2 Provide a much greater level of opportunity than any other test.

#3 Give a better experience for the customer to see and understand why they should change their brake fluid.

Click Here to learn more about copper testing brake fluid.




Phoenix Systems LLC   435.673.0777


New BrakeStrip Plus provides 2x the service opportunities and helps service centers deliver a safer and more reliable vehicle to their customer.

  1. GEORGE, Utah – With a desire to deliver more value to their customers, Phoenix Systems announces the retirement of its popular BrakeStrip at the end of 2018. The new and improved BrakeStrip Plus will take the place of BrakeStrip beginning January 2019.

BrakeStrip Plus is an innovative test strip which features a brake fluid test pad on one end and coolant test pads on the opposite end. The new strip will provide service centers 2x the service opportunities and help deliver more reliable and safer vehicles.

“We developed BrakeStrip Plus to give users the ability to determine the condition of both brake fluid and coolant in less than 90 seconds,” said Jeremiah Terry, Manager at Phoenix Systems. “BrakeStrip Plus reveals brake fluid and coolant problems before they occur and helps keep a vehicle functioning at its best. Our goal is to offer BrakeStrip Plus without increasing the price.”

For the past eighteen years, over 100 million brake fluid test strips have been used to diagnose worn out brake fluid and have produced over $3 billion in brake fluid service opportunities for service centers worldwide. The new BrakeStrip Plus will increase this tradition of service and is protected by multiple patents and patents pending. 

For more information about BrakeStrip Plus, visit

Click Here to download 300dpi product images.

About Phoenix Systems

Founded in 1994, Phoenix Systems is committed to providing cutting-edge tools and technology for the automotive undercar industry.  The company has pioneered many new technologies resulting in more than a dozen patents to change the way vehicles are serviced. BrakeStrip with brake fluid copper testing technology is the industry leading brake fluid test.  The company’s Reverse Bleeding Technology is available in a variety of brake bleeder systems used by both auto care professionals and do-it-yourselfers. For more information, write to 1076 East Commerce Dr #400, St. George, UT 84790; call 435.673.0777; or visit   


Brake System Troubleshooting Tips


Don’t attempt working on your brakes if you aren’t experienced with brake systems. These troubleshooting tips assume a person is familiar and equipped with jacking and supporting safety stands, brake tools, seal and bearing inspection techniques, shoe, drum, rotor inspections, and knows how to adjust, fill and bleed brakes.

AUTOMOTIVE HYDRAULIC BRAKE SYSTEMS: The car that you drive has hydraulic brakes. The brakes in your car consist of a “pump” (master cylinder) that you operate with your foot (brake pedal) connected by brake line tubing to a hydraulic cylinder (wheel cylinder) that pushes the brake shoes against the brake drum or disc brake caliper and rotor. The harder you push the pump with your foot, the more pressure you generate, thus the harder the brakes shoes are forced against the rotor or drum to stop you. These systems use brake fluid to do the work.

TRAILER SURGE BRAKE HYDRAULIC SYSTEMS: Surge Brakes on a trailer are also hydraulic brakes and work very much the same-with one difference. In a trailer surge brake system, the “pump” is located on the trailer-as part of the hitch assembly. This special sliding hitch assembly is called a surge brake actuator. It has a master cylinder built into it, but instead of using your foot to operate it, it uses the weight and the momentum of the trailer to do the pumping.

Here’s how Surge Brakes work: Picture the truck and trailer traveling down the road at 45 mph. The truck and trailer are traveling at the same speed, and the truck is pulling the trailer. When you apply your brakes in the truck to slow down, the truck is no longer pulling the trailer, and in fact the opposite occurs, and the trailer now tries to push the truck (thus the name “surge brake”). This energy causes the surge actuator to slide, or compress. This compression operates the master cylinder, causing it to build brake fluid pressure. The harder you brake the tow vehicle, the harder the trailer tries to push the truck. The harder the trailer tries to push the truck, the more pressure the surge actuator builds up. The more pressure created, the harder the trailer brakes work. Even though the brakes on the trailer are not connected directly to the brake pedal in your truck, what you do with your foot in the truck is indirectly telling the trailer brakes what to do.

There is a restrictor orifice built into a surge brake system. Its job is to dampen the response of the trailer brakes, and here’s why: Let’s say you were towing a trailer downhill, and were applying steady brake pressure on the truck brakes to maintain speed (to prevent the rig from gaining downhill speed). The trailer is “pushing” against the truck-causing the trailer brakes to apply. Now the trailer wants to slow down, but in the process of doing so, it causes the truck to begin “pulling” the trailer again, and the brakes on the trailer release. The minute the trailer brakes release, the trailer begins pushing on the decelerating truck again, causing the brakes to apply. This on-off-on-off-on-off pulsing trailer brake application is not desirable. The restrictor orifice dampens the on-off pulsing effect by slowing down the travel of brake fluid from master cylinder to wheel cylinder and back. Many people don’t know the orifice is there, or don’t understand its purpose.

