Over the British summer I noticed that temperature gauge was creeping up a bit higher than usual whilst stuck in traffic and having spent a few uncomfortable moments with the internal heater turned full on to compensate and cool down the engine I decided it was time to investigate further. Having checked the level of coolant was ok and that the fans were kicking in roughly when the needle hits the half way mark on the gauge, I went for the next common cause the thermostat. At around £20 for a Porsche one they're not cheap, but going through the cars history I could see it hadn't been replaced for a long while.
THE TASK
The thermostat can be a tricky thing to get at, most guides say that need to approach it from the underside of the car. This isn't true, as long as you have the right tools and remove the distributor cap then you can get to it from the top front of the engine.
You will need the following:
Stumpy flat-bladed screwdriver
Long flat bladed screwdriver
Long bent-nose snap ring / circlip pliers
Small torch
Dentists mirror
Catch bowl for old coolant
13mm spanner
THE HOW TO
(Amateur mechanic job time approx. 1 hour)
Pull off the HT leads that connect to the distributor cap, remember which order they attach. Then remove the distributor cap using the small dumpy flat-bladed screwdriver to release it's locking pins.
Place a catch bowl under the engine bay, and then release the screw on the hose clamp, pull the hose off the water pump, a rush of coolant should come out. Watch to see if the coolant is dirty/murky/oily as this could indicate other problems.
Push the end of the hose out of the way below the water pump inlet. The thermostat is then located directly inside the water pump inlet as shown by the orange arrow. Put your fingers inside the hole and have a feel around to suss out the position of the snap ring. Use a torch and a small mirror if you have to, it is very tricky to see the location of the snap ring holes.
The next part is where the frustration levels are likely to rise. If you have anything other than snap ring pliers I suggested at the beginning of this tutorial then you are going to make life very very difficult for yourself.
Take the snap ring pliers and locate the two prongs into the holes in the snap ring, squeeze the snap ring and make sure you pull it out parallel to the hole entrance. This is likely to take several attempts, I think it took me about 4-5 goes before I got it out.
This is what you should end up with
Once the snap ring is out you should just be able to pull out the thermostat, take note of which end goes in first. There is a rubber washer that runs around its outer edge, make sure it doesn't get left inside the water pump.
Here's the thermostat removed from the water pump. The base shows that it is rated at 80 degrees centigrade.
The next step involves testing the thermostat to make sure it is opening at the correct temperature. Simply plop it in a pan of water and boil it until the temperature reaches its range. If it opens all the way at the temp stated your thermostat is fine, if it opens later then it is time for a replacement.
Here's the test.
Here's a photo of my old (left) and new (right) thermostat. Notice the difference in the size of the rubber seal around the edge.
Once you've determined whether the thermostat is faulty or ok it's time to fit it back. The process is the reversal of removal. The only watch out is making sure the snap ring sits squarely into its recess, before you insert the thermostat run your finger round the inside of the water pump inlet and you'll feel the recess the snap ring fits into. Once the thermostat is fitted and all the hoses are connected back up you need to refill the system. First set the heater switch to maximum inside the car. Then you need to release the coolant bleed screw on top of the upper most radiator hose (shown by orange arrow below). Then fill the system at the header tank until coolant can be seen coming from this hole. Close the bleed valve and belch the system by squeezing the top hose (shown by blue arrow). Repeat the process until you can't fill the coolant tank any more.
Next run the car up to temperature, this will cause the thermostat to open and release coolant into the rest of the system, keep an eye on the fill level of the coolant tank. Turn off the car and fill then belch the system repeatedly until no more coolant topping up is needed. Run the car up to temperature again and check the fill level. If all is ok just have a final check that none of the hoses are weeping and you should be done, if not just keep topping up the coolant until the level stops dropping.
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