1997 Mercruiser 5.7 EFI blown head gasket

[khe]

On the way in from boating this afternoon, my boat began to lose power and I could tell that it had a bad misfire. After getting it home, I did a compression test and below are the results:
1: 170 psi
2: 165 psi
3: 0 psi
4: 160 psi
5: 0 psi
6: 160 psi
7: 150 psi
8: 145 psi, 150 psi wet after squirting oil down the cylinder.

I believe I have a blown head gasket between cylinders 3 and 5. I think I should replace both head gaskets even though it was only the one side. The engine is raw water cooled, operated in freshwater. What would have caused the gasket to blow? Age, corrosion from the fresh water?

Are the gaskets just automotive gaskets or are the marine gaskets different in some way?

 

[Scott06]

Need to use marine gaskets as automotive gaskets will corrode in the raw water.
most of the time this is due to overheat

 

[khe]

Need to use marine gaskets as automotive gaskets will corrode in the raw water.
most of the time this is due to overheat

That's what I am seeing when looking at photos of the parts. The intake gaskets are also different between the marine and the automotive version - the auto version has one of the ports restricted with a small hole vs. open in the marine application.

The only time the engine overheated was about seven years ago - weeds plugged the water intake. When the alarm went off, I shut it down and a big ball of weeds came floating to the surface. I replaced the water pump impeller in the lower unit as a precaution.

This afternoon, there was no overheating of the engine - it was running just shy of 170° the whole afternoon. Maybe the overheating seven years ago weakened the gaskets and it took all this time to rot through?

I think it is prudent to do both sides even though only one side was bad.

 

[airshot]

Yes...do both sides !! If they were original gaskets, they were 26 yrs old, you really cant complain....

 

[khe]

I'm seeing differences in the OEM head gaskets under the same 27-75611 part nos. One is an all steel gasket, another version is steel rims near the cylinder bores with a graphite type gasket and another version that looks like an automotive gasket.

I am wondering what caused the gasket to go bad - just the years of being in contact with the raw water even though it was fresh water and not salt water?

 

[dubs283]

Best to send the heads to a machine shop for a valve job while you've got them off.

You can look up the correct oem head and intake gaskets using the engine serial number

 

[Bondo]

That's what I am seeing when looking at photos of the parts. The intake gaskets are also different between the marine and the automotive version - the auto version has one of the ports restricted with a small hole vs. open in the marine application.

Ayuh,..... The gaskets yer lookin' at are pre-vortec gaskets,....
Bein' a '97, yer heads should be vortecs, 'n there's no heat cross-over passage,....

For the head gaskets, I suggest you buy a set of fel-pro marine head gaskets,..... they're 'bout the Best,....

I agree with dubs too, send the heads to a machine shop for a thorough inspection, 'n rebuild,.....
Vortecs are light weight castings, prone to cracking,.... which could be the cause of the problem,....

 

[khe]

Best to send the heads to a machine shop for a valve job while you've got them off.

You can look up the correct oem head and intake gaskets using the engine serial number

The engine has about 1750 hours on it - not sure what the recommended valve service is but the way shops are booked where I live, I probably wouldn't get the heads back before the end of the boating season. I need to be ready for a trip on July 1st so just changing the head gaskets is going to be tough to get it done in time. We haven't had rail in a month and now that I need to work on the boat which is too big to fit in my garage, it's going to rain for almost a week straight...

I looked up the OEM part numbers in Mercury Marine's parts catalog - when I search those part nos. to find a prospective source, that's where I see all the differences within the same part no.

 

[Scott Danforth]

Get felpro marine head gaskets

Find a different machine shop. Should be a 3-day turn around.

New heads from GM are only $850 a set

 

[khe]

Ayuh,..... The gaskets yer lookin' at are pre-vortec gaskets,....
Bein' a '97, yer heads should be vortecs, 'n there's no heat cross-over passage,....

For the head gaskets, I suggest you buy a set of fel-pro marine head gaskets,..... they're 'bout the Best,....

I agree with dubs too, send the heads to a machine shop for a thorough inspection, 'n rebuild,.....
Vortecs are light weight castings, prone to cracking,.... which could be the cause of the problem,....

I don't believe the heads on my engine are the Vortec heads - the HP at the prop is 220 and I think the LX version of the 5.7 had 250 HP at the prop. would have the Vortec heads but I won't be sure until I get the heads removed. Those were the two of the available engine choices for '97 that had the EFI from the Sea Ray Sundancer brochure.

