I'm guessing this 700R4 is in your C30? The radiator mounted cooler isn't enough if you're pulling weight! The trans can completely melt down & not effect engine coolant temps!
Yes, it's in the C-30. We had issues with the first incarnation of this trans. Had the heater hose mounted in stock position, electric fans, and a failing fuel pump. Heading out of Bay Area (CA) to TX with a loaded cargo trailer, it wouldn't make it up the first pass. Got hot starving for fuel. We pushed on, babying it up various mountain passes, decided on I-10 as it's flatter (but still some pulls), finally just before Phoenix, we replaced the fuel pump along side the road. From then on, no issues. Brought it back to CA empty, no issues until I-35 stopped outside of San Antonio, then temp started rising. As long as we were moving, no problem. Yes, the fans were failing. Traffic stopped on the Grapevine due to a truck driver losing a trailer, but I kept it moving, still got hot. Vintage Air heater control valve not closing, so hot coolant from the heater core dumping right onto the trans cooler, not good. Fluid has been spitting out the TV cable. Made it back to CA where I removed the fans, installed a stock clutch fan, and routed the heater hose to the water pump like the BBC cars were. Pretty sure it had a high stall convertor, further adding to the heat. Drained the fluid numerous times, it "glugged" while draining, and overflowed if you tried to put more than 4 quarts in at time.
Later I drove the empty trailer out to a relative's place (about 80 miles) to load up the trailer with engines and other parts. On the way out there I pushed it pretty hard, figuring my cooling issues were fixed. I don't think I had re-routed the heater hose at that point, just installed clutch fan. Engine stayed cool. Just before I got there it wouldn't go into 4th (OD). Driving back home (loaded) we figured it wasn't shifting right, and better take it in before the trip to TX. Trans shop said the 3-4 clutch pack was toast. We wanted a 4L80, but couldn't find a core, and if we did it would be expensive, plus buying the computer to run it. After a month, still no core available, so I opted to beef the 700 (billet input shaft & drum, 5 planetary gearset from 4L65, etc). Regular convertor, now it creeps forward at idle, which it didn't do before. They checked the vent, said it was open and clear. It has the hydraulic lock-up in OD (DD too), they recommend NOT installing an electric lock-up due to heat issues. With the planetaries turning and the convertor unlocked, you're asking for an overheat. Also recommended staying in direct drive while towing.
Drove the fully loaded truck & trailer to TX, temp stayed cool the whole way, even climbing the Grapevine (5% grade for 5 miles). But still there is fluid on the manifold where the TV cable mounts. I called the shop who did the work, they said get it checked out here (TX) or maybe if it goes back to CA. So far I haven't. Haven't drained the fluid either, so I can't say if it glugs. With no load it runs and shifts excellent, still fluid on the manifold. I did keep it in direct drive for the most part, occasionally going to OD if downhill and/or tailwind.
The shop says the radiator cooler is the most efficient as it's water-to-fluid & an air-to-fluid cooler is not as efficient. Adding an aux. cooler adds more hoses and possible leakage, & not necessary. I asked if I should get a fluid temp gauge, he said no, that'll just scare you. LOL.
Thanks for the input, I'll call the shop and ask about the pump-to-case gasket.
