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hi folks im new on the forums,glad to be a member

i have a nightmare cooling problem on my 98 523i after driving more than 20-30 miles the car starts to overheat with MASSIVE pressure buildup in the hoses and expansion tank which can only be resolved by leaving overnight or bleeding.

i have changed the water pump and gasket,thermostat and housing + seals,viscous fan and tested the aux pusher fan which operates normally to no avail.

i first susspected a leaking head gasket but there is no white smoke from the exhaust,plenty of heat in the cabin until it starts to overheat,and cruicialy no mixing either on the dipstick,oil cap or in the resovoir also car has loads of power when running ok.

i have bled the system numerous times on an incline with the cap off and bleed srew removed only to sort the problem out for a few days also there are no leaks in the morning on the garage floor it only leaks from the reavoir when the pressure builds and it overheats.....

it all seems fine then the temp starts fluctuation only for it to shoot into the red after a few miles,strange thing is some days its fine with no problems,i have noticed a faint smell of collant in the cabin from time to time..

im at my wits end as i cannot think of anything else that needs replacing even my local indie mechanic is stumped insisting that its just trapped air....

if anyone has had similar problems please share... as i love these cars .even guesses lol would be cherished as the next step is just to scrap the car or the head gasket will make that decision for me real soon lol....
 

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something I Heard

Talking to a mate about simular things he said that you have to bleed the system dont drive it leave it over night if your expansion tank down re-bleed it then leave over night then re-bleed if expansion tank down until you come to it and the expansion tank is up re bleed should not need to bleed and everything should be ok

My mate said it took him nearly a week of doing this to get it to bleed correctly. Hope this helps
 

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Discussion Starter · #3 ·
hi guys the system has been bled at least 5 times following the bmw tis procedure and once bled i manage to get about an hours worth of driving before the temp start to rise,once this happens i notice that the hoses are firm and there is a leak from the expansion tank again,

what could cause the hoses to pressurize ?

im gonna strip the cooling system today to check for leaks or damage...
 

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This is the correct way to bleed the cooling system.

1.Jack the front of the vehicle up onto stands as high as possible,
2.Turn the ignition on,engine off,heater on fan setting 1 and temperature fully hot,
3.Remove the rad cap/expansion cap,remove the bleed screw from the rad and IF you have them the bleed screw(s) from the thermostat housing/top hose, return pipe or EGR thermostat.
4.Fill the radiator up and keep pouring till there are no more air bubbles coming out from the bleeds, when good then install bleeds and tighten down(don't snap them),ensure the rubber O-rings/seals are still on the screws/on the bleed holes.
5.Suck some water out so it's not full to the brim, replace the cap and then start the car. Run her up and check for heat from the vents when warm and check if over heating still persists.
6.If good then check the water level again in the morning when cool.
 

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Discussion Starter · #5 ·
hi folks thanks for the replies, personally i think the head gasket is failing its the only thing that could explain the constant pressurization and the fact it takes so long to manifest itself with other cooling problems the symptoms surely would show up a lot sooner and more regular.


the only thing i find strange though is that there are no other HGF symptoms no loss of power,no coolant in the oil,no oil in the collant,plenty of heat in the cabin,and no sign of mayo on the cap or at the dipstick also not a trace of white smoke from the rear.

problem is i live in Belfast N.ireland so trying to find somewhere to do a coolant gas test is night on immpossible as is trying to get the car to them in one piece.

sadly looks like scrappy time for this car.............. a sad end for such an otherwise fine machine as i know from experience the damage,hassle and cost a HGF can cost on these babies exact same thing happened with my last e39 only it was a thermostat and the missus drove it to destruction whilst overheated...

thanks so much for all your suggestions folks....its a shame as i really love these e39's they are a great car , i personally think its criminal the way the cooling system was so badly designed by bmw i have driven e34,e36,e46 with no where near this amount of hassle,we can only hope bmw have got their act together with the new 5 series.
 

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My brother in law had a Honda CX500 motorbike, the head gasket had gone on that and you could see the header tank boiling away like a kettle. No oil in the coolant though, because the gasket had gone between the cylinder and waterway, not an oilway. You really need a sniffer test to see if there's hydrocarbons from the fuel in the coolant to confirm.

I'm sure I've read somewhere that M52 heads tend to warp or crack, maybe yours has cracked and the gasket is 100%, it's the crack that pressurising your system.
 

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Discussion Starter · #7 ·
hi doug that sure sounds like my problem as i cant believe that afer following the bleeding proceedure the guys mentioned on here it's still pressurising the bottle big time...

does anyone have any experience of k seal on m52's or bmw engines in gereral may give that a try..
 