 

[Scott Danforth]

Non vortec motors went away September of 1995 when the vortec motors came out

Any non-vortec motor after September 1995 is a left-over old stock motor stored in a warehouse and used later

Do you have 12 intake bolts (non-vortec) or 8 intake bolts (vortec)

 

[Bondo]

I don't believe the heads on my engine are the Vortec heads - the HP at the prop is 220 and I think the LX version of the 5.7 had 250 HP at the prop. would have the Vortec heads but I won't be sure until I get the heads removed. Those were the two of the available engine choices for '97 that had the EFI from the Sea Ray Sundancer brochure.

Ayuh,..... Count the intake manifold bolts,......
12 is pre-vortec,..... 8 is vortec heads,....

 

[khe]

Ayuh,..... Count the intake manifold bolts,......
12 is pre-vortec,..... 8 is vortec heads,....

Thanks for the information! Hopefully the rain stops so I can start tearing it down tomorrow evening. If it is the pre-vortec, are those heads prone to cracking like the vortec heads are?

 

[Bondo]

Thanks for the information! Hopefully the rain stops so I can start tearing it down tomorrow evening. If it is the pre-vortec, are those heads prone to cracking like the vortec heads are?

Ayuh,..... I wouldn't blame the head gasket, til the heads are inspected,....

Light weight castings have been the norm, for decades now,....

 

[dubs283]

If it is the pre-vortec, are those heads prone to cracking like the vortec heads are?

It doesn't matter.

The heads will be off, doesn't happen very often so use the opportunity to have a machine shop go through them

Decent machine shop with normal volume should be about two week turnaround

If they find they're not repairable they can most likely source other heads for you

 

[Lou C]

That looks like severe overheat or lean fuel
Mix/over propped
Make sure to find & correct the cause. Top end overhaul on the SBC is a pretty easy job. Make sure to clean the cyl head bolt holes in the block with a thread chaser. I used Fel Pro marine head & intake gaskets when I did my V6 a few years ago. Heads need to be checked for cracks.

 

[Scott06]

I'm seeing differences in the OEM head gaskets under the same 27-75611 part nos. One is an all steel gasket, another version is steel rims near the cylinder bores with a graphite type gasket and another version that looks like an automotive gasket.

I am wondering what caused the gasket to go bad - just the years of being in contact with the raw water even though it was fresh water and not salt water?

If it got hot that would be the first thing i would think may have done it. might be worth doing a leakdown test or put compressed air in each cylinder to ensure it is the head gasket between the two vs valve damage . Put air in one, should come out other spark plug hole if it is the gasket

if it is the gasket and heads look ok and u arent going to have a valve job done would at least put a machinst straight edge on head and block to check for warpage. If warped replacing head gasket will fail ….

would also check plugs for lean as suggested by lou

 

[khe]

If it got hot that would be the first thing i would think may have done it. might be worth doing a leakdown test or put compressed air in each cylinder to ensure it is the head gasket between the two vs valve damage . Put air in one, should come out other spark plug hole if it is the gasket

if it is the gasket and heads look ok and u arent going to have a valve job done would at least put a machinst straight edge on head and block to check for warpage. If warped replacing head gasket will fail ….

would also check plugs for lean as suggested by lou

Seven years ago, it got to 190° and the alarm went off so I shut it off to clear the water intake. From that point until a couple of days ago, it's been fine. At this point, the only thing I know is that I have zero compression in cylinders 3 & 5 and I assume it's a headgasket. I definitely will check the flatness of the head when it's off.

 

[khe]

That looks like severe overheat or lean fuel
Mix/over propped
Make sure to find & correct the cause. Top end overhaul on the SBC is a pretty easy job. Make sure to clean the cyl head bolt holes in the block with a thread chaser. I used Fel Pro marine head & intake gaskets when I did my V6 a few years ago. Heads need to be checked for cracks.

The temp. gage never went above 170°. When I had the plugs out, they all looked on the black shade. They weren't grey which would indicate overheating.

The prop is the same prop that's been on the boat when I bought it eight years ago and over 1000 hours of use.

I need to get it apart and I'll post photos. I'm wondering if this is just a 26 year old engine that over the years of raw water cooling has decided to puke a headgasket or is there some other underlying cause that damaged the headgasket?

 

[Scott Danforth]

I dont think its the head gaskets. A leakdown test will tell

we still do not know if this is a vortec motor or a non-vortec motor.