Accert engine fan help

hotfarm1066

hotfarm1066

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Aug 16, 2014
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04 kenworth T800 engine fan only runs with fan switch on, or with a/c on. Not too many electric cats in this area, so not much experience on them. Which temperature sensor tells fan to turn on, or is there multiple signals and ecm run fan. TIA
 
Engine coolant temp at approx 217 degrees.
The fact that the AC can trigger the fan means the ECM is still in control unless someone has done a lot of wiring.

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Is there an issue with it over heating or something that is making you worry about it? If the coolant temp is staying in check then it may not need to run to keep cool. ie. you may be overthinking.
 
It's a customers truck, he says gets warm enough lights come on turn fan on cools down. I don't have truck to confirm yet. So is there only one coolant temp sensor? If the gauge reads should the fan run?
 
Dash gauge should be OEM side. If you have Cat ET software I would plug in and verify the dash gauge is accurate. It is possible the ECM sensor is off though. ECM thinks the engine is running cool so it never tells fan to kick on.

Step one would be to measure coolant temp and take it for a drive and get it warm.

Check the dash and the ECM readings to verify if they are accurate

If the ECM is reading low replace sending unit.

If dash is reading high then work on the OEM side of things.
 
There are 3 water temp sensors and all are in the same relative location. One for dash gauge, one for ECM and one for idiot light. Believe whatever 2 of them are saying. If it hasn't been done for a while it might be a good idea to blow out the radiator. The shop rag test is a good indicator of how much air is passing through the radiator. Start the truck and turn the fan on, then stand in front of it with a cloth rag and put it on the grill. If it hangs on the grill in multiple locations both low and high it's pretty clean. If it falls off it's plugged.

Alarms shouldn't be going off until above 220*
 
jfaulkner said:
There are 3 water temp sensors and all are in the same relative location. One for dash gauge, one for ECM and one for idiot light. Believe whatever 2 of them are saying. If it hasn't been done for a while it might be a good idea to blow out the radiator. The shop rag test is a good indicator of how much air is passing through the radiator. Start the truck and turn the fan on, then stand in front of it with a cloth rag and put it on the grill. If it hangs on the grill in multiple locations both low and high it's pretty clean. If it falls off it's plugged.

Alarms shouldn't be going off until above 220*
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Sorry if I wasn't clear. This is the answer i was looking for. Truck was just dropped off, haven't took it out yet, but from his explanation it is getting hot. Thank you guys for the help and quick replies.
 
hotfarm1066 said:
Sorry if I wasn't clear. This is the answer i was looking for. Truck was just dropped off, haven't took it out yet, but from his explanation it is getting hot. Thank you guys for the help and quick replies.
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FYI before you put too much work into it, see if it's pressurizing the coolant. Acerts blow head gaskets and high coolant temps are a real good sign of it.
 
Ok it is the cat sensor where do they hide it? The gauge sensor and idiot light is in the t-stat housing, so the other sensor can not be to far away.
 
I have been seeing issues where the sensors have a weak ground signal, or a plus voltage on the ground side and that throws the temp sensor out of wack. The one instance the ground for the ECM was weak, and that in turn threw out 9.1V to the temp sensor other than the 8.0 required. that brought the temp sensor from 184F to 230F. Alarms were going off, engine was cool.
 
hotfarm1066 said:
Ok it is the cat sensor where do they hide it? The gauge sensor and idiot light is in the t-stat housing, so the other sensor can not be to far away.
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In the same housing but the plug is facing the fan and below the others. Easy to get to if you have a 2nd elbow, and more fun if the motor is hot.
 
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