Emergency Breakaway System: Federal law requires all trailers to have a “breakaway” system. If your trailer ever came loose from the tow vehicle while underway, the breakaway system will activate the brakes on the trailer to slow it down and stop it-hopefully preventing an accident. The breakaway system usually consists of a cable or chain that is attached to the tow vehicle on one end, and a lever/latch assembly on the trailer surge actuator. Since the chain or cable is attached to the tow vehicle, if the trailer come loose from the truck the cable pulls the lever energizing the trailer brakes. A latch mechanism keeps the lever in the energized mode even if the breakaway chain or cable is ripped away by the separation of the truck and trailer. The lever mechanically pushes the master cylinder piston to generate emergency brake fluid pressure, and the latch assures that the pressure is maintained until the latch is disengaged manually by using tools. The breakaway system can be helpful in performing tests and even for bleeding the brakes, so understand it and use it to help you keep your brakes in top shape.


  • Brakes don’t seem to work at all
  • Brakes work on some wheels, but not on others
  • Brakes operate in reverse when you don’t want them to.
  • Brakes won’t release after a sudden stop.

Brakes don’t seem to work at all: First, do a simple test to see what’s going on. Find the breakaway chain or cable, and pull it until it latches in the locked position. An easy way to do this is to find something that you can use as a lever. Jack up all the tires and wheels that have brakes. Manually rotate the tires/wheels using your hands in the forward travel direction and see if they lock up. Check each wheel that has brakes, as it is possible for some of the brakes to work, but not all of them.

Important: The surge actuator slide must be pulled and pushed (full stroke) to create pressure and bleed air from system when making repairs or tests. The slide will offer resistance due to the orifice and shock absorbers, so expect to stroke it with effort.

Got Brake Fluid? If none of the brakes work, remove the master cylinder cap and look inside to see if there is any brake fluid in the reservoir. If not, we recommend you rebuild or replace the master cylinder and wheel cylinders. The absence of brake fluid-especially for any length of time allows corrosion to form in the entire system-including the steel brake line tubing. Corrosion is the enemy as it creates rough surfaces inside the wheel and master cylinder bores destroying the piston seals. Corrosion will also flow around with the brake fluid and eventually will plug up the orifice. You can test for corrosion contaminants by using Phoenix Systems BrakeStrip Brake Fluid Test Strip and you can stop corrosion by adding a 1oz bottle of Phoenix Systems Brake Shot to your master cylinder. In some cases it is possible to hone the cylinder bores, and replace the seals to rebuild them, but usually the bores are pitted beyond repair. Missing brake fluid means you have a leak. You must find the source of the leak and fix it. Don’t just add brake fluid and go back on the road

Inspect the brakes at the wheel.: If brake fluid exists in the system, a process of elimination is needed to find why the brakes aren’t working. It is possible the brake shoes are worn completely out, or the drum brakes are greatly out of adjustment. We recommend you remove the brake drum and visually inspect the shoe linings. While the brake drum is off, have an assistant manually operate the brake system using the breakaway lever. Have them work the surge actuator from “off to on” and closely watch the wheel cylinder to see if the push rod is moving in and out. If not, the wheel cylinder may be frozen, or the master cylinder is not pumping, or the orifice may be clogged.

INSPECT/TEST MASTER CYLINDER: To test the master cylinder, remove the brake line or hose from the rear of the master cylinder located on the surge actuator. DO NOT remove the orifice fitting that the hose or brake line attaches to. This orifice is very, very small-perhaps as small as the diameter of one strand of hair on your head and can easily clog with debris. Engage the master cylinder using the lever to see if it forces a fine stream of brake fluid thru the orifice fitting. If not, remove the orifice fitting, and then test it again by engaging the master cylinder. If it now pumps fluid, hold the orifice up to a strong source of light and see if you can see thru it. If not, it is clogged and is preventing the brake fluid from reaching the wheel cylinders. Unclog or replace the orifice, reinstall it in the master cylinder, then test again. (If the clog is on the master cylinder side of the orifice fitting, it prevents pressurized brake fluid from operating the brakes. If the clog is on the wheel cylinder side of the orifice fitting, it creates problems when the brakes try to release, because it prevents the flow of brake fluid back to the master cylinder reservoir) If the master cylinder won’t pump in all of these tests, it needs replacement. If the master cylinder does pump, proceed to the next step. (Note: it is possible for a master cylinder to pump fluid at a low pressure, but could have internal piston seal leakage that prevents it from building up adequate pressure to operate the trailer brakes.)

