i have a 2007 f250 6.0 150,000 miles

just did egr delete
arp head studs
new heads.

i just went on road trip to sturgis and went threw 2 gallons of coolant each way.

its not blowing white smoke.
no coolant in oil.
And no leaks.

where is my coolant going??

 

My buddy ran into this sort of problem with his pathfinder. I know Nissan and non American but I have never traced the coolant system before and I know he found that coolant leaked into his transmission. Could have blown it as well but did not. I'd say start looking into routing the system couldn't be to hard with help of technician

 

Where the new heads trued? Verified flat? I have got out of spec heads before thus causing a popped head gasket on new heads. Also check for the the little crusties left behind from coolant evaporating, not just the obvious wet area. Four gallons seems excessive but if the coolant system wasn't properly "burped" or "bled" it would cause a need to add coolant. Hope this helps good luck!