overheating!

[ojw]

I've just become the pround owner of a 1991 520i, however the gloss of my purchase has been taken off by the fact that it is overheating!

Doesn't seem to be a big problem, it only happens if the car is stationary, and the gauge just creeps up gradually. If the car is travelling it seems to be ok. THe car has 93k on it with a full service history.

I've picked up a few bits of info from other posts, but just wanted a bit more moral support to let me know if i'm thinking along the right lines. So, when the temp is high both fans appear to work, the main fan appears to run all the time - is this normal?

The rad top hose is warm, the bottom cold - does this indicate that the radiator is blocked?

ALso, the air coming out of the heater inside the car does not appear to be very warm, despite the temp gauge being well towards the red - does this indicate an airlock anywhere?

Looking at the archives, it seems it might be any of the water pump, thermostat or fan, but i'm trying to work out which is most likely so i can start with that - any ideas?

Thanks in advance!

[GaryE]

Hi ojw,

Don't allow your car to overheat at all, I've had very much the same problems as you describe and I ended up replacing a lot of parts to get the beauty back up and running. (6 coil packs needed!)

Make sure you've read www.bmwe34.net - Specifically to your problem, take a look at http://www.bmwe34.net/e34main/trouble/overheating.htm

As your car is overheating when stationary, I would say its either your thermostat or water pump, or both. The fact that the top hose connecting the radiator is hot and the bottom pipe is cold, almost certainly indicates a faulty thermostat, or a massive air lock. Both cheap to fix.

First make sure you have a fully bled system, I bleed the system by taking the radiator cap off, and placing my finger over the bleed hole (small hole very close to top of expansion tank) and grab hold of the lower hose and squeeze and release. I do this over and over until no air bubbles come up. If your getting lots of air bubbles come up, then this could be the problem!

If you are not sure when your thermostat and water pump has been replaced, I would advise doing both of these to ensure prolonged life with your beemer. Although it sounds like a nackered thermostat to me.

I can't stress enough, I wouldn't advise driving the car when the temperature indicator goes above the half way mark - your asking for trouble! I learnt the hard way ...

Good luck.
Gary

[Jay 535i]

This thread describes an overheating problem I had, and how I solved it. Maybe it will help you:

http://www.bimmer.info/forum/showthread.php?t=12836

Don't be thrown off by the thread's title. In the end, it had nothing whatever to do with the aux fan.

[Kalevera]

Welcome!

The cooling system on a 520 should be easily accessible, so there's no reason not to just take it apart. One thing I would do immediately is a cooling system pressure test to determine if there's a leak somewhere. Buying a car that overheats is suspect, and underscores the importance of having it carefully inspected prior to purchasing. Most people, even in countries other than the US, get rid of these cars for a reason.

How high does the needle go if the car is left to idle? Forgive me if you know this already, but 12'o clock, or a tick mark below, is the standard temp.

The 520 will have the expansion tank mounted on the side of the radiator. The inlet between the radiator and the tank could be clogged, but the fact that the lower radiator hose is continually cold suggests a flow problem. However, if there was no flow, the car should overheat regardless whether its under way or not.

My vote is for a bad water pump. Remove the belt and inspect for leakage at the bearings see if there's any play in the shaft. A '91 may also have a plastic impellered pump, which should be replaced. We saw one from a '91 or '92 525 a few weeks ago that was original -- didn't show any signs of cracking, but it was replaced with a metal impellered unit, regardless.

best, whit

[ojw]

Hi all, thanks for the help. a bit of an update, now i've taken the car on a couple of runs:

As long as the car is moving, the needle stays at 12 o'clock. Even a bit of stop start traffic doesn't really get it moving upwards.
Gary, i tried bleeding it as you described, it gurgled a bit, not sure if any air came out though! Although after doing this, i took it for a spin. On getting home, the bottom hose was hot, although as it was left standing the temp did start to creep up.
It will go up to the red if left, although it has to be left for around 15 mins to get this far.
Looking through the threads i've got a feeling it might be the main fan. When setting off i don't think i get this whoosing noise that people describe, although this is the first auto i've driven so it doesn't sound like a normal car to me anyway - are there any more conclusive ways to check the operation of the fan?

thanks,
owen

p.s. with regard to having the car inspected, it was only £500, so didn't think it worthwhile. There are none of the "sinister" signs, like smoke, oil in water/water in oil, so i'm hopeful it's not a serious problem to fix. i will be taking the car for a service at some point soon, but funds don't quite permit it yet!

[JonE]

Hi Owen,
Sounds to me like the viscous fan clutch may be shot. If you don't feel ALOT of air blowing around behind that engine fan when it starts to creep up in the hot range on the temp guage, then it could be shot. Also, when you turn the car off after it has been somewhat hot, then that fan would usually come to an abrupt stop, if not, it may be freewheeling (spinning) also indicating the faulty clutch of the engine fan. This would help explain why your temp is fine while moving down the road, air is being pushed through the radiator and doesn't need the help vs. when car is at a standstill like in heavy traffic with no air moving through the radiator.
Hope that helps, and I think Bruno's site may have good info for you as well, http://www.bmwe34.net/e34main/trouble/overheating.htm
JonE

[GaryE]

The fan should be whipping it round when the engine is on, you should be able to feel clearly that air is moving around. When I put my hand about a foot above the back of the engine I can feel air from the fan.

