Perplexing compression numbers

[CampionGuy]

Good evening iboaters,

88 Merc 3.7l. I have an overheat problem and after a few visits to a "reputable" local shop I still have the problem, although not when running on the muffs. Today running at around 3400rpm it quickly overheated again, 210F on the gauge, and upon my own inspection while running I found steam from the valve cover when I removed the oil filler cap and steam from the EGR hose. When I got home (thanx to the kicker) I did a compression check and found some interesting numbers. #4-169, #3-172, #2-172, #1 was 169 the first time and the second time it was 210. There is a water from cyl#1 when cranking, kinda like a heavy mist with a few droplets. Oil seems clear, not noticeably discolored as I have seen with motorcycles. The coolant level drops a little when sitting. I understand it may be a head gasket, crack or manifold problem (I haven't pulled any said items yet) but why the huge difference in the compression numbers in cyl #1? Forty pounds is obviously a lot.
As a sidenote injuries forced me to use a shop for a couple years. They charged me $1100 the first time including bellows, t-stat, pickling, impellers, tune-up, oil change, etc. then wanted to charge me $1200 the second time but I refused until a test run was completed. They haven't been paid. I haven't been able to successfully use this boat for two years.
Thanx,
Doug

 

[Barnacle_Bill]

Re: Perplexing compression numbers

#1 could very well be where the crack or blown head gasket is. Hopefully its just the head gasket.

 

[CampionGuy]

Re: Perplexing compression numbers

That's what I figure as well but...what would make such a huge variance in the #1 cyl numbers from the first check to the second? I checked all four and then went back and checked them again. Then checked #1 again because I couldn't understand.

Doug

 

[Don S]

Re: Perplexing compression numbers

Do a leakdown test on #1 cylinder. Leave the heat exchanger cap off while doing the test and see if there are bubbles in the coolant. If there is, either a cracked head, block or blown head gasket is the problem.

 

[wire2]

Re: Perplexing compression numbers

Water in cyl 1 will decrease the combustion chamber volume and measured compression will soar.

 

[CampionGuy]

Re: Perplexing compression numbers

From info I have gathered, the block on the 3.7 is aluminum with steel sleeves. If the block is the problem can it be welded and re-sleeved or is a repower in order? The 3.7 pushes my 21' Campion cuddy at 37mph WOT cruises at about 27-29mph at 3700, it is strong enough for me to deep water slalom start (6'2" 240#'s and 43yrs so it's gotta plane quick) and yet it is ok on fuel. Would a 4.3 do the same job and is it a straight swap or modifications required like mounts, leg, fuel pump, etc? Any other suggestions? This of course assumes a worst case scenario but is useful guidance for repower if/when needed.
Thanx,
Doug

 

[CampionGuy]

Re: Perplexing compression numbers

Hello........again,

The exhaust manifold that is on there is aluminum so if it is cracked I assume it can be welded? Or am I just whacko? I guess I am going to get offline and start pulling stuff off now. Any help is appreciated.

Thanx,
Doug

 

[plassiter1]

Re: Perplexing compression numbers

what is the normal compression for this engine?

170 sounds ok to me.

 

[Don S]

Re: Perplexing compression numbers

The exhaust manifold that is on there is aluminum so if it is cracked I assume it can be welded?

Not if the crack is inside the exhaust ports and impossible to get to.

what is the normal compression for this engine?

170 sounds ok to me.

The 170 part is ok, its when it goes to 210 on the second test that is the problem.

 

[CampionGuy]

What the heck is this?!

What the heck is this?!

OK so...I found this inside the water passage of the exhaust manifold. I'm 94% sure it's aluminum. About as thick as a business card. As you can see it tapers toward the ends and they look like they are clean cut, as if that is the whole piece or perhaps has a mate the same (somewhere). Well oxidized on one side, not so much on the pictured side and came out of the stern end of the manifold. I managed to squeeze it out of there after noticing it when inspecting the passages. The clean area I rubbed with steel wool.

What the hell is it?????
I think I need to know where this came from as ummm...could be a problem???

I haven't got the head off yet. My Dad fell off a ladder.