TEST THE BRAKE LINE FOR BLOCKAGE: Remove the brake line from a wheel cylinder, and have an assistant pump the master cylinder using the lever. Look at the end of the brake line you just disconnected. If brake fluid is being pumped thru the line, the master cylinder, orifice and brake line seem to be working, so assume the wheel cylinder(s) should be suspect at this point.

Bad Wheel Cylinder? If you have proven the master cylinder is working, the orifice isn’t clogged, and the brake tubing is clear, the wheel cylinder should operate when the master cylinder is engaged using the lever. If it doesn’t, the wheel cylinder most likely has a frozen piston. Although you really can’t bench test the wheel cylinder, you can peel back and remove the rubber boot to look for rust or corrosion that would prove a stuck piston. If you have a stuck piston, replace the wheel cylinder with a new one. It’s a very inexpensive part.

Brakes work on some wheels, but not on others: If the brakes work on even one wheel, it would indicate the master cylinder and orifice are ok. The wheels that don’t work will have one of the following problems that you’ve already learned how to test and fix:

  1. Frozen piston in wheel cylinder or disc caliper.
  2. Worn out or misadjusted brake linings.
  3. Blocked or kinked brake line tubing to that wheel.
  4. Leaking wheel cylinder that has brake shoes and drum soaked with brake fluid.
  5. Leaking wheel seal that has brake shoes and drum soaked with grease.
  6. Severely worn or glazed brake drum or rotor.
  7. Air in the fluid lines. (Bleeding required. Use a Phoenix Systems Reverse Bleeder for best results.)

Brakes work in reverse when you don’t want them to: The principle of surge brake operation says that the brakes will apply whenever the trailer pushes against the truck while in motion. The reverse side effect of this is that in reverse, the truck can push against the trailer also causing the brakes to apply. If for instance you were backing up on soft grass or mud, (or uphill) the trailer really doesn’t want to back up easily, but must be forced by the truck. This is enough to apply the trailer brakes. The harder you try to force the trailer, the harder the trailer brakes apply. Trailer surge brake manufacturers deal with this in different ways:

  1. Use Free Backing brake assemblies on the axle that allow the brakes to disengage only in reverse. This is the most common method.
  2. Use an electric solenoid valve that allows the brake fluid to bypass back to the reservoir while in reverse. The electric valve is wired to the reverse lights on the tow vehicle. This ensures the brakes only bypass in reverse. This is the second most common method, usually seen on boat trailers more than other types of trailers. This system usually uses a 5pin flat plug trailer wiring connector instead of a standard 4 pin electrical connector.
  3. Use a mechanical pin to prevent the surge actuator from compressing and building up pressure. This pin is supposed to be used when backing up only, but if left installed can prevent the brakes from operating-even if traveling in forward. This is a very uncommon method.
  4. Use a manual valve that bypasses brake fluid to the reservoir. It requires the operator to manually open the bypass valve when in reverse, but to remember to close the valve before towing in forward motion. This is also a very uncommon method.

Brakes won’t release after a sudden stop: This is not a very common problem, but it can occur. What causes this is the brake fluid pressure cannot release and travel back to the reservoir due to a mechanical or hydraulic problem. Check the following items to identify the problem.

  1. The orifice is clogged on the output side of the orifice. The clog is acting as a check valve allowing the fluid to come out of the fitting, but won’t let it go back in.
  2. The surge actuator slide assembly has mechanically jammed (stuck) in the compressed position, and will not allow the master cylinder piston to return to it’s relaxed position preventing the fluid from returning to the reservoir and releasing the brakes.
  3. The piston in the master cylinder is stuck in the compressed position preventing the internal return spring from pushing the piston to its parked position-allowing brake fluid to return to the reservoir and releasing the brakes.
  4. The steel push rod that pushes the master cylinder piston is adjusted too long or is bent and will not allow the master cylinder piston to return to it’s relaxed position allowing the fluid to return to the reservoir and releasing the brakes.

Boat trailers in particular work in a very harsh environment. A boat trailer axle is literally submerged underwater when launching or loading a boat. Fresh water is bad enough, but salt water is extra tough on the brakes, bearings, seals, drums, rotors, etc. Purchase and install a flush kit on your drum brakes. This kit allows you to hook up a garden hose to the brakes and flush the salt water out with clean tap water extending the life of the brakes and running gear on a boat trailer. Boat trailers don’t get used as much as other types of trailers, making them even more prone to brake problems due to rotted seals, corrosion, etc.

A very simple test to perform before you travel on a trip, or after the trailer has been sitting for a while is to hook the trailer to your tow vehicle as you would normally. Engage the brakes while parked by pulling on the breakaway system cable or chain until it latches. Next, place the tow vehicle in gear, and begin to slowly drive forward. You should feel the trailer brakes working and offering very stiff resistance. Don’t forget to unlatch the breakaway system before using the trailer normally.

