i have the identical problem you do, all the same symptoms except i get a ton of overflow from the reservoir and i have a koyo radiator...... but i think i found out what the problem is. two things... first one may or may not really but much of a factor, but if you dont use dex cool coolant or just a type of coolant thats made for
aluminum radiators, little clogs can build up which may lead to slightly more overheating. anyways im sure as everyone knows a radiator has coils going back and forth stack on top of one another very tightly. what happens often especially in the case of having a turbocharge system is the coolant gets too hot leading to more pressure. in some cases the coolant can get so hot that it will cause one of the lines of the coils to expand, crushing the one above and below it. this will eventually stop the flow of coolant until the coolant gets hot enough and builds enough pressure to where it finally burst through filling ur reservoir tank/ overflowing. also if you have ever had your heater on to help keep the car cool you'll notice the heater stops working suddenly even when the car is overheating. this is because the flow of coolant has stopped. ive had my car turbo-ed for 4 yrs and never had a problem until recently, but ive been using just regular universal prestone coolant. i really dont think the type of coolant makes that great of a difference but maybe it happened when i raced my car to hard in 98 degree weather?? what im going to do now is get my radiator pressure tested at a radiator shop and buy another koyo radiator if it is damaged. pictures on the way soon =D
