Blown headgaskets ? or not

boatman747 · 12-10-2005, 12:16 PM

I had some external engine work done and apparently an intermiten short has appeared . On the seatrial we were running about 75 mph and the engine totally shut down .It fired right up but now it steams its ass off.Could a sudden rush of water due to the shut down blow both head gaskets that quick . No water or foam appears on the dip stick . Runs great but way to much steam .Could it be something other than a head gasket ?Port engine never shut down and runs great .I guess an intake gasket could do the same but I think chances of blowing are doubtful' We know we have a short because sometimes the coil sends spark and sometimes it doesnt . I replaced the coil and the same situation occurs . For the last 4 days it has fired right up . One day i moved it from the rack to the water no fire but I had fire in the rack .Never had a problem until the motors came out of the boat this time .

GOODT · 12-10-2005, 12:58 PM

best way to check for head gasket problem would be to do a leak down test on that motor. as for the short you just need to check the purple wire going to the coil and check for signal from the dist. This can be do with a test light at the coil also (will flash as engine is cranked, hook one end to batt + and put other end on - side of coil if you have signal will flash)

canajun · 12-11-2005, 08:23 AM

Do a compression check on the motor. You can get a compression tester at Autozone or any other car parts place for $30 or so.

To do the test, remove the coil wire (so the motor doesn't start), then, one at a time, remove the plugs, insert the tester hose, and crank it until the compression goes up as far as it is going to (3 or 4 strokes). If you have uniform (within 10 or 20%) compression, it is not a head gasket. If you have 2 adjacent cylinders with low pressure, you almost for sure have a blown gasket. It is possible to have a blown gasket that affects only one cylinder, though.

If you have good compression, I'd bet that it is the gasket between your exhaust manifold and the riser. This happened to me last summer. The motor would hydrolock when I tried starting, but would run decent when I pulled it out of the water, but like you said, with excessive steam. I had water in the back two cylinders on the port side, and also the #3 cylinder on the other side because of the cross over in the intake manifold. It was worst when I let it sit in the water, because the cooling system would stay pressurized, and the water would just leak until the pressure dropped.

The root cause was because I put on a new manifold to replace a cracked one, and used new gaskets, but I re-used the steel block-off plate. (My friend, a Merc Certified mechanic approved, for the record) Bad move. New gaskets and a new $9 plate later, and the problem was fixed!

Good Luck!

formula31 · 12-11-2005, 09:27 AM

Not to ruin your day but the last time I had an unscheduled wot shutdown on a wet exhaust engine it cracked a head between an intake and exhaust valve. Steamed like crazy. If you shut one down at high rpms with a wet exhaust it can revert water back into the cylinders.

canajun · 12-11-2005, 05:53 PM

He speaks the truth.... scheduled or otherwise, hard stops are worse than hard starts because of the risk of hydrolock. Bent valves, cracked heads, busted cranks, bent rods, pistons with holes punched through them, broken cam lobes--water just doesn't belong in your cylinders.

You mentioned that you had external engine work done. If the exhaust manifolds were pulled and the risers messed with, I would not overlook the obvious. It took me 3 weekends of fooling around to figure it out on mine.

A compression check would indicate about all of the above as well. Although if it was a crack in the head, you would probably have to do a leakdown. Like I said in my last post, a problem on one side can show on both because of the crossover point.

Whatever you do, don't go out and hammer it until you get it figured out, or you will for sure be dealing with one or more of the aforementioned problems. Remeber from grade 9 physics--water does not compress. Your rods will.

boatman747 · 12-11-2005, 07:44 PM

Thanks for the info guy .s . I will check it out this week .I thought gils off shore exhaust didnt have this gasket problem ? Am I wrong?

canajun · 12-12-2005, 07:38 PM

You never know. I actually had ordered head gaskets (before the compression check) because I was so sure that was what it was, and I pulled the intake manifold, just in case--well, I put an Edelbrock manifold and bigger carb--because after I did the comp check, I was sure it had to be an intake leak. If somebody re-used something or torqued it down wrong, even the best stuff leak.

Now that I think about it, I think the thing that tipped me off was that I could see rust where the water had pooled in the exhaust ports in the manifolds. Since you're going to end up ripping things apart, I'd suggest starting there.

Good luck with it!