My 400's been overheating and I suspect the thermostat is stuck closed. I am considering removing the stat entirely and running it for a while to test this theory. From what I know of engines the only drawback to this is that the engine will take longer to warm up. Can anyone think of anything that might be damaged by this "test?"

I eventually will replace the stat, if indeed that's the culprit.

 

Stupid question but the rad isnt blocked is it? Ive ran cars like that and didnt suffer any ill symptoms. I dont know if it works the same on the cats, isnt the stat for turning the fan on when it gets hot? There also is the possibilty there is air in the system?

 

And the stupid answer is I don't know. I don't THINK so, but it's a possibility. The thing suffered a head on colision last winter and I replaced the radiator. But it sat for a month with no radiator and rags blocking the hoses and now I am wondering if I left one of those darn rags in (I doubt it, I left them hanging out the ends of the hoses).

The fluid level is full and I do not think there is any air in the system. How would one check this?

 

Well hehe, if you even suspect the rag deal (i doubt you left it in there) take it off and check. But i would think if that was the case you would had a melt down a long time ago. You should be able to take the rad cap off, start the bike and see fluid movement. If you dont have a manual i will consult mine when i get home and see what the proper procedure is.

 

OK well from what i see here, it the same as a car. Fill the system with the recommended amount of coolant, put cap on, run motor for 5-10 mins, let cool down, take off cap and top off to 1/2in above the core. Basic things to check are: low engine oil, oil pump, float in carb out of spec, intake manifold leaking, coolant low, fan malfunction, fan switch malfunction, and lastly the stat. I was wrong, there is a stat aside from the fan switch itself. Ohh and what ai meant by the rad being block was blocked with mud :]

 

Actually, it is not recommended that you run without a Thermostat.

Two things can happen.

1) The coolant may circulate through the system too Fast, not allowing enough time for the coolant in the radiator to cool. Creating more overheating troubles.
2) If the opposite happens and system works too well, you may have troubles getting the motor up to operating temperature. If the motor can't get up to the proper operating temperature, it can cause excessive cylinder wear. This is from the heat caused by the fuel igniting, coming into contact with the cooler than normal cylinder/head/piston.

 

Agreed

 

My gf's overtemp light came on so found the temp switch and jumpered it at the connector. Was better fan running the fan all the time than constantly overheating.

 

Ok, I won't remove the stat then, though I suspect it's stuck closed.

FYI, the fan DOES run, the temperature sensor appears to be working, the radiator is clear of mud (well, maybe not at this particular moment, but it was), the radiator level is correct, I can check the oil, but am pretty sure it's fine, the only thing I can think of is the stat.

Thanks for all the help, everyone!

 

Just call the dealer and price a stat, if its real cheap id just replace it. Also when i had my KLR250 years ago, it was overheating. I went over it and over it. I finally pulled the water pump housing off. The bolt that held the impeller in place had backed out. This may be something to check as well and easy to check i might add.