Overheat E39

[Waynester]

E39 523, 110,000 miles, almost zero issues in last 4 years ownersip.

I noticed while stuck in traffic the temp gauge climb, if I opened the heater to 32 degs the temp returns.
I checked the coolant level & it was a little low so I topped it up.
Car still trying to over heat!

I have not allowed the temp to get anywhere near the red maximum, have checked the oil, very clean no emulsion?

One thing suddenly occurred to me yesterday was the fan not kicking in, can this be the only thing at fault? If so what fuse covers the fan, don't have Haynes with me.

Only other thoughts I've had were water pump and/or stuck thermostat?

[skoff]

My money is on a small leak somewhere in the cooling system... I'd get a pressure test done.

[Simon1397]

When this happened to mine the head gasket followed soon after

[Gaygle]

This is classic blown thermostat, although the fan not functioning is just as likely.

Edited by Gaygle on Tuesday 25th January 12:04

[Gaygle]

skoff said:

My money is on a small leak somewhere in the cooling system... I'd get a pressure test done.

I can't see how a small leak would cause the car to overheat. As long as there is enough coolant and it is being pumped around properly, a small leak shouldn't really affect it?

[Gaygle]

Simon1397 said:

When this happened to mine the head gasket followed soon after

Sounds like you let yours fully overheat/get very hot as a blown HG is often what happens as a result. OP, if you don't let your car overheat, you shouldn't have to worry about the HG.

[skoff]

Gaygle said:

skoff said:

My money is on a small leak somewhere in the cooling system... I'd get a pressure test done.

I can't see how a small leak would cause the car to overheat. As long as there is enough coolant and it is being pumped around properly, a small leak shouldn't really affect it?

Just from personal experience, I have been through 2 radiators in the last 13 months (damn you 12 month warranty!). On both occasions the temperature went up, but when I topped up the water to get me home, it was low by less than half a litre. Both caused by small leaks. The temperature only went up when the car was sat in traffic, so I think the E39 works on pretty tight tolerances.

[bull996]

As there has been no previous issues and most of the coolant was still in there, its unlikely to be the thermostat.

I would put my money on the viscous fan coupling having broken...£40 from Euro Car Parts. Its almost certainly that, they always go at some point. However, it could be the water pumo, so while you are doing the fan, do that as well, its only £35. Some would also say do the thermostat (£8.50) and thermostat housing (£10)-all are in the same area and are accessable once the fan shroud is off.

[Gaygle]

bull996 said:

As there has been no previous issues and most of the coolant was still in there, its unlikely to be the thermostat.

I'm confused? Why can't it be the thermostat if most of the coolant is still there? And why does he need to have previous issues for it to be likely that it is the thermostat?

[bull996]

Gaygle said:

bull996 said:

As there has been no previous issues and most of the coolant was still in there, its unlikely to be the thermostat.

I'm confused? Why can't it be the thermostat if most of the coolant is still there? And why does he need to have previous issues for it to be likely that it is the thermostat?

I guess it didnt read right. It could of course be the thermostst, but I dont think it is.

I know a car can overheat if the thermostat locks shut, but in my (not incosiderable) experience of e39 cooling systems and thermostats, they usually stick open, leading to cool running.

I suppose we need more info-eg does the temp return to normal when on the move etc. Here is the "newspaper test" for the fan.

With the engine OFF, try and spin the fan by hand, if it turns with no resistance, its fooked and needs replacing...

Have the engine running on idle, and get a rolled up newspaper. Try and stop the fan with the paper (but be careful!) if it stops its fooked, if it shreds the paper its OK

[Renn Sport]

This happened to my brothers old E39 and my brother inlaw's E39. In both cases it was just rad replacement and a thermostat.

Good luck.

[Simon1397]

Gaygle said:

Simon1397 said:

When this happened to mine the head gasket followed soon after

Sounds like you let yours fully overheat/get very hot as a blown HG is often what happens as a result. OP, if you don't let your car overheat, you shouldn't have to worry about the HG.

First time it happened was in the lion enclosure at Longleat, we sat in the car getting quite warm for quite a long time until the engine had cooled.

[Waynester]

Thanks chaps, it has only started doing this in the last 2 weeks, and only then in traffic. It hasn't touched the red zone thankfully but the fan is definitely not kicking in.

Had a look for leaks & all is dry.

Once out of heavy traffic & moving the needle comes down to the 12 o clock position.

I'll give the fan a test. Trouble is I leave for work in the dark & drive home in the dark so somewhat hinders looking the car over until the weekend.

Time to get my hands dirty then.

[physprof]

get thermostat changed and have a look at the viscous coupling for the fan as well.

[bull996]

Waynester said:

Thanks chaps, it has only started doing this in the last 2 weeks, and only then in traffic. It hasn't touched the red zone thankfully but the fan is definitely not kicking in.

Had a look for leaks & all is dry.

Once out of heavy traffic & moving the needle comes down to the 12 o clock position.

I'll give the fan a test. Trouble is I leave for work in the dark & drive home in the dark so somewhat hinders looking the car over until the weekend.

Time to get my hands dirty then.

I spent most of last week after work with a torch in my mouth pointing towards the engine bay of mine!

[dcb]

Waynester said:

Thanks chaps, it has only started doing this in the last 2 weeks, and only then in traffic. It hasn't touched the red zone thankfully but the fan is definitely not kicking in.

Had a look for leaks & all is dry.

Once out of heavy traffic & moving the needle comes down to the 12 o clock position.

I think it's sticking thermostat, not unknown on older cars.

[Patrick Bateman]

How would a failed thermostat cause this if they fail in the open position?

[Huff]

Off the top of my head - some (all??) e39s have an ECU-controlled 'thermostat' - i.e its a controlled valve, rather than a purely temp-controlled waxstat. Other known issue can be the water pump: certain models have a plastic impeller that separates from the driven shaft, so at low speed not enough liquid flows. It gets worse quickly. Replacement is DIYable, not expensive.

A google of 'E39 cooling system' will no doubt drown you in things to look at. Knowing that the temp gauge is smoothed - ie it only moves out of 'straight up' if something is grossly wrong - do look into why sooner rather than later!

[eliot]

Huff said:

. Knowing that the temp gauge is smoothed - ie it only moves out of 'straight up' if something is grossly wrong - do look into why sooner rather than later!

Precisley - its just a needle that moves over to the red to tell you something.

Dont mess around get yourself a radiator, thermostat and water pump and change the lot right now.
I tried to skimp by just doing the rad initially. Then the pump went, so just changed that, then the stat (overheated) and then the radiator again and finally the HG went.

[pwd95]

Nice looking machine Wayne. Got myself an old low milage E36 now too. How you keeping.