Blown Head Gasket?

[Hardcore]

Is there a definitive way to tell if the head gasket is blown?

I have a 1990 Yamaha 150 2 stroke. I fired it up and took off and in about 100 yards the overheat alarm went off, i stopped and shut it down within seconds. seaweed had blocked the intake. i fired it up a few minutes later and i was getting a big white cloud of steam from the exhaust.

The motor runs perfectly and the plugs look great. Later on once it was totally cool i notice that when i first start it i get the blue smoke and as it gets warmer i get some(not like the first time) white smoke/steam and a little bit of water spitting out the exhaust. Is the water in the exhaust used to cool the exhaust? Maybe its that water turning to steam. This is a new motor to me. Thanks.

 

[Silvertip]

Re: Blown Head Gasket?

The exhust is underwater (exits through the center of the prop). The fine mist you see is the exhaust bypass at idle and it is supposed to dribble a little. How much smoke/steam/vapor you see depends on the air temperature and temperature of the water and temperature of the engine. But to answer your question about how to tell if a head gasket is blown -- yes you can tell. You do a compression test. While low compression can point to other issues (such as a scored cylinder) you still need to pull the head for inspection. A close look at the gasket and checking the head for warping due to the overheat is essential.

 

[robert graham]

Re: Blown Head Gasket?

I've had seaweed set my alarm off before, but no long term effects or damage to the motor. I doubt you have a problem, don't let paranoia get to your head! Good Luck!

 

[iwombat]

Re: Blown Head Gasket?

You can also check the condition of your plugs. If one looks like it's been steam-cleaned then you've got an issue. Compression test is the best way to check though.