Overheating & VERY Frustrated

[JScritch]

1992 525i Auto (M50)

Water pump went out about 3 weeks ago (completely froze bearing) which took out the belt and 1 fan blade.

Replaced the water pump and ever since the car has been getting hot (red area). Never had any heating problems before the water pump failure.

I have to date replaced water pump, fan, fan clutch, radiator cap and expansion tank o-rings (were leaking). Stupid car still gets hot.

Now, if I turn the interior heater on high temp full fan the engine temp drops and stays regulated to 1/2-3/4 on the gauge, but the minute I shut the interior heater off the temp climbs.

I've bled the system (using the one bleed screw next to the radiator cap) so many times now it's getting ridiculous. I am losing ZERO fluid (except when I bleed it) and both radiator hoses are getting warm/hot to the touch.

At this point I'm at a loss. The only part I haven't replaced is the thermostat, but I'm having a hard time believing that is the issue. Any ideas or suggestions would be appreciated.

This is my first BMW and I'm about ready to call it quits if I can't get this thing reliable.

[Evan]

I think you're using the wrond bleed screw. It should be at the bottom of the radiator... not near the cap.

[632 Regal]

Do a search on bleeding, there are many many posts on the subject and how some can be a total biatch to complete

[JScritch]

1. The bleed screw on the M50 525 is right next to the radiator cap unless that screw is something completely different.

2. Does my problem really sound like a bleeding problem? I have a hard time at this point to believe it's just air trapped, but maybe I'm just not familiar with it. I've read just about every "bleed/overheat" post the search pulled up. They all sound similar.

3. I'm really suspecting my fan clutch, even though it's brand new. My fan seems to turn at the same speed regardless of engine temp. I don't get the "bus noise" that some people describe.

4. What does it indicate when I turn on the interior heat full blast and the engine temp drops?

[Evan]

1. Your bleed screw is on top of the radiator...

4. The heat comes from the engine coolant... heat dissipates from your heater core and into your passenger compartment. Engine temp drops because of this heat transfer. Think about it.

5. Bleeding can be a pain in the ass... be extra patient and go to www.bmwe34.net to get more info on checking the fan clutch, etc...

There's thousands of dollars of info on that site.

[GS535i]

I do not know the specific lay out of your engine; however, if there is a pressure equalization line ( ~10mm od) running from the top of the rad to an expansion tank - assure that there is no blockage in this line. Blow it clear with air, etc.
On the M30, there is a too small orfice where this line enters the expansion tank - and if plugged, can cause a boil over in a heart beat.

[Evan]

great point... on the M50 the expansion tank is on the radiator. i want to stress that bleeding is usually a process. out of the 50 times ive bled a cooling system, ive never had it right the first time... and it usually takes me three tries to get it all right.

im not saying your problem is definitely the bleed... but i would be surprised if it isnt since everything was running fine until you worked on it

[GAM]

I would replace the thermostat. The overheating may have made it bad.

[Paul in NZ]

you bleed with heater on full????

[Javier]

inside the engine, not flowing through radiator in order to heat up the engine. When operating temp. is reached, tstat closes the re-circulating circuit and opens the extended circuit to force water to go through the radiator, the higher the temp, the higher it opens to increase water flow through radiator.

The heater circuit is derived from the engine re-circulating circuit, acting as radiator, even wile the tstat is closed, so it cools some water for your benefit.

I would replace the tstat also. If you want to be comfortable with it, just drop it in a boiling water pan, it should be wide open before water hits boiling temp. If you have a cooking thermometer, you can also verify at which temperature is it opening.

You said you changed pump, fan clutch, and some extras, why didn't you also changed tstat at that time? It is generally the weakest part in the system.

Javier

[Evan]

Good Idea, Javier. I've done the boil test and it's a good way to see if your T-Stat is working or not.

[Dave M]

[QUOTE=JScritch]1992 525i Auto (M50)

I've bled the system (using the one bleed screw next to the radiator cap) so many times now it's getting ridiculous. I am losing ZERO fluid (except when I bleed it) and both radiator hoses are getting warm/hot to the touch.

QUOTE]

1) Assuming ZERO fluid loss also means that the coolant is not oily and that your oil isn't milky with coolant. You can get a net loss near zero with a bad head gasket when fluids are swapped. Not likely, but just a thought.

2) How hot? At operating temp (12:00 on the temp gauge) you wouldn't want to hold onto it for more than a few seconds. The lower hose should be noticeably cooler to the touch. Starting the car cold, you should be able to feel the 'moment' the thermostat opens and hot coolant begins to circulate through the rad. IF this is the case, your thermostat is operating properly and I would suspect a bleeding issue.

3) At highway speeds, does the needle go beyond 12:00? If not, and your overheating is occurring during stop and go you may have a bum fan clutch. With your hood in the 'open' position (lid down, but hood lever pulled), you should feel a fairly strong breeze out the sides. As well, when you shut the car down, the fan should stop quickly, rather than spinning freely for a few seconds.

4) When you bled the system, did you fill it with the car on an incline (ramps, jackstands). I have never failed to fill the system properly with the car on an incline. You start so far ahead of the game if you can get that much more coolant in before bleeding. I barely have to bleed the system following the fill, just pour a bit more into the expansion tank with the bleed screw open once its running. I'm not sure why its such a PITA for some. Maybe I've been lucky.

Anyhow, you’ll figure it out, hopefully before something blows ;)

Dave M

[JScritch]

First, I want to thank everyone that replied with help.

I have now replaced the thermostat and spent the last two days meticulously "burping" it and it seems to be running properly now.

But, I have a new issue. Everytime I turn the car off after driving I get the "Coolant Level" message on the dash. When I physically check the level it's right at mid-tank on my expansion tank where it should be.

Is there a simple test for the coolant level sensor or should I just drain the tank & replace it?

[632 Regal]

replace the sender, sometimes they get gummed up, other times they just get stupid, for the cost I would just replace it and be done for another dozen years or so.

First, I want to thank everyone that replied with help.

I have now replaced the thermostat and spent the last two days meticulously "burping" it and it seems to be running properly now.

But, I have a new issue. Everytime I turn the car off after driving I get the "Coolant Level" message on the dash. When I physically check the level it's right at mid-tank on my expansion tank where it should be.

Is there a simple test for the coolant level sensor or should I just drain the tank & replace it?