4L60E Tranny Temp

[Rico]

Mine gets to 142 C. and the high temp threshold seems to be 129. Has been a problem since new. They didn't put a thermostat in there did they?

[joecar]

Ouch... TFT at 142C/288F is way too hot and indicates a serious problem;

overtemp fries the rubber seals and they become brittle and allow internal leaks/slippage;
overtemp fries the ATF and causes it to varnish which stickies the valves/solenoids and kills the clutches/band;
overtemp causes the ATF to lose it's lubricating properties.

4L60E/4L80E does not have a thermostat;

The problem could be that the TFT sensor (located in the pressure switch block inside the bottom of the trans.) and/or it's wiring has failed and is indicating the temp incorrectly.

Ignoring what the TFT says, does your trans. physically seem overheated or does it seem normal temp...?
Do you have a DMM with a temp probe or a laser/IR temp probe, if so measure the temp of the trans. pan when hot; is it really overheating...?

What does the ECT say...?

Is the ATF the colour/smell dark/grey/black/burnt...?

If your trans. really is overheating, the ATF will be discoloured and will smell burnt.

If your trans. really is overheating, proceed...

Are you hauling excess weight...?
Are the trans. cooler lines and/or cooler blocked...?
Is the TC and/or trans. slipping...?
Is the ATF level low...?
Does the ATF contain particles (clutch or metal)...?
Is the filter clogged with sludge and/or clutch material...?

Have you measured the line pressure using a gauge on the line tap on the side of the case, if so is it pegged at 230+psi...?

If your trans. survives and the problem is corrected or goes away (that's even scarier), immediately change the fluid and flush the TC and cooler and lines (disconnect the cooler return line and cycle new ATF thru trans).

[emarkay]

Exactly - here's some more info from a few sources:

"...Normal driving will raise fluid temperatures to 175 degrees F., which is the usual temperature range at which most fluids are designed to operate. At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins to form on internal parts which interferes with the operation of the transmission. If the temperature gets above 250F (121C), rubber seals begin to harden, which leads to leaks and pressure losses. At higher temperatures the transmission begins to slip, which only aggravates overheating even more. Eventually the clutches burn out and the transmission calls it quits. As a rule of thumb, every 20 degree increase in operating temperature above 175F (80C). cuts the life of the fluid in half! At 195F (91C) , for instance, fluid life is reduced to 50,000 miles. At 240 (115C) , the fluid won't go much over 10,000 miles. Go to 295 or 300 (145C) degrees F., and 1,000 to 1,500 miles is about all you'll get before the transmission burns up..."

You have had this temps since it was new??? Do you have a tranny temp gauge to confirm this? I really don't think you'd have gotten very far on that tranny if it was periodically reaching the 285F range!

[Rico]

Wow! Good info guys!

Here's the history:

It seems that when I would run a big hill and heat the tranny, when I reached the top and let off, it would take a while (20-30 sec) to shift into 4th

2001
Stock truck, empty, drivin like I stole it, in the mountains, hard pulls and using trans to hold back too

Oil was browned and stinky after first summer. I had the oil flushed and parked it for winter.

2002
Installed TransGo shift kit. This includes disconnecting preasure control and replacing various springs. (Oil pump preasure and solenoid springs) All shifts were now HARD, all the time. No more slippy soft shifts. Oil and filter changed again at end of season

2003

Truck wasn't used too much but still hard. Oil did not get smoked anymore, but tranny still seems to get into overtemp mode on occasion.

2004

As before

2005

Installed tranny cooler finally. But still does strange things once in a while.

2006

Time flies. Finally got EFILive and see what the PCM sees for temps. well maybe. I should try to measure the fliud someother way and/or try another temp sensor