THANKS for the replys,my truck Gm 6.2 diesel still has the prob,its not the clutch fan,you can check it with a heat gun,mine is fine.heres the drill i go out in the morning and start her up,she fires rite up,pop the hood and the headder tank is full of coolant,l pop the rad cap off and theres lots of air bulbbles in the flow.get the shop vack out put it on the blower and push all the coolant in the headder tank back in to the rad,its warm by know and it looks soap suds in my rad,witch i did not put soap in there.off to work its about 30 miles to work @60 mph, she runs @190F steddy,get to work and pop the hood and there is the bulbbls going to my headder tank, not lots but one a secon,if i let it idle for 10 min and it gets sierous! shut her down. if it was a head gasket there would be fule in my coolant,or my eng oil would be grey or milky,both are good no fule in the coolant,on water in the oil? ive been a marine mach for over 20 years,built and worked on a lot of motors and i should know this one!! the vapor lock theary is good but iam not sure about that,my clutch fan is working,this motor has well over 500.00 miles on it,ive put over 300.00 on it in the 8 years ive owned it,when i bought it i put and hour meter on the motor,4.852 hrs on rit know,with a DIESEL its better to go by hrs then miles,i chang my oil every 100 hrs, what the hay,its $10 and 1/2 hour to do,rite!an it dosent see over 3000 RPM.allways like to here what people have to say.