i built a na 516 cu in engine last year and it is putting water in the oil,before the build i had the block magged and it showed no cracks.dyno,d engine before installing it in the boat and was happy with the results,603 hp at 5500.i install it in the boat [24 sunsation] and it runs great but is getting water in the oil.this engine has brand new edelbrock aluminum marine heads .i removed the engine,tore it down to the bare block and had it and the heads pressure cheched,no leaks,at that time had the block and heads milled ,just a clean up cut to insure flatness.i put it on my runstand and ran it at 180 deg for 40 minutes with no water in the oil so i figure the problem is cured and i reinstall it in the boat,guess what,water in oil again.once again i remove the engine from the boat,remove the oil cooler and exhaust system and run it on my run stand,water in oil in 15 minutes.now i block off the thermostat opening,put 1 block off plate on 1 side of water pump hole and a - 8 fittind on the other,i put 35 lbs of air pressure on it for 30 minutes and no leak can be found.im at my wits end with this pos so im looking for ideas .the boat owner has been cool with all this but im starting to get pizzed about this mess.

Was it still up to temp when you pressurized it with air? Maybe thermal expansion causing some of the problem finding it? What did the pressurize the block and heads to ?

i did the test with air the next day so engine was at room temp,i went with 35 lbs air pressure with water also in block.the wp in the boat was 23 lbs at 70 mph.

Possibly warped intake manifold .

i thought about that but no air is leaking with 35 lbs air pressure.

you would think the extra pressure should expose any cracks or leaks. is it possible to run it up to temp and apply the presure again? this is an odd one.

Only thing I can suggest is to do the air test with a hot engine .

that is the plan for tomorrow.

also worth checking is your exhaust integrity; 600+ hp takes a cam with lots of overlap, so with any breach in the exhaust system............

i ran it on the run stand with car headers.