E36 Compact overheating problem...

[Mr Doricar]

Hi guys,

Ive got a weird problem which I was hoping someone could comment on. The car was absolutely fine, never overheated at all, but one day the heater stopped working. After I tried to fix the heater by checking the matrix, fitting a new thermostat and water pump. Since then the car overheats and the expansion tank gets very hot and fills with bubbles. Have bled the coolant system, but no joy. Any ideas?

I dont think its headgasket as there is no brown coloured milky residue in the oil cap or the radiator.

Any ideas?

Thanks in advance

[DesktopDave]

Sounds like you have two problems...the heater system may have a leak or obstruction in the heater core or a broken heater valve.  When you opened the system a bubble in the thermostat housing or water pump will air-lock the system.  If the system isn't pressure-tight it won't build the necessary 15psi.  Then it forms steam bubbles and overheats.  Go to the passenger side hose and give it a good firm squeezes.  You shouldn't hear any gurgling or swishing, and it shouldn't have much give.

To eliminate the core & valve from the system, you can 'loop' the heater hoses with a cheap "Help" adapter.  Auto parts stores will most likely have them in stock.  Alternatively, parts stores sell a cheap pressure tester, but it takes a bit of practice to use and will need an adapter to fit the screw-on BMW cap.

Bleeding that M42 cooling system is difficult, no doubt about it.  My e30 was overheating when I bought it, took me three tries and two coolant bleed screws to get it sealed up.  I usually fill both sides of the main hoses then park it up a steep hill before attempting to bleed it.

I also use a very high ratio of distilled water (66/33 water to coolant, with a 1/2 bottle of water wetter) to thin it out.  No problems even in sub-zero temps with that setup, BTW.

Use a big flat-bladed screwdriver to tighten that carefully and just enough to seal.  Nothing about that car has annoyed me more than seeing a six-foot gusher is coolant spewing from the stub of that ridiculous $3 part.  It's a PITA to get it out without damaging the expansion tank too.  Next time I'm getting the brass aftermarket substitute from Pelican!

[Mr Doricar]

Hi Dave,

Is that right? I didnt know they were such a bitch to bleed. In that case i'll give it another try. I would bypass the heater completely but its pretty damn cold here in the UK so I need it this time of year,

Do you think if the headgasket had blown that it would be obvious? I hope its a simple cheap problem to fix.

Thanks for your help

[DesktopDave]

Does it ever get that cold in the UK?  You should have a northern US winter 'cross the pond.  That'd thicken your blood right up...JK

Yep, the head gasket would be unlikely, and fairly easy to diagnose with a compression test.  Bleeding is far more likely.  I use a few rules of thumb when working on my cars.  This one is a cardinal rule...if some system I just worked on isn't right after I've been there, I suspect that immediately.  Sounds simple, but I've ignored it many times and suffered great frustration.

My overheating problem was cheap & easy, I hope yours is the same way...about $15 for 4L coolant (BMW makes great stuff but I used Zerex G05 this time), $9 for water wetter, $3 for 4L distilled water and $10 for three new bleeder screws.  Never know when you'll need another, eh?  $39 is pretty good, I was really worried about it until I got it buttoned up.  The big cost will be the valve if that's your trouble.

Your e36 compact has the single temp HVAC, right?  They all did over here.  That's a lot easier than the dual-temp system with the little valve servos controlling the temperature.  The diagrams at RealOEM will detail your exact system setup.

[Mr Doricar]

Well for me zero or -1 is cold enough! I prefer a warmer climate

I think its the single type yes. I'll have a go over the weekend and see how I get on.

Thanks for the sterling advice old chap what what*




* Gotta speak proper British for you yanks

[DesktopDave]

Not sterling 'till it works, eh?

But we DO speak proper English!