Thanx,
Doug

 

[CampionGuy]

Re: Perplexing compression numbers

By the way, I filled the coolant resevoir last night and this morning the level was down. #1 piston was toward BDC and the cylinder was full of water up to the plug hole. The other cylinders were dry. Looking at the valves from the exhaust side the #1 valve stem is wet right up to the head and the rest are dry. I can't see any cracks in the head or block from the outside or inside the exhaust ports.

I hope I am making sense.

Doug

 

[RCSConstruction]

Re: Perplexing compression numbers

If that leak were from a headgasket you would surely be able to tell by watching and smelling the radiator fluid,,, Or a cheap 25.00 block tester from napa that tests from the radiator looking for gases.
That cyl. filling up like that would leave me to believe you have a crack in iron somewhere.

(that piece looks like some casting material or maybe the exhaust flanges were decked/cut or even old exhaust gasket material.??)

 

[CampionGuy]

Re: Perplexing compression numbers

Thanx RCS

What smell should I be looking for in the coolant? Exhaust gases? And does this tester have a name? Perhaps a coolant exhaust gas detector? OK I am a smartass at times but I am trying to remain positive. The pictured piece is possibly stainless, looking closer at it this morning (in the daylight) it bends more like stainless would, not as mallable as aluminum. Aren't the gaskets fibrous gaskets on the manifold? At least, the one I removed is. I don't think it could it be a piece of head gasket as it couldn't see it getting through the valve but stranger things happen.
I guess this maybe premature guesswork as I am waiting for the dew to burn off so I can get at the head.

Thanx,
Doug

 

[CampionGuy]

Re: Perplexing compression numbers

Ummm...the exhaust port doesn't go into the cooling system. Never mind that comment.

Doug

 

[RCSConstruction]

Re: Perplexing compression numbers

Watch the heat exchanger/radiator to see if it rises and/or has bubbles coming up to the top. With the cap off the coolant shouldn't rise. You will also smell gas.
The tester is called a block tester.
Most gaskets are paper but some have metal in them, especially exhaust gaskets. It is usually a stainless steel fire ring much like a head gasket.

 

[CampionGuy]

A picture is worth.......

A picture is worth.......

Well...Does anyone think this MIGHT be the problem???
My guess is there shouldn't be daylight between the cylinder ring on the head gasket and the outside of it. And the 2" long metal "bubble" in the second pic shouldn't be there.

Can I use any steel straightedge to check the head for warpage or do I need to spend the $90.00 for a 24" chunk of steel? I am in the granite business and have granite slab which is as near to flat as any surface can be. If I put the head on a piece and try to rock it would it be sufficient? There aren't many machine shops around my area so access is limited. Any suggestions? The head, cylinders and block show no sign of cracks which is a relief. Any suggestions as to what else to check now that it's disassembled? Still doesn't explain the metal piece I found in the coolant resevoir, old thermostat or rad cap piece?

Thanx,
Doug

 

[CampionGuy]

Re: Perplexing compression numbers

Any ideas how much I should be paying for machining of the head in case of warpage?

Thanx,
Doug

 

[Don S]

Re: Perplexing compression numbers

Any ideas how much I should be paying for machining of the head in case of warpage?

Thanx,
Doug

Get some estimates/quotes from the different places in your area. They aren't going to change the prices because someone from this forum mentioned they can get it for a particular price.

 

[CampionGuy]

Just a side note.....

Just a side note.....

Thanx Don. I realize that but I was just looking for a guideline. In a small community it is easy to get burned on specialty work.

On a lighter note I would just like to thank all who contributed to this post and iboats for hosting this forum. It's wealth of knowledge and combined experience of contributers is an boon to the backyard mechanics of the boating world. Kudos to the experts, you know who you are, for taking the time to help. I will contribute to the forums as much as I can to try and repay my debt of gratitude.
:redface:

Humbly yours,
Doug

 

[Reel Poor]

Re: Perplexing compression numbers

My advice would be to have the head surfaced and the valves checked. With the amount of rust on the sealing ring on the head gasket I would question the ability of the valves to properly seat. They may also have rust and/or pitting in the seats not allowing them to close/fully seat. If this is so it wouldn't take much to burn a valve and you would be pulling the head again. This is a good time to read Don S' signature line.