Sorry to open this so far down the road. I am working on a 1998 Mack E7-460 that is blowing coolant out of the overflow tank. It is pressurizing the system. The customer had it to Mack last year and they installed a new head and one cylinder. It was fixed for three weeks and started doing the same thing. He called Mack and they are scratching their head. He doesn’t want to spend a lot of money on this truck so he brought it to me since my labor rate is cheaper.
I pressure checked the cooling system for three days and didn’t lose any pressure. I have also removed the rocker arm assemblies and pressurized the intake manifold to 50 psi and I can’t see any bubbles in the tank indicating a crack between the valves.
It had a sleeper but has been removed and made into a day cab. I am really scratching my head as to why after 40 minutes of driving it over pressurizes the radiator cap. The Mack dealer installed a new thermostat and air compressor as well sounds like they were just throwing parts on the engine hoping to fix it.
Any help would be appreciated. Thanks
