Overheating 528 (1996) - advice please

[deutscher]

The wife's 528i has had an occasional, but regular, overheating problem over the many years we've had it.

The problem has always been caused by a failed thermostat. They seem to last about 30,000 miles, although one failed after about 5,000 miles.

Is this a known problem?

The car has just had its fourth one fitted, but overheated again the following day.

My money is on yet another faulty unit being fitted, but are there any other explanations?

Your views appreciated.

[mat205125]

Occasional and regular eh? I know what you mean though!

I'd say slinging thermo after thermo under the bonnet isn't your perminant cure.

Have you tried flushing the system? You need to know if there is a blockage somewhere. Does the radiator actually get hot when the thermo opens?

Stupid BMW viscous fan means you don't get the obvious fan cutting in noise that other cars do I guess.

I'm keeping my fingers crossed the route cause is a cheap component, but fear that there is the possibility that a perminant fix could prove expensive if it's engine related!

Best of luck!

[StuB]

Thermostats are a fairly common failure on M52's. Shouldn't keep going that regular though????

[Egbert Nobacon]

StuB said:

Thermostats are a fairly common failure on M52's. Shouldn't keep going that regular though????

Also very prone to airlocks in cooling system. When refilling mine I had to follow a particular method that was outlined on www.bmwland.co.uk and it solved the airlock problem.

I seem to recall that you had to ensure that the heater matrix was full and this involved having the heating controls set in a certain way so the coolant would pump through whilst being filled.

Good Luck

[ian_cab28]

Can't really help too much on the regular replacement of the thermostat (surely some other cause?, I read that they were damaged by overheating episodes). My 528i overheated due to a fine age/heat related crack on the back of the plastic thermostat housing (water ok but steam on one side of stat preventing opening of stat). In terms of refilling the coolant after I'd drained the rad and the block, on refilling the coolant I had the heater on as suggested but the level in the side bottle on the rad didn't go down...I end up placing my mouth over the neck of the filling point and blowing it through until no air was popping out of the thermostat bleed screw, this seem to work really well, no need to top up after a few day use, no fear of the head being empty on start up. After all the bubbles stopped coming out and only coolant was being pushed out of the bleed hole, I found that the bleed screw had to be nipped up whilst pressuring the system(via my mouth!) otherwise it sucked air back in and water rose back into the side bottle, I did this and then topped up the side bottle, next to no trapped air by this method.

[deutscher]

Thanks for the advice guys.

Turned out that the failure of the previous thermostat and subsequent overheat blew out the radiator and damaged the water-pump seals. Nett result: had to replace the radiator and water-pump as well!

We've had the car from new and it's now done 175,000 miles so I suppose I can't complain too much about two water-pumps, three rads and four thermostats over this time.

Edited by deutscher on Friday 13th October 08:50