V8 EFI FAN SENSOR? - FANS ON PERMANENT, NO HEATER

philalden · Post by **philalden** » Mon Feb 18, 2008 8:46 am

Hi all, they say there are no dumb questions - lets see! I've got an old Disco with a V8 3.9. when i bought it, it was seriously overheating. I changed the rad which was blocked solid. Ive noticed that the fans are permanently on due to the plug for the sensor being unplugged and shorted by the addition of a piece of wire! Heater never gets warm - i think as a result. Think I've found the sensor (behind the alternator); the sensor doesn't seem to be a proper match for the plug but it fits contact wise. I tried runnign up the temp with the plug on what I think is the sensor and fans didn't cut in. I'm guessing that the sensor is knacked. Could one of the boffins out there tell me if i'm right about havin found the sensor and would changin that be the likely route to having the fans workin properly. Many thanks for any pointers to solving this v. irritating prob. Regards - Phil

ChrisJC · Post by **ChrisJC** » Mon Feb 18, 2008 9:05 am

Has it got a thermostat? The heater should still warm up if the fans are permanently on.

Sounds like somebody removed the 'stat and hard wired the fans on to compensate for a knackered rad.

Chris.

ramon alban · Post by **ramon alban** » Mon Feb 18, 2008 10:27 am

PLUS - in all probability the heater matrix is also blocked solid.

Could try pressure flushing in both directions followed by a caustic soda burn out. This SD1 helper may help you also.

http://www.vintagemodelairplane.com/pag ... ant01.html

philalden · Post by **philalden** » Mon Feb 18, 2008 5:16 pm

Thanks guys, looks like i'll be busy the w'end! Should i just get a new stat and fit it as well as the sensor? i'm pretty sure the sensor is knacked because the fan didn't cut in when i plugged it back in and fired up - engine overheated.

ChrisJC · Post by **ChrisJC** » Mon Feb 18, 2008 9:24 pm

Just another thought - a disco 3.9 should have a viscous fan. If it has electric fans with a temp sensor on the thermostat housing, then that's for the air-con, not for normal engine cooling.
The viscous fan should be on the end of the water pump shaft. So the engine shouldn't overheat ever even without the electric fans.

Sounds like somebody has made quite some 'improvements'!!

Chris.

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V8 EFI FAN SENSOR? - FANS ON PERMANENT, NO HEATER

V8 EFI FAN SENSOR? - FANS ON PERMANENT, NO HEATER

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