Overheating (again-sorry)

[wrunyan]

I joined this list in desperation. I've been restoring Jags, Porsches, and Austin-Healeys for decades, but can't crack this one. My '94 525i is boiling over. I have replaced the thermostat. No go. Radiator was replaced two years ago. Replaced the sending unit for electric fans. No go. No "cream" in the oil. Engine runs great. No white smoke. Coolant pump replaced two years ago. It does take quite a while (ten minutes or more) of highway driving before it boils (and with a warmup to correct temp before hitting the road).

But . . .

I do notice that the electric fans don't come on, even when the car is boiling over. Fans work great with a shunt at the end of the line with the ignition on, per factory manual (I did replace the sending unit). So, is coolant not circulating owing to 1) blocked radiator, despite relative youth, or 2) defective new thermostat? The lower hose never gets hot hot, just warm.

I tested the new thermostat (from a company that I'm sure many of you know well) and it opened only about 1/8 inch or less in boiling water.

So, the 64 thousand dollar question is: "Is it an idiosyncrasy of BMW thermostats to open only this amount, or should they pop open big-time like the ones I know and love from other makes?

I know; I need to check radiator cross flow, cooling system pressure, etc.

Thanks, Bill Runyan

 

[~R~]

please let me know if and when you figure this one out.
I have the same problem on my 1990 535i.
no cream in the oil, no white smoke, replaced water pump, thermostat, fan clutch and radiator just got cleaned/rodded. coolant doesn't seem to be circulating.

thanks, R

 

[BMWlover]

Overheating solution

I think you need to BLEED the trapped air in the cooling system.
Keep bleeding until there's no bubble from the bleeding hole.
But still I don't understand why your fan does not work even in overheating.
And the following reference can be a good guide to you.

http://www.bmwe34.net/e34main/trouble/overheating.htm

I joined this list in desperation. I've been restoring Jags, Porsches, and Austin-Healeys for decades, but can't crack this one. My '94 525i is boiling over. I have replaced the thermostat. No go. Radiator was replaced two years ago. Replaced the sending unit for electric fans. No go. No "cream" in the oil. Engine runs great. No white smoke. Coolant pump replaced two years ago. It does take quite a while (ten minutes or more) of highway driving before it boils (and with a warmup to correct temp before hitting the road).

But . . .

I do notice that the electric fans don't come on, even when the car is boiling over. Fans work great with a shunt at the end of the line with the ignition on, per factory manual (I did replace the sending unit). So, is coolant not circulating owing to 1) blocked radiator, despite relative youth, or 2) defective new thermostat? The lower hose never gets hot hot, just warm.

I tested the new thermostat (from a company that I'm sure many of you know well) and it opened only about 1/8 inch or less in boiling water.

So, the 64 thousand dollar question is: "Is it an idiosyncrasy of BMW thermostats to open only this amount, or should they pop open big-time like the ones I know and love from other makes?

I know; I need to check radiator cross flow, cooling system pressure, etc.

Thanks, Bill Runyan

 

[~R~]

I have done a lot of research in various sites. many of them point out that if you have a faulty temperature sensor either the one on the radiator or the one near the thermostat your car will overheat. another thing to look for is for a small hose that runs from the radiator next to the big upper hose to the reservoir tank. according to their experience these hoses tend to clog with time.
I have not checked my car yet but I plan to on the weekend.
please update if you fix yours.

R.

 

[wrunyan]

Well . . . .the mystery is solved. I pulled the coolant pump, and there it was--the infamous "high quality plastic" impeller in pieces. I know, I know, you pay a gillzillion dollars for great engineering and somewhere they stick in . . . .

BTW, the "special BMW tool" for removing the fan is really quite easy to make yourself.

W. Runyan