Mercruiser 165 straight 6 head gasket

I purchased a 1977 Glastron V174 that has a mercruiser 165 straight 6. The engine starts right up. Hour meter looks original and reads 287. I can find no freeze plugs and have no idea how to check for block damage. It really is amazing how well it runs consideirng...

Like an idiot I didn't pull the oil dipstick when I bought it and it was running fairling well on the muffs. Today I pull the dipstick and it is white...milky white. So I go ahead and run a compression test:

1 110
2 140
3 110
4 0 Hissing noise
5 0 Hissing noise
6 30 faint hissing noise

It is obvious I have a blown head gasket, but how do I check for block damage once I get the head off? I am guessing with a head this long the chance of it not needing to be decked will be rare? How prone were these warpage? This engine really did fool me, except for the slight lope at idle and the rich exhaust you would never have guessed it is this damaged...it ran pretty good.

Thanks for your help.

Re: Mercruiser 165 straight 6 head gasket

Hissing noise...coming from where on the engine?

The intake?

The exhaust?

The outside of the engine?

The big thing right now is to not let the engine sit with a bunch of water in the combustion chambers and sump. Protect it if your are going to let it sit for a while.

You might want to re torque the head bolts and see if any were loose.

Make sure you did not swallow a valve and have it punch a hole in the head.
It probably is a head gasket and or a warped head.

Follow the book when you are ready to pull the head.

Once you get it apart you can use dye penatrant to search for a crack in the block. Visually inspect the head and use a straight edge. Head cracks show well. Oh, be carefully not to damage the head gasket before you have a chance to inspect it, find it is an automotive one that has failed round the edges.

Good luck and stay safe.

Re: Mercruiser 165 straight 6 head gasket

The hissing noise was heard when running the compression test on # 4, 5 and slightly on 6. It is the dead head gasket. We will pull the head tonight and see how bad the gasket is. I have already orderd the marine gasket set so no more problems with an auto gasket if that is causing the problems. We will check the block and the deck. I am really worried about running into a cracked block.

Where can I get penetrant dye? Autozone?

Re: Mercruiser 165 straight 6 head gasket

I can find no freeze plugs and have no idea how to check for block damage.
We will check the block and the deck. I am really worried about running into a cracked block.
Where can I get penetrant dye? Autozone?

Click to expand...

Ayuh,... What do you mean No coreplugs,..??
As for the Dye,...
You don't need it... Drain the cooling system,+ Pressurize it with Air,... About 15psi...
You Hear the Leaks,... Just follow the Sound....
No Doubt, atleast the Headgasket in your case...

If it's a Cracked block,... It's probably along the inside edge of the oil pan rail...
Just opposite the outside drain plug....

Good Luck,...

Re: Mercruiser 165 straight 6 head gasket

The head gasket is seriously blown between 4 and 5 and somewhat between 5 and 6. The bottom end looks okay and was holding clean water when we pulled the head. The only problem is a messed up drain plug on the block I might have to drill out. The head looks to be seriously warped and I am pretty sure water was coming straight out of the water jacket and down into the oil drain. For as old as it is we were really impressed with the cylinder walls. I am having the metrologist at work check the head and then I will take it to the machine shop assuming it is serviceable. Pictures tomorrow. Thank you for your help.

Re: Mercruiser 165 straight 6 head gasket

All freeze plugs look good in the head and the engine.

Here are the pictures of where I am at so far.