John Deere 755 4x4 overheating

grouchybear · Jul 14, 2011

I have a John Deere 755 4x4 I'm not sure what year it is, it has a three cylinder diesel ( Yanmar ), I have replaced the thermostat, radiator cap, had radiator rebuilt, flushed block, installed a temperature gauge thinking that the idiot light was bad, however it runs hotter than I think it should. Temp. gauge usually reads around 260 to 280 degrees, however it does not shut itself down. I shut it down and you can hear it boiling and antifreeze will run out the overflow hose, antifreeze is 50/50 mixture. It seems the design is very poor, directly in front of the radiator is the hydraulic oil cooler, than in front of that is the diesel fuel tank, it appears that only a few inched of the radiator is exposed, most of it is blocked by the cooler and fuel tank. I live in Arizona and it is usually 80 to 95 degrees when mowing, the mower is a 48" woods brush hog. I don't know what direction to go next to fix this problem any suggestions I would appreciate.

grouchybear · Jul 14, 2011

Would appreciate quick reply.

kencunningham · Jul 14, 2011

Maybe the impeller on the water pump is worn?

grouchybear · Jul 14, 2011

Thank you for your reply, I did remove the water pump and it seemed ok.

V1Rotate · Jul 14, 2011

I assume that the radiator fan is in good condition and that the belt is tight. How about the head gasket? Did this overheating problem suddenly occur or did it start to happen gradually? A bad head gasket can leak hot exhaust gases into the cooling system making it overheat. Does the coolant look dark or have an "exhaust" smell? Does the engine oil have any coolant in it?

project_X · Jul 14, 2011

grouchybear said:
I have a John Deere 755 4x4 I'm not sure what year it is, it has a three cylinder diesel ( Yanmar ), I have replaced the thermostat, radiator cap, had radiator rebuilt, flushed block, installed a temperature gauge thinking that the idiot light was bad, however it runs hotter than I think it should. Temp. gauge usually reads around 260 to 280 degrees, however it does not shut itself down. I shut it down and you can hear it boiling and antifreeze will run out the overflow hose, antifreeze is 50/50 mixture. It seems the design is very poor, directly in front of the radiator is the hydraulic oil cooler, than in front of that is the diesel fuel tank, it appears that only a few inched of the radiator is exposed, most of it is blocked by the cooler and fuel tank. I live in Arizona and it is usually 80 to 95 degrees when mowing, the mower is a 48" woods brush hog. I don't know what direction to go next to fix this problem any suggestions I would appreciate.

Definitely water pump. My Yanmar 1602D has the same engine, in 90+ weather, I can usually mow for no more than 4hrs with out my temp warning light coming on. The problem is, I don't have a water pump. With a functioning water pump, I would expect to not overheat....

grouchybear · Jul 14, 2011

I checked the antifreeze is nice and green, there is no water in the oil, water level is full and there is no milk coloration in the oil indicating water in oil.

grouchybear · Jul 14, 2011

project_X said:
Definitely water pump. My Yanmar 1602D has the same engine, in 90+ weather, I can usually mow for no more than 4hrs with out my temp warning light coming on. The problem is, I don't have a water pump. With a functioning water pump, I would expect to not overheat....[/QUOTE.Water pump is fine I checked it and it functions as it should.

kebo · Jul 14, 2011

Is it possible a water hose might have a blockage or restriction in it??? If that's ok, it sounds like you have checked and eliminated just about everything else it could be. So, maybe it's not getting enough cool airflow?? Would it be possible to supplement airflow with a temporary electric fan to see if that helped any?? You can probably pick up a small 12vdc fan fairly cheap at just about any junkyard to try one and see.

dieselscout80 · Jul 15, 2011

Is a hose collapsing and restricting coolant flow (lower hose on radiator)?

oliver28472 · Jul 15, 2011

What rpm are you running when bush hogging? A friend of mine's Mitsubishi ran hot but he was not running at pto speed when bush hogging.

grouchybear · Jul 16, 2011

No the hoses are all in good condition. Thanks.

Don87 · Jul 16, 2011

grouchybear said:
No the hoses are all in good condition. Thanks.

Did you check the hoses with the engine running at PTO speed to see if they are collapsing?

If all else checks out, It almost has to be the head gasket, as V1rotate suggested.

edit: unless.........just for giggles..........check the air filter and housing for obstructions.

I had a 4 wheeler that I bought used, it would run great for 20 minutes, then get hot and shut down.........air cleaner housing was filled with dog food and corn.

grouchybear · Jul 17, 2011

I run it at 3000 to 3200 RPM

kebo · Jul 17, 2011

Wow, I didn't realize that little Yanmar 3 cyl would run 3200 rpm's! Both of the 750's I had would top out at about 2500 rpm's as I recall, but they are gear drive. The 790 that I have now (which is also a 3 cyl Yanmar & gear drive) tops out at 2600 rpm's. Maybe because the 755 is HST is why it runs the higher rpm's?

V1Rotate · Jul 17, 2011

Here's another thought, I know you replaced the thermostat, but how do you know that the new one is any good? One way to check it is to put it in a sauce pan filled with water and put the pan onto your kitchen stove. Most thermostats will open at 195 degrees, if you have a thermometer that reads that high you can measure the temperature of the water and watch for the thermostat to open. If you don't have a thermometer, just watch the thermostat to make sure it opens before the water starts to boil at 212 degrees.