JD 950 over heating

[TimberHole]

Here is my scenario. JD950 overhauled 1 year back. Radiator boiled and tested, new water pump, thermostat, hoses and belt. Radiator is free of debris. All compressions are 400 psi. Radiator leak test holds pressure. Sniff test of the coolant does not show combustion byproducts. Head did have cracks but cracks were pinned by an old school shop that knows what they are doing.

When using a 6’ brush hog it takes about two hours to over temp. Also over temps after mowing even if just driving back to the barn. Idiot light followed by sings it is actually getting hot. Running 50/50 mix of JD antifreeze.

My current suspects:

1) Cracked head or head gasket -Was number one but compression test, sniff test and pressure test all show normal. I resisted the urge to pull the head tonight. Tractor runs perfect and no smoke.

2) Timing? I did not retime the pump after removal for engine overhaul. Pump was installed with the same number of shims as used prior to removal. What effect on temperatures does the timing have in a Diesel engine?

3) Radiator - Even though I had the radiator serviced I am wondering if buildups inside the radiator might be limiting heat transfer? Maybe get a new radiator?

I realize these are hot conditions but I do not feel like I am over working the tractor and it should be able to maintain temperature doing this work. This is a great tractor and I want to figure this out.

Ideas????

 

[oldnslo]

2 hrs of working before over heating is a slow temperature build up so would suspect poor coolant circulation/ heat transfer. My experience cracked block or head you will see some evidence like smoke, coolant loss, coolant oil mix etc.

If you let the tractor sit at low RPM does it cool down overtime or keep heating up?

Not sure on timing effects for temperatures.

 

[CADplans]

I think the 6 foot bush hog is WAY too much mower for the tractor,,
so, depending on the grass height being mowed,, the attachment may be the cause of overheating.

 

[yanmars]

I have a Yanmar 336d tractor. Nearly the same as the JD950 with a similar engine by Yanmar. Mine only does that when I am mowing tall grasses/weeds etc. and I get debris in the radiator that I have to blow out. Then the temps are OK again. Not saying that is your problem but a consideration. Mine has a screen in front of the radiator that needs to be pulled up to get the radiator blown out. Hope you can find your problem.
I would think you have about 33 HP, 27 HP at the PTO. I have heard about 5HP per foot of mower. You might be right at the limit especially if it is thick and tall.

 

[TimberHole]

2 hrs of working before over heating is a slow temperature build up so would suspect poor coolant circulation/ heat transfer. My experience cracked block or head you will see some evidence like smoke, coolant loss, coolant oil mix etc.

If you let the tractor sit at low RPM does it cool down overtime or keep heating up?

Not sure on timing effects for temperatures.

Thanks, you are reinforcing my current thinking. I brought the tractor home to pull the head but resisted. Instead I am focused on the cooling system. I ordered an OEM thermostat today. I’m also seriously considering replacing the radiator even though I just had this one serviced. I did notice tonight there used to be rubber seals on the cowl which separate the grill side and the engine side. The gaps are not large but I ordered rubber seal to make it like new again. I also ordered a new OEM cap and a gauge to replace the idiot light. I’m going to figure this out even if it breaks me!

 

[TimberHole]

I have a Yanmar 336d tractor. Nearly the same as the JD950 with a similar engine by Yanmar. Mine only does that when I am mowing tall grasses/weeds etc. and I get debris in the radiator that I have to blow out. Then the temps are OK again. Not saying that is your problem but a consideration. Mine has a screen in front of the radiator that needs to be pulled up to get the radiator blown out. Hope you can find your problem.
I would think you have about 33 HP. I have heard about 5HP per foot of mower. You might be right at the limit especially if it is thick and tall.

How big of a mower are you using?

 

[TimberHole]

I think the 6 foot bush hog is WAY too much mower for the tractor,,
so, depending on the grass height being mowed,, the attachment may be the cause of overheating.

You could be right but I think it should be able to handle it. The grass wasn’t that tall, screens were clear, I was mowing in a low gear and the tractor wasn’t lugging that I could tell.

 

[JimRB]

In VW world there are good water pumps and bad water pumps. I never paid attention to what made bad water pumps, maybe a plastic impeller that slips when hot. Injectors have been tested to properly spray and flow? I have a JD 870 with about the same hp and 5 foot slasher cutter. Never have I overheated it but sure have gotten the transmission case hot.

 

[Leejohn]

I think it's the head and you are getting exhaust gas into the cooling system and locking up the cooling system.

 

[TimberHole]

I think it's the head and you are getting exhaust gas into the cooling system and locking up the cooling system.

950’s have a reputation for cracking heads so I’ve had this thought more than once. That said, nothing is pointing to the head. Compressions 400 on all cylinders, no smoke, 2 hours to heat up and I did the chemical sniff test on the coolant. Wouldn’t be surprised if your diagnosis is ultimately correct though.