M42 overheating issues - any ideas?

[kmack]

I have a '91 318i sedan witht he M42 DOHC motor.

This morning was the third time the car has started to overheat. And it was 54* out this morning!

I bought this car about 2 months ago. Very clean. Lots of things look new under the hood including the radiator. And not that "I just Armor-alled everything" look either.

After about 3 weeks, the car started getting hot while driving. Almost up into the red on the gauge, but not quite. Pulled off and opened the bleed screw. Went on my way. Everything ran fine until about a week later. Did the same thing. Opened the bleed screw and it cooled down. Both times it happened while I was sitting still at a light.

After the second time, I noticed that it would get warm while sitting, but if I revved up the motor (while not moving), it would cool down. So it seemed like more of a pump issue than an air-flow issue.

I pulled the thermo housing and water pump out. Thermostat is new. Pump looks good and has the metal impeller, all appeared in good shape. Only thing I could find was that the port that runs between the two chambers in the thermo housing was blocked with gasket sealant. I talked to a local BMW shop and they said I should not have any gasket sealant anywhere near this area. So I cleaned it up and put it all back together.

I flushed the radiator out with a hose and all the coolant was very clean. Looked brand new. Filled the system and bled it for a while. From then on the car ran fine. Mostly at the center gauge mark or just slightly above. I would open the bleed screw after every driving trip for the next 3 days after the 2nd overheat.

This morning, it got hot again. Pulled off, opened the bleed screw, cooled down and I was on my way. I also noticed that the heater was not working this morning. No hot air at all, even when it got hot. After I got back on the road, though, it started blowing "warm" air.

All hoses have been replaced. Fan clutch has been replaced (although I'm not sure it needed it). Thermostat and H2O pump have been inspected and are in good order. Radiator has consistent heat throughout cores (no cold spots felt on radiator core when at temperature).

Is this just a continuing air-in-the-system problem? What else can I look at? I do not want to go thru the cost of replacing the pump and radiator if I don't have to. And they don't look like they need to be. Anybody have some good info on this motor they can share?

[asubimmer]

really sounds like the tstat to me. You checked it how? You can try drilling a hole in it to make sure if it gets stuck closed you still can move some fluid.

[mikeltang]

similar things happened to my 318is...after i changed my thermostat to a lower temp everything worked fine again..but i also changed the radiator at the same time too...my track instructor blew out my radiator..

[dirty30]

Just went throught the same thing:

Changed:

-waterpump
-thermostat
-FAN SWITCH
-Flushed radiator, inside AND outside through fins (you'd be suprised how much this helps)
-coolant flush
-Redline water wetter
-electric fan

You may think I just shot- gunned the whole thing but the vehicle was due for it. Just hit the 240,000 mile mark. Fixed the problem!

[kmack]

You just reminded me. I also have some Red Line Water Wetter in the system. Didn't make any noticable difference in the temperature.

[M42]

Is your fluid level low after you bleed the system?
are you bleeding it correctly ? Did air bubbles come out when you unscrewed the bleed screw?

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

If it cools down after you bleed it then it still has air in it .
Follow the above link for correct procedure.
Let us know how you make out.

[porsche gt1]

To me it sounds like something is in your system and plugging it up. If you say that one time it was not blowing hot air and then the the next time it was I would say you have something trapped in the system. I would check in the heater core area as it seams to effect your heating. I would not be surprised if it was a piece of the gsaket sealant that you found.

[e9nine]

I went through a smiliar ordeal. Turned out to be the radiator as I had already gone through a new thermostat and water pump recently.

[kmack]

Update, things I noticed last night....

Did some checking of the cooling system last night and here's what came about...

Coolant level was still ok. Let the motor run straight for over an hour and a half with the cap off and bleed screw open. No heat from vents inside the car. Never really got much above half way on the temp gauge.

Things I noticed:
- there was some sort of (soft) foam-like material inside the bleed screw hole. I pulled it out. What is it? Is it supposed to be there?
- top hose coming off the radiator came up to temp and was hot to the touch. You couldn't hold your hand there for long.
- bottom hose coming off the radiator was warm to the touch. You could hold your hand there for a long time.
- top hose coming out of the heater core was cool.
- bottom hose coing out of the heater core was hot to the touch.
- Both tanks on the sides of the radiator were hot to the touch. i could not get to the center core area of the radiator this time to feel it, but I had when I replaced the fan clutch. It had even temp across the core then and was hot to the touch.
- I pulled the tee-connection on the top hose from the heater core. With engine running, no coolant was flowing. I stopped the engine and blew compressed air back into the heater core. Started the engine. No flow unless revs were higher than 1500 rpms. Even then the flow was less than I expected. But...I was getting warm air out of the vents now, so I was getting flow through the heater core. No change on the temp gauge.
- Ran the car for another half hour with the out flow line of the heater both disconnected and connected. Bled the system some more and watched the gauge. No change in temp. Stayed at half way mark.
- Both hoses coming off the radiator now were hot to the touch.
- Both hoses coming off the heater core were hot to the touch now, as long as the revs were above 1500 rpms. Below that and the hose temp would cool off on the top hose (out flow side).

I took the car to work with me today and it ran fine. Temp stayed rock solid (even though I think it should read a little less than the half way mark on the gauge). Heater worked great also. A good thing since it was pretty chilly this morning.

That's what I've found so far. I know at some point I need to pull the heater core and flush it out really, really good. That's in the plans. Anything else?