DIY Network

Thermostat Inspection and Replacement From "Auto Primer" episode DAPR-103

When an engine heats up, the thermostat opens up like a door to allow the coolant to circulate through the radiator and through the motor to cool it down.

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In this episode of DIY's Auto Primer, host Leilani Munter covers maintenance of your vehicle's cooling system and shows how to deal with failed hoses. In this third segment of episode 103, Leilani shows the steps in inspecting and replacing a worn-out thermostat.

Materials:

Standard automotive tools (socket-wrenches, screwdrivers, nut-drivers, etc.)
Thermostat
Razor Blade
Coolant
Screwdriver
Wrench
Eye protection

Safety Alert: Always wear eye protection when working with power tools or hazardous chemicals.

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Your car's thermostat should be replaced every two to three years.

Replacing a Thermostat

The thermostat is an important element in your cooling system. When an engine heats up, the thermostat opens up like a door to allow the coolant to circulate through the radiator and through the motor to cool it down.

Your car's thermostat should be replaced every two to three years. It's a simple procedure to replace it, and the part is inexpensive. Timely replacement of old thermostats may save you a lot of money and headache by preventing a serious breakdown in your cooling system.

Important Safety Precautions

Though work on your vehicle's cooling system is typically not a difficult automotive procedure, there are several safety issues that you must be aware of before you begin work. Here are some very important safety precautions:

Safety Alert: Radiators and engines get extremely hot, and opening a radiator before it has cooled is extremely dangerous. Before you begin work, be certain to let your engine cool fully.

Safety Alert: Coolant, or antifreeze, is extremely toxic and harmful to the environment. Because it has a sweet smell but is highly poisonous, it is especially hazardous if young children or animals around. Always keep coolant away from children or pets. Wash your hands thoroughly after working with coolant to prevent contact with the eye.

Safety Alert: Always dispose of automotive fluids and other hazardous materials responsibly. Many auto centers have auto-fluid recycling centers.

Safety Alert: As a standard safety precaution, disconnect your car's negative battery cable before you start any mechanical or electrical work on the vehicle. For this procedure, this is especially important if the car has an electric cooling fan.

Steps

• Locate the thermostat. It will be located on top of the water pump.

• Remove the bolts securing the housing and remove housing to reveal the thermostat (figure A).
  
  
• Lift out the old thermostat (figure B) to inspect it.

  Figure A

  Figure B

  
  

• Remove the old gasket and clean away any remaining gasket residue with a razor-blade scraper. (Don't worry about trying to save the old gasket. A replacement gasket comes with the new thermostat.)

  Important: Before scraping and cleaning the gasket surface, place a clean rag in the opening of the thermostat housing (figure C) to prevent residue from dropping down into the motor as you're cleaning.
  
  

• Once the surface is clean, place the new thermostat in position, spring side down, and place the gasket in position (figure D).

  Figure C

  Figure D

  
  

  Figure E

• If there is any damage or roughness to the gasket surface, it's especially important to use a gasket sealer (figure E) to ensure a good seal. Follow the manufacturer's instructions printed on the sealant container. Be certain to use a sensor-sensitive sealant. (Silicon sealants can withstand high temperatures and will not foul emissions sensors.)

• Replace the housing cover and secure with bolts.
  
  
• Replace the radiator hose and refill the system with coolant.

• Start the vehicle and, after about five minutes, check for leaks.
  

  Figure F

Safety Alert: Whenever working with radiators or antifreeze, always put on safety glasses before you begin work.

The fluid In your radiator is typically a mixture of water (preferably distilled water) and antifreeze (or coolant). A good rule of thumb for the mix is 50 percent coolant and 50 percent water -- unless your area experiences severely cold weather. In extremely cold climates, the recommended ration may be as high as 70 percent coolant to 30 percent water. Check the label on your coolant for information on the proper ratio (figure F).

When filling your radiator with fluid, you'll want to know the total capacity of your car's radiator so you'll know how much to mix up. Your owner's manual will tell you that information.

Mix the antifreeze and water in a bucket. Using distilled water will help prevent mineral buildup inside your cooling system.

Figure G

For added assurance of the proper mixture, you can easily check the ratio of water to antifreeze in your radiator using an antifreeze hydrometer. This easy-to-use tool (figure G) is available at most auto centers. Simply dip the tip of the hydrometer into the coolant mixture and use the squeeze bulb to draw some of the mixture up into the tool. An indicator, or floating indicator-balls, inside the tool will tell you the mixture.

	Figure H
	Figure I
	Figure J

Refilling Your Radiator

• Once you've mixed up the proper ration of antifreeze to water in a bucket, check to make certain that the petcock valve, at the bottom of the radiator, is closed.

• Remove the radiator cap to expose the fill-opening on the radiator (figure H). To remove the cap, press down firmly on the top of the cap as you twist.

• Slowly and carefully pour the mixture from the bucket into the radiator, using a funnel to prevent spills (figure I).

• Remove the funnel and replace the radiator cap.

• Start the engine and let it warm up for a few minutes, then check the level again. Add more of the mixture as necessary.

• Next, add some of the mixture to your cooling-system reservoir to the "cold" line, or slightly above it (figure J). Don't overfill.
  

In the segment that follows, Leilani shows some items that you should include in an emergency kit in case a breakdown should ever happen to you when you're out on the road.

RESOURCES :

The Complete Idiot's Guide to Trouble-Free Car Care
Author: Dan Ramsey
ISBN: 0028635833
Alpha Books

Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896

How Cars Work
Author: Tom Newton
ISBN: 0966862309
Publisher: Black Apple Press
To order this title from Amazon, click here.

What's Wrong With My Car?: A Quick and Easy Guide to Most Common Symptoms of Car Trouble
Author: Bob Cerullo
ISBN: 0452269938
Publisher: Plume (1993)
To order this book from Amazon.com, click here.