Temp light at low rpm

[Tom_Stewart]

I am about to finish this rehab project on a ym2500 when I found another problem...after running at 2500 rpm for a while in my neighborhood, I pulled up to my shop and lowered the rpm to idle (approx 800 rpm) the temp light then came on....increased idle back to 1800-2000 and the light went off after 5-10 seconds or so....

I let it cool and took radiator cap off, cranked it and water appears to be circulating well....the temp sensor is new.....

Service manual does not show a thermostat and given that the water appears to be circulating ok; What should I look for next.....no water leaks and no water in oil...

Thanks,
TS

 

[irwin]

Would be nice to know actual temp. maybe get an infrared thermometer, check it at different running settings see if there is a difference in temp when idling vs 2000rpm.
I see it's a new sender, was it replaced because of this? if not could be bad new part, I see that too often in auto repair parts. could be worn out waterpump vanes. You said no fluid loss, so don't think it would be head gskt, but be careful make sure all the air is bleed out. could be radiator is partially clogged, or even engine block coolant passages could be blocked partly. but before I'd get too into repairing I'd want to know what the real engine temp is when warning light is on..check many different places on block and head- see if anything is too high( besides the exhaust system)...good luck

 

[California]

I think this $10 gadget from Harbor Freight is sufficient for troubleshooting.

Harbor Freight non-contact thermometer

That light might be connected to the oil pressure sender, or alternator. I would double-check that it is wired to the temp sensor, as the first troubleshooting step. Try grounding the wire at the temp sensor to turn the light on. Also look for unintended grounds along the length of the wire. And when overheating turns the light on, pull the wire off the sensor and verify that the light goes out.

 

[irwin]

I think this $10 gadget from Harbor Freight is sufficient for troubleshooting.

Harbor Freight non-contact thermometer

That light might be connected to the oil pressure sender, or alternator. I would double-check that it is wired to the temp sensor, as the first troubleshooting step. Try grounding the wire at the temp sensor to turn the light on. Also look for unintended grounds along the length of the wire. And when overheating turns the light on, pull the wire off the sensor and verify that the light goes out.

Good thinking.. diagnosis is a process of elimination. checking that the light is properly hooked up is a good first step.

 

[kenmac]

I have tried using these lazer therometers when doing a/c work & they aren't even close to the actual temp ( mabe I paid too much for my unit ) anyway, I ended up buying a clamp on temp. reader. I would check my sending unit & air flow across the radiator at idle or low RPM.

 

[YanmarFever]

Have you tried tightening your fan belt?

 

[Mickey_Fx]

Since no one has mentioned it, I'd also check on system voltage. What is the voltage when Idling and what is it at higher rpm's. How quick did the light come on when you reduced the rpm's? If within a sec or two I would focus on electrical. Turning off 5-10 sec after increasing engine speed could just be a sign of low battery and taking a little time to get battery voltage back up again.

 

[Tom_Stewart]

Thanks for all of your valuable input....Here is what I have done so far....

I took off the radiator cap and ran up rpm to 2500....after some of the fluid vibrated out....I noticed that occasionally I would get a bubble or two....let it run for 15 or 20 minutes to get rid of air and tried to replicate the hot light and it did come on at low idle....usually took 5-10 seconds to light up....

So, I took off the radiator and took to a radiator shop.....He called me back a couple of hours later and said that the radiator would have to be re-cored at best....too many clogs that he couldn't get free.... so I decided on a new radiator.

I went ahead while I was there and took off the water pump and inspected...no leaks and the pump looks great......

Ordered a radiator and water pump......

I now think that the radiator just wasnt circulating well.

Thanks again for all of your input.....tractor is looking great...I will post some pictures soon.

TS

Will keep one of the pumps as a backup.....

 

[YanmarFever]

Be sure to replace the fan belt sinse its off already

 

[Mickey_Fx]

Hope the radiator repair takes care of the problem. When you mentioned air bubbles, thought of bad head gasket come to mind.