My viscous fan was pooped, and had to replace. After installing the new viscous fan coupling I could clearly tell that my old one wasn't up to scratch. When you turn the engine off, and when the engine is cold the fan should stop dead almost straight away after you shut down the ignition. When the engine is warm, the viscous fan takes a little longer to come to a halt, but it doesn't free spin. I beleive its wax inside the fan coupling, hence the differences from cold and warm.

Gary, i tried bleeding it as you described, it gurgled a bit, not sure if any air came out though!

Yep, I think you need a second pair of eyes to check if any air comes out, but the gurgling sound you mention sounds like air was trapped. The level in the expansion tank will drop if there was any air, make sure you get all of the air out and refill up to the marker line (never put cold water/antifreeze in a hot/warm engine!).

£500 not bad for a luxury vehicle, eh?! I paid £1100 about 12months ago for the same year/model. With petrol prices like they are, it seems everyone is trying to offload their petrol guzzling beasts - great time for bargain hunting if you can afford it. Got any pics?

Gary

[ojw]

i'm now fairly convinced that the fan is not working properly, it certainly doesn't stop straight away when the engine is shut down, and it doesn't seem to be moving much air about!
So it seems a sensible place to start, so, any tips? Am i correct in thinking it's not an electric fan, but driven from the engine via this viscous coupling thing? Forgive my ignorance, i'm not completely mechanically retarded but i;m generally used to simpler cars!

While i'm busy searching the net for cheap parts, any suggestions for suppliers? I've used GSF and Eurocarparts before for peugeot and vw parts, are they decent for E34 bits?

Gary, it's the best £500 i have ever spent! I needed a cheap car as i've just sold a £4k impreza to fund a house purchase, but didn't want to potter around in a battered old fiesta or similar. I have run old luxury cars before for banger money, and they really do give awesome value for money - i don't do much mileage, so the fuel consumption doesn't bother me. Will post some pics tomorrow if i get time!

[uscharalph]

Hi all, thanks for the help. a bit of an update, now i've taken the car on a couple of runs:

As long as the car is moving, the needle stays at 12 o'clock. Even a bit of stop start traffic doesn't really get it moving upwards.
Gary, i tried bleeding it as you described, it gurgled a bit, not sure if any air came out though! Although after doing this, i took it for a spin. On getting home, the bottom hose was hot, although as it was left standing the temp did start to creep up.
It will go up to the red if left, although it has to be left for around 15 mins to get this far.
Looking through the threads i've got a feeling it might be the main fan. When setting off i don't think i get this whoosing noise that people describe, although this is the first auto i've driven so it doesn't sound like a normal car to me anyway - are there any more conclusive ways to check the operation of the fan?

thanks,
owen

p.s. with regard to having the car inspected, it was only £500, so didn't think it worthwhile. There are none of the "sinister" signs, like smoke, oil in water/water in oil, so i'm hopeful it's not a serious problem to fix. i will be taking the car for a service at some point soon, but funds don't quite permit it yet!

I was having similar problems on my 525i w/ M20 engine. We completely overhauled the cooling system for around $450.00 in parts. That meant new radiator, fan clutch, water pump, thermostat, hoses, belts and radiator cap. Yours may be solved in a different way, but I figured most of that stuff was 16 years old, so why not remove all variables.

[GaryE]

i'm now fairly convinced that the fan is not working properly, it certainly doesn't stop straight away when the engine is shut down, and it doesn't seem to be moving much air about!
So it seems a sensible place to start, so, any tips? Am i correct in thinking it's not an electric fan, but driven from the engine via this viscous coupling thing? Forgive my ignorance, i'm not completely mechanically retarded but i;m generally used to simpler cars!

While i'm busy searching the net for cheap parts, any suggestions for suppliers? I've used GSF and Eurocarparts before for peugeot and vw parts, are they decent for E34 bits?

Gary, it's the best £500 i have ever spent! I needed a cheap car as i've just sold a £4k impreza to fund a house purchase, but didn't want to potter around in a battered old fiesta or similar. I have run old luxury cars before for banger money, and they really do give awesome value for money - i don't do much mileage, so the fuel consumption doesn't bother me. Will post some pics tomorrow if i get time!

Yep, its not an electric fan, its attached to the waterpump and the fan is attached to the viscous fan coupling. An electric fan would be a better solution and if you have the money for it, its a recommended upgrade. http://www.bmwe34.net/e34main/upgrad...trical_fan.htm

I use GSF for most parts, however for some items your better off going to a BMW dealer, the parts prices arn't that different and you get the added benefit of better quality from BMW. I got my thermostat from BMW - its german and looks much better quality than the french one GSF sell.

Gary