1991 Trail Boss 350L 2x4 overheating HOT light

[trailboss350]

Hey all - I am new to the forums but I hope you can help and in the future I can return the favour.

I have a 1991 Trail Boss 350L 2x4 that is running hot after being on for about 10 minutes. I have checked the coolant - levels good. Burped the coolant using the 10mm bolt on top of the engine - good. The fan however was bypassed from the censor on the rad directly to power when the key is turned. Now I am thinking that may be the issue or a faulty water pump. (The hose at the top of the engine is hot but the one at the bottom and to the rad is cold). Any further suggestions or recommendations on previous attempts are greatly appreciated! 

Thank you in advance!

[Ajmboy]

Welcome to QUADCRAZY 😁

Is the fan on all the time with the bypass? What's interesting is that there is definitely an underlying issue if the fan needed to be bypassed to the ignition and was not going on with the temp sensor. How do you know its overheating, is it hot, light come on, boiling over?

[trailboss350]

The fan runs the entire time when the key is on. I assume it is overheating because after a short period of time the HOT light comes on. 

[Ajmboy]

Just now, trailboss350 said:

The fan runs the entire time when the key is on. I assume it is overheating because after a short period of time the HOT light comes on. 

Have you replace the sensor? You can get it on Amazon for $27

[trailboss350]

Is this sensor on the engine or the rad itself? Also, would this sensor cause the engine to overheat or just cause the fan to turn on and off? If the fan is on the entire time it should not be overheating still. 

[Ajmboy]

I'm thinking maybe its not overheating and its just triggering the light because like you said, with the fan on all the time it shouldn't be over heating. But I could be wrong. 

If that's not the case, it could be coolant flow. 

 

[Ajmboy]

Also, have you checked the thermostat?

[trailboss350]

I have not yet changed that part but would this come on after 5-10 minutes or right away if it was faulty? Also, the hose at the top of the engine is hot and the bottom one is cold. Could it be anything else? Thanks again for your help!

[Ajmboy]

34 minutes ago, trailboss350 said:

I have not yet changed that part but would this come on after 5-10 minutes or right away if it was faulty? Also, the hose at the top of the engine is hot and the bottom one is cold. Could it be anything else? Thanks again for your help!

Sounds like coolant is not circulating then and that would lead to a bad thermostat. I don't have a manual, there must be a thermostat in that ATV.