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-   -   Intermittent OVERHEATING on e34 w/M50 - HELP!!! (http://www.unitedbimmer.com/forums/showthread.php?t=16765)

volvodefector79 11-01-2009 08:26 AM

Intermittent OVERHEATING on e34 w/M50 - HELP!!!
Hi! OK - a little bummed, here. It was just Halloween (my birthday), and I get stuck with the greatest treat of all - car trouble. :uhoh

So, the problem was confirmed yesterday... it actually began last week. My '95 525i and I are driving on a rural road, going about 65, and my cluster chimes at me that coolant temperature is high. I'm usually pretty good about looking down at my gauges every minute or so, so this happened quickly. As soon as I saw that my temp needle was near red I killed the engine and coasted off on a side road.

My first impression was that I must have busted a radiator hose (upper/lower) or sprung a leak somewhere. Not the case. As I examined the car everything was orderly, and no leaks anywhere.

I then thought it may be a stuck thermostat, but upon feeling the upper radiator hose, it was HOT. So I'm thinking that isn't it, unless it opened up and allowed the coolant to pass (or is stuck partially closed). I had the car sit for about 6-7 minutes, then turned the key to pre-ignition. The temperature had returned to normal! Fast, huh? That's what I thought.

So I started the car back up, ran smooth as usual, and for the remaining 80 miles I drove that day (highway and city) it was perfect. :wtf

This made me think that perhaps the coolant system was not bled properly... I followed a DIY on this (cold engine, set heat to high, run for 30 seconds, lower heat, make sure it's topped off - then run up to normal operating temp, elevate front wheels, use bleed screw to release air until bubbles stop and liquid comes out). I didn't see a whole lot of bubbles, so I'm assuming that when I had the shop replace the thermostat a couple of months ago, they did it correctly (plus I probably would have had problems before now, especially when the weather was warmer).

OK - so I thought this may have been a sensor anomaly, so I drove it two days ago. A-OK until the highway, then it spiked to halfway between normal and hot. Lowered my speed, and it was good (temp gauge back to normal). And in the city/idling conditions, coolant temperature holds perfect - not hot, gauge right in the middle where it should be.

Re-bled yesterday, just in case I missed something. Drove it yesterday afternoon. Same thing - works perfectly driving here and there around town. And during a 25 minute idle while my wife waited in the car with our baby during my haircut (it was cold out, and he was sleeping), no elevation in temperature at all, as she checked it every minute or so. But once on the highway to visit my parents, the temp needle (sure enough) starts to climb. It reached about 3/4 way to the red, and I slowed and we went back home (switched cars to our uber-reliable '95 MB C280... starting to wish we had two of those).

ANYBODY - any ideas? I've heard that if it indeed has the original water pump, the impeller may be suspect, as they were plastic (all the replacements have a metal impeller). Or does it sound like this might still be the thermostat, stuck closed (or at least partially closed)?

AND Ive read that when the auxiliary coolant pump (electric motor that helps circulate the coolant for the heating system) starts to go, it can keep up with city driving, but can't keep up during highway jaunts. BUT, I don't think this is the issue, as we have heat (at least on the passenger side - driver's side tends to be a bit cool with dual climate control). I would think that if this were the case there would be little/no heat.

SO - let me know if you BMW guys/ladies have any thoughts or similar experiences. I REALLY appreciate it!!!

volvodefector79 11-05-2009 11:42 PM

Thanks for the help... (sarcasm).

It was the water pump.

Maybe next time! ;-)

3050rpm 11-06-2009 08:58 AM

Sorry to be a day late and a dollar short, but was the water pump the type with the plastic impeller blades, or a newer metal one?

volvodefector79 11-06-2009 11:17 AM

Hi! No problem... I was on the right track anyway. Indeed, it was one of the water pumps (original - '95 w/120 k miles) with a PLASTIC impeller. Hopefully this one will last another 120k !!!:cheers

Thanks for your interest! Have a good weekend...

3050rpm 11-06-2009 11:53 AM

Wow, one lucky fella! When mine went, it was a sudden, catastrophic failure, while driving on the highway. No hint whatsoever of impending doom, the temp gauge went off to the red zone and that was it, off to the shoulder of the road, cut the engine, and a call for a tow. Fortunately no engine damage. That's one reason why I felt I couldn't give an intelligible reply to your initial posting, the symptoms you described didn't correspond with my experience, or how the plastic pumps behaved when they failed, again, usually suddenly. That, and I figured nearly all those pumps would have been replaced by now. As I said, one lucky fella...

I can't recall at what mileage mine failed, it was maybe five or six years ago, maybe around the 100,000 mile mark. From what I read, the plastic pumps generally crapped out in the 50,000-80,000 mile range, so you got well over that. I've had no problem with the new pump, so I think you can rest assured you can get well over 120,000 with the new one. Happy motoring!

mii82sa 11-08-2009 03:26 PM

same problem on 2005 x5
Hi all,

I'm facing the exact same problem on my 2005 X5. My car has only 47k. When driving on the highway, the temperature gauge would suddenly kick to red for 5 seconds and then go back to normal. This would happen several times on long highway trips, i.e. >20 miles. When I took the car to the stealer, they changed the temperature sensor (last month). But the problem was not resolved. So, I took it to a different stealer at another state where I recently moved, and they recommended I replace the thermostat. I then replaced the thermostat but did it at a bmw repair shop becasue the stealer wanted to charge me hundreds of dollars for it. Anyway, again the problem was not resolved. I took the car back to the same bmw repair shop and they said that there is nothing wrong with your coolant system but the problem still exists.

I'm getting really frustrated. It only happens when I drive on the highway (60 mph or more) and would only last for 5 seconds. However, when I drive in the city, the temp gauge stays in the normal position.

Your recommendatios will be highly appreciated. I'm not really a car expert, so I might just take your recommendation and get it applied by a nearby technician.


Clarksonvalley 10-09-2012 11:02 AM

Have you had a compression check or a leak-down check? Could be a head gasket ready to go - higher HP loads on the highway my be causing combustion gas to leak into the water galleries on a intermittent basis.


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