So...after a sucky summer of work I finally get to run my boat with my new-to-me headers. You all know where this is going. After about two hours of run time with no noticeable problems I park the boat. I go to start it but the starter motor stalls. I've been cranking the radio as I clean so I put in a fresh battery and the same thing. I pull the plugs and water comes pouring out of #5. I pull the headers and the port side couldn't have more water if you hooked a hose to the back of it. The starboard side was dry as a bone so it's not a reversion issue.

I ran a compression test and the port side was definitely weaker with #5 off the charts at 270. I checked the others and came back to it and it came down to 210. Why?


#1 160
#3 165
#5 270 210
#7 160
#2 185
#4 180
#6 175
#8 180

So where do I go from here? Pulling the entire engine is quite an undertaking where I live so I'd rather not if I don't have to, but I want to make sure my engine is solid as well so it can happen if need be.

I would bet you still have water sitting on the crown of the piston. High compression is much better than low compression in this situation. Did you try blowing out the cylinder with compressed air?

water doesn't compress,it was probably left over in the cylinder.I'd oil down that cylinder and all the others as split over lap will allow water to jump cylinders.

does it still run?hows the oil look

Not yet.I figure the water just sealed things up a little tighter and the tester nipple is still wet when I pulled it off.

Water ruined you compression gauge . Try it back on the other cylinders i bet they all measure low now also.

I haven't tried to run it as I'm sans exhaust. The dipstick is clean. There's slight condensation on the bottom side of the valve cover but the oil trapped there on the head looks clean. The last run was out in 55* water.

I went back and checked #1 and #3 and they read near identical to the first reading. Fwiw - this is all on a cold engine, throttle closed.

Change the engine oil NOW and WD40 all of the cylinders and turn it over with the starter. Then squirt oil in all of the cylinder holes and turn it over again. Pressure test the header and have it repaired if possible. Listen for an odd knock when turning it over with the plugs out. It is possible to bend a rod if hydrolocked.. BEEN THERE DONE THAT.

I don't hear any knock, but it does have a rhythmic slow spot and the volt meter drops. It doesn't just spin consistently around even with the plugs removed.

I'd also be concerned, why the even side bank, has a consistant 20+psi more cranking pressure, than the odd bank (minus the water filled cylinder). I've seen that before, when shoddy work was performed. Like, heads unevenly milled, head work not matching, inconsistant chamber volume, possible different head gaskets, etc etc. You may have half an engine at 9:1, and the other half at 8.5:1