I got a 1998 35 ft rv with 460 that is giving me fits. I have changed the radiotor, thermostat, hoes, water pump belts,put banks headers, and clutch for fan, all new sensors. Runs great up to about 60 mph while on toe. Then it starts to climd fast untill you back out of it it ideals cool and does towns cool. I have tried every thing i Know. Thanks for the help

 

Probably need to do a check to see if you may have a head gasket leaking compression into the cooling system

 

I look for bubbles in radiotor did not see any. I dont lose any fluid exsept when it boils over. Thanks

 

You most likely won't see any bubbles until pressure builds up.The chemical in the tester will detect any traces of exhaust gasses

 

Thanks I will try that.

 

Are you sure that it's actually seen it overheat or is this just what you see on the gauge?

 

It has boild out the reservoir before. I have read forms that the trains. might be slipping and heat the motor up but it does not seem to be slipping. Would loseing vacuum at higher speeds couse problems to the fuel system? There is a vacuum switch that takes the fuel from close to opeon loop I think. Would this lean or flud it THanks