thermostat & cooling system

Hi guys,

I require some guidance on a small matter with regard to my cooling system. Firstly, the other day I had been for a long drive to an out of town shopping centre. Upon return to the car and having sat waiting to leave in traffic my engine overheated and suddenly blew its load all over the road.

I managed to nurse it to services not far away before the coolant warning light came on and refilled the cooling system as I could not see any leaks or broken hoses (I attributed the failure to me not putting the cap back on the expansion tank 100% properly a couple of days prior). This is because all of the fluid was around the expansion tank not the radiator and the cap was a little loose.

However, after letting the car cool down I drove off and soon the engine got up to normal temp. (about halfway on the gauge) the needle was moving pretty erratic and occasionally reading in the red. I stopped the car a few times on the way home to check the coolant level which was fine no stem etc and the heater matrix was all good too. I spoke to a local garage and they reccommended replacing the thermostat as a precaution even though I thought it could have been a dodgy sender unit as the engine appeared to run fine.

Nevertheless, I got a new thermo and began the renewal today having drained and flushed the system only to find that the thermo I had been provided was the wrong sort . Having found what I do need  it is a sealed unit which turns out is reasonably expensive.

Therefore, here is my dillema do I go ahead and purchase the new thermo (anyone know the part number its for a '90 E30 M3 w/ S14 engine) and will this fix the problem or is there some other gremlin I don't yet know about, so some advice would be appreciated folks.

The gauge did jump about a little before this ever happened but never ran into the red and the engine always ran fine even though its a bit lumpy but apparently thats normal for this car.

Hi,

if the car boiled over, then it can't just be a problem with the temp gauge and could possibly be a problem with a loose (or faulty) radiator cap or damaged hose. But it could also indicate a thermostat problem or that the electric fan isn't coming on (I guess you don't have a fan on the front of the engine). A thermostat problem could give the temp gauge symptons you describe - going up into the red then dropping back down as the thermostat erratically opens and closes. I don't think I would like to take too many chances and for peace of mind would change the thermostat (it's a small price in comparison to a warped head) and radiator cap - make sure you get the cap for the M3, I believe it is different to other E30s and is rated to a higher temp/pressure.

Cheers, Tim.

I have known all the above faults, and can't really add to them. My temp gauge needle on the Evo2 never goes above the 1/3 mark on the gauge. As it creeps above the third mark the radiator fan comes in on slow speed, if the temp get just over half way it switches into fast speed, then quickly falls back to the 1/3 mark. I fitted a new thermostat, radiator and cooling fan switch to it. Previous to the fitment of those components, the car used to run 2/3 all the time with the fan cutting in just before the red.

My SE though, used to run 1/3 of the way up the gauge and the fan cut in at the 2/3 point. But I changed the thermostat on that one and it now seems to run more 1/2 to 2/3 all the time. This may also be something to do with the slow speed fan not cutting in. Also I have replaced the instruments (getting rid of dreaded grey faces) and temp gauge sensor and since then the gauge has flicked up and down. I am sure this is me not tightening the gauge securing nuts up tight enough though.

I'd imagine the flicking of your gauge would more than likely be the gauge or securing nuts to the printed circuit for the gauge. Or it could be a wire shorting to earth too? Your overheating, I would check the connection to the radiator fan (EDIT) SWITCH - usually fitted in the thermostat housing. Infact I would replace that connector as a matter of course.

HTH

I know that when this happened on my aluminum engined 525i, it blew the headgasket and I had only driven it for a few miles before I noticed the steam from under the bonnet. The service attendant had left the cap off and all the coolant boiled out, letting the engine run dry. I got no warning though from the temp guage...it stayed dead centre. It only moved into the red once I put the cap back on and sealed the system again...

I am sure an E30 M3 engine is VERY different, but worth adding the words

BB

You must not have a fan... It shows it on realoem nut does not list it?

http://www.realoem.com/bmw/showparts.do?model=1005&mospi d=47266&btnr=11_0613&hg=11&fg=35

BB

Roger that chaps it does have a fan just could not see it before in the engine bay. I'm just going to warm her up just now and make sure the fan works. Will let you know.

Yes, completely flushed yesterday and the water ran very clear.

You are right there is a relay so there is another possibility. Will give it a go and will let you know how I get on. Thanks very much for your help.

Try taking the plug on the thermostat housing off and bridging two of the wires together ( i can't remember which two ) using an old piece of wire.  If this is wrong someone will correct me. This should make the fan run but if it doesn't then look at fuses. It is a common problem on M3's and usually means a new fan. They are about £200 from the dealer or try Kirby at C3 as he is slightly cheaper.

andyclient has summed it up fairly comprehensively. The only thing I would add is that each of the two fan circuits is also controlled by a relay.

Slow speed is K1 - This is in the fuse box, the row nearest the centre of the car and the one nearest the front of car in this row.

High speed is K6 - This is in the fuse box, the row nearest the wing of the car and the one second from the front of car in this row.

And there are two further fuses involved - Nos. 19 and 20.