Heater 101

Heater 101

Heater 101

Winter is here a little earlier than expected and with that comes the chance of your heater system not functioning properly. We have all been there. The first real cold morning comes along, and we patiently wait for our car to warm up, so we can turn on the much-welcomed heater and BAM, cold air. Something within our heater system has failed and that is not ok. Here is a little guide to understanding what might be happening and some suggestions on how to fix the problem.

A car’s heater and heater core are part of the engine cooling system, though the heater does not provide the removal of heat from the engine as the normal function. It is meant to provide in-car passenger comfort during the cold winter months. The heater core is mounted in the air distribution duct system and is usually under the dash area of the front passenger side of the vehicle. The heater core resembles a small radiator and functions as a heat exchanger with the engine coolant flowing from the top of the engine through the heater core and back to the water pump in most designs. Engine heat is picked up by the coolant through the process of conduction and is transferred by convection to the cooler outside air passing through the heater core to the vehicles interior. An electric blower motor is used to force air through the heater core. This provides a ready source of heated air to be used to improve passenger comfort when needed. In some systems the engine coolant is constantly flowing through the heater core any time that the engine is running, whereas in other systems a control valve is used to stop the flow of coolant when heat is not needed.

Most failures of the heater core are due to a leak. This is easily detected by noting a wet floor carpet just below the case on the passenger side of the vehicle or if fogging of the windshield is occurring (moisture coming in from ducts). Replacement of the heater core, unfortunately, is not so simple. Because of the many different variations of installation, it is necessary to follow the manufacturer’s shop manual instructions for replacing the heater core.

The following is a typical procedure only and is not intended for any particular make or model vehicle:

  1. Remove the coolant
  2. Remove the access panel or the split heater/air conditioning case to gain access to the heater core
  3. Loosen the hose clamps and remove the heater core hoses
  4. Remove the cable and vacuum control lines (if equipped)
  5. Remove the heater core, securing brackets and clamps
  6. Lift the core from the case

The heater control valve regulates the flow of coolant through the heater core to control core temperature by opening and closing a passage to increase or decrease flow. The heater control valve may be in the inlet or outlet to the heater core. When the control valve is open, a portion of the heated engine coolant circulates through the heater core. The heater control valve may be cable operated, vacuum operated, or operated by a bidirectional electric solenoid or motor. The control valve depending on the valve position selected, meters the amount of heated coolant that is allowed to enter the heater core, from full off, to full flow. The HVAC control panel temperature selector regulates the operation of most heater control valves, whether actuated by a cable, vacuum diaphragm, or electrically energized. Some heater core assemblies have a mechanical heater control valve integrated into them to regulate coolant flow through the core. Other than a leak, which is usually obvious, the valve fails due to rust or corrosion. To replace the valve:

  1. Remove the coolant to a level below the control valve
  2. Remove the cable linkage, vacuum hose, or electrical connector from the control valve
  3. Loosen the hose clamps and remove the inlet hose from the control valve
  4. Remove the heater control valve as applicable. Remove the outlet hose from the heater core. Remove the attaching brackets or fasteners from the control.
  5. Inspect the hose ends removed. If they are hard or split, cut 0.5 to 1 inch from the damaged ends. The better thing to do is replace the hoses.


Heater hoses and clamps are basically about the same as radiator hoses and clamps except they are generally smaller in diameter. It is a practice of some technicians to use a hose that is too large for the application and overtighten the hose clamp to stop the leak. A hose clamp that is too large for the hose is often distorted when tightened sufficiently to secure the hose.

Heater hoses are replaced in the same manner as radiator hoses. It is much easier to use the wrong size hose, however. For example, a ¾ in. hose fit very easily onto a 5/8 in. fitting. The hose clamp then must be overtightened to squeeze the hose onto the fitting sufficiently to prevent a leak. It is not so easy to slide and 5/8 in. hose onto a 5/8 in. fitting. The intent, however, is to use the proper size hose for the application. It is a goo practice to replace all heater hoses if any are found to be defective. The following is a typical procedure:

  1. Remove the coolant to a level below that of the hoses to be replaced
  2. Loosen the hose clamp at both ends of the hose
  3. Turn and twist the hoses to break them loose
  4. Remove the hose. Do not use unnecessary force when removing the hose end from the heater core.

As with cooling system hose clamps, heater hose clamps should be replaced when a hose is replaced. It is most important that the proper size clamp be used for the hose. If the clamp is too large, it will be distorted before being tightened enough to secure the hose onto the fitting. When this occurs it is extremely difficult to stop a leak. Make sure you test your coolant every six months. You can do this with Phoenix Systems Coolant Test Strips.

CoolantStrip 100 Coolant Test Strips


CoolantStrip is a New test strip used to determine when to correct or replace your coolant. CoolantStrip is recommended for use with all coolant colors. Changing your coolant when needed will help prevent breakdowns, improve safety and extend the life of critical engine components.


Brake Job Done Well

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