nipponbird

It's clear that you've made your mind up and I don't say this for you to reopen the case, but I've played a lot with oil coolers on Corvair engines, which I've installed in VW bugs. First of all keep in mind that an oil cooler needs an oil thermostat valve to open at a given temperature, unless you have an oil temperature gauge installed in the oil gallery, you won't know what time it takes for the oil to warm up with a slapped on oil cooler. If you run the engine at lower oil temperatures than it was designed for, you'll accelerate wear in that engine. Factory installed oil coolers all have an oil temperature thermostat (mostly installed where the oil leaves the engine enroute to the oil cooler to isolate the cooler while the oil is below a certain temperature), which is nothing else than a plunger and spring that is of course temperature sensitive.
Furthermore: make very, very sure that the oil lines to an oil cooler cannot rupture. You will lose the oil in the engine in about 20 seconds flat if that happens and if you don't switch the engine off in time, look forward to a complete rebuild.

fastnoypi

The OP is discussing a cooler for his transmission, a thermostat is typically not needed.
You are correct that you need a thermostat for an external oil cooler for an engine.

nipponbird

Thanks for pointing it out, but I'm aware of the OP's needs. What goes for an engine oil cooler usually (pay attention to the "ususally") goes for a tranny oil cooler too.
I would like to know why you say a thermostat is not needed for a transmission oil cooler as it is the opposite in most cases.

The set-up the OP now has, is fluid which has already had a temperature drop from the stock oil cooler. There is little room for the man in the street to determine scientifically at what temperature the fluid re-enters the tranny from his aftermarket cooler. Of course it is now at a lower temperature than when it should've only the stock cooler to negotiate. Thus the tranny must reheat it to operate at the desired temperature on which the designers have decided, which can affect a lot of factors calculated by the tranny's ECU.
My point is: bin it, it is probably counter productive.

fastnoypi

The thermostat bypass is typically not needed in a transmission cooler situation because usually the setup is in loop and temp regulated by the ATF reservoir tank integrated in most automatic transmission radiators. Normal operating temperature of ATF is between 150-200F . Each 20* increase above 200F significantly breaks down the ATF protection and reduces longevity.
Fwiw, the coolant side of an automatic transmission radiator or any radiator tries to regulate temps between 180F minimal and 220F before fans kick on.

hayafalcon

I hope you just left the aftermarket cooler in place, It can't hurt anything and likely will help keep the trans and front diff cooler and that's always a good thing. One tip if you are concerned about the cooler suddenly springing a leak.....just collect an adequate length of rubber hose and a few clamps and a screw driver. Keep them in the car. Now your covered. If it leaks you can bypass it on the fly in about 10 min. Same goes for the original cooler. I had mine start leaking really bad while in town. I was able to find a hose and clamps at a Reilly's and bypassed the cooler til I got home. Turns out it was just the stub end on the cooler outlet. The little pipe was cracked. I removed the bypass and I just pushed the outlet hose on farther and reclamped it. That was 3-4 years ago and still holding. Haya...