Mercruiser 5.7 problems

[ukstu]

Hi all,
I have read this forum for some time but never registered so first off, apologies for the first post being to ask for help.

I currently have a Mercruiser 5.7 V8 with Alpha one (1989-92). I have had this engine for coming up 5 years.

I have had an issue with moisture in the oil for a while, i put it down to condensation as the only trace was in the rockers, not so much the oil in the sump. (there was however a fair bit in the oil this time when i emptied it).
I have had both heads off over the last year or so and had them skimmed, valves re-seated and a couple of new seats etc. I am fairly confident that both heads are fine.
When i re-built at the start of this year compression on all cylinders was good.

The boat has now come out of the water for the winter and i have just serviced and winterized it. After running up on antifreeze i removed all plugs to fog and thought i would so a compression test just for peace of mind.
Here is where the surprise came.
I found that when i turned the engine over for the compression test i had antifreeze coming out of Cylinder 2, alot of it. and the compression readings were:

180 - 8 7 - 175
60 - 6 5 - 170
165 - 4 3 - 0
130 - 2 1 - 180

My thoughts are that compression is generally good in most cylinders but the following has stumped me:

Cylinder 2 - how can there be compression when it has a leak into it?
Cylinder 6 - Does this point towards the head gasket?
Cylinder 3 - How can this have nothing at all?

The boat 'seemed' to be running fine with no issues throughout the season. Are there any known 'bad' head gaskets out there? any to avoid? Seems odd that a head gasket would have failed so quickly..?

I hope that all makes sense.
Any advice anyone could offer would be gratefully received.

 

[Lou C]

Zero compression suggests a stuck valve but the engine should run rough then. You can have a water leak into a cyl from a head gasket depending on where the damage to the gasket is and still have close to normal compression. I had this with my engine a few years ago. Comp test results were close to normal but a slit in the fire ring was letting water in the cyl. Sounds like you should do a leak down test and a cooling system pressure test, but it sounds like those heads are coming off again. Make sure to use Fel Pro marine head gaskets, automotive ones will not hold up if it is a raw water cooled engine. Also, clean out the cyl head bolt holes with a thread chaser and make sure the head bolts threads are clean. I would up replacing all of mine with ARP bolts.

when you had the heads off did they check for cracks? How was the mating surface on the block? for the gasket to seal it must be absolutely clean and flat to less than .003". Same on heads.

 

[alldodge]

Cylinder 2 - how can there be compression when it has a leak into it?

Liquid in a cylinder increases compression a lot

Cylinder 6 - Does this point towards the head gasket?
Cylinder 3 - How can this have nothing at all?

Would agree, stuck valves, head gasket or a crack

Are you in salt water?

May have some ring issues

 

[ukstu]

Thanks for the quick reply.
I will read into a leak down test, not done that before. What does a leak down test show that a compression test doesn't? I don't know the difference.
Also, with regard to refitting the heads, thanks for the advice of cleaning threads, not done that before. Where do you stand with re-torquing the bolts on these engines. I have always re-done them on other engines but you cant with these because of the inlet manifold, or am i missing something?

 

[ukstu]

Yes salt water.

 

[ukstu]

Could a manifold to riser gasket failure cause fluid into the cylinder or would that then be all cylinders (timings or valves dependent),
I only ask after doing some more reading, i do have some rust marks around the top of the manifold / bottom of risers that makes me wonder if the gasket there is still good..?

 

[tpenfield]

You could run a cylinder leak test to try to narrow things down, but I believe the engine will be coming apart regardless.

 

[alldodge]

Could a manifold to riser gasket failure cause fluid into the cylinder or would that then be all cylinders (timings or valves dependent),

Being in salt water your manifolds would need to be replaced every 5 to 7 years. Yes the gasket can cause a lot of your issues, and I would just pull the motor and tear it down to see what you have

 

[Maclin]

What does a leak down test show that a compression test doesn't?

A leakdown test is a more focused diagnostic when compression is not in range, uses air pressure and listening for air leaking out of the cylinder. It is performed with a special adapter to introduce air pressure into the cylinder via the sparkplug hole. Air pressure is introduced while the cylinder is at TDC on compression stroke, both valves closed. Then listening for the air leak, coming from intake manifold or exhaust (valves), or crankcase (hole in piston or REALLY bad rings).

 

[aimlow]

Raw water cooled? Blocks, intake manifold, exhaust manifold all rust out. Cylinder head gaskets seldom leak coolant into a cylinder without also blowing coolant OUT when running. Silicone intake gaskets? That's probably the problem right there.

Need more engine info.

 

[ukstu]

Thanks for all the replies, very helpful and interesting.
I will certainly be stripping down, will conduct a leak down test also to see what comes back.

 

[ukstu]

Raw water cooled? Blocks, intake manifold, exhaust manifold all rust out. Cylinder head gaskets seldom leak coolant into a cylinder without also blowing coolant OUT when running. Silicone intake gaskets? That's probably the problem right there.

Need more engine info.

Engine S/N is OC772014, approx 700 hours.
Raw water cooled, coolant only in for winter whilst on trailer.

I can't remember what the intake gaskets were if i'm honest. What would be the recommendations for intake gasket replacements? Also, do they need to be sealed in place? I know i did that last time.
I've found the Fel-Pro head gaskets locally so will go with them this time.

