CAT D8N Trans temp hot

We have a CAT D8N ( 5TJ ) And just did a full machine rebuild 120 hours ago, Then transmission temp gauge is maxing out to 250F And the warning light is on. We shot the trans case with a infrared gun and it's sitting at 220F, The trans filter housing is at 193F. Oil is clean, no burnt smell, shifting fine engine cooling temp is ok, no trans filter bypass light. Any thoughts possible wiring or sender problem. We are about to pull the operators floor pan and shoot the trans sender, but the dirt is coming in to fast to stop it for any long period of time.
Thanks !

You may have an apparent difference between the gauge showing 250 and the temp gun showing 220 - but even 220 is still too hot IMHO.
The 193 measured on the filter housing would be very close to setting an alarm off on most machines.

What happens to the Power Train temp gauge reading if you disconnect the 424 Yellow wire from the Power Train oil temp sender..?
Also try disconnecting the 424 Grey wire from the Power Train oil temp switch and see what happens. FYI the switch is supposed to open at 265+/-5 DegF with rising temperature and close at 245F with falling temperature.

You might not have a trans filter bypass light for other reasons. Have you checked to confirm if the transmission filter is actually bypassing or not..? Try removing the switch and operating it by hand.

What happens first thing in the morning when you start up from cold..? Does the temperature rocket up quickly or do you have to put the machine to work..?

Has it still got the original non-emissions-rated 3406 in it or has it either been updated to a 3406C Tier I or even a C13 Tier III emissions..?

For me, simple as it sounds, even with no warnings lights displayed and clean oil would be replace the trans filter. Makes a huge difference on temperature.
Oh and keep it genuine.

Wow - Thanks everybody, I think we have a wiring or sender issue, Infrared gun read 193F, transmission outlet reads 143F. We are going to change the High Efficiency filter to a standard CAT flow filter, replaced sender then retest.

I wouldn't change the High Efficiency filter for a standard just yet, I'd simply change it for another one of the same part number. Also cut the filter open and see what sort of material (if any) you can find in it.

To test the sender wiring, disconnect the 424 Yellow wire from the sender (at the sender location not behind the dash panel) as suggested above and see what happens.

If you want an Electrical Schematic for the tractor please drop me a PM with your email address.

Found a problem Transmission Test P # 1 is 180psi spec calls for 350 PSI, I'm checking SIS WEB now, but P1 releases the brakes, low oil pressure could be dragging the brakes. Replaced the filter and found a tiny amount of brass which could be in valve body screen clogging it.

The plot thickens...
Keep us posted.

UPDATE : Removed the rear transmission plate and all the bolts for the valve body that sits on top of the transmission where completely backed out, removed it anyway, disassembled anyway to check the screens, nothing found reassembly now. Will update after.

Another CAT dealership rebuild 120 hours ago ?

Reassembled valve body, TORQUE valve body bolts, tested pressures cold & hot in spec ( P1 390psi ) , put machine back to work for 3 hours trans temp gauge did not go over 180F. good to go ! Cause loose trans valve body causing P1 & P2 pressure drop.

Excellent work.
Later Bob

dirt123 said:

Reassembled valve body, TORQUE valve body bolts, tested pressures cold & hot in spec ( P1 390psi ) , put machine back to work for 3 hours trans temp gauge did not go over 180F. good to go ! Cause loose trans valve body causing P1 & P2 pressure drop.

Click to expand...

I hope the lack of transmission pressure hasn't caused damage to the clutch packs. Next time you change the oil I would suggest that you remove the transmission suction screen and see what sort of particles in what quantities are lodged in it.