650J Over Heating

My 650J gradually overheats over about a 4 to 5 hour time frame. Is there a thermostat in the cooling system or could it be something else. Thanks for all assistance.

I'd blow the radiator out good first. Then I would check the fan belt tension. Does it have a fan clutch? That's another possible source. You may have to pull the radiator and have it rodded out as you may have lime scale inside it.

I like using A/C coil cleaner in a pump up sprayer then a strong water hose. It is amazing to see how much dirt come out!

When they get start to lose effiency I like to pull the radiator out and wash the fins out real good. Then lay the radiator down flat and fill it with muriatic acid and let it soak for 15 minutes, then wash out really good. You can only do this with a copper radiator. The acid will eat up an aluminum radiator. Something else I do to flush out the system is remove the thermostat so there is better flow. Then put a water hose in the top of the radiator and open the drain. Run the engine to circulate the water through the system. Try to regulate the flow of water so that its the same amount coming in as draining out. Just let it run until no more junk is coming out of the drain.

Also check the bottom radiator hose. Have had rust and flakes build up over time and solidify and partially block the lowest part of the bottom hose.

I forgot to say that I don't think the thermostat has anything to do with it since it takes a few hours to get hot. Thermostat problems usually show up soon after start up. Besides, the old one in there is probably better than the Chinese crap you'll get as a replacement.

Steam the radiator out with a pressure washer but be careful to blow straight through the fins or you'll bend them over.

JD, my agency runs almost exclusively JD 650J for fire attack, and we have been dealing with overheating issues since we first placed them in service 6 years ago
we are experiencing the overheating sometimes within an hour of operation (bearing in mind the heat and humidity, the fact that we are in close proximity to a wildland fire, and pulling a trail type fire plow through heavy underbrush)


blow out your radiator (we drop the grille and blow inwards, the run up the engines and blast it all out). We're in the midst of changing all our coolant to tropical grade antifreeze, removing the sand screen (between the radiator and fan) and a thermal wrap around the muffler. checking and blowing out or replacing your air filter regularly may help as well

Thanks for all the help on this - blowing the radiator out helped, but it still runs hotter that normal. The conditions I am operating in are really dusty which has a negative effect on cooling efficiency. I am going to have to check hoses and rod out the radiator. Thanks again!