no a/c = overheates but with a/c on all is oke

[lezonebay]

temperature dropped enough last night that in a morning I shut the a/c off - pushed the snowflake button to off.

within minutes (1-2) the temp gauge shut up to HOT RED and i shut the engine off. Turned a/c button on, and temp gauge is back to normal quarter mark. Engine ran only about 1-2 minutes and outside temp was around 40F so its normal.

i tried one more time and with a/c off the temp goes up pretty quickly.

I bled the system a few weeks ago (upper/lower hoses, tank was off, etc. lots of work on the front) and temp gauge with the a/c on was a rock steady straight up.

I noticed that the car needed lot more time to heat then any other car of mine but no other symphtoms.

Could it still have air in the system ?



1997 BMW 840CiA
1990 BMW Z1
1999 BMW 528iT (Hauler mobile)
2002 Astro Van AWD
2003 Nissan 350Z Enthusiast Package
1987 BMW 535i with 5spd manual (for sale)
1992 BMW 735iL (needs head and interior)
1977 BMW 320i (project racecar)
2007 Mazda CX9 AWD (Wife mobile)
1998 Yamaha Blaster+Breeze

1995 850CSI CD00177 (SOLD)

[Craig in Canada]

Check both of your fans. With the AC on it runs your electric fan (assuming it works).

You probably have a failed main fan clutch, so the main fan isn't working and the car is relying on the electric fan for all the cooling. You may also have a failed temperature sensor for the electric fan meaning that it isn't coming on when it should to relieve the temperature problem (but is when the AC is on).

You need to check everything concerning proper operation of the fans. With a failed main fan it puts a lot more stress on the system and I suppose that anything else marginal (blockages, t-stat not opening completely, whatever) would be amplified and might show up as overheating. In theory a properly working electric fan is also capable of providing all of the cooling the engine needs although it may sound like a jet engine while doing it.

[lezonebay]

that one coming on at all. The gauge is steady so the sensor must be good. Where is the electric fan switch ? Isn't the relay supposed to turn on the electric fan ? If that one fails usually the opposite happens, isn't it ? With a/c on the car would overheat as the electric fan does not work ?

I will check the fans both the mechanical and electric but it seems crazy to me that with the a/c on the system is oke, without a/c the gauge shows overheating. Once the a/c was turned on, the coolant temp was actually lower then operating temperature.


crazy car... making my life crazy too :-)

1997 BMW 840CiA
1990 BMW Z1
1999 BMW 528iT (Hauler mobile)
2002 Astro Van AWD
2003 Nissan 350Z Enthusiast Package
1987 BMW 535i with 5spd manual (for sale)
1992 BMW 735iL (needs head and interior)
1977 BMW 320i (project racecar)
2007 Mazda CX9 AWD (Wife mobile)
1998 Yamaha Blaster+Breeze

1995 850CSI CD00177 (SOLD)

[Craig in Canada]

The gauge is not the same sensor which operates the fan. The gauge sensor is in the head, the fan sensor is in the rad.