Is it the head gasket?

[chasfgr]

Having had similar symptoms, I know you have to go through, in ascending costs, about 5 steps.
1. Head off, if lucky you have a leak from cooling sysemn due to faulty hed gasket. Probability <40%
2. You have a track from cooling channel to cylinder, possibly cured by head skim c,15%
3. As above, but the eroded area is on the clock - engine out strip and grind block, about 10%
5. exhaust manifold leak int heat transfer unit.
6. Cracked head or block. >6%.


You just have to go throught each in order to find the final.
The best indicator is:_ do you have displaced coolant - or do you have to top-up the header (with no coolant discernable in engine compartment.


Mine turned out to be a track on the block - which took me 4 years of cost and concern, till I bit the bullet and re-engined with a new 3YM instead of the 2GM.
I was lucky my prop and sterngear fitted (with shortened shaft.

[deblen]

Some additional info on this engine series :


https://www.cruisersforum.com/forums...-158867-2.html