1995 5.7L 350 Mag Alpha - Water in Starboard Cylinders Only

[ThndrSki]

Hello, I was wondering if someone could possible help me diagnose some potentially bad news. Today I took my boat with a 1995 5.7L 350 Mag Alpha Mercruiser to the Gulf to run it around after using it the entire Memorial Day weekend, running approximately 45 gals of gas through it.

This weekend, launched the boat, tried to start it and it acted flooded. Finally got it started and it was running rough, missing, stumbling, etc. I briefly tried to idle away and gave it some throttle in neutral to about 2500 RPM thinking I might have fouled the plugs and when I went to go again, the engine died. Upon trying to restart, the engine was hydro-locked I found later on just the starboard side. Removed all 8 plugs, sprayed penetrating spray in each of the "wet" holes, and was able to get it started with the same results.... Stumbling, missing, etc.

The starboard manifold was hotter to the touch, and I could notice some steam coming from the starboard thru-hull exhaust. I also noticed the temp gauge (while running on the hose) go from 150-100 instantly at one point, and come back in about 20 seconds to 150 but could not repeat it. If you gave it full throttle in neutral, it would just sputter and stumble basically at idle.

The oil on the dipstick is clean and pure - but I had the engine started a few hours later and flushed it on the hose running rough.

I replaced all my manifolds last season with Mercruiser OEM, and I live in Tampa, so no freezing. Like I said, this boat worked PERFECTLY all weekend 1 week ago!

 

[alldodge]

Hello, I was wondering if someone could possible help me diagnose some potentially bad news. Today I took my boat with a 1995 5.7L 350 Mag Alpha Mercruiser to the Gulf to run it around after using it the entire Memorial Day weekend, running approximately 45 gals of gas through it.

This weekend, launched the boat, tried to start it and it acted flooded. Finally got it started and it was running rough, missing, stumbling, etc. I briefly tried to idle away and gave it some throttle in neutral to about 2500 RPM thinking I might have fouled the plugs and when I went to go again, the engine died. Upon trying to restart, the engine was hydro-locked I found later on just the starboard side. Removed all 8 plugs, sprayed penetrating spray in each of the "wet" holes, and was able to get it started with the same results.... Stumbling, missing, etc.

The starboard manifold was hotter to the touch, and I could notice some steam coming from the starboard thru-hull exhaust. I also noticed the temp gauge (while running on the hose) go from 150-100 instantly at one point, and come back in about 20 seconds to 150 but could not repeat it. If you gave it full throttle in neutral, it would just sputter and stumble basically at idle.

The oil on the dipstick is clean and pure - but I had the engine started a few hours later and flushed it on the hose running rough.

I replaced all my manifolds last season with Mercruiser OEM, and I live in Tampa, so no freezing. Like I said, this boat worked PERFECTLY all weekend 1 week ago!

I would start with a compression test, you may have blown a head gasket

 

[NHGuy]

I would suggest testing your risers for leaks.
Also check your exhaust manifold to riser gasket conditions. Remove the risers very neatly. Take them straight up so as to avoid disturbing their appearance. Carefully inspect the gaskets that are left on both the riser and manifold surfaces. Look for any tracks water could have taken from the cooling passages to the exhaust tracts. If it looks like water got in through the seal you dodged the bullet. Just clean the surfaces and put in new Mercruiser graphite coated silver gaskets. Forget those green aftermarket ones.
But you might be smart to just get risers anyway. You just did manifolds, the risers could be in the same shape as the old manifolds were.

 

[ThndrSki]

I would suggest testing your risers for leaks. Also check your exhaust manifold to riser gasket conditions. Remove the risers very neatly. Take them straight up so as to avoid disturbing their appearance. Carefully inspect the gaskets that are left on both the riser and manifold surfaces. Look for any tracks water could have taken from the cooling passages to the exhaust tracts. If it looks like water got in through the seal you dodged the bullet. Just clean the surfaces and put in new Mercruiser graphite coated silver gaskets. Forget those green aftermarket ones. But you might be smart to just get risers anyway. You just did manifolds, the risers could be in the same shape as the old manifolds were.