 

[alldodge]

Only sealant used on gaskets is a dab in the corners of the intake where heads mate with the block, otherwise just the gasket

 

[aimlow]

Intake manifolds rotted out on the bottom of the coolant crossover at the front of the engine. intake manifolds corroded at the crossover, and the silicon gaskets started leaking. They only torqued to 10# or so, other wise they would be instantly damaged.

Usually when the heads are milled, the bottom gasket surface of the intake needs to be milled also.

I've seen GM blocks rust out in 10 years down here in Florida. Blocks and heads are "thin wall cast", with a lot less iron in them than they used decades ago.

 

[Lou C]

Fel Pro also makes a nice set of marine intake gaskets. You may have to get the mating surface cleaned up if it is corroded. I used a bit of OMC gasket sealer on that area of the intake. Although my engine was used in salt for 15 years I did not have rust through in the block, heads or intake. However the cooling ports in the heads were getting eroded and the machinist I had check them thought they might not seal 100% on the new head gaskets. I re-used the intake and installed a pair of re-man heads on my original block. Bought a spare marine intake (they are not that easy to find) for the pre-vortec 4.3 off of ebay for a good price...

 

[aimlow]

Fel Pro also makes a nice set of marine intake gaskets. You may have to get the mating surface cleaned up if it is corroded. I used a bit of OMC gasket sealer on that area of the intake. Although my engine was used in salt for 15 years I did not have rust through in the block, heads or intake. However the cooling ports in the heads were getting eroded and the machinist I had check them thought they might not seal 100% on the new head gaskets. I re-used the intake and installed a pair of re-man heads on my original block. Bought a spare marine intake (they are not that easy to find) for the pre-vortec 4.3 off of ebay for a good price...

This! Fel-Pro is top quality stuff. Do not cheap out on gaskets.

 

[Scott Danforth]

Hi all,
I have read this forum for some time but never registered so first off, apologies for the first post being to ask for help.

I currently have a Mercruiser 5.7 V8 with Alpha one (1989-92). I have had this engine for coming up 5 years.

I have had an issue with moisture in the oil for a while, i put it down to condensation as the only trace was in the rockers, not so much the oil in the sump. (there was however a fair bit in the oil this time when i emptied it).
I have had both heads off over the last year or so and had them skimmed, valves re-seated and a couple of new seats etc. I am fairly confident that both heads are fine.
When i re-built at the start of this year compression on all cylinders was good.

The boat has now come out of the water for the winter and i have just serviced and winterized it. After running up on antifreeze i removed all plugs to fog and thought i would so a compression test just for peace of mind.
Here is where the surprise came.
I found that when i turned the engine over for the compression test i had antifreeze coming out of Cylinder 2, alot of it. and the compression readings were:

180 - 8 7 - 175
60 - 6 5 - 170
165 - 4 3 - 0
130 - 2 1 - 180

My thoughts are that compression is generally good in most cylinders but the following has stumped me:

Cylinder 2 - how can there be compression when it has a leak into it?
Cylinder 6 - Does this point towards the head gasket?
Cylinder 3 - How can this have nothing at all?

The boat 'seemed' to be running fine with no issues throughout the season. Are there any known 'bad' head gaskets out there? any to avoid? Seems odd that a head gasket would have failed so quickly..?

I hope that all makes sense.
Any advice anyone could offer would be gratefully received.

when was the last time your manifolds and elbows were replaced?

moisture just doesnt appear. you have had your motor screaming at you for a while that something is wrong.

cylinder 1, 4, 5, 7 and 8 have water in them. any cylinder compression greater than 150psi is cause for alarm (that is why Mercruiser publishes the cranking compression numbers.
cylinder 2 may be ok (not bad for a used 30 year old motor)
cylinder 3 and 6 most likely have rusted valve seats, and probably rusted bores.

at a minimum you are pulling the exhaust and replacing, and then pulling the heads to have them serviced. however if you have had leaking manifolds for a while and the salt water sat in your sump, you may need a whole new long-block

 

[Lou C]

If in salt water then the issue with the exhaust system is for sure a real one. My old engine has been used in salt water approx. 16 years and its on its 4th exhaust system. It came to us from freshwater and I changed the OE manifolds (OMC Batwing one piece Manifold + Elbow type) because I had no idea of previous hrs or use. That was in '04. Then in '11 I installed the next set of batwings. By the next needed replacement the bat wings had long since gone No Longer Available. So I got the parts to convert it over to the late OMC/Volvo center riser style. All this costs money but its the only way to avoid the damage water in your cyls and eventually oil will cause.

 

[ukstu]

Thanks again all for the replies.
The manifolds and elbows are coming up to 5 years old, I would have to wait u til I next go down to the boat to check the log to see how many hours are on them but I would estimate somewhere in the region of about 100. All salt water use.

These were on my thoughts to inspect / replace if mecessary next year.
i think the long and short of it is that these will be getting replaced now anyway.

so the plan is to remove manifolds and elbows then remove both heads and see what’s going on with valves and head gaskets.

fingers crossed there is something obvious..

out of interest, before I strip it down, is there any way of pressure testing the block for leaks? I don’t see why there would be any cracks on the block whatsoever but it could be another elimination.


oh, and as for the condensation in the rockers, I had read a few times that with the V8’s this is quite often seen. Guessing that was wrong, hence why I didn’t see it as a problem before now.

Thanks to all.

 

[alldodge]

is there any way of pressure testing the block for leaks? I don’t see why there would be any cracks on the block whatsoever but it could be another elimination.

Yes, easy peeze since you have closed cooling
Remove HE cap and install radiator pressure tester cap and pump it up