Strange cooling system issues

Wed Mar 04, 2009 7:42 pm

The cooling system / heater on my 325i is playing up - noticed it today. The engine gets up to temparature within a mile or so, but I get no warm air from the heater for about 4-5 miles - and then it seems to come through all of a sudden.

Even stranger is that once the hot air is coming through whilst you're driving along its fine, but then when you stop, or if the car is doing less than 1500rpm ( e.g in a traffic queue ) the air coming through goes from hot to cold within about a minute - the heater won't put out any hot air again then until you're driving along and the engine is doing more than 1500rpm.

I'm guessing this could be down to an airlock in the system somewhere or a partially blocked heater matrix ?

Its not losing any coolant and has no headgasket issues as far as I can tell.

Any ideas ? if it is an airlock is there a bleed valve or is it a case of running it with the expansion cap off until air bubbles have stopped coming through ?

Wed Mar 04, 2009 7:46 pm

that sounds like an airlock, nothing a good bleed wont fix. if the front of the car is higher than the back, be it on a hill or on a jack, that will help.

Wed Mar 04, 2009 7:50 pm

Cheers fella - thats what I hoped and thought - It could probably do with a coolant change anyway so I might flush it through and treat it to some fresh coolant tomorrow - hopefully that will do the trick.

Wed Mar 04, 2009 7:54 pm

its always a good thing to change the coolant regularly so that'll be good for ur engine. there is a drain plug on the block somewhere but i couldnt find it so i flushed the rad and refilled it with water and drained then repeated that a few times til the water drained out was clear

Wed Mar 04, 2009 7:59 pm

Yeah I've done it on a few other cars but not on an E30 before - will try and give the heater matrix a blast through with the hosepipe as well - can't hurt !

Wed Mar 04, 2009 8:01 pm

dont flush too fast thru the matrix as it can damage the heater valve apparently. but yes a good going thru with the hosepipe would be loads quicker than filling the rad and running it and turning it off to drain the rad etc etc

Wed Mar 04, 2009 9:50 pm

Heater assembly will certainly be damaged if you flush it under pressure the wrong way! You will damage the electric valve.
First thing to check for your problem is that the flow is the right way around now. Are the two heater hoses the right way around? The one from the rear of the head must go the bottom stub.
If this is correct, then you probably do have an airlock. Fill the coolant bottle right up, and pull the top heater hose off, to allow any air out, along with a little coolant.
If the airlock returns, then you probably do have a head gasket problem - or worse!

Wed Mar 04, 2009 9:57 pm

This problem seens to be happening to alot of people in one go, this is the fifth one, including mine that i know of.

Thu Mar 05, 2009 7:46 am

Brianmoooore wrote:Heater assembly will certainly be damaged if you flush it under pressure the wrong way! You will damage the electric valve.
First thing to check for your problem is that the flow is the right way around now. Are the two heater hoses the right way around? The one from the rear of the head must go the bottom stub.
If this is correct, then you probably do have an airlock. Fill the coolant bottle right up, and pull the top heater hose off, to allow any air out, along with a little coolant.
If the airlock returns, then you probably do have a head gasket problem - or worse!

Thanks Brian - I will leave the heater matrix alone in that case - it does give out properly hot air on the maximum setting so rather than risk damaging it by flushing I will just concentrate on getting the airlock issue resolved.

There is absolutely no evidence of "mayonnaise" gunk in the filler cap or dipstick tube, its not actually using any coolant ( I check it regularly ) and there is no evidence of oil in the coolant - if the head gasket was on the way out surely there would be evidence of these issues ?