Raditor problem!!

nikeshoes21 · 10-13-2010, 08:59 AM

i just replaced my radiator my fan and overflow bottle and the overflow hose.On my 97 BMW M3, but when i drive about 5 to 6 miles come to a stop its over heating but my gauge still reads normal. i dont think my Auxiliary Fan is coming on. could i have missed somthing. HELP!!!

markdas · 10-13-2010, 09:26 AM

Sounds like air in the system? Im not sure about yoru M3 but depending on where the temp sendor is positioned, it could be telling the gauge that all is well, where its sat but you could have an air lock in the rad area so its not allowing it to flow properly.....

Our E30 has been a bit temperamental to vent a few times, try running it with the expansion cap off, keep squeezing the hoses top and bottom of the rad and the water pump hose......confirm your thermostat is good too.....

Is there any chance that in changing the rad you have left crap in the system and now its blocking up somewhere.....flush and reverse flush it with a hose and start again!

Good luck

nikeshoes21 · 10-13-2010, 12:58 PM

Thanks ill try that the temp reads normal right in the middle. but what about the fan

Rrrockhound · Rrrockhound's Garage

If the gauge reads normal, how do you know it's overheating?

Manolito · 10-13-2010, 09:22 PM

The Aux fan comes on only if the A/C is on, or if the temperature sensor in the side of the radiator hits a high threshold. You can check the Aux fan by unplugging the temp sensor in the radiator and shorting either side to the center (ground) hole in its plug with the key in the On position. One side should get you low speed fan and the other side should get you high speed fan. As I recall, the two speeds use two different relays, and the low speed fan relay is the one in the back corner of the fuse box. I had a relay fail.

Your problem is probably air, but could possibly be the thermostat. I just had a thermostat fail (stuck shut) in one of my '97s a few months ago. I usually put the front of the car on ramps when I bleed the cooling system. Not sure if it helps. Be sure the heater is on and the cabin temp is set high so the heater valve is open when you are bleeding it.

If you don't already have an aluminum thermostat housing, get one next time you pull off the thermostat. I have had two plastic housings fail on one of my cars. My aluminum housing is on its way.