everyone is this the sighn of a blown head gasket

1989 mercruiser 5.7L help needed pleae.

well as most of you guys know i alway have some issue with this enging,

yesterday i decided to change the spark plugs and have a good look to see how each cilinder is burning.

reason from day one i seems to get a little staem from the port valve cover , and after a long run if i shut down and fish for say 30 min and when try to restart the engine spins slow but it catch every time.

the engine runs great but i can only get 30 miles per gps at 4000 rpm and it will go no more only 4000 rpm even if i drop down in prop size it just seems to stop at 4000 rpm,

i bought a new tach and both reads the same.

anyway guys i pull the sparkplugs and the two back plugs on the port side cilinder seem like they did not fire they look real clean. but the other two has the normal wear looks.

on the starboard side the back ones look kinda clean too only one looks real wear.

my compression is on all cilinder 145 to 150,

so guys is this a head gasket issue or a crack block???

the risers and manifolds is new not even a season old,

also will a bad intake gasket cause water to enter a cilinder??

last the oil is super clean no milky stuff, i just change it and it look real clean.

any info will help guys i have two more togs trip plan before i pull for the season, i just dont knoe how to do that darn leakdown test well i might pay the mechanic to do that for me.

thanks for whatever info you guys got.


1989 merc 5.7

Re: everyone is this the sighn of a blown head gasket

An intake manifold gasket would cause water in the oil, not one particular cylinder.
Water will steam clean a spark plug if water is getting into the cylinders from a blown head gasket. But a cylinder that isn't firing because of a bad plug or plug wire will also look like new.
A leakdown test with the cooling system filled with water and a hose to see air bubbles comeing out attaced to the thermostat housing will tell you if there is a bad head gasket or not. (of course it will not tell you if it's a bad gasket or a cracked head or block) Only that there is a leak from the cylinder to the cooling system.

Re: everyone is this the sighn of a blown head gasket

ok thank again.

one more thing don if i keep it at say 3800 rpm all day the heat guage stays normal but if i keep it at 4000 the guage will start heating up antill i come to a full stop and let it idle for a few min then it will come back down to normal.

i am leaning to a head gasket ,

when at idle if i pull one spark plug one at a time the engine will stumble a little wait did i check those two , i might miss those two i will try them first thing in the morning before head out to fish,


thank you much.