M936 Hydraulic oil overheat

[ClintA]

Yesterday we were pulling pipe out of a windmill using the M936. The boom up and down did not want to respond as it should and noticed that the Hydraulic oil got hot enough to fry an egg on top of the tank so we shut it down to let it cool off. After about 5 minutes all the sudden she blew the plug off the top of the hydraulic tank and spewed oil up for just a few seconds. What might cause this? thanks in advance

 

[gimpyrobb]

I've heard any temps over 180* start to damage your seals, so be careful. If you were doing hard lifts, that heats the fluid up real quick. How many hours in a row were you using her?

 

[Suprman]

Interesting. I dont think there is a hyd cooler on the wrecker body. I have ran mine for 6 hours straight really loading the heck out of it. Maybe the hot sun beating down on the tank got the fluid really hot and system friction really got it up there. If there was pressure built up in the system from all that heat maybe the hyd pump couldnt pump fluid properly. Does it work now that its cooled down? Maybe a bad bearing could cause the hyd pump to generate alot of heat and get the fluid hot but it is alot of fluid in that tank it would take a while to get it that hot from the pump.

 

[ClintA]

The pipe was not all that heavy, about 200 feet of 2 inch pipe but with no water in pipe (hole in pipe letting the water out) and after we let it cool down all was just fine. When it overheated we were not idling it down when unscrewing pipe (about 1 1/2 hours) then after it cooled down we would take the time to idle down and put in neutral but not kill the engine. Right before we got done pulling pipe it got hot again, not as bad but if we had to keep going it would have done it again I think?

 

[Suprman]

Fire it up use a infrared thermometer to see if the hyd pump assembly or anything else is getting really hot. I have moved big weight with mine without issue.

 

[gimpyrobb]

I'm guessing since you said it overflowed from expansion the hyd tank is full? It has to be something else, maybe a plugged filter? one of the control levers stuck open letting fluid by a little? Tough issue to troubleshoot!

 

[Suprman]

There is a filter in the system.

 

[Wildchild467]

Is there a breather for the tank?

 

[Jbulach]

It sounds like something (pump or motor) is getting hot enough to actually boil the fluid after you shut if off and stopped circulation, causing the tank lid to blow off.
Kind of like an overheating motor, usually it's best not to shut them off but instead remove the load and try to cool them down slowly while idling.

 

[74M35A2]

One of the hydraulic circuits are likely stuck on. Either partially or fully. Check each and every one of them individually. Maybe something like an outrigger, etc.... The only way to really heat fluid that hot is to be compressing it. I'd run each circuit to their half way point, and then let the truck sit and run and see if anything is moving by itself. Cylinders, winches, swing motor, everything on the hydro branch. If all OK, then need to next check system relief valve pressure vs spec. It will likely be one of these two. If there is a filter, change it.

 

[ClintA]

I cleaned the filter not long ago, it had some trash in it but not bad, it points to "clean" and fluid is full in tank. I know when she gets hot the boom control will want to stick both in up and down but when it's all cool all works like a champ. I think personally that the hydraulic pump might be going south on me but I am not sure. Point me in the direction to find the "hydraulic circuits"? I googled but found nothing. Also I bought this wrecker from a fellow SS member and the fill lid on the tank was a rubber plug with a butterfly nut on top (kind of like the dipstick on a NHC 250 is this the right one?) for it does not look Military? If I have the wrong one could that be the issue, maybe there is a breather the truck is missing like wildchild said? Thanks all SS friends

 

[Suprman]

The cap has a breather. The hyd pump is connected to the wrecker body pto driveshaft.

 

[ClintA]

The cap has a breather. The hyd pump is connected to the wrecker body pto driveshaft.
View attachment 640520

Yea, mine does not have that kind of cap, that just might be part of the problem, I don't know? I bet it was lost and they (whoever) just put that rubber plug in it?

 

[Suprman]

I'm pretty sure the system has to breathe a little bit. Maybe an old style valve cover breather would make a suitable replacement.

 

[gimpyrobb]

Point me in the direction to find the "hydraulic circuits"? I googled but found nothing.

The circuit is the 4 control valves. Each control stick operates a hyd circuit.

 

[Csm Davis]

Yea, mine does not have that kind of cap, that just might be part of the problem, I don't know? I bet it was lost and they (whoever) just put that rubber plug in it?

The cap for the hydraulic tank has a filter and a dip stick and that is why it popped off, every wrecker I have run (20+) has gotten hot enough to burn you if you were not careful they aren't made to run continually at high rpm I have looked at adding a cooler to mine, I think they need one on the 936's, the older wreckers don't have to be run as fast.

Sent from my SM-G900V using Tapatalk

 

[Jbulach]

If your running just motors (winches/rotators) you do not need a vented system, however for running your cylinders you MUST have a vent.
I wonder if negative or positive pressure in the tank and return line from not having a vent cap could cause the relief to dead head?

I'm betting 74m correct and your pressure is not bypassing when all your hydraulic levers are in the neutral/hold position. I put a pressure gauge in line directly after my pump so I could monitor my pressure. Maybe you could easily plumb one in, to help you troubleshoot? Also need to check your temps as previously stated.


M925A2 with dump hoist

 

[Wildchild467]

What engine RPM do you run when you are operating your wrecker? I know the max engine speed when using the front winch was something like 1800 rpm. Any faster than that it will push the seals out of the control valve I guess. Just wondering if too much RPM is causing issues and making it build excessive heat?