D8 "JJ8" Transmission overheating"

Sameh · May 10, 2024

This machine has a problem of transmission overheating, the level is OK and no air within the transmission oil. I checked the engine coolant temp and fan motor found it OK, the overheating only with the transmission and torque oil. Oil cooler is OK. I checked the screens of scavenge for torque and transmission and found no obstruction. The only wrong thing is the torque converter inlet pressure is 160psi and specs is 130psi. I changed the torque inlet relief and the same pressure is present. Please advise is that high pressure make overheating? Or anybody has another advice to do.
@Nige

Nige · May 10, 2024

Sameh said:
I checked the engine coolant temp and fan motor found it OK,

What is the coolant temperature into & out of the radiator.?

Sameh said:
the overheating only with the transmission and torque oil. Oil cooler is OK.

You state that "the cooler is OK". How did you check the cooler to come to that conclusion.?
What is the oil temperature into & out of the cooler when the powertrain oil is overheating.?
What is the coolant temperature into & out of the cooler under the same conditions as above.?

Nige · May 10, 2024

Sameh said:
The only wrong thing is the torque converter inlet pressure is 160psi and specs is 130psi.

Converter inlet pressure is only really relevant at first startup when the oil is cold.

More important, what is the converter outlet pressure with the powertrain oil at normal operating temperature, the engine at full throttle, and the transmission stalled in 3rd speed against the brakes.?

Sameh · May 10, 2024

Nige said:
What is the coolant temperature into & out of the radiator.?

You state that "the cooler is OK". How did you check the cooler to come to that conclusion.?
What is the oil temperature into & out of the cooler when the powertrain oil is overheating.?
What is the coolant temperature into & out of the cooler under the same conditions as above.?

* The cooler shell tubes all is clear no one is plugged and no oil leak.
* I didn't measure temp difference across the radiator because the coolant temp doesn't exceed 83°c.
* truly I didn't measure the temp difference across power train cooler when overheating, I depended on cooler inspection to know its condition.

Sameh · May 10, 2024

Nige said:
Converter inlet pressure is only really relevant at first startup when the oil is cold.

More important, what is the converter outlet pressure with the powertrain oil at normal operating temperature, the engine at full throttle, and the transmission stalled in 3rd speed against the brakes.?

The outlet pressure is as specs 55psi at the mentioned conditions.

Nige · May 10, 2024

Sameh said:
I didn't measure temp difference across the radiator because the coolant temp doesn't exceed 83°c.

And right there is a clue……..
The coolant temp should be going way above 83 when the powertrain oil is overheating if the powertrain cooler and the radiator are working correctly.

Start by shooting all the temperatures I mentioned a couple of posts above. Radiator in/out and oil cooler in/out for both coolant and oil. Post back with your results.

Sameh · May 11, 2024

Nige said:
And right there is a clue……..
The coolant temp should be going way above 83 when the powertrain oil is overheating if the powertrain cooler and the radiator are working correctly.

Start by shooting all the temperatures I mentioned a couple of posts above. Radiator in/out and oil cooler in/out for both coolant and oil. Post back with your results.

Look bro, yesterday I increased the max. Pressure of fan pump to 2800 "when I checked it was 2100pai" and then test the machine for 2 hours, no overheat happened. I parked the machine and when I inspected the oil levels today, I found no oil in transmission sump. When I drained the TC sump to check the scavenge screen, the TC drained more than 40Liters. Something prevent oil to exit from TC. I checked the scavenge screen and scavenge pump and found they well. I checked powertrain inlet and exit ports plus lines found all good. May be something inside the TC make this problem?

Sameh · May 11, 2024

Sameh said:
Look bro, yesterday I increased the max. Pressure of fan pump to 2800 "when I checked it was 2100pai" and then test the machine for 2 hours, no overheat happened. I parked the machine and when I inspected the oil levels today, I found no oil in transmission sump. When I drained the TC sump to check the scavenge screen, the TC drained more than 40Liters. Something prevent oil to exit from TC. I checked the scavenge screen and scavenge pump and found they well. I checked powertrain inlet and exit ports plus lines found all good. May be something inside the TC make this problem?

I checked the powertrain oilcooler inlet and exit ports plus lines.

ahart · May 11, 2024

Sameh said:
Look bro

Gotta be the first time in forum history @Nige has been referred to as “bro” let alone addressed by “look bro”
Going to be hard to beat this on a Saturday.

Dave Neubert · May 11, 2024

Bro Nige could be a new screen name

Sameh · May 11, 2024

ahart said:
Gotta be the first time in forum history @Nige has been referred to as “bro” let alone addressed by “look bro”
Going to be hard to beat this on a Saturday.

What's the problem? I'm sorry if it's not appropriate to say this. I learned a lot from him.

ahart · May 11, 2024

I never said there was a problem with it, just that it’s a first. I just find it funny, that’s all.

Mobiltech · May 11, 2024

Sounds like high internal leakage in the torque which would cause heating.
Torque would need to come out and be rebuilt.

Sameh · May 11, 2024

Mobiltech said:
Sounds like high internal leakage in the torque which would cause heating.
Torque would need to come out and be rebuilt.

This internal leak will result in charging all powertrain oil to the TC and emptying trn sump? Advise please.

ahart · May 11, 2024

Can you confirm the serial number? JJ8 is coming up as a D8, if you’ve got leakage in the torque, you can do a stall test and shut machine down and measure the amount of oil that comes out of the torque against spec. I would also check the scavenge section of the pump and make sure it is performing like it’s supposed to, run the hose into a bucket and make sure it pulls the oil out quickly. To clarify, leakage inside the torque can produce more oil than the scavenge section can keep up with, a weak scavenge section can also leave too much oil in the torque.

Sameh · May 11, 2024

Sorry it's D8 not 10, I wrote it by mistake. I checked the scavenge and it provides oil but truly I don't know how healthy is it. It has two inlet ports from TC and trn sump and I have no specs for the flow exiting how much should it be.

ahart · May 11, 2024

Draining 10 gallons out of the torque is a lot, can you put the torque scavenge line in a 5 gallon bucket of powertrain oil and see if the pump picks it up? It’s possible there’s a blockage in the hose or something of that nature.

Sameh · May 11, 2024

I thought about that if any hose is plugged or two hoses exchanged in place of each other but found nothing. May be I'll change the powertrain pump by another and see the result.

ahart · May 11, 2024

I would do the bucket test before you swap pumps. Could quickly rule out the pump and move in the direction of the torque. How many hours on this machine?

Sameh · May 11, 2024

ahart said:
I would do the bucket test before you swap pumps. Could quickly rule out the pump and move in the direction of the torque. How many hours on this machine?

You are right. I'll do this first. The machine has only 120 hrs.

D8 "JJ8" Transmission overheating"

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