I'm having a little problem with the engine on my GT-R overheating. If I let it sit and idle in even mild (18-20 degrees celsius) temperature, the coolant temp almost goes through the roof and my oil temp climbs up to 110 degrees c. The current setup is a Koyo 2 row aluminum rad measuring 26" x 18" x 2 1/4" and the fan is an electrically controlled 14" fan which is much smaller both in diameter and blade size to the stock fan. However, the rad is twice as big. Would the extra coolant not keep the motor cool? If not, what fan should I find to fix this overheating problem. I think I have figured out the oil temp problem, being that I put in 0w40 synthetic which I had a bad feeling about anyway. Im changing it out after just about 200 km to 10w40 synthetic because I don't trust that lighter oil. Could the overheating also be cause in part by the lighter oil? Is it possible that I have already damaged my turbos by running the lighter oil? By the way, the motor is stock with the factory boost restrictor removed and HKS pod filters and a 3-inch Apex'i cat back exhaust. Also, I am getting a stumble on accleration after 5500 RPM. Does the factory ECU actually retard the performance so much as to get a bad miss and very rich conditions? Any help would be appreciated because I am not experienced enough with cars to figure this out without expert advice.