Outdoor Power Equipment and Small Engines - overheating

I have a small Yanmar 20 hp 1301 deisel tractor with a 4 foot bush hog. After about 30 minutes of mowing (sometimes longer) the over heating lite will come on, and I can take it to a hose and spray water on the radiator and the lite will go off, and I can go back and mow again for a while, or I can just keep going and it will eventually start boiling over, I have removed the radiator, and checked it all out, it is clean and not clogged there are no leaks. The water pump seems like it is circulating water, I have replaced all the hoses,fan belt(seems like new belt helped some) the cap, The fan seems to be ok. but it still heats up. So what else could it be? bad thermostat? any help would be appreciated, RH

How did you check water pump operation? The T-stat could be bad, but you wouldn't see much circulation if it was. It sounds like you're not circulating enough water through the radiator, or maybe the fan shroud is missing? Still, it's overheating pretty quickly even if the shroud was missing. Don't run it too hot...those engines can get badly damaged from overheating and costs thousands to fix when they've been overheated badly enough. It will cook the pistons if you let it.

Yes, I guess the thermostat could be bad, But the water pump? how can I check that? In my past experience with water pumps, they always get very noisy, and usually leak some when they go bad? there are no signs of leakage anywhere. I will find out how difficult it is to replace thermostat. Hopefully that will remedy the problem.

I forgot to say that I checked the water circulation by looking into the radiator with the cap off while the engine is running at normal temperature, and watching the water movement. The fan shroud seems to be in good shape, but I am thinking that maybe I could maybe extend it to make it larger for more air, but I dont have much room for that, also someone suggested that I could buy a small electric fan for more air, But again, there is not much room in there! :confused: :confused: :confused:

Don't know anything about a Yanmar. Doe's it have a thermostatic fan clutch? If so, is the clutch engaging when engine overheats?
Just a thought,
Mike

I wouldn't add fans or lengthen the shroud, because it worked fine like it is at one time. Something is wrong. I have seen impellers on water pumps rust off. The pump will still be quiet and leakproof, but ineffective. Especially in equipment that sits unused a lot and has little or no antifreeze in the cooling system. Was/is the water rusty? Can you lower the water level and see the water in the radiator shooting through the flues?

I dont think it has a fan clutch, But I think I will replace the T-Stat, and if that dont fix it, then the water pump is next. I was just thinking that maybe I should check the plastic, or nylon fan itself, and make sure it is in good shape, and not bent up or missing pieces or anything, cause this would cause it to not blow enuff air onto radiator, yes? :confused: :thinker

PS I should mention that I have been having this same problem for a long time, It just didnt start overheating one fine day, it has been doing this for at least 2 years now,and its been a big pain in the neck, but dont worry I aint about to give up, I will get this bug worked out soon I hope. RH

No the water is not rusty, and the water does sem to be circulating some, but maybe not enuff?

Probably not enough, but you can lower the level in the radiator and look at the flues with the engine running. If you can see water shooting out the flues, then the pump is doing ok. If it is just trickling through them then it's not circulating well.