While test driving the new-to-us Geo Metro, one of the first things I noticed was that the engine wasn’t getting up to operating temperature. It was a chilly -10C evening, and the temperature gauge would barely reach the top of the “C”.
The thermostat is the temperature-controlled valve that opens and closes to allow more or less coolant out to the radiator to keep the engine at its happiest temperature point. When you first start your cold car, the thermostat should remain closed, recirculating the warming coolant through the engine instead of sending it out to the radiator. Upon reaching the ideal temperature, the thermostat will begin to open a little, allowing some of that heat to be shed by the radiator.
Usually when the thermostat fails it gets stuck closed which causes your engine to overheat. This one somehow got stuck open which prevented the engine from ever getting to its proper operating temperature. This causes the engine to constantly operate in the “cold start” mode, which feeds in extra fuel to help start and run the engine until it is warm enough. The colder engine also has the potential to wear down metal surfaces as the oil isn’t as slippery when it isn’t at its proper operational temperature.
Replacing it requires the coolant to be drained. The Metro has a drain on the bottom of the radiator.
Opening the radiator cap speeds the draining process.
The thermostat housing is on the transmission side of the engine just below the distributor, attached to the upper radiator hose. It is secured by two bolts.
With those two bolts removed, the housing can be pulled back from the engine.
…which exposes the thermostat:
The thermostat can be easily pulled out by hand, as it is only held in by the gasket at this point. Here you can see the old, jammed-open thermostat next to the new one on the right:
Before the new one can go in we need to prepare the sealing surfaces. Off comes the old gasket, usually in many pieces:
When removing old gaskets, I will first use a razor scraper to get off what I can (careful not to scratch the soft aluminum). Then comes a wire brush, and finally, if necessary, some light sandpaper. Ideally there should be nothing of the old gasket remaining on both sealing surfaces.
I also cleaned the rust from the bolts with a wire wheel, and treated them with anti-seize. The new gasket also got a coating of non-drying gasket treatment, which helps it seal and makes future gasket removal a snap.
When installing the new thermostat, care must be taken to install it in the correct orientation. Do you remember which way that was? Do you? Well, luckily most thermostats have an arrow printed onto them with the words “to rad” to help you put it back in correctly. The thermostat goes in first, then the new gasket, and then the housing is reinstalled. As always, care must be taken when torquing the bolts into the aluminum engine so as not to strip the threads.
Time to refill the radiator:
When refilling, you might notice that less coolant goes back in than came out. Here is what I was left with:
To get the rest in the engine must be “burped”. This involves running the engine up to temperature with the radiator cap open, refilling as bubbles appear. It can be slow and tedious, but air bubbles in the coolant system can cause lots of problems down the road.
Cost breakdown:
$22 - thermostat
$3 - thermostat gasket
== $25
Incidental supplies:
gasket treatment
anti-seize
The thermostat is the temperature-controlled valve that opens and closes to allow more or less coolant out to the radiator to keep the engine at its happiest temperature point. When you first start your cold car, the thermostat should remain closed, recirculating the warming coolant through the engine instead of sending it out to the radiator. Upon reaching the ideal temperature, the thermostat will begin to open a little, allowing some of that heat to be shed by the radiator.
Usually when the thermostat fails it gets stuck closed which causes your engine to overheat. This one somehow got stuck open which prevented the engine from ever getting to its proper operating temperature. This causes the engine to constantly operate in the “cold start” mode, which feeds in extra fuel to help start and run the engine until it is warm enough. The colder engine also has the potential to wear down metal surfaces as the oil isn’t as slippery when it isn’t at its proper operational temperature.
Replacing it requires the coolant to be drained. The Metro has a drain on the bottom of the radiator.
Opening the radiator cap speeds the draining process.
The thermostat housing is on the transmission side of the engine just below the distributor, attached to the upper radiator hose. It is secured by two bolts.
With those two bolts removed, the housing can be pulled back from the engine.
…which exposes the thermostat:
The thermostat can be easily pulled out by hand, as it is only held in by the gasket at this point. Here you can see the old, jammed-open thermostat next to the new one on the right:
Before the new one can go in we need to prepare the sealing surfaces. Off comes the old gasket, usually in many pieces:
When removing old gaskets, I will first use a razor scraper to get off what I can (careful not to scratch the soft aluminum). Then comes a wire brush, and finally, if necessary, some light sandpaper. Ideally there should be nothing of the old gasket remaining on both sealing surfaces.
I also cleaned the rust from the bolts with a wire wheel, and treated them with anti-seize. The new gasket also got a coating of non-drying gasket treatment, which helps it seal and makes future gasket removal a snap.
When installing the new thermostat, care must be taken to install it in the correct orientation. Do you remember which way that was? Do you? Well, luckily most thermostats have an arrow printed onto them with the words “to rad” to help you put it back in correctly. The thermostat goes in first, then the new gasket, and then the housing is reinstalled. As always, care must be taken when torquing the bolts into the aluminum engine so as not to strip the threads.
Time to refill the radiator:
When refilling, you might notice that less coolant goes back in than came out. Here is what I was left with:
To get the rest in the engine must be “burped”. This involves running the engine up to temperature with the radiator cap open, refilling as bubbles appear. It can be slow and tedious, but air bubbles in the coolant system can cause lots of problems down the road.
Cost breakdown:
$22 - thermostat
$3 - thermostat gasket
== $25
Incidental supplies:
gasket treatment
anti-seize
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