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Discussion Starter · #9 ·
hi folks got a coolant gas test and a compression test done today took about 1 hour thankfully i was told all was fine i know this is great news but it only serves to deepen the mystery.

i also had the car bled today on ramps....for the sixth time this week

to my horror the overheating started again in heavy traffic...im just gutted i felt like just walking away from the damm car...

to date

new water pump
new thermostat
new thermostat housing and gasket
new water hoses
new radiatior
new radiator expansion cap
new viscous fan coupling
new drive belts
new aux fan
compression test .......came back fine
coolant gas test.....fine absolutly no colour chang in the test liquid tested 4 times to be sure with car cold normal op temp and after thrashing
i cant think of a damm thing left to change in the cooling system
i spent the afternoon calling on 5 independant mechanics all are baffled.......

even my local Bmw Main dealer told me it would be a waste of money bringing it to them as i had replaced everything they would have

please can anyone out there shed some light on this madness is there any possible component i have overlooked in the cooling system

whilst this is driving me to distraction there is a small mechanical part of me possibly the boy slavin over old escort pintos all those yeas back that enjoys this mechanical madness.................lol
 

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Discussion Starter · #11 ·
hi no it was from eurocp but i also tried the original cap and another off a friends 5 series
with the same overheating

i do notice a check light come on randomly its like a red circle stop sign that flashes on the dash clocks just prior to the overheating,although sometime this light comes on at startup when cold..

also there seems to be no rhyme or reason to the overheating i can thrash the car to the redline and even travel on 30-50 mile journeys with no problems, some days the car is fine although it seems since the new therm/housing and rad went in this week its got worse.always seems to happen when not moving in traffic sometime it will drop to normal others its screamin into the red the only regular thing is that it never happens at startup or strangly at idle in my driveway i had it idling for nearly 1 hour with constant revving with nothing happening.....

it's madness absolute madness....

thing is i love these babies and i refuse to be beaten as the car is great in every other way with a full bmw dealer service history from new with the same owner.
 

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Discussion Starter · #13 ·
hi thx for reply is this the brass type screw in thingy on the left of the radiator if thats it no i havent changed it yet i looked on realoem but it doesnt show the correct part for my car a 08/98 523i is there another sensor im not aware off somewhere else ?
 

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Discussion Starter · #14 ·
also i put the car on a diagnostic scanner the only fault showing is an maf fault which i know of as one of the fillaments is broken and the car has little power from takeoff,could that affect the cars cooling.....
 

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Discussion Starter · #16 ·
hi thx for the reply what is the funtion of this switch could it cause the overheating im gonna check it out tomoro and replace if needed,what control the aux fan ? i believe its supposed to come on to aid cooling at peak times is it possibel to test whatever it is that switchs tis on off..thanks ever so much
 

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There's a low speed and high speed fan relay on your car for the fans, when the temp gets too much the fan should cut in, have you checked to see if the air con fan works?

They can seize.

I also wonder if it's a cracked head :frown.....:eek, we have had a couple like that, overheat at random moments, we would block test them for ages or run the car up and when it did start overheating jump out and check the pressure of the hoses, if REALLY solid then suspect a cracked head.
 

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Discussion Starter · #18 ·
ok i tried putting head sealant into the cooling system kalimex kseal which made no difference,i also replaced the double temperature switch which is the last component left related to the cooling system left to change,will let everyone know after testing..
 

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Have you made sure it's not a massive air lock ?, I had trouble with my 328, it was right behind the heater matrix and it kept pushing the coolant level down and causing the low coolant level warning to come on. When i revved the engine with the bonnet open, rad cap on, bleed screw on, you could see it bubble up the bottle and push the coolant level down as air had nowhere to go. Mine also had a ******* leak in the rad which only showed itself at certain times. New rad and bottle sorted that along with a proper bleed at a BMW specialist. I had 2 mechanics try to bleed mine and it took a BMW specialist to sort it. It sounds just like the problem I had. I'm no expert but I hope it helps.
 

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Happy to say I've not experienced cooling problems first-hand but having read of LOTS of others, yours really does sould like an airlock / bleeding problem.

Here is a copied and pasted bleed procedure from a man who definitely knows his stuff. I'll PM you the link. Greg.
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Cooling system bleed procedure – M62 engine (E39 – 97 version)


- with cold car
- top up coolant to proper level.
- leave rad cap loose

This stage bleeds air trapped in the heater system.
- turn on ignition switch to position 2 (no start)
- set temperature selectors on the climate control to max temp.
- manually set the fan speed to low (lower end of speed range)
- start engine (check that climate settings have not changed)
- after 5-10 seconds of running rev the engine 3-4 times to about 2500 RPM - hold
there for about 5 seconds each time.
- shut off engine (should not run for much longer than about 30 seconds - you just want
to shut if off before it starts to generate any heat and expand the coolant).
- inspect the coolant level and top up again if necessary.
- tighten the coolant fill cap.

This stage bleeds air from the engine, rad and fill tank.
- now warm up the engine (drive a bit if you wish)
- with engine running CAREFULLY / SLOWLY open the bleed screw. Hold a rag around the area to prevent any excess splashing. Keep the screwdriver in the slot of the bleed screw so you can close it quickly.
- you should have some air/steam escape - progressing to some bubbles of coolant.
- as soon as it progresses to the stage where you are seeing liquid coolant come out then close the bleed screw. Do not over tighten - it is all plastic threads and you can easily turn too far at which point the screw jumps back a thread and you have to re-tighten. Just make it snug with all coolant stopped.
- when the car is cold again re-check the coolant level and top up again if necessary.

You may have to repeat the bleed procedure 1 or 2 more times over the next week. Can "probably" skip the stage for the cold start bleeding of the heater system.

If the level continues to fall below the correct level then have the system fully pressure tested - explaining to your service manager what you have already done.

It is very important that all leaks be sealed so that the system can operate at full pressure. The engine computer is programmed to keep the coolant temp at about 108C at "most" times (there are exceptions) and the only way it can maintain that temp is if the pressure can be maintained - system fully sealed.
 
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