2003 325i Confusing Overheating Issue

[vtgts300kw 90]

A few things have happened which are obviously related, outlined below.

The other day the coolant light came on intermittently ( like it was being affected by the coolant sloshing around ). Then yesterday I noticed that I couldn't get any heat from the AC, it just blew cold no matter the temp I set it at. Sitting in traffic last night, the temperature gauge rose above normal, stopping short of the tripping the red light, I moved about 10m up the road and it went back down to dead center, where it sat for the remaining hour I was stuck in traffic. I got home and topped up the coolant ( it was sitting below the minimum mark ). Started the car this morning and it cme up to temperature as it usually does, then after sitting in traffic for 10 minutes, it rose sharply. I then got out of the traffic, drove up the road and it quickly went back to normal. It also tripped the coolant light again. Drove 10 minutes into work and the needle sat dead center. Haven't checked the coolant level as it's hot.

Any ideas?

Edited June 2, 2015 by vtgts300kw

[Allanw 1071]

The gauge doesn't move from normal, until the coolant on the sensor is HOT - it will show normal until at least 115C, probably 120C.

Also, be aware that the gauge ONLY reads the temperature of the coolant it is in - if the coolant no longer touches the sender, it often just reads normalish. The sender is very low in the M54, so it's not too likely to happen, but the gauge climbing means things are getting HOT! The OBC in our E39 is set to gong for high coolant temp at 130C or 135C, so you don't really want to get that far.

I'd stop driving it if it were mine.

If you have coolant loss, you've got a leak somewhere probably, and the overheating and lack of heating in the cabin will probably be because of air - certainly the heater will be.

You do NOT want to overheat an M54 badly, because you'll need a headgasket done, and that usually involves fitting timeserts to the block - which is REALLY difficult to do with the engine in the car on a 3 series, because the back holes are far enough back that the scuttle gets in the way of a straight drilling line.

On an M54 powered E39, the easy way to bleed the air out, is to turn the ignition on but engine off, heater on highest temp, fan on lowest speed, top up the coolant, and bleed bubbles out the bleed screws - while keeping the level as close to correct as possible. I assume the 3 series has the same auxilliary coolant pump.

This might help too: http://bimmersport.co.nz/topic/47848-e39-obc-secret-menu-ktmp-coolant-temperature/?hl=%2Bsecret+%2Bobc+%2Bmenu

[B.M.W Ltd 950]

No aux pump on the three. I'd be looking for leaks first with a pressure tester

[vtgts300kw 90]

Bled the coolant system, took it for a drive around the CBD and the temp fluctuated between 92-94 ( via OBC ). And I got heat back into the AC. Will check the coolant level before I leave work to see what's been lost, and try get it pressure tested tomorrow.

[Allanw 1071]

No aux pump on the three. I'd be looking for leaks first with a pressure tester

Lucky someone knows! Thanks Glenn!

[vtgts300kw 90]

Expansion tank was leaking. I've pulled it off and replaced it ( along with the thermostat, what an insane design ), but the top radiator hose does not seem to want to fit properly. I can get the 2 ends to fit snugly and locked in ( at least I think the radiator end is on far enough ). But the 3rd hole, back into the expansion tank, doesn't want to marry up to lock into place. Any tricks? It's at least 5mm away from being able to clip in.

I also discovered that someone has hacked a hole into the intake for the alternator. Why??!!

Edited June 4, 2015 by vtgts300kw