Monday, October 11, 2004

A tale of two thermostats

Changing thermostats should be easy. four steps:

  • Remove two bolts

  • Remove the thermostat housing

  • Replace the thermostat

  • Installation is reverse of removal



Sure, you could drain the coolant, but you shouldn't lose much since the thermostat is on the top of the engine, right?

Things aren't so easy if you changed the thermostat on my Corvette a few years ago:

  • Pull off some hoses and engine accessories to get to the thermostat housing

  • Reach a wrench down there (Weren't those supposed to be studs? Why are they bolts?)

  • Lefty-loosy.

  • Lefty-loosy a bit harder. Snap! Shit!

  • Try the same for the other bolt. Snap! Damn!

  • Pull of the thermostat housing, remove the thermostat, stare at the two snapped bolts.

  • Realize the following: The car came with studs holding the housing in for a reason; Someone had already changed the thermstat and replaced the studs with grade 2 bolts; Cheap steel bolts make the aluminum corrode, which makes the steel rust, which siezes the bolts.

  • Try the following without success: torching the bolts; vice grips; hammer/pounding on the bolts; bringing out the big torch; welding a nut on the bolt

  • End up drilling / tapping a new hole inside of the old/siezed bolt.

  • This time, use grade 8 bolts (that won't likely snap) and anti-sieze.

  • Installation is a bit easier than reverse of removal



That was 2 years ago. I've forgotten about the pain and now have a good interview analogy (on how doing an extra 5% can save LOADS of time in the future). A few weeks ago on my drive to work (when it was 30 degrees outside), I noticed that my 300m had very little heat and the temperature gauge wasn't nearly as high as it should be. The obvious problem was that the thermostat was either opening too soon or was stuck (It turns out that it was opening early; found that out thanks to some boiling water and a thermometer). Time to change it.


  • Search for the thermostat on the top of the engine; give up searching for it.

  • Break open the shop manual. Realize that the thermostat is on the bottom of the engine.

  • Lift the car, find the thermostat housing, lower the car.

  • Drain the coolant. This is done by turning a petcock (what a terrible word: petcock) on the bottom of the radiator. Naturally, the petcock is plastic, so you can't use any tools to turn it. Unfortunately, the petcock is inaccessible from the top and needs to be turned from the bottom;. Unfortunately, it's a bit inside and practically impossible to turn by hand, since I can't really get a good grip around it.

  • Who cares what the manual says; turn the petcock open using pliers. I am smart enough to wrap the pliers in 4 layers of shop towl, no damage done to the plastic.

  • Kill time for an hour and a half while the coolant drains out very slowly.

  • Lift the car, realize that the oil filter needs to be removed before getting to the thermostat housing.

  • Remove oil filter

  • Remove the three hose clamps using the most useful tool in the world

  • Try (and fail) to remove one of the hoses.

  • Pull the thermostat housing off, thread it around the frame to get to the thermostat.

  • Change the thermostat.

  • Installation is reverse of removal



The probems with the vette were due to a poor mechanic; replacing studs with cheap bolts and not using any type of lubricant where corrosion is likely. The problems changing the thermostat on the 300 are largely due to poor engineering / bad packaging. At least I didn't need to remove anything large (like the engine) or use any real specialized parts.

I bet that getting the thermostat changed at a shop would be about twice as expensive with the 300 as it would with a "normal" vehicle. This begs the question: is it worth getting not-your-first-choice-vehicle because it may be more difficult/more expensive to work on? Personally, given the amount that things need real fixing, I doubt it.

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