The air/oil is more efficient at cooling but the water/oil is better at warming the oil up and speeding up engine warmup. The best setup is what a few of the guys here have done and keep the water/oil cooler and add an air/water cooler. if you fit an after market air/oil cooler you must use some kind of thermostat in the system.
I've kept the heat exchanger and fitted a Mocal 235mm 13 row cooler with 'stat. Car does take longer to warm up than before. With the lower gearing ( more revs ) from a 3.89FD my oil temps were much higher before on track, that was my reason for the air/oil cooler, testing it out at Cadwell Saturday. Edited by: GVK
any kind of heat exchanger works on differential temperatures - the rate of heat transfer is proportional to the difference in the temp between the medium being cooled and the one doing the cooling. Water in the engine on track at over 80 degrees, ambient air temp between 0 and 30 degrees. so an air cooled oil cooler should always be more effective than a water cooled one. Also - the heat has to go somewhere, an air cooled oil cooler will produce warm air, which can be ducted away and an endless supply of fresh cool air introduced. A water cooled oil cooler will result in higher water temps, which then have to be dealt with by the car's rad - an air cooled water cooler. I would always go for the air cooled oil cooler, it cuts out the middle man, gets the heat more effectively dissipated to the air and will help keep the water system in the engine cooler (which on track has enough to do cooling the block etc) The main downside is that the oil will take longer to warm up, so get one that has a thermostat (oilstat) and you should get pretty much the best of both worlds.
Cheers chaps, I thought I'd get this straight before I build my cooling system. Looks like I may eliminate the oil/water cooler for the time being.
I read 'somewhere' that the mk1 air cooler was designed for the continent, and they realised it was a total waste of technology as cars didnt get hot enough in the UK so didnt bother putting them on the mk2. but then thats a random 'i read somewhere'
GVK, How did you fit the sandwich plate?, isn't the threaded tube too short? I thought there were only two tubes available, one for a sandwich plate (mk1 style) and the longer one for the heat exchanger? cheers, David.
Good question David, can't remember much about that side of it - remember taking the thin nut off the threaded tube to allow the sandwich plate onto the tube, there was a threaded sleeve that fitted inside the sandwich plate supplied with the Mocal kit.
Well worth fitting the Mocal, last time out at Cadwell + Snetterton, oil temps were 3/4 way up the gauge after 20 mins. (circa 130-140 degrees if checking on MFA).) Yesterday at Cadwell, flat out for 25-30 mins and gauge sat dead halfway (110-115) Gauge reads 25 degs too high, but I've allowed for that.. Edited by: GVK