A/T Oil Temp light comes on, kills engine

Hi all. I have a 2003 Sequoia 4WD that I just bought to haul a 3600 lb RV. 244K miles. Body in great shape and ran great, but the previous owner didn't keep a record of the last timing belt change. We drove it on 2.5 hour trip the first weekend we had it, but I began to worry about the timing belt. The owner had died and I bought the vehicle from his son. So I replacing the timing belt, water pump, and the fan belt last Friday. Everything seemed great but it took me about 13 hours to complete start to finish. Drove it a little around town Saturday, short trips of no more than 10-15 minutes each. Drove it twice on Sunday, about 15 minutes each way with a one hour rest. A second trip pulling the RV for the first time just to the gas station and back. Everything fine. Forty and 50 degree outside temps this whole time. Today it dropped to about 30. So in prep for another RV test drive, I warmed it up for about 20 minutes, during which the engine had died and the A/T oil temp light was on. I started it again and got out of the driveway before it started dying. I let it cool off for another 2 hours and it started right up. I drove about 10 minutes on the freeway when it lit again, began to shudder, and died at the end of the exit ramp. Limped home. Tried to measure the transmission fluid tonight but couldn't get the engine to stay on long enough to warm up. Still, the fluid measured on the stick and was at about room temperature, not hot. During the timing belt repair, I splashed a healthy amount of radiator fluid and there was probably transmission fluid in there too (I don't see color that well but there seemed to be different blobs of color in the liquid). Once I buttoned everything up and cleaned the floor, there were no leaks afterwards.
It's been very difficult finding good info on this problem.
Leaving the trans cooler lines disconnected so long during the timing belt repair, might I have lost enough transmission fluid to cause this? If so, how much do I add if I can't properly fill the fluid? Is this just a bad coincidence and something else is going on? It just seems to convenient to have happened so quickly after my repair.
I appreciate any help!

 

What level was the fluid on the stick at your room temp reading?

 

I don't think you lost that much fluid from disconnecting the lines, maybe 8-10 oz is what I seem to remember from my timing belt last year. Even if the fluid is not hot, how much fluid is showing on the dipstick with the engine running? Fluid does expand and move further up the dipsitck as it heats up, but the difference between cold fluid and hot is only about 1/2 to 3/4 of an inch on the dipstick.

 

My experience with automatics says you should change the fluid. Period. Now.

 

It covered above the cold mark and possibly all the way to the hot mark. There was no lack of fluid on it.

 

This morning I got it into my garage and let it sit for an hour. Before starting it up I inspected the lower radiator where the small hoses connect. I pulled one and there was fluid there. No visible signs of pinching or leaks. Tracing the hoses to the tran cooler and back to the transmission; everything looked ok although the hoses near the transmission are dirty. No signs of leaks. Then I started up and ran it in Park for about 4 or 5 minutes when it died and lit the A/T Oil Temp light. I put it in N without the engine running and looked at the stick. It covered to the Hot notches, very similar if not the same as yesterday.

 

Possibly a transmission fluid control thermostat failing.

 

Seems strange that 5 minutes of idling will heat the fluid enough to expand it on the stick. OP you make no mention of how hot the dipstick or fluid is to the touch when you checked it. The AT overheat light comes on around 300f, so if truly a overheat condition your fingers should be getting zapped pretty well. If the fluid is just a bit hot to touch, that's about the same as the hot water in your home, 120-130f. If so, I think Glock is correct you need to start diagnosing an electrical issue. If the fluid is cooking hot after 5 minutes you may have a failing pump or blockage in the ATF cooling lines preventing fluid from circuiting.

Go burn your fingers and report back

 

The fluid control thermostat is more of a spring-type sensor, not electrical... pretty sure. Similar in theory to a typical antifreeze/coolant thermostat but much smaller. It has a built-in return valve that's actuated by temperature. At least that's the way it works on other trans cooling systems I've tinkered with. It's an inline sensor and must be installed in the right direction, normally has arrows stamped onto the part. The installer has to be positive on which direction the fluid (transmission oil) flows when installing... or it's NO flow, hot hot hot fast. Plugged by the valve. This can also occur if the fluid control thermostat is clogged with a particle, or just plain failing due to age or trauma (like me?).

 

A possibly encouraging update! A good friend mechanic pushed me harder on the symptoms and challenged the A/T Oil Light circumstances. He suggested that the light was coming on when the engine failed, not before. Which he believed was a kind of generic fault light that accompanied the battery light. Of course when I'm freaking out as the engine is dying on the road I'm not paying as close attention as I should. Also, I learned today that the check engine light, which had been lit due to P0420 codes (catalytic converter), was also throwing P0352 and P0353 which have to do with coils not firing properly. My friend noodled this with the coincidence of my timing belt replacement and suggested that I may have messed up something with the cam sensor cable which has to be threaded through the grommet of the cam pulley cover. Sure enough, I had routed that wire awkwardly around another pipe so close to the fan belt that I used a zip-tie to keep it out of the way. My friend suggested I might have pinched it or done something to affect the operation of that wire, which is critical to the proper firing of the engine, and suggested by the new codes. He didn't think this was an overheat situation either and, like you suggest, was an electrical problem. Soooo, I clipped the zip-tie, freed the wire to a more natural path, and re-seated the plug. Just tonight I sat at idle of about 700 rpm for over 15 minutes without an issue. I'll do a longer test tomorrow and check the transmission fluid while warm, but I am encouraged! You guys are the best! I'm definitely over my head here and you all have been excellent! Will update again tomorrow!

 

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