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Porsche 928: How to Replace Thermostat

A car's thermostat can become damaged or worn if the car ever overheats. And if this ever happens to your Porsche 928, you'll want to replace the component immediately to ensure your car continues to operate at peak efficiency. Fortunately, it's a fairly simple task that you can do at home in less than 30 minutes.

By Jeffrey Bausch - March 25, 2015

This article applies to the Porsche 928 (1979-1995).

There’s a ton of routine maintenance that goes into owning a car, and this is especially the case if you own a classic sports car like the Porsche 928. One thing that falls outside the “routine maintenance” category, but still warrants routine watching and checking up on, is your car’s thermostat.

If you’re unfamiliar with this particular component, note that the thermostat is a valve on your Porsche’s cooling system which regulates how much of the coolant gets recirculated back into the engine, and how much gets sent out through the radiator to be cooled before it recirculates through the engine. By doing this, the thermostat is able to keep the temperature of the engine in a very specific range no matter how cool or warm it is outside. This range, which falls somewhere between 180-190 degrees Fahrenheit (80-90 degrees Celsius), is designed to operate for engine efficiency and to get the maximum power without overheating and damaging any parts.

A thermostat, on the whole, is a fairly simple component when it comes to design, so there’s very little that can go wrong with it. However, if your car overheats, it could damage the thermostat. A good way to judge if your thermostat has been damaged is if your temperature gauge ever gets more than ¾ of the way up its range; if it reaches the red line, chances are the thermostat is damaged.

If you find yourself in this scenario, you might want to replace the thermostat in your Porsche 928. Here’s how you can do it yourself.

Materials Needed

  • Thermostat (part #92810612917)
  • Antifreeze
  • Phillips screwdriver
  • Ratcheting wrench set (with extender)
  • Rag or turkey baster

Step 1 – Drain the radiator

Granted, you only need to go below the thermostat housing level, but this is a good time to flush out the entire system and replace with new antifreeze. It’s worth noting that the radiator doesn't have a traditional drain cock; rather, there’s a drain plug. Fortunately, this is much easier to work with. It’s located on the passenger-side bottom of the radiator and comes off fairly easily with a Phillips screwdriver.

Figure 1. Radiator drain plug location.

Step 2 – Remove the old thermostat

The housing unit is right on top of the engine (piece where the driver-side radiator hose ends). It’s held in place by small bolts. Remove them using a wrench set (you might need an extender to get to the hard-to-reach bolts), then pull the housing unit and you’ll see the thermostat.

Pro Tip

There’s more coolant on the other side of the thermostat, so be ready for it to pour out when you pull the component out. Most will pour on to the top of the block—just wipe it up with a rag, or suck it up with a turkey baster.

Figure 2. This is the thermostat housing location.

Step 3– Place the new thermostat in

The element should be positioned on the engine side and the gasket on the radiator side. Next, reattach the housing unit and put the plug back into the radiator (assuming all the coolant is out of the system now).

Figure 3. Thermostat placed in the housing.

Step 4 – Replace coolant

Fill coolant and top off with a mixture of water and non-phosphorous antifreeze. Start the Porsche 928 and turn the heater on (this opens the heater circuit). Continue to top off the coolant until the level stabilizes.

Go back a couple days later to see if the system needs a bit more water due to air getting out while the car is running.

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