Could be a blocked or too small cooler, my 502s did this and with new larger coolers it stopped. If you lost an impeller in the raw water pump it can block them, you can try to back flush it to see. Also what oil are you using, some are just not thick enough, like a 30 weight, I used 50 and it helped. Could be a T stat, some have them on the oil coolers too. It is a chase, you need to start cheap and easy and move to hard and expensive...like new coolers.