Head gasket or crack in Mercruiser 165?

[jimfj]

I have a 1976 Merc 165 IL6.

Did a compression test after running the motor and letting it sit for about an hour.
1. 125
2. 110
3. 140
4. 140
5. 140
6. 140

I am getting a fine mist of water out of #2 when the engine is cranked w/o plugs. No water at all in oil. Engine runs perfect after 1500-1600 rpm.
The engine has a bit of a miss below that. Starts when you hit the key and has plenty of power.

Headgasket or crack in block? Where do you start in trouble shooting?

Full tune up has been done including setting dwell and timing, both are spot on factory set. This is my first I/O and I'm learning and i have the factory manual but the troubleshooting section doesn't get deep into this.

Jim

 

[Coors]

Re: Head gasket or crack in Mercruiser 165?

duplicate thread. pressurize the block

 

[ziggy]

Re: Head gasket or crack in Mercruiser 165?

had me some similar compression numbers on my last L6. ft. two were a little lower though. i went for a air leak test as i didn't suspect a water issue. for me, the air leak test leaked between 1 and 2 plug holes. i fig. head gasket prior to teardown. after tear down. it was a cracked block in the ft. port head bolt hole, right behind the water pump.....hope you have better luck than i did.......block pressure test seems like a good idea too....

 

[jimfj]

Re: Head gasket or crack in Mercruiser 165?

Yes Coors it is a duplicate thread because I am trying to get answer to my question.

I don't understand what "pressurize the block" means or the procedure of going about it.

Will that tell if the head gasket is bad or just tell me if the block is cracked

jim

 

[Coors]

Re: Head gasket or crack in Mercruiser 165?

Don has a thread in here about how to do it, use search. If you don't have the gauges, harbor freight does, with instructions. You need to do it, and tell us the results.

 

[Reel Poor]

Re: Head gasket or crack in Mercruiser 165?

I would put a little bit of oil in the #2 cylinder and check the compression again and see if the numbers change. But....If your getting water from the cylinder and no water in the oil you may as well pull the head. A cracked block is going to put "some" water in the oil. You could do a cylinder leak test if you want but either way the head will end up comming off.

How to do a cylinder leak down test