radiator fan always on

[bigtisas]

I noticed the radiator fan turns on as soon as I start the car. It happens everytime. Even when the engine is still cold in the morning. Outside air temp was around 64F (17C) and the temp gauge is at blue mark.

Shouldn't the fan only turns on when the engine gets hot?
Faulty themostat?

[Jon K]

Do you mean the aux fan?

The mechanical drive fan will always be "on" obviously - not to say you didn't know that.

The aux fan turns on with AC and hot temps. Could be your sensor or resistor bad.

[DaveVoorhis]

I'd suspect a defective sensor on the right-hand side of the radiator or a stuck relay. Check the sensor by unplugging it. The fan should stop. If it doesn't, try unplugging the relays one at a time in the auxiliary relay box in front of the fuse box. If that stops it, you've got a bad relay.

[bigtisas]

Thanks. I'll check the sensor and the relay.

[Amskeptic]

I noticed the radiator fan turns on as soon as I start the car. It happens everytime. Even when the engine is still cold in the morning. Outside air temp was around 64F (17C) and the temp gauge is at blue mark.

Shouldn't the fan only turns on when the engine gets hot?
Faulty themostat?

Try pulling the relay and do a continuity check through the usual 30/87 contacts. There should be none. They often stick due to overamperage.
Colin

[bigtisas]

Now i understand why my car takes so long to warm up the engine. It's because the fan (I believe the aux fan) is always on. It typically takes 10 mins to just pass the blue mark on the temp gauge.

[winfred]

the aux fan will run on low whenever the ac switch is on regardless if the engine is running or if the ac works, you can test for the sensor by just unplugging it plug's brittle don't manhandle it) theres two relays a high and low speed in the smaller box on the left fender well forward of the fusebox, i can't remember the positions but theres only 2-3 relays in that box, try smacking them first then you can unplug them one at a time till you find the offending relay that shuts the fan down, then switch it with another relay that has the same pins from the car and see if the fan still runs

[Blitzkrieg Bob]

failing, it should warm up pretty much the same regardless of the fans.

[Adnan]

I noticed the radiator fan turns on as soon as I start the car. It happens everytime. Even when the engine is still cold in the morning. Outside air temp was around 64F (17C) and the temp gauge is at blue mark.

Shouldn't the fan only turns on when the engine gets hot?
Faulty themostat?

Hi,

I checked the schematics and concluded that it was a faulty high/low pressure switch on the A/C system (located just under the windshield washer fluid reservoir). In other words, disconnecting the switch solved the problem. I bought a new one from BMA, pulled the R12, popped the new one in, recharged the system and all's well.

Good luck!

Regards,
Adnan

[bigtisas]

I checked Bentley. I was referring to the mechanic fan (the fan between radiator and engine), not the aux fan. Sorry for the confusion.

But how come the mechanic fan always on? In my old car (an Acura Integra), the fan only comes on when the engine is hot. And it stays on after ignition is off if the engine is still hot. The e34 mechanic fan seems like "attached" to the ignition regardless of the engine temp. ???

[Jon K]

I checked Bentley. I was referring to the mechanic fan (the fan between radiator and engine), not the aux fan. Sorry for the confusion.

But how come the mechanic fan always on? In my old car (an Acura Integra), the fan only comes on when the engine is hot. And it stays on after ignition is off if the engine is still hot. The e34 mechanic fan seems like "attached" to the ignition regardless of the engine temp. ???

Attached to the ignition? Whew baby we need to clear a few things up.

Its a mechanical fan, not an electric fan like on your Acura. Inline motors use fans connected to the waterpump pulley with a viscous clutch. The fan will ALWAYS BE ON because it is hooked up to the engine. Its mechanically driven by the revolution of the engine - you cannot turn it off, just remove it. Don't do the latter.

[winfred]

if it never freewheels and is always howling the fan clutch is probably locked up and bad, if it goes long enough the fan blade could explode, the blade will never completely stop but it will idle down when not needed and can be stopped almost by hand

[bigtisas]

Thanks for the explanation folks. On the other hand, an electric fan design is probably make more sense, right? The mechnical fan has two problems. 1) it delays the engine warm up time. Why cool the engine when I want the engine warm up faster in the morning. 2) After I shut off the engine, coolant stop flowing. I prefer the fan to stay on for a few minutes to cool the hot engine.

[DaveVoorhis]

On the other hand, an electric fan design is probably make more sense, right?
Not necessarily. A properly designed cooling system with a mechanical fan is as effective as an electric fan.


The mechnical fan has two problems. 1) it delays the engine warm up time.
It doesn't. The thermostat controls warm-up time, and the thermostatic fan clutch keeps the fan from loading the engine when the thermostat is open but the radiator is relatively cool, as when the vehicle is moving.


2) After I shut off the engine, coolant stop flowing. I prefer the fan to stay on for a few minutes to cool the hot engine.
Electric fans that remain on after the engine has stopped may slightly reduce heat soak by cooling the exterior of the engine, and may slightly accelerate cooling to normal operating temperature if the engine is started again soon after the engine is stopped, but the M50 doesn't heat up much when stopped and it cools down almost immediately when started. Keep in mind that even if an electric fan is running when the engine is stopped, the water pump isn't pumping coolant through the engine.