engine cooling fan constantly on

[chan]

I came to this thread after getting my van back from MOT and engine fan constantly on (when key moved to 2nd position and when engine running).

Followed the comments and found that the sensor cable had come loose on drivers side of engine - not very loose at all, but a gentle push back together solved the problem. Couldn't believe it! So, thanks for posting the answer up here, saved me a trip back to the garage (if they would have known what to do anyway!).

Update:
Came back on today, checked the connection, definitely in properly so no idea how to stop it now

[g8dhe]

Are you sure the Air Con is OFF ? Otherwise the tempeartaure sensor may have failed.

[Syne]

Would disconnecting the battery for a while help?
Failing that it's either replace the sensor or install a manual switch with a digital temp gauge as to accurately judge when it should be manually turned on.

[Syne]

Are you sure the Air Con is OFF ? Otherwise the tempeartaure sensor may have failed.

Do you know by what method the fan activates when the air con is on? Is it a switch or does the ecu play a part?

[teenmal]

Would disconnecting the battery for a while help?
Failing that it's either replace the sensor or install a manual switch with a digital temp gauge as to accurately judge when it should be manually turned on.

You really don't want to be messing about with manual switches etc. The ECT sensor is married to the ecu /ems and you don't want a divorce as has been known a divorce can be costly.
Owing to the fact that the sensor is only about £10 and is probably about 20 years old it would be worth changing anyway.

[g8dhe]

Are you sure the Air Con is OFF ? Otherwise the tempeartaure sensor may have failed.

Do you know by what method the fan activates when the air con is on? Is it a switch or does the ecu play a part?

Yes the ECU is involved, signals from the AirCon feed the ECU and its the the ECU that controls the relays that operate the fan(s). There is also a separate Scavenger fan directly infront of the engine this is controlled by a sensor by the handbrake again via the ECU.

[Syne]

By most accounts, these fans come on only when temps are extreme. I know I only ever heard my fan when the sensors unplugged or back when first bought it - because the head had gone. I'm thinking that maybe the manual switch is a good idea to remove a bit of heat before it gets out of hand, coupled with a temp gauge to fire warn,
Because - being honest-the bongos temp guage is bobbins, not much in the way of accuracy it just
Sits at 11, then if it moves up you've already had problems.
I'm not sure there really would be any conflict with the ecu as I can't imagine the ecu monitors weather the fans are being used or not, it would just send power when x temp is reached and cut when temp y is sensed.

[mikeonb4c]

My fans came on in the Peaks last weekend in fairly cool weather, when i stopped straight after labouring up a long incline. The trigger was probably lack of forward motion airflow over a hot/hard worked engine. I fitted an over-ride circuit to my scavenger fan 10 years ago and despite warnings of ECU complications from experts at that time it has never caused problems. At that time no-one seemed aware of the trick with the sensor by the handrake so my mod just uses a separate 30amp direct / switched / fused feed. Can't say whether you'd upset the ECU trying a similar trick with rad fans and its probably bad practice anyway as its much more critical that they operate promptly when needed so first priority is to make sure the sensor driven operation is reliable.

Personally, i think the Mazda temp gauge is probably typical of many damped gauges and is designed thus so as not to over alarm non techie drivers.

[Petebongo]

Just found this post. I have a similar problem where fan randomly comes on thrn goes off. Sometimes just gor a second.

The sensor reference is that the temp sensor in the head or another one? The temp gauge appears to move but doesnt go past 11 oclock.

Cheers

[g8dhe]

The sensor at the very front of the engines only feeds the dashboard gauge it plays no part in controlling the fan, the gauge is also heavliy damped electrically so it doesn't go beyond the 11:00 position until its basically too late on a diesel!

The temperature of the engine and of the housing is from two separate sensors feeding the ECU that then controls the fans, glowplugs and automatic transmission according to temperature.