Forgot to mention I did the risers with the new manifolds. I used the Mercruiser silver gaskets and not the green ones. I'm going to borrow a compression tester and see what it says, but with it running like crap with my symptoms, it doesn't sound good. Anyone know for sure if a blown head gasket would allow leakage to all 4 cylinders? Or maybe this is a cracked head.

 

[NHGuy]

Tski...you have to please let us know what your solution turns out to be.

 

[ThndrSki]

Will do, as soon as I find out I will post a solution to this thread - I was able to run a compression check on all cylinders today with a messed up starter (grinding) and a cold motor, these were my readouts:

Starboard: (Side that had water)
2 - 150
4 - 145
6 - 150
8 - 140

Port
1 - 150
3 - 155
5 - 150
7 - 130

The engine was able to start just like it did in the water, runs really rough, but with the engine cover open I noticed it dieseled and ran backward for a second, enough to draw water in the cylinders I would imagine... I had the flame arrestor off and it shot some gas up in the air as it backfired.

So I'm thinking the running rough was the cause of the water intrusion. The only thing that happened in between when it ran great and this was it rained during transport.

The engine does not want to start when any throttle is given at all, only in neutral/idle.

 

[NHGuy]

well, those compression #s are ok. The gas geyser is from the dieseling, it should not have broken anything. Now check wires, timing, carb etc. If the carb is giving too much fuel the motor can diesel. The fact that it won't start unless the throttle is closed points to the carb as a problem too. And when it runs backward it will suck water in the exhaust. Maybe the side that got wet had a bad flapper. Are the plug wires good? Set the timing back to a conservative 8 degrees if it's advanced.

 

[bspeth]

Could the water have gotten into the carb from the rain?

 

[ThndrSki]

Could the water have gotten into the carb from the rain?

No, the carb is definitely high and dry with a great cover preventing this. Plus it let me start it and run for a while before it hydro-locked. One side was bone dry, the other had water in all cylinders on starboard side.

 

[ThndrSki]

I opened this thread a couple weeks ago and wanted to post a resolution.

I believe I have it fixed - It appears to be the coil. I tried adjusting the carb using the guidelines (and it ran great the last time I used it a week ago) to no avail. Couldn't seem to dial anything in. I had just replaced the plugs and wires, so I didn't believe that would be the cause. Checked the distributor and cap, and all looked good.

That's when I moved to the coil.

According to the Mercruiser Service Manual these are the readings I should get for a Thunderbolt IV coil:

Description Specification
Coil Part Number 392-7803A4
Primary Resistance .60-.80 Ohms
Secondary Resistance 9,400-11,700 Ohms


I pulled the coil ran a test of primary and secondary resistance readings and this is what mine read:

Primary (test between the + and - terminals on the coil): 2.0 Ohms
Secondary (test between + and coil tower to distributor): 7,750 ohms

I happened to have an old spare coil from when I first got the boat 4 years ago and put that in and VROOOM! Started right up and no popping/backfire. So I think it was doing just enough job to start, but not run at higher RPMs where higher resistance would be bad.

This coil lasted about 4 years, but it was a NAPA marine coil crossed referenced specifically. I'm ordering a new Mercruiser coil as we speak. If anyone has any suggestions for true OEM parts, please let me know.

Thanks for all those who gave suggestions. I'm not sure if the rain had anything to do with it, but it was toast. I brought the old coil inside to look at it, and it will leak oil from the coil tower if held upside down as well.

Thanks for all who posted suggestions.

 

[NHGuy]

Nice, glad you didn't have mechanical damage!

 

[ThndrSki]

Nice, glad you didn't have mechanical damage!

Me too NHGuy! The only thing that is scary with thru hull exhaust which sits in the water is, one problem where the engine runs poorly and bam. There's water in your cylinders.

Scary!