A word of caution you can cool an engine too much especially the oil. All oil filters have a bypass thermostat valve in them that will allow oil to pass through unfiltered until the oil warms ups then it will start filtering it. If you cool the oil too much then this valve may never close so the filter can do its job.

I dont believe an external oil cooler is pratical on a street car...

it has the same over cooling problems i mentioned in my last post. (especially in colder climates) and the risk/reward ratio is far too high. your better off keeping the engine coolant in the proper operating range and letting this regulate your oil temp than you are by adding an external cooler.

an external cooler adds another point of failure for a street car, one stray rock and unless you just happen to notice your oil pressure gauge drop to 0 lbs, youve left an oil slick on the road and that thump youll hear will be a rod crashing through your block.

I agree I wouldn't run an oil cooler on a street car either, but I would recommend running an external trans cooler in line with the current system or eliminate using the one in the radiator and going to a stand alone system.

As far as the oil thermostat not working on the oil fiter if it was to fail, meaning not allowing the oil to be filtered the dirt, sludge and other normal wear of the metal parts within the engine would find their way onto the bearing and eventually destroy the engine.

If you do use a cooler for the oil or trans, make the inlet at the bottom of the cooler, and the outlet at the top. This will purge air out of the system. If it goes in the top, you will always have some trapped air and reduce the cooling of the fluid.

There are coolers available with a shut off/bypass t-stat. They are harder to find. They will route fluid around the cooler, with out affection flow through the lines.

If you are going to use a trans cooler in addition to the existing one in the radiator, run the fluid through the radiator cooler first, then the add on cooler. Other wise the radiator can heat the cooled fluid.

The coolers are good for extra loads, high performance driving (not necessarly the way the car is built) and trailer towing. Usually they are not necessary for normal driving. And the cold climate problems noted above need to be considered. I have seen them installed with manual bypass valves which could be changed according to need. Usually this is more trouble than it's worth, but it may be right for you.

read little history on the C4 last night (can anyone tell from my post times that i have insomnia)

they had an oil cooler on the C4's until one of the middle years like 90... it was the same year they changed over to mobil-1 synthetic..

they determined that an oil cooler wasnt needed with synthetic oil.