@Simon @Gaygle
I think both of you had thermostat problems with your M3s...not sure if already solved but Road&Race just posted a video of him solving exactly the same problem you guys had so thought I’d highlight it to you.
BMW wanted almost £1200 to fix it!!!
Yeh saw this yesterday. I did mine a couple of weeks ago!
I put a comment on the YT video with my experiences:
I did this job about 3 weeks ago, using the exact same parts for the same prices (FAE 33155 coolant temperature sensor from Amazon for £13.31, and Mahle THD179 from eBay for £21).
Four things I learned from doing the job it:
1) Getting that ******* vacuum pipe back onto the back of the plenum chamber took twice as long as the rest of the job. If I ever meet the man who decided to put that hose there...The issue is when putting it back in the hole on the plenum, you need space to get your hand in there to firmly squeeze it in until it clicks. Unfortunately, you have to do this job with your fingers alone. I finally did it by putting the vacuum hose back into the plenum at a slight angle, to get one side of the clip to click in first, then levered the other side of the clip until it clicked.
2) The plenum must be seated properly for the jubilee clips to do up firmly (otherwise they'll feel loose when you tighten them, because all they'll be doing is squeezing the rubber seals). You may think you have seated it firmly, but the chances are you haven't - on the underside of the plenum, on each side of the 8 intake holes, there are two protruding oil PCV plastic clip things that lodge into a rubber diaphragm on the top of the engine. These should sit flush with the diaphragm when they are in properly. A number of times I seated the plenum, and thought i had it done properly, only to see I could fit my finger in between the diaphragm and the PCV protruding bit. The best way to get this to happen properly is to put all your weight on the top of the plenum, and rock it side to side and the protruding pieces of PCV plastic should go into the diaphragm fully.
3) Buy two new O rings for the two pipes that go into the engine block, and enter the back of the thermostat housing that. They cost pence from BMW, but if you get the car back together and you haven't replaced these old, hardened rubber rings and they start to leak, you'll swear lots.
4) For god sake, ignore anyone who says you don't need to drain the system. You just need to empty the coolant reservoir with a syringe or something. If you don't, when you remove the thermostat housing, the pressure generated by the weight of the water in the reservoir will cause the water to start overflowing from the thermostat housing, most of it draining into the V of the V8. You will then spend the next hour sucking up every bit you can from above the engine, getting the nasty sticking horrible glycol all over your hands and on your driveway causing a giant mess/environmental damage. Ask me how I know this...