E34 535i - Overheating

It certainly sounds like the coupling. You'd get a used one on ebay for less, search on "bmw breaking". If the coolant level is OK I can't think of anything else.

After inspection, it would appear to me to be a build of RadWEld. It seems to have backed up at the small return hose.

I had used this months & months ago when I was losing water but couldn't find where. It worked for some months, until what turned out to be a crack along the seam of the expansion tank made itself known.

Now I have paid for my mistake, and have loads of dark rusty brown sludge to try and clear.

Will 2 or 3 flushes with something such as speedflush shift most of this? Or are there better "home remedies"?

You can test your fan clutch by sticking your fingers in there and trying to stop it when cold. If it stops easily it's ok, if it chops your fingers off then it needs replacing. Hope this helps.

Steve

It sure sounds like the fan clutch again. If there was a way to bypass the clutch (make it direct drive) for a while that would be a good test. But I don't know how to do that without destroying the clutch (drilling a hole through it and putting screws through the body).

I thought it was the other way round?!

I am currently in the process of flushing the cooling system. However, I didn't think that there felt like much air being belown by fan today (despite the fact that it seemed ok yesterday). Valuing my fingers some what, I did the test with a newspaper. Fan stopped very easily.

Dammit! Now I do need one of these and rather quick!

You are correct it operates the opposite to the response from Tbird-Steve. Maybe that is how the fan clutch works on a Tbird, bit not any BMWs. The clutch is supposed to have less resistance when cold and then become harder to stop (or turn) when hotter.

Doubt the fan clutch can go bad that fast. My 535 also tends to get a little hot in traffic, however that's because the fan shroud is missing, but it never overheats. Another thing to check is that the electric fan in front of the radiator is working. It doesn't hurt to remove the radiator and run water backwards through it and also use a high pressure washer to remove any dirt that's stuck between the fins.

Ulf

The shroud is intact, and I don't have the electric fan. Was that for cars with aircon?

In the UK, yes.

The extra noise. When the clutch 'locks' up, the fan can attain higher RPM

- and you can normally hear this.

Which doesn't prove its locking at high temperatures.

OK. Update:

I have replaced the fan clutch. I have also flushed the system through with some speed flush. Man, loads of crap came out.

The return hose was well and truly blocked, as was the expaansion tank where the return hose fed into. All unblocked now though.

Ran a hose through until the water wasn't so brown any more.

It is fine now. No overheating. Stays on centre.

Have added another bottle of speedflush. Will then flush through again next weekend. Hoepfully most of the radweld sludge will have been removed once I have done that.

Bloomin' typical. Two different problems both at the same time. Pah!

Hopefully that will be the end of it now.

Thanks.

Does it have an auxiliary electric fan? Does this run when it gets hot? Check all the usual if it does not come on.

I don't know what speedflush is but thi smight be a little better.

When you flush your cooling system you want to get rid of two things, oils and rust/scale.

First run a cupfool of tide (or similar) liquid laundry detergent. This cuts all the oils out. Flush with water. Now you can attack the rust and scale with some chemical that can actually get to it now that they're no longer being shielded by an oily barrier.

The safest and stongest chemical to use is citric acid or "sour salt". Any good Mercedes dealer has an auuterly charming white plactic cannister they sell the stuff in as radiator flush. It's not actually not that expensive and is a damn convenient plance to keep it. A paper or plastic bag of a random caustic white power is not cool.

You won't have to do this twice. It works reeeeeeeeeeeeeeeal good.

If you're still having a problem a bottle of Redline water wetter will increase the efficiency of your cooling system. A lot of friends in the US south swear by this stuff although it sounds like you may not need it.

Try the stuff they use to prevent corrosion in central heating pipes. Just add it to the coolant and run for a few days then drain and refill with the correct coolant mixture. You might have to do it a couple of times if the build-up is really bad.

Using a power washer on the rad fins is not a good idea as they can=20 become deformed and provide less heat transfer afterwards making the=20 OP's problem even worse.

--=20 Regards

Steve G

CH inhibitor doesn't clean pipes - it's used to prevent rust in the iron rads, etc. Some also have leak sealing properties - which might be fine for relatively large bore CH pipes, but not so good for tiny car rad ones. CH cleaners do exist - but be sure they are safe on aluminium, as a new head will be expensive. I'd stick with the correct product, though, as the price isn't high.

Hi I have been round the houses I had the same problem .. your problem is the impler its come lose from the water pump.!! you need to replace the water pump this is a common problem with the desin of the impler and water pump . else you will end up replacing everything. The Impler slip as the water pump rotates ad does not push enough water and is completely random

Sounds like you may be right.

After changing the fan clutch and thoroughly flushing the system through, all was ok for over a week. Now it seems to start getting hot in traffic, but cooling again when I'm on the move at a good pace.

I have ordered a new thermostat & water pump. Hopefully that will be the end of it.

and... man! How expensive are the thermostats for these things! Blimey!