Diesels must have adequate cooling or you run the risk of warping the heads due to that extreme heat from the injectors. Very important that they do not run LOW on water or oil due to their cooling effects. On an average diesel the combustion temperatures can reach temperatures hot enough to melt aluminum. I've actually seen the tops of pistons on big rig Cummins engines have a spiderweb pattern, or ripple pattern due to the injectors firing too hot and puddling the aluminum. I've even seen holes the size of quarters or bigger burned through the tops of pistons in them as well. But all diesels run hot in the heads and that's why it is critical to have adequate cooling into that head and also cooled adequately in the radiator. Another thought ...Is the oil level normal when you checked it and saw the bubbles and the oil seemed super hot? I'm wondering if somehow the oil level sensor might be messing up due to the heat and thin oil and causing it to shut the engine down? I haven't seen the diagram and not sure if that Yanmar has an oil shutdown as well. Wouldn't hurt to check. Hope this helps.
Periodic shutdown problems with a JD748 lgt
- Thread starter Racer's Edge
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Diesels must have adequate cooling or you run the risk of warping the heads due to that extreme heat from the injectors. Very important that they do not run LOW on water or oil due to their cooling effects. On an average diesel the combustion temperatures can reach temperatures hot enough to melt aluminum. I've actually seen the tops of pistons on big rig Cummins engines have a spiderweb pattern, or ripple pattern due to the injectors firing too hot and puddling the aluminum. I've even seen holes the size of quarters or bigger burned through the tops of pistons in them as well. But all diesels run hot in the heads and that's why it is critical to have adequate cooling into that head and also cooled adequately in the radiator. Another thought ...Is the oil level normal when you checked it and saw the bubbles and the oil seemed super hot? I'm wondering if somehow the oil level sensor might be messing up due to the heat and thin oil and causing it to shut the engine down? I haven't seen the diagram and not sure if that Yanmar has an oil shutdown as well. Wouldn't hurt to check. Hope this helps.
Racer's Edge
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I also believe the problem is related to the engine running hot. After the engine has done one of its shutdowns, a certain symbol is displayed on the electronic dash. My JD Operator's Manual says that the presence of that symbol indicates among other things--low oil pressure. A savy parts person at another dealer told me the Yanmar oil pressure sensor drops ( signals low pressure) at 3-6 psi. But according to JD Technical, neither low oil pressure nor high engine temprature will directly trigger a shutdown. Theoretically, it is supposed to just light up that symbol mentioned above.
Spoke to the dealer rep yesterday. He said they have determined that somehow the system is getting a signal to shutdown the fuel flow. He said they were being visited that day by the John Deere District Service Rep. Upon examining the facts and the tractor, the factory rep suggested getting the fuel pump and some other parts of that system checked out by a speciality shop. Perhaps they will find evidence of overheated fuel injectors as mentioned in a previous post!
Spoke to the dealer rep yesterday. He said they have determined that somehow the system is getting a signal to shutdown the fuel flow. He said they were being visited that day by the John Deere District Service Rep. Upon examining the facts and the tractor, the factory rep suggested getting the fuel pump and some other parts of that system checked out by a speciality shop. Perhaps they will find evidence of overheated fuel injectors as mentioned in a previous post!
Racer's Edge
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Got my mower back from the dealer and have mowed about 5-1/2 hours with no periodic shutdown problems. The John Deere District Service rep had visited my dealer and somehow that resulted in a test of supplying the mower with diesel fuel from a separate tank. They tried it and the mower cut grass for 3 hours without stopping. They took out the built in tank and found that the in tank pickup filter was slowly clogging up. I didn't even know it had an in-tank fuel filter! The complete stoppage was taking about 45 minutes to one hour and then came the shutdown. The Deere in-tank assembly has a mounting plate, a pickup line with screen filter and an excess fuel return line from the fuel injection. According to the JD dealer, the entire unit must be replaced to make the repair.
They cleaned the tank, replaced that pickup assembly and put it all back together. They say the unit then mowed for over 3 hours with no shutdowns. BTW, I buy my off road diesel at a local Cooperative which sells so much fuel that they supply several local gas stations as well as farmers, contractors, and other off road users. I am currently using 2, 5, and 6 gallon plastic containers so the fuel is almost always fresh. Have now found that my 'cans' appear to have gotten dirty over time and need to be replaced and/or thoroughly cleaned. This experience shows me that clean fuel is a must for diesels. But even with that, maintenance of the supply containers is required.
They cleaned the tank, replaced that pickup assembly and put it all back together. They say the unit then mowed for over 3 hours with no shutdowns. BTW, I buy my off road diesel at a local Cooperative which sells so much fuel that they supply several local gas stations as well as farmers, contractors, and other off road users. I am currently using 2, 5, and 6 gallon plastic containers so the fuel is almost always fresh. Have now found that my 'cans' appear to have gotten dirty over time and need to be replaced and/or thoroughly cleaned. This experience shows me that clean fuel is a must for diesels. But even with that, maintenance of the supply containers is required.