Had 3 reconditioned injectors (because of some diesel smoke at idle), new exhaust manifold (hairline crack which was a recall but I was past the mileage cutoff so I had to pay)and valve adjustment, filters, oil, etc. done by dealer on 06 isuzu fvr with 275hp 6hk1x (GMC t7500 twin) engine. After 25 miles got a low coolant warning light, stopped and coolant level was correct, I figured an air bubble as the level looked a little high. let it sit while I called and dealer said just verify coolant level is ok, there is no level sensor other than in the overflow tank behind the cab and no other cap to check, restarted and no more warning light. drove 10 miles home, no problems, then 3 more very short trips of under 6 miles with no issues, runs great, no more idle smoke.
Now first real trip after the service, 100 miles, starts to run on what feels like 5 cylinders right at the destination, shuddering at low speed. No smoke. Park it and figure I'll check it later. speculate maybe a connector has come off an injector or something. 8 hours, come outside and see the coolant is low, I open the cap and it is under great pressure as if it was hot. It takes a gallon in the reservoir. I drive 200 yards to the dock, skipping a bit still, and I check for any leaks, I see no smoke or anything. Shut it off, load, then restart and I see coolant is rising significantly in the tank all the way to the cap, then starts to go down and I see steam coming from an overflow hose by the oil pan, (presumably crank case vent) then get a big steam cloud from the exhaust still at the dock, all in under 3 minutes. Shut down, call the dealer and he wants me to restart to see if I'm getting pressure/steam from the oil fill cap (after checking the dipstick, which looked good) the starter made a few degrees of rotation then stopped, both of us suspecting hydro lock from water in a cylinder.
Towed 100 mi back to the dealer. Any ideas? I've heard of seal problems around injectors leading to oil in the coolant, but not vice versa. Any advice on what they did wrong would be handy when I speak to the dealer as they are checking it out now and I do not want to get screwed on this. Its under 200mi since the work was done at $5k+