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© 2001 Brian F. Schreurs
Even we have a disclaimer.

Although cold-temperature thermostats flood the market, we decided to stick with the stock temperature range (83 degrees C), using Wahler thermostat #4083.83 (Porsche #928 106 129 17) with a new gasket (999 701 632 40). Honestly, running a cooler thermostat won't benefit an otherwise stock car very much, if at all, and running too cool can actually cause problems of its own! In a similar vein, it's a really, really bad idea to go without a thermostat, whether your car is a Porsche or a Dodge.

There it is, the thermostat housing.

We can't emphasize enough how easy this project is. Easy easy easy.

First, you've gotta drain the radiator at least below the level of the thermostat housing -- but you know you're late chaning your coolant, so why not just take this opportunity to completely drain the system, eh? Be sure to have replacement antifreeze handy -- nonphosphorous stuff, since the Porsche V8 is a bimetallic engine. Nonphosphorous antifreeze is special stuff; you'll know you found it when you pass out from the $9 per gallon price tag. So far the only brand we know of (other than the stuff you could get from a Porsche dealer) is a Quaker State formula.

Remember: if it doesn't say non-phosphorous right on the bottle, it probably ain't.

The radiator doesn't have a drain cock in the traditional sense. Instead, it has a drain plug, which is actually easier to work with. You'll find it on the passenger-side bottom of the radiator; ours was blue, and came out readily with a Phillips screwdriver.

The coolant will sort of slowly chug out, good while you're trying to get the plug out, not so good when you're waiting for the system to drain. Go pop the cap off the reservoir and see what happens. Cooooooooool.

With coolant drained, it's time to remove the thermostat. The housing is right on top of the engine; it's the piece where the driver-side radiator hose ends. It's held in place by two 10mm bolts; one easy to see, one not so easy. Extensions help. Remove both bolts, then pull the housing off. There's the thermostat. Easy.

And there's the thermostat. Easy.

There's more coolant on the other side of that thermostat, so be prepared for it to pour out when you remove the 'stat. No big deal; a lot of it will collect in a valley on the top of the block, which you'll want to suck out with a turkey baster or hand pump. Messy but harmless.

Put the new thermostat in, with the element on the engine side and the gasket on the radiator side. Reattach the housing and put the plug back into the radiator.

Top off the system with a mixture of water and non-phosphorous antifreeze. Start the car and turn the heater on (so that the heater circuit is open) and continue to top off the coolant until the level stabilizes. Check back on it in a couple days to see whether it needs a bit more water due to air being purged.

Like we said. Easy.

Thermostats are a fairly simple device, but even they can fail. This procedure will correct any faults that were caused by a thermostat of the wrong temperature range, one that's stuck open or closed, one that doesn't move as far as it should, or one that responds at the wrong temperature. And, since it's cheap and easy, it should be near the top of cooling system diagnostics.

In our case, we found the thermostat in the car was rated for 87 degrees C, much too warm. So the swap did in fact result in cooler running temperatures. Money well spent!