Merc 260 - cracked head or broken gasket?

[soaked]

1979 Mercruiser 260... in a 23' Carver.

When changing spark plugs, coolant escaped from behind the #5 plug. I changed the oil and found coolant in there, too.

I have pressure tested the cooling system and it's leaking, but I can't tell from where... Any tips on how to determine of the head is cracked or if I am "lucky" and just have a bad gasket...

PS, the motor has been run quite a bit this way - maybe 30 hours or so. I have owned the boat for 3 years, ran numerous fishin trips the first year, then only a few last year (spent 4 months trying to remove a starter without pulling motor and outdrive - fun!). The motor has run smooth the whole time, without any stutter or mis that I could detect. It steams a little when on the muffs, but I assumed that was normal...

 

[Mkos1980]

Re: Merc 260 - cracked head or broken gasket?

Eather way the head needs to come off. When the head is removed you can take it a machine shop to get pressure tested. If it passes, check for deck and head straightness. If that passes go with a new gasket. You can usually tell a bad head gasket once the head is off.

How are your exhaust manifolds, any chance one of them is cracked right by Number 5 dripping back into the head when the engine is off?

 

[soaked]

Re: Merc 260 - cracked head or broken gasket?

Manifolds are new (last year) so not likely the problem. Good point on head coming off either way. Unfortunately, where I live, I am the closest thing there is a to a professional mechanic or machine shop... I either do it myself or it doesn't get done.

Would pressure testing the cylinder with the head on, tell me anything different?

 

[wperson]

Re: Merc 260 - cracked head or broken gasket?

I would say that taking a comp test on nr 5 won't help you that much.
Did you find the water after winter storage?
It's not that easy to blow a head gasket and even if you do you wouldn't get
any water in the cylinder.
I would start with the exhaust manifold and Elbow gasket to determin if it has
leaked in to the nr 5 through exhaust valve.

 

[soaked]

Re: Merc 260 - cracked head or broken gasket?

Great questions that deserve a bit more info... thanks for your time.

The motor has a closed cooling system.

Yes, the water I found in the oil was "after winter storage". However, I did run the boat for about an hour last month while trouble shooting some eletrical issues, and what ultimately turned out to be a bad new starter.

I removed the exhaust manifold from that side of the motor to access the starter, and in doing that repair work, I believe it is likely that a disconnected coolant hose from the riser, dropped down and splashed water into the exhaust port on the head. To make sure, I drained and looked at my engine oil and then pressure tested the cooling system. The oil contains coolant, and the cooling system will not hold pressure.

Given your comment about water in the cylinder being an unlikely outcome of a broken head gasket, I am inclined to think that me being a sloppy mechanic may have caused that observation. But it still seems that water in the oil and a leaky cooling sytem are real problems to resolve, and without a good mechanic to lean on, I am seeking the wisdome of others here...

Thanks big-time for your time and responses to my toubles...

 

[JustJason]

Re: Merc 260 - cracked head or broken gasket?

Pull the intake manifold off and see if there's any evidence of tracing. It would/could cause coolant in the oil and coolant in 1 cylinder only.

 

[soaked]

Re: Merc 260 - cracked head or broken gasket?

What is tracing? What will it look like? I might sound like I know a little, and suppose I do - but really other than a fair sense of internal combustion engines and a lot of under-the-hood time on a chevy in highschool... I am a total Novice.

Oh, and the second line in your signature block is TOTALLY my story right now... In a matter of days, I went from one crusty wire that needed to be replaced, to a potentially cracked cylinder head... and have done tons of other unrelated fixes in between! So much for catching Kings this year... at least the sunny weather makes for comfortable out-door mecahnic work!!!

 

[JustJason]

Re: Merc 260 - cracked head or broken gasket?

pull the manifold off. the best you can pull off the gaskets in 1 peice. Look on both sides of the gasket on the part that seals the water jackets and look to see if coolant leaked, up, down, left, or right. Should be fairly apparent.

 

[wperson]

Re: Merc 260 - cracked head or broken gasket?

What is tracing? What will it look like? I might sound like I know a little, and suppose I do - but really other than a fair sense of internal combustion engines and a lot of under-the-hood time on a chevy in highschool... I am a total Novice.

Oh, and the second line in your signature block is TOTALLY my story right now... In a matter of days, I went from one crusty wire that needed to be replaced, to a potentially cracked cylinder head... and have done tons of other unrelated fixes in between! So much for catching Kings this year... at least the sunny weather makes for comfortable out-door mecahnic work!!!

Is it a half or full cooling system you have? If you do, you can have some problem with the blockoff gasket.
If you can disconnect the hoses from exhaust manifold and connect them together and pressure test again, thats one way to test a leak.
I had a leak there and while running no problem no problem but when turning of the engine the little pressure in the water system pushed water into to the exhaust manifold. I migth have gone that much water in to number 5 during winter storage and pass by the pistonrings to the oilpan.
If the heat exchanger is high mounted lets say higher then the gasket, the water theoreticaly could self drain thru the gasket to the manifold.

 

[soaked]

Re: Merc 260 - cracked head or broken gasket?

I think half. It cools the manifolds, but not the risers... they are used for sea-water discharge, I think, which probably provides some cooling... but not part of the closed system.

I suppose the block-off gasket could be part of the problem, thanks for the tip... now I just gotta figure how to test it???

 

[soaked]

Re: Merc 260 - cracked head or broken gasket?

New info, in hopes that it will provide more insight.

This evening, I cranked the motor for a few seconds, without the plugs in on the side I am working. Both the 3 and 5 plug holes got wet. I dried them a repeated the exercise and again, they got wet - a little water even splashed out onto the sea pump below the exhaust manifold...

I may be getting sidetracked by the water since it could have resulted from an inadvertant splash into the head when the manifolds were off, while I was working on the starter... the real problem is the fluid in the oil and the cooling system not holding pressure.... which as far as I know, could be from a few different sources; such as cracked head, bad head gasket, bad intake manifold gasket, or bad block-off gasket...

Not sure where to start or stop for that matter.

 

[P 0 P E Y E]

Re: Merc 260 - cracked head or broken gasket?

Before taking the engine apart, I would suggest performing a coolant pressure test with the spark plugs out.

While the pressure tester is putting positive pressure into the cooling system, listen near the suspect cylinders, you may want to turn the engine a little to cause the pistons and valves to change position as to expose more clues

listen.

Find out where the leak is not, first