M 936 Hydraulic temperature sensor?

Saw this and wondered what it is? Temperature sensor? Pressure? If so where is the light or gauge?

Wire number?

Picture?

Sorry the pictures didn't stick

I'm guessing an MWO.

I just checked my 2 A2's and neither have that modification.

I have not seen that before on any of the M936's that I have seen.

Not on my unissued M936A1 either. Cool idea though. I've toyed with the idea of adding a large oil cooler as the fluid will get smoking hot after 30 minutes of continuous use...

Not on my A2

It looks like a coolant temp sensor.

Was there a guage somewhere?

Any wire number?

Okay had time to go looking for the wrecker this is on and it's on Golden eagle's wrecker. As I thought it is a temperature sender, there is a gauge on the gondola. So my next question is how hot is to hot?

Depends on the type of hydro fluid. The flash point ranges from about 200 up to 320 degrees F. The gauge seems to suggest 320 in the wrecker is the flash point. like that modification, thanks for the post Jeff.

Csm Davis said:

So my next question is how hot is to hot?

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There are lots of variables, but the rule of thumb is not to exceed 180 degrees F. However, the maximum temperature can be quite a bit lower lower if you have a low viscosity hyd oil. The lower viscosity is what hurts the wear parts in hydraulic pumps & motors, but high temperatures shorten the life of every component including hoses. Some of the pumps we used on drill rigs cost almost $10,000, so we paid attention.

These trucks get the oil hot really fast and I would guess over 250 in 15 minutes and that is on the 10wt in them.

That appears to be the same temp sending unit as installed in the HMMWV, it's for the Engine temp Gauge.
so unlike the cold advance and Thermal switch in the water crossover that are normally closed, this TSU just sends
the signal, gauge requires 24v and ground.

Csm Davis said:

These trucks get the oil hot really fast and I would guess over 250 in 15 minutes and that is on the 10wt in them.

Click to expand...

Infrared heat guns have become really inexpensive, I got one at Costco for about $40.00. It would be worth checking out what the temperature actually is. If it is anything over 200, it is bad news. The variables with the biggest impact on what the maximum safe temperature for a hydraulic system are the types of hydraulic pumps and/or motors are in the system and what type of oil. My understanding is that the military ran motor oil in hydraulic systems and Allison transmissions to simplify supply problems and were willing to accept lower lifetimes from the equipment.

The chart below shows how motor oil viscosity changes with temperature. Ball park minimum operating viscosity is 100 SUS or 20 cSt. You can see on the chart how most of the oils drop below that between 180 and 212 degrees F. Hydraulic oil also has other additives that are optimized for hydraulic systems that motor oils don't have. I think the ISO 46 hydraulic oil is the "rule of thumb" choice for most locations in the US.



This other chart is more complicated, but it shows how even the viscosity of the ISO 46 hydraulic oil is down under 50 SUS at 210 degrees F.

The 10W range at only 100 degrees F is barely more than 100 (looks like range @100 is 105-165 SUS) and drops to 40-44 at 210 degrees. It could drop under 100 SUS at less than 125 degrees.



If you use the hydraulics much, and the oil temperature is over 180 degrees, additional coolers will pay for themselves very quickly no matter which oil you use.

The m939 with the nhc 250 use the same part number for the tranny temp sensor and also for the coolant but different gauges. The sender appears to be the standard one used on most mv's. I would think the resistance is different for both gauges so it reads accurately.

The gauge looks like the standard trans temp one on the M939

Looks like a nice addition especially under sustained use.

juanprado said:

The m939 with the nhc 250 use the same part number for the tranny temp sensor and also for the coolant but different gauges. The sender appears to be the standard one used on most mv's. I would think the resistance is different for both gauges so it reads accurately.

The gauge looks like the standard trans temp one on the M939

Looks like a nice addition especially under sustained use.

Click to expand...

My thoughts exactly. Penty of 24 v. sources up under the boom. Just need to drill and tap that end fitting. Note to self, " Add to project list for m936".
By the way I finally brought the M936 home Sat. night after the MVPA convention. Drove it home in the dark with anther bud following in a CUCV Contact Mait. Truck. Man did we look official. It had been stored a a bud's business since delivery. Wife returned home Sun and says," I see you have another truck". My response was, "wait till you see what this one can do". Going shopping for jewelery tomorrow.....

Where is location of the transmission sending unit on the m939?

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TEAMJENSEN said:

Where is location of the transmission sending unit on the m939?

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Click to expand...

Check your last posting in the other thread.

Thank you! I was able to find with your help the sending unit and now have the transmission temp reading correctly. I appreciate the help and the picture was very helpful.

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