OT: e39 528i overheat

[tim]

Dear Bimmerfolk,

My neighbor's '98 528 is acting up again. The other day, he had a problem with a wiper relay. Today he shows up in my driveway for our golf game, comes inside for 5 minutes leaving the car idling, and when we get out to go, the coolant gauge is in the red and the light is on. ****! We went in my e34, which of course, saved the day as usual.

I suspect a relay since I didn't hear the aux fan. Or perhaps a bubble near the thermostat or a bad unit. Outside chance of water pump impeller failure. This is a well maintained car.

I restarted hours later to do a dignostic. Held the middle on the gauge for a minute and then shot right up. I did not hear the aux fan come on. The top hose was hot, and the bottom hose was tepid and flaccid (I know that sounds bad). I ran the heater at full blast and it brought the temp back to middle right away but the needle was fighting higher.

I have my theories, but I'd like to hear yours as well, especially if think it might be an easy fix!

Thx

tim

[uscharalph]

Is this a symptom of the weeper hose failure / clog?

[tim]

I'm not familiar with the weeper hose issue. My expertise is more with m60's and m62's.

-tim

[tim]

bump

ne1?

[tim]

Update:

I checked the Jolly Rancher fuses behind the glove box- ok
I jumped the Aux fan and confirmed operation in two speeds-ok
I removed the temp sensor but could not check it as I didn't have a multimeter.

At this point I'm thinking

a) thermostat
b) water pump
c) faulty temp sensor

What do you think?

[bimmerd00d]

My mom's 2000 528iA did the exact same thing. center, then it shot to red. replaced the water pump, t'stat, and radiator and all has been well for the past 40k miles, never gets above middle....ever.