Periodic shutdown problems with a JD748 lgt

[Racer's Edge]

Have a 2010 John Deere x748U. Over the past month it has begun to just shut down after about 1 hour of full throttle mowing with my 62 inch deck. Last summer did have some problems with it overheating under these conditions, but it just shuts off now with the temp gage at about the normal setting. Changed oil and oil filter immediately when this began to happen. No improvement. My dealer says it may be a defective electronic dash. Any ideas anyone?

 

[Rivets]

You don't give us much info to work with, so I'm going to ask for more info.
1. What are the model and serial numbers of the unit?
2. What is the brand and the model and serial numbers of the engine?
3. How does it react just before shutting down?
4. What have you tried to resolve the problem?
5. What has your dealer done to resolve the problem?

From what you posted, the first thing I would do is fire your dealer. He does not sound to competent, but maybe he has done other things that you don't tell us.

 

[Racer's Edge]

Unit is : John Deere x748 Ultimate Model No. *M0x748A051079*. Engine is: Yanmar Diesel Model No. 3TNV76-XJLTE, S/N *CH3011D28495*. There is absolutely no hint of the impending shutdown other than the fact that the temp gage will have risen to just slightly above the middle of the area between C and H. Upon the shutdown the oil dipstick seems to be hotter than I would like. The oil is hot as well and almost always has tiny air bubbles in it. I told the dealer rep that air bubbles in the oil stream are an absolute no-no in autos, but he said it is 'normal' with mowers as the oil sloshes around quite a bit. The oil being used is John Deere Plus II, 15W-40, the oil filter is the John Deere specified filter. The mower's engine, radiator, oil cooler, deck, etc. are blown clean with an air blower per the JD Manual periodically during every mowing.

 

[lawn mower fanatic]

Have a 2010 John Deere x748U. Over the past month it has begun to just shut down after about 1 hour of full throttle mowing with my 62 inch deck. Last summer did have some problems with it overheating under these conditions, but it just shuts off now with the temp gage at about the normal setting. Changed oil and oil filter immediately when this began to happen. No improvement. My dealer says it may be a defective electronic dash. Any ideas anyone?

:welcome: to LMF!

 

[Rivets]

My knowledge of diesels is limited, but I do know that air bubbles in the oil is not good. Air does not lubricate. Also, air in the oil is an indication that the oil is getting very hot. I would be a cooling system check. I don't know if your engine has a temperature cutoff switch, But if it does that could be your problem. I would give the the cooling system a good flushing, particularly the radiator, which may be partially plugged. I would also get the temp gauge tested, as it may not be reading correctly. Again I say that I have limited knowledge of the Yanmar engines. Good luck, I hope some others chime in as I need to learn more.

 

[Carscw]

Have a 2010 John Deere x748U. Over the past month it has begun to just shut down after about 1 hour of full throttle mowing with my 62 inch deck. Last summer did have some problems with it overheating under these conditions, but it just shuts off now with the temp gage at about the normal setting. Changed oil and oil filter immediately when this began to happen. No improvement. My dealer says it may be a defective electronic dash. Any ideas anyone?

Does the temp gage always read normal or does it start out low then rise to normal?

I agree that it most likely is the temp shut off switch.

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[Racer's Edge]

Thanks Guys, for the comments and suggestions. To answer a few of the questions-- The Oil Temp Gage starts at the C or Cold setting and rises to about halfway now. The tractor has a coolant overflow container with a mark for the 'max' fill when cold. Last summer it was overheating when stressed by mowing tall grass for an hour and/or longer periods--the temp gage would go into the red area and it did shut down on me about twice before i learned to watch that gage, and when it approached red--shut it down and let the engine cool down. Thru trial and error, I discovered that the mark is below what creates a balance in the system. So I fill it slightly higher now.
The change in the overflow container level seemed to stop the radiator overheating. Also the fins on the radiator are clean externally, but I have sprayed cleaning water thru both the radiator and the oil cooler. Have blown out the outer air cleaner til I can see daylight thru it, lubed all three spindles, etc. The dealer rep says the shutdown is accomplished by a signal to a pump to stop fuel flow! What triggers that signal is the $100 question.

 

[Rivets]

I think you answered your own question. What triggers this signal? Overheating the engine would seem to be the answer. Before you do damage to the engine which will cost big bucks I would do two things. Replace the temp gauge and flush the cooling system with an appropriate cleaner. Your engine is telling you that it's too hot and shuts down, the gauge is not reading properly.

 

[Racer's Edge]

Thanks for the comments and suggestions. Did take my JD748 tractor to the dealer. It has approximately 250 hours on it and the warranty runs to 750 hours. The dealer rep said the tractor did the same thing with them after about 45 minutes of heavy mowing. They did changeout the temp gage by replacing the electronic dash. The new gage did not indicate overheating but the engine stopped as usual in another mowing test that duplicated my conditions. Did suggest they consider a coolant system flush. They said they will consider this, but at present they are awaiting further suggestions from the John Deere Technical department.

 

[Rivets]

Wish I had a wiring diagram of this unit. Would like to see if the temp sensor is wired to shut down the engine. Does anyone out there know where we can get one?