E36 M52 overheating slightly

Funny thing happened today. For the first time in well over six months it was warm enough to drive with the heating turned off in my '96 328i. In fact I
think the E30 will leave it's hibernation in the garage soon :-)
Anyway, I noticed after about 50 miles the temp gauge was just above the 3/4 mark. Turned the heater on half way and it was fine. Check the coolant and it was fine, heater blew nice and hot so there must have been plenty coolant in it. Drove 30 miles home with the heater half on, no problems.
About a month ago the car blew the coolant hose from the back of the head to the heater. I had to very gently drive about 18 miles (mostly down hill) like that but it was -12C outside and I kept the coolant topped up, car never went into the red zone as I stopped quite a bit to let it cool (with the bonnet open on a freezing night). I even drove with the bonnet open and hooked on the safety catch to increase airflow to the engine. Car has been fine since, used no coolant and no overheating. But I've always had the heater on.
If there were any head gasket / head warping I'd surely be losing coolant? Even if the cylinders were pressurizing the cooling system (had that on an M60 and an M40 before).
I replaced the thermostat a year ago incidentally.
So I'm thinking it might be a failing water pump? Pretty sure I have the pump with the metal shaft and plastic impeller. When these fail do they do so catastrophically or might they just slip a bit and cause my problem?
Can't see it being the viscous coupling, it was only about 18C today and I was doing 60ish mph.
I'll give the radiator a good hose off in case there's lots of winter gunk blocking the cooling fins. But failing that I'm thinking water pump. If I'm not losing ANY coolant then the head must be fine surely?
Any thought other than replace the water pump?
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Email: snipped-for-privacy@unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland
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gunk and rust and stuff builds up on the water coolant jacket inside the cooling system ...
a back flush is use full to scrub that out sometimes.
Using chemicals and harsh detergents is a big warning from me to be very careful as the weldings do work their way loose from the inside with such caustic items in the cooling system.
Be very careful with the BMW cooling system, it works very well but it is not strongly built and must be kept well with the maintance done spot on.
You can always take the thermostat out and put into a pot of heating water with a thermometer and see if the thermostat is operating properly for its temperate range, this visual test will confirm it for you and leave that out of the car science in the fact pattern.
Your car is suppose to cool itself with out the help of the car heater being on ... if the thermostate really is good .. then the issue is to replace the radiator core after a flush of the system.
My guess is your radiator core is plugged up.
sumbuddie hopes this helps.
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Okay, this is a sign you've got a problem that needs to be addressed somewhere. Hoses shouldn't just blow.... although if you had one blow you might want to check the others for dry rot.

Could be.
More likely than a failing water pump is a clogged radiator. Less likely than a failing water pump but still possible is a clogged block.
I would make sure water runs well through the radiator and it isn't clogged up. You can't rod these out like you can with the 2002... you have to just bite the bullet and replace them when they get clogged.
The plastic impeller pumps usually fragment and stop working completely, sometimes clogging up the block in the process. So I'd probably change it pre-emptively anyway.
You _could_ try an acid flush. The stuff is available at your friendly local auto parts store. It will remove a lot of the old deposits both in the block and (if there's some flow still left) the radiator. That's the good news.
The bad news is that if your radiator or your head gasket are held together by crusty deposits, you will find they start leaking severely even when they were fine before you did the acid flush. So you're risking making some things worse at the same time you're making some things better. --scott
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Think I'll pull the rad and give it a back flush. Ran the car today with no heater and no problems. But I'm not 100% happy.
As for the dead hose it was 14 years old :-) That back hose has a weakness in my option. One end is larger than the other and from what I've read they fail where the neck size decreases. All the other hoses seem fresh, in fact the whole engine bay is immaculate.
I thought maybe it wasn't bled right, but I had another go and I'm pretty sure that wasn't the issue.
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If you gonna pull the rad any way ... and back flush it ...
put it in a boil tank and cook it clean ...
sure to keep most of its strength that a way ...
IMO and all that acid rot ...
sumbuddie wear blind sea
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