You can get an OE Isuzu head gasket from our resident Isuzu Guru Jerry Lemond in Dacula, GA. JLEMOD on this forum, you can message him. Or contact him at [email protected]
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Drain your oil, if it is contaminated with coolant you don't want that mixture in there for long, coolant eats bearings.
Besides a compression check, do a pressure test on the cooling system, that may tell you something.
If you have to pull the head, easier to remove the hood then pull the head and intake out as a unit. You can undo the EGR pipe and unbolt the exhaust manifold; tie it to the side, out of the way.
If you want to remove the intake before pulling the head, about the only way to do that is to remove the upper plenum. Then you'll have access to the mounting hardware.
If the head is original and, especially if the casting # at the firewall end is low (i.e. #1 or #2), recommend getting a new head. By the time you have the head pressure-checked, surfaced (as required) and a valve job, you'll have a ton of $$$ into machine shop labor and material. New head is somewhere around $650 from Clearwater Cylinder Heads in Florida, a much better, more reliable option. New design and better materials drastically reduce the possibility of cracking and exhaust valve burning, which was a big problem with the earlier run of factory heads.
Very important to have a good head gasket in there and I wouldn't use anything but OE, as long as they're available. Fel-Pro would be the 2nd choice.
Anyway, check everything over carefully, maybe it's not a blown gasket. G'luck with the repairs.......ed