Overheating Z3

[Andrew Lockwood]

I have a 2001 Z3 with a 1.9 M43 engine and electric cooling fan.

I have been having issues with the heater for quite a long time. They improved for a short while after replacing the thermostat, but then deteriorated again fairly soon. Now, after being off the road for six months, it is heating up very quickly (much quicker than I recall before) and then overheating.

As far as I can tell, the thermostat seems to be working OK. The return hose stays cold, then starts to get hot when the coolant reaches around 105 degrees, though as I don't think the coolant is circulating, I am not entirely sure what is causing the stat to open - steam possibly?

However, the radiator never gets warm - it is cold across its entire surface, even when the coolant is up to 120 degrees. Also, the fan does not cut in, but then, that is not particularly surprising if it is sensing the temperature of the coolant in the radiator! I flushed and refilled the system fairly soon before taking it off the road, so it has been bled and is topped up.

I am guessing that the two most likely faults are a blocked radiator (but what is the likelihood of it becoming completely blocked - the radiator is cold across its entire surface), or a broken water pump. But again, it hasn't, and doesn't make any noise that would suggest it is damaged.

I was just wondering if my issues are symptomatic of a particular problem with this model?

I was also wondering if there is any way I can check the pump without taking it off. For example, if I took the top hose off the radiator and started the engine, presumably the coolant would shoot out if the pump is working, but wouldn't if it is not?

 

[Andyboy]

If the pump works, you'll see coolant jetting out of the return hole just inside the expansion tank. The pump fail when the plastic impeller breaks up so it won't make any noise. I'd remove it and check.

M43's are prone to head gasket failure - I've changed plenty. It'll just constantly introduce air into the system. But check the pump first. I'd be surprised if it's the rad. A cold heater means an air lock or a water pump failed.

Try bleeding it again. Bleed screw out and rad cap off, hold it at 2500 rpm with the heater set to hot until you get warm air. It might need some coolant adding if you had a big air lock.

 

[Andrew Lockwood]

Try bleeding it again. Bleed screw out and rad cap off, hold it at 2500 rpm with the heater set to hot until you get warm air. It might need some coolant adding if you had a big air lock.

Thank you! That seems to have largely cured the problem. I had to add about 3 litres of coolant during the process. The heater is now working (nearly all the time) and the engine is not overheating, though I haven't actually felt any heat coming off the radiator yet, even though the cooling fan cuts in sometimes.

 

[Andyboy]

Excellent!