SOLVED!!! More temperature issues...it's gotten worse

[Got Mayhem?]

Awhile ago I posted about my engine either running ice cold or overheating depending on whether I was moving or sitting still. Believing it was a bad thermo I purchased a new Wahler 88 degree and went to put it in last night. Removing the housing I found out that the previous owner had taken out the thermostat for some unknown reason.

I put in the new thermostat and started the car up. I began the process of bleeding the system and noticed the car was getting hot. I suspect I have a bad fan clutch as well so I wasn't particularly worried/surprised. I turned the car off. After letting it cool down I bled it some more. This time it got hot much faster than ever before. I killed the engine and steam/bubbling noises were coming from around the thermostat housing. I noticed that the hose coming off the housing on the driver side was hot but the passenger side hose was cold.

This morning I went to give it another try. I bled it some more and once it got hot I turned the car off. There was little steam or bubbling this time. Same as last time: one coolant hose hot, the other cold. After cooling down I took it for a small drive to see if it would be at the right temp while driving. It wasn't. As it got hot I turned around my road to go back home. Suddenly the temp gauge went insane and started going all over the place. Parked it, listened to the coolant system steam and gurgle. Went to make this post.

What the heck is going on guys?

[DesktopDave]

Could be a cracked pump impeller.  Some were plastic...if it's not pumping enough coolant the head will get hot very quickly.

I bought a cheap IR thermometer to check insulation in my house...I've used it on occasion to determine what's going on with cooling systems.

I'd be very tempted to get a compression check.  Your car might have been overheated in the past.  An easy band-aid is to toss the thermostat so it stays cool while it's moving.  That's hard on the motor though.  Or you have  small leak in the head...if so it'll be pressurizing the coolant system and blow coolant  out until it overheats.

[Got Mayhem?]

Finally fixed it...I think.

This morning I began with the intention of removing the thermostat in order to go to emissions. It wasn't what I had wanted to do but I was out of time to try anything else. On a whim I started the car to see what it would do after sitting for a few days. To my surprised it began heating up as it normally should after a cold start. Inspired by this good sign I began bleeding the system again. After an insane amount of coolant and at least half an hour of idling gigantic air bubbles began to come out. Even better, the car wasn't over heating, my heat was working, and the coolant level had finally evened out where it was supposed to.

With everything looking good I got the courage to go and drive to emissions. Not only did I make it there without overheating or leaking, but I passed emissions as well! It got better. The sheet I got from the emissions guys said they read an engine temperature of 189.6 degrees F. This was a near as you could ever really get to the intended temperature of my 88 deg C (190 deg F) thermostat.

Conclusion: coolant systems are awful and difficult to diagnose. Thank god my head is fine. And Wahler make great thermostats.

Thanks again for all the help everyone!

[DesktopDave]

I'm glad to hear that!  Most likely you saved that motor.

Your pump might have been air-locked.  If a bubble sits in the pump housing the impeller just helplessly spins.  Since there's no flow, the coolant cannot purge the bubble.  The car just overheats.  Did you do anything different this time?

Did you mix the coolant any thinner than usual, or clear that bleed passage in the thermostat housing?  Drilling a hole in the thermostat is occasionally tried as well.

[Got Mayhem?]

Hm, it does seem likely that my pump may have been air locked. It definitely showed all the symptoms of that, as coolant didn't seen to be going anywhere in the car earlier this week. When bleeding it this time I followed these instructions to the letter:

http://www.esatclear.ie/~bpurcell/318ismaintenance.html#bleed

The coolant was just the usual 50/50 mix every time. I cleared that bleed passage when I originally installed the new thermostat. It was pretty nasty previous to that. I didn't drill into the thermostat, however I was considering doing that if I ended up taking the thermo out again. As of right now it seems like I have great flow throughout the system. Both hoses get hot, as opposed to only the driver side one previous to this last bleeding attempt.

Basically I've decided that the M42 is a very simple engine to bleed. It just takes patience and a lot more coolant than you would expect for this tiny 1.8L.

[DesktopDave]

Lifting the front of the car helps too.  I bleed the system on the slope of my driveway. Between that, the water wetter, and the 33% coolant mix it's pretty easy.

[Got Mayhem?]

A great suggestion, though I ended up doing mine on a flat surface my friend just bled his M20 with the front end jacked up a bit. He said it made it go much smoother than previous attempts. The M20 has a pretty cool bleeding system as well, at least on the later years. The bleeder screw is right on top of the thermostat housing.

[DesktopDave]

Yeah, I always liked that about the M20.  The M30 in my 633CSi is the same way, very convenient indeed.  Even better, it uses a rebuildable (real metal) radiator!  Not great for weight, but definitely for service.

There are a lot of great things about those old motors.  I even prefer the belt drive...especially as the M42's cam drive isn't exactly robust.   Change a $40 belt every 50k miles?  Absolutely!  Cheap, simple &  quiet.

[Got Mayhem?]

I know what you mean! Having been part of both a M42 and a M20 rebuild at some point I've noticed a lot of pros and cons between them. In my opinion the 4 cylinder has a lot of great ideas thrown in (Oil filter housing, lots of engine bay space, etc) but nothing really that makes it a clear choice over the 6. For a 20+ year old car my 318i does handle very well, but I've always questioned whether a stock 325i could really be that much more clumsy in corners due to the extra displacement and cylinders.

Also, this could have been my own silly errors, but when doing my head gasket no matter how hard I tried the timing skipped on my M42 at some point and I had to spend a lot of time getting it back right. Sure, the chain looked and sounded great for its age but as you said Dave a belt isn't that much more of a hassle in the long run...

M20 also gets points for the noise level. When I started my first 318 I was surprised at how loud it was! Now I know that it's just normal for this engine. First time driving the one I had now even I was paranoid about every little "tap" and "tick". I guess the benefit of all of that is a really tough DOHC motor. 200k and smooth as butter, both on this engine and the one in my old 318is.