7710PQ hyd overheating

We have a late SN 91,xxx (hi pressure common rail fuel system) 7710 power quad that we are having trouble figuring out what the problem is. The complaint is that the hydraulic system is over heating on it and setting CCU015 code (hydraulic temp hi) and turning the hyd temp warning light on. It seems to be mostly RPM related, as we can get it to overheat with the tractor parked and the engine running at wide open throttle. We have tested the power quad air pump and it tests fine and the hydraulic system tests we have done all seem fine too. The main hyd pump stays on low pressure standby, unless a hyd function is activated, so that seems fine. Just running the tractor none of the hydraulic valves or components seem to build up any heat at all. The only thing that seems to build up any excess heat is the power quad unit itself. The power quad works fine and does not seem to drag in forward or reverse nor does it labor the engine in any of the speed ranges like it would if it had a warped clutch or brake element. We are about to the point of rolling the drive train out and taking a look at the power quad unit, but the owner wants to sell the tractor and doesnt want to spend a lot of money on it, but he will if he has to. I just hate exploratory surgery so I would like to be pretty confident that the problem is in the PQ unit before we go through the work.

We did find a DATC solution (#57370) that talks about a restricted return oil passage from transmission to differential housing, but I am not sure how this passage way could of suddenly got restricted after 20 years and almost 10,000 hours of operation. It would requires PTO housing removal to inspect for this and that is not a 5 minute job either.

Any thoughts?

Thanks!

Have you checked hyd oil coolers to be sure they're free of debris that could be blocking air flow? Also hyd system could have an internal leak causing hyd oil to heat. Check temp of each individual hyd control component with a laser thermometer.

(quoted from post at 11:59:18 01/13/22)
Have you checked hyd oil coolers to be sure they're free of debris that could be blocking air flow? Also hyd system could have an internal leak causing hyd oil to heat. Check temp of each individual hyd control component with a laser thermometer.

Click to expand...

Thanks for the reply.

This tractor does not have air cooled oil coolers. It has 2 coolers plumbed in series, cooled by engine coolant, which likewise are plumbed in series.

As stated in my original post "Just running the tractor none of the hydraulic valves or components seem to build up any heat at all."
So yes, we have checked all hyd components with an IR temp gun.

The heat does not appear to be coming from the hydraulic system, but it seems is coming from the PQ unit itself.

190-210F coolant temp doesn't seem to me to have much cooling affect on hot hyd oil.

Do any trans clutches seem to slip when engaged?

(quoted from post at 15:17:13 01/13/22)
190-210F coolant temp doesn't seem to me to have much cooling affect on hot hyd oil.

Do any trans clutches seem to slip when engaged?

Click to expand...

I agree about trying to cool the hydraulic oil with hot coolant, we discussed that here, but it apparently works when everything is right.

The PQ transmission works fine. Right now we are test running it in the different PQ speeds to see if one speed creates more heat then the others.

For some reason a reply by rockcreek4630 ended up in a separate thread. Here is a copy and paste of his reply.

"I believe you have two problems. 1 you have
a cooling problem either the coolant isn't
circulating or you have reduced hyd flow to
the cooler. Next how does the range shift
when cold if it is a little hard to shift
the clutch cooling valve could be bad they
are known for that and it creates heat."

And here is my reply to rockcreek4630

From the info I can located it looks like the clutch cooling valve problems only apply to newer tractors built after this one was built.

I have checked the cooler relief valve and lube relief valve and neither spring was broken and the valve spools were free.

I am thinking the next test is going to be to flow rate the cooler flow.

Thanks!