Mystery E30 M42 Overheating issue!

Thu Jun 30, 2011 11:41 am

Last week my e30 started to overheat to about 3/4 on the gauge, so I replaced thermostat because the hose on the outlet side felt colder than the inlet. It sorted it because they then felt the same temperature once warmed up, but it still was overheating. I bled and bled and bled the system. The heater comes on really hot instantly and it's got really good return flow back into the radiator, so I don't think there is any air trapped.
So next I replaced the viscous fan, the new one had more resistance than the old one, so I was confident it was that. It wasn't and the same problem is present. So then I had the water tested for any head gasket issues - nothing showed up, so then it was up to the water pump, which got taken out, and it is fine!
Which is odd, because when i revved it to 2.5k the needle would start to drop on the gauge so I was confident it was that!

So it could be radiator? -it doesn't leak.
gasket leak into the cylinder?????
Either way, the next thing I try will be expensive!
Anyone got any ideas?

Sun Jul 03, 2011 12:42 pm

I have fitted a new rad and it is massively better, but sill not %100. Very odd.
I'll give it a week to make sure there is no air trapped since the rad swap. If it qoesn't get any better then I'm gonna put a new rad cap on it to see if that helps.

Mon Jul 04, 2011 12:44 pm

Fail - it creeps up to 3/4 but much slower.
Next stop is a new temp sender.

Mon Jul 04, 2011 8:47 pm

Is it using any water?

Was the viscous fan you fitted brand new?

Tue Jul 05, 2011 10:52 am

It isn't using any water and the fan thermostat and radiator were all brand new

Fri Jul 08, 2011 10:54 am

i would double check your thermostat to make sure it is opening, also may be that the new thermostat is opening less or later than the old one..

I had the same problem, when i revved the water pump would circulate and drop the temp, top hose hot and bottom cold.
Changed the stat now all is cool.

Also if you have a rusty colour showing in your tank it could do with a flush. some people use tap water as coolant and it just corrodes everything internally slowly but surely.

Let us know how u get on al.....

Sat Jul 09, 2011 11:29 am

It has got better, so I'm confident it's something silly but I'm just gonna drive it for a bit to see if anything falls of/ blows up.

Mon Jul 11, 2011 2:10 am

Well I can't devote anymore time to this and I'm gonna get something more sensible for towing my race car, so I may just break this for parts so if anyone wants a fully polypbushed rot free shell or any of the nice parts I've gathered on this car then check out the for sale section.

Mon Jul 11, 2011 11:04 pm

sorry to hear that mate,
let me know if u want a hand

Tue Jul 12, 2011 12:33 am

Cheers Tam I'm renting a big unit now so I can leave it there and do it at my leisure.

Tue Jul 12, 2011 7:37 pm

That sounds good, try renting a big unit in london!
Theyre just too expensive.
I'm busy till friday, will give your ecu another go then.
Think its a problem with the spark.

Tue Jul 12, 2011 8:42 pm

u going to the motor show by any chance, the germanmotorshow.co.uk thing in southampton?
24th july

Tue Feb 28, 2012 11:57 pm

Mystery problem identified, and quite simply actually. I finally got round to doing a compression test, which turned out to be completely irrelevent as when I removed the first spark plug it was dripping in oil:

Must be piston rings or perhaps a headgasket leak between oilway and cylinder.

Sun Mar 04, 2012 1:03 am

It doesnt look like this oil is from inside the engine (in the cylinder). The rocker cover probably leaks a little oil from the inner edge of the gasket, which will collect arround the top of the plugs. This is confirmed by the oil tide mark around the bottom of the socket in the picture. As soon as the spark plug is loosened and removed this oil that has collected on top of the plug flows down, coating the threads and the electrode, exactly as per your pic. If you had a plug this wet in the engine it would have a serious missfire at least.

I have not posted this to diss-prove your theory by the way, just dont want a potentialy good M42 off to the scrap heap when it could live on!

Tue Mar 06, 2012 2:08 am

Ok thanks, that makes sense. I wish I'd continued with compression test now. It may have saved me an engine swap. Oh well, all will be revealed when I strip the engine down.