John Deer 950 Over heating

Mark Kalisz · Posted: Sun Mar 01, 2009 10:12 am Post subject: John Deer 950 Over heating

If the temps are above 50 degrees the tractor over heats. I took the radiator cap off when the engin was cold to see if the pump was working.
When the thermastate opened -or at least I though it opened- the level in the radiator rose and spilled over. I did this this morning when the temp were at 15 degrees and it took about 5 minutes of idel for this to happen. Just wondering where to start. Radiator flush, thermastate or pump. There was no circulation that could be seen just a steady raising of the anti freeze.

Misterfixit · Posted: Sun Mar 01, 2009 12:32 pm Post subject: Re: John Deer 950 Over heating

When you say it overheats, are you going by the temp guage, that it boils past the radiator cap, or both?

A stuck closed thermostat can cause what you're observing, but I don't know that it should within 5 minutes idling at 15 degrees ambient. Not knowing the specifics on that particular Yanmar, I'd guess around 180 would be stock thermostat temp. So yeah, from 15 degrees to boiling over in 5 minutes seems a bit quick. Are you seeing any bubbles in the coolant when it starts to surge upward? At those temps I hope you have at least about a 30% mix of antifreeze/coolant in there. You may have combustion pressure getting into the cooling system somewhere (cracked block, head gasket etc).

Verify whether its a pressure issue, or a heat + pressure issue first.

Mark Kalisz · Posted: Sun Mar 01, 2009 1:39 pm Post subject: Re: John Deer 950 Over heating

I don't think that the water temp got above 180 degrees. It was just barely steaming and the water raised over the cap level. I was able to put my finger into it with out any discomfort.
There was no bubbles or movement of water. Just the steady raising of the anti freeze level.
Someone else had put a new thermostat in it and I am thinking that possible it was put in backwards or the radiator is plugged. Tomorrow I am planing on pulling the thermostat to see if there is any flow into the radiator. If there is I at least know the pump is working, Good idea????
If there's no flow then I suspect the water pump or radiator is plugged but that's just my laymems opinion.
Trying to do a process of elimination before tearing into something I don't need to.
Thanks for your reply and hopefully you know where I am going with this.

Jerry/MT · Posted: Sun Mar 01, 2009 4:23 pm Post subject: Re: John Deer 950 Over heating

You say that the tractor is overheating and then you say that the radiator overflows just a few minutes after start up when you think the thermostat opens.It sounds like you may have two separate problems.

Most of these tractors should not be filled with coolant to the radiator cap. They should be filled just above the top of the core to maybe a half inch over the core. The rest of the space is for the thermal expasion of the coolant. That maybe what you are seeing on start up.

Overheating can have a lot of different causes. Make sure that you have the correct presure cap on the radiator, that your water pump drive belt is tight and that you have the correct thermostat and that it is working correctly. Make sure the lower hose does not collapse at high rpms. Finally, make sure the air filter is clean. Diesels are different than gas engines in that they run at varialble gas temperature (varable fuel to air ratios) and when you reduce the airflow with a dirty filter, it causes the gas temperatures to rise in the cylinders. That puts a higher heat load on the cooling system. You also want to make sure that there are no bubbles in the coolant with the engine running. That can cause the radiator to belch coolant out of the overflow and it"s usually caused by a head gasket leak.

Mark Kalisz · Posted: Sun Mar 01, 2009 6:02 pm Post subject: Re: John Deer 950 Over heating

Thanks Jerry, I will check the air cleaner filter first. I can tell you that there are no bubbles while the engine is running and the level never changed durning start up. It began to rise only after the engine had been idling for about 5 minutes. I shut it off just before it started to enter into the overflow tube. It continued to rise briefly after shut down but only about a half inch.

Jerry/MT · Posted: Mon Mar 02, 2009 11:56 am Post subject: Re: John Deer 950 Over heating

How far was the coolant below the cap BEFORE you started the tractor? Better yet, how high above the radiator core is the cap and how high above the core was the coolant?
If you overfill the radiator, as the fluid starts to heat up, it will expand and the excess will run out the over flow. That"s called thermal expansion and has nothing to do with overheating and everything to do with overfilling.

Dan in North Houston · Guest Report to Moderator

If your 950 is like my 850, you should have a screen that fits in front of the radiator. It is in a metal frame and can be removed from the top. It is hard to clean the radiator with a hose unless you remove it.

Mark Kalisz · Posted: Tue Mar 03, 2009 4:32 pm Post subject: Re: John Deer 950 Over heating

Yep, I pulled it out and used a vacuum to clean out the radiator. I did pull the thermostat and checked for flow thru the radiator and it is working just fine. Reinstalled everything along with changing the air cleaner and ran the hell out of it for about a half hour and everything's
working great. SO for now I am good to go. Will have to see what warmer temps bring.
Thank-you everyone for you advise.