As a follow up, I had a chance to work on the car over the Christmas holidays. My thermostat needed to be replaced, as it was stuck open and I started to run too cool when I had the heat on over the past few weeks. I took this chance to do a bunch of stuff:
- replace the drive belt that started to crack
- replace the thermostat, which was broken
- look for the coolant leak
- do a couple of flushes and get back to blue coolant
- put in a new expansion tank thermostat
- replace the water pump (I have no idea when it was last done
I was going to do the radiator, but I looked it all over and it wasn't leaking, so I figure I'll do that later, when it leaks.
It turns out the leak was from the new expansion tank I had just installed. I traded a leak from the bottom of the old one, to a leak from the seam at the top in the brand new one. BavAuto shipped me a new one free of charge.
It was pretty straightforward to put in all the new parts, I love that I dont need the 32mm bike wrench to undo the fan. I was a bit worried I wouldn't be able to get to the engine coolant drain bolt, but it was no problem. I jacked up the car and removed the passenger wheel. Then, I just used a ratchet and socket and pulled real hard.
In all, it took about an hour to replace everything, since I did most of it before when I did the expansion tank and the Oil Filter Housing Gasket.
Now, my drama comes when refilling the coolant. I had the heater on full blast and only got a about 4 liters of distilled water in there before the level indicator in the expansion tank indicated full. I then started the car, but the coolant level wasn't dropping. Weird. I revved the engine a bit and watched the temp gauge like a hawk. it started ticking up, but the heater was still blowing cold. Nothing was coming out of the bleeder screw. I added more water, but still nothing. I shut off the car and move to an incline. Start the car again, and still, I'm only like 5 liters in. Finally, after a couple of minutes and revving the engine a bit, I"m seeing coolant move and I'm starting to spray water all over the place from the coolant tank (which is still without a cap and bleed screw. I proceed to put about 2 gallons in total and drive around the block a few times until the temp gauge is square in the middle.
I bring it back and I am getting a bit of a burnt smell coming from under the hood. I see smoke (or maybe steam) coming up from the block in the engine bay. Weird. I'm not expecting anything exotic, as I'm only filling with distilled water to wash out the orange coolant. I'm wondering if the engine overheated for a bit, even though the temp gauge never showed overheating, as water may not have been going through the whole block.
Oh well. Nothing I can do about it now. I wait a few hours and drain the distilled water and refill again. This time, thing went smoother and I got about 2 gallons in immediately without drama. I drove about 20 miles to dinner and all seems well. We'll see if I did anything bad to the headgasket or head with the first fill. I'll drain again tomorrow morning and this time fill with the BMW coolant.