overheated 20W50 Synthetic oil

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Jan 15, 2024
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I have 2 ZT2800 drives with 20W50 Trax synthetic in them. My right drive stopped running normally and I removed and disassembled. All the parts have a sticky texture on them and the pistons in the pump assemblies some of which were stuck in the down position. Cleaning the pistons and holes allowed them to operate normally. A screw in the swash plate was actually welded in place (could not even be chiseled out.) From looking at the parts to me it looks like the drive overheated again. The oil though puzzles me. What happens to synthetic oil if it is overheated? Appreciate any feedback.
 
I have 2 ZT2800 drives with 20W50 Trax synthetic in them. My right drive stopped running normally and I removed and disassembled. All the parts have a sticky texture on them and the pistons in the pump assemblies some of which were stuck in the down position. Cleaning the pistons and holes allowed them to operate normally. A screw in the swash plate was actually welded in place (could not even be chiseled out.) From looking at the parts to me it looks like the drive overheated again. The oil though puzzles me. What happens to synthetic oil if it is overheated? Appreciate any feedback.

Did you mean Triax oil?
 
Hydrostats almost never run hot and after hundreds of hours the oil drained out clear in mine and wasn't burnt and I opened one up to fix it and it wasn't sticky either. Used it for an hour each time i ran it so it had enough time to heat the oil. I used basic supertech 20w-50 and changed 3 times which each interval around every 5-6 years. There's something wrong with your unit, or you use that mower very hard, or that triax stuff is :poop: which is likely the case.
 
As a new ZTR owner I'm interested in what the failure mode is that causes the overheat and what oil temp they "normally" run at. Thanks
I presently have a Toro ZX4800 which is now 13 years old. I have always had an issue with the right hand drive, replaced after 2 years, rebuilt after another 4 years. I have used various recommended oils although the last 2 changes (do every year about 200 hours) was with the Triax. It is possible the oil is not any good BUT this unit has prematurely failed with other oil. Both ZT 2800 drives have the Hydrogear fan on them BUT are CRAMMED into a location that I cannot see would give good airflow. The fans themselves have a protective covering over them that has to be reducing the air flow through the holes by at least 30% if not 50% and these designers felt it was fine to locate other items over the units to further block air flow. It is typical for a RH drive to receive more wear than the left as most people turn to the left to avoid the cuttings blowing in their face. Hydrogear claims the ZT 2800 should never need service other than oil and filters for the life of the machine unless abused.

Teardown of the drive showed the following: A sticky residue throughout the drive and parts. The screw in the end of the Swashplate-Trunnion was literally welded in place. Could not be chiseled off or removed it was literally welded in. The pistons that rotate within the swashplate had been peened over on the edges and the interior of the swashplate had worn with an edge that was not supposed to be there. Six of the pistons in the drive assembly were in the compressed state in the holes and would not move. They would not go up and down. After using solvent on the parts the pistons operated normally. The surfaces of the blocks and center section were not scored but the surface of the charge pump had minor grooving. This to me "suggests" high temperatures. Let me add that this engineering issue is not the only one this unit had. Frankly I have no idea what was in their minds when they put the 4800 together.

It is my opinion the Toro zx4800 has serious design issues when it comes to the location of the drives. A person CANNOT even get your fingers on the belt as it is crammed against the frame of the machine. It is necessary to drop the drives if changing the pump drives is needed.

I purchased a new machine and plan on scrapping the Toro disaster. The Hustler is significantly different than the Toro. The drives are out in the open with nothing blocking them. The manufacturer removed the fan from Hydro ZT 2800s and installed their own which is roughly twice as large and has no guard over it (frankly do not see a reason to have one anyways.)

I do plan on installing some type of thermocouples on the new drives to monitor the temperature of the new ones. I have not been able to find any information out there.

I do not tow with the ZTR and do not beat it but I do have 2 acres to cut along with 100+ pine trees to mow around and it gets hot here. If anyone has any info regarding the expected running temperature of the Hydro gear drives I would appreciate it.
 
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