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The thermostat in your vehicle is responsible for keeping the coolant inside the engine, and preventing the coolant from flowing into your cooling system. When you start your your car in the morning, the thermostat is closed to help the engine warm up to operating temps. When the engine is warm enough, or reaches the thermal value of the thermostat, it will open and allow coolant to rush into the radiator.

In theory this process both speeds up the warm-up time of your engine, decreasing emissions and increasing your fuel economy. It also ensures that your engine stays at operating temperature, as it will close and open should the coolant temperature sensor indicate a too cold condition.

Some thermostats come with thermostat housings incorporated into them


Your thermostat is a basic valve that's a wax-pellet actuated diaphragm. The pellet in your thermostat is what helps set the temperature in which your thermostat opens. When this part goes bad or sticks closed or open, you'll be greeted by a host of flashing check engine lights the next time you start the car.

Overheating conditions will trip several warning OBDII trouble codes, from P0171 to P0174 as your ECU or PCM struggles to maintain closed loop operation. Because there's so many fluctuations in engine temperature, the ECU can switch from the warm fuel map to the cold startup map. This will cause serious driveability issues, and could cause your engine to run too lean or too rich.

If you are having problems overheating, try to carefully touch the lower radiator hose to make sure that your thermostat isn't stuck closed. If the radiator exiting your thermostat housing is still cold, but your engine coolant temperature sensor shows hot, replace your thermostat right away.

White sweet smelling smoke from your exhaust is a bad sign of overheating.


Are you having problems with your thermostat and aren't sure where to start? Check out our How To Section over at My Pro Street for more details, articles and DIY How Tos about all things automotive.

Here's a few of our recent articles about thermostats, overheating and how to install, service and locate your thermostat.

How To Replace a LR4 Thermostat
How To Replace a LR4 Thermostat

To replace your 4.8 liter Sierra thermostat, you’ll need coolant as well as a 10mm socket and wrench. The part number for the factory thermostat for your Sierra is GM part number 12562740, 12571261, or 12562740.

The temperature rating for these thermostats is 186 degrees, and that is the stock rating for your Sierra.

If you are still having overheating problems, we suggest stepping down to a 160 degree thermostat.

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Honda Passport Thermostat DIY
Honda Passport Thermostat DIY

If you've got overheating problems in your Honda Passport with the V6 engine in it, it's always handy to know how to replace your thermostat.

This DIY Guide shows you how to replace the Honda Passport thermostat in a 3.2 liter 6VD1 engine.

The part number for this replacement thermostat is 89712-31614 and you will also need the replacement thermostat o-ring or gasket which is part number 89712-31620.


Change your 4G63 Thermostat
Change your 4G63 Thermostat

Our DIY Guide features a 2005 Mitsubishi Evolution VIII with the 2.0 liter 4G63, and we’ll be replacing it with Mitsubishi part number MN143463 which is also MD310106.

This very same thermostat can also be found under MD328070, MD332446, or MD337408.

Because we'll be working on a turbocharged vehicle, make sure to allow time for your engine to cool before draining your coolant.