Unofficialbmw.com

[jinxed523i]

I have a '98 523i with 110k (new engine block fitted at approx 95k). Before Christmas the car overheated just once, out of the blue. Stopped it, checked everything, nothing amiss, got back in, started it....temp. normal!!! Nothing else went wrong for several weeks, then all of a sudden the overheating reappeared, usually sudden ie. rapid rise to the red zone. Often it would just as quickly go back down to normal, only to then go off the clock.
Dropped it into my mechanic. He diagnosed a blown head gasket. This seemed a reasonable suggestion. Got the job done, fitted a new water pump, thermostat, and coolant etc. Needed to get helicoils fitted to re-fit the head bolts due to one pulling its threads during rebuild.All back to normal!!!
Several weeks went by, then out of the blue, the car overheated again...same symptoms. Brought it straight in, but for several days the machanic could not reproduce any fault. Stripped and tested pump, fitted new thermostat (again) and finally removed rad to check for blockages. Indeed it was blocked with fine silt, so new rad fitted. All checked for leaks...off we went again. No faults for several days, then overheat again. This time he took coolant sample to test for combustion gas evidence, none detected....
Finally, he thought he detected a leak (using some type of detecting fluid)around a hose junction, so stripped and replaced. Handed me back the keys, saying it was fixed, no leaks, no overheating.

I didn't even make it home (20 minutes sunurban driving)!!

Now, if I bleed the system before i leave home, I can make it about 15 minutes before blower goes cold and temp rises rapidly. It may or may not go striaght back down, but then goes off the clock just a few minutes later. Going home 9 hours later, car behaves normal...

Can anyone help??? Is there something obvious I'm missing?? Losing my marbles at this stage, can't go anywhere more than 20 minutes from home, and don't want to give car back to mechanic again??

Help, please?

Jinxed523i

[edjack]

Six cylinder E39s are such that it is very difficult to bleed all the air out of the system. Most DIYers elevate the front end of the car as high as they can during the bleeding operation.

This may be the problem.

Also, have you checked the operation of the viscous drive fan? It may not be spinning the fan blades fast enough.

The fan blades should be "sticky" to turn when the engine is stopped, and more so when the engine is hot.
_________________


Ed BMW CCA member since 1987 (Nr. 62319).
'97 540i 6 speed Aspensilber over Aubergine interior.

[jlevie]

[jinxed523i]

Thanks folks,
Still no result. Cylinder block has been hot & cold tested again. Engine block has been pressure tested. surfaces have been skimmed/checked within tolerance. So no cracks...........

Given that there is now a new rad, new thermostat, several new pipes and couplings and a new pump.........can anyone suggest any other solutions before we put the engine back together and resort to seeking divine intervention or voodoo magic??????????

[edjack]

I am totally flummoxed! Search this site. If no answer, post your dilemma here. There may be someone out there with a solution.

http://bimmer.roadfly.com/bmw/forums/e39/forum.php
_________________


Ed BMW CCA member since 1987 (Nr. 62319).
'97 540i 6 speed Aspensilber over Aubergine interior.

[alanfp]

Guessing - could it be that there is blockage somewhere in the water ways that are preventing a good flow of coolant around the system? Intermittent nature being the result of the blockage moving around, then getting stuck at a junction, then getting dislodged.

As I say, it's just a guess.