Mercruiser Woes-What Next?

oldfielder · #1 11-25-2010, 01:35 PM

Since we like to share our triumphs as well as tragedies here on CSC-here's a crappy story:

Well, my years of trouble free performance and never getting towed in have come to an end this fall.
My 5.7 stalled at idle the other day while I was crushing the bass on jigs. Hmmm-that's funny this motor never stalls. Start it up again-same thing a few minutes later. Try again to start-no sir, just a spinning starter.
You guessed it(maybe)-I ingested saltwater through a failed exhaust manifold. Turned it over by hand to get the water out of the cylinders on that side. Fogged those cylinders. The next day I discover that the water leaked down into the oil, so I pulled that all out and pickled the motor with diesel because I'm going to mom's house for the holiday.

So here's where I'm at:
The motor is a 99 and doesn't owe me anything, but saltwater ingestion just can't be good.
Do I
a.) Try to save it and hope the internals are good and ride around nervous for the next few years.
b) Go for a rebuild
c.)Drop in a new motor and be done with it.

Don't tell me to bracket it and put on an outboard 'cause I aint go the coin for that ; )

Anyway, any of you motorheads out there feel free to give me advice or moral support.
And, to all, Happy Thanksgiving!
Doug

Tiny · #2 11-25-2010, 03:20 PM

Just went through the same thing...we chose to rebuild it ourselves (I have a few experts in the family :-)) on a 4cyl inline it cost us $600 in parts, $200 in machine work...labor...free...sort of :-). I'm glad we did it this way, it always costs more than you expect...because we lapped the head, replaced the valves and seats, bought new manifold and exhaust riser...bla, bla, bla...

kerneltugboat · #3 11-25-2010, 04:43 PM

From everyone I talked to, manifolds primarily used in salt water last 6 years tops, anything beyond that you are on borrowed time. My dad has the same package, 2000 mercruiser with a bravo one. He had the usual fuel pump issues early on, but has over 3000 hours with no major issues and it runs great. His manifolds went at 6 years and he flushes with fresh water after every trip. I would put new manifolds and run it until it starts giving you major problems. When the time comes, and you decide you don't trust it, then go new...outdrive and engine. I like mercruiser and Volvo. I would not go near the composite drive butt the new sea core othat looks like my dph drive is really cool.

Bushwacker · #4 11-25-2010, 04:51 PM

If it's a raw water cooled engine, I'd check the cross-over passage in the front of the intake manifold (where the thermostat is) too. Your engine is old enough that the exhaust manifolds may have already been replaced, but salt water in that intake manifold passage could still get you. I've seen it happen on older engines!

Islandtrader · #5 11-26-2010, 10:03 AM

I tend to agree with the other posts. From experience and from all the old salts here in FL. Manifolds will last six years. Cheap insurance to change after 6 years. 90% of engine failure comes from the manifolds.

If it were mine and $ were a concern here is what I would do. Replace the manifolds and run it to see what gives. If if checks out your good to go. If not then go buy a short or long block take all the stuff off your old block and put it back in the water. In 5 years change the manifolds and keep on going.

Keep us posted on what happens.

oldfielder · #6 11-26-2010, 01:57 PM

The block is fwc-what they call a 1/2 closed system. I guess what I'm wondering now is which route to go and whether I need to tear down the motor-or at least the side that failed. I was definitely on borrowed time with the exhaust. It's just funny that it failed right after some other repairs that I had done.
I really am handy, but I think tearing open the block is way beyond my skill set.
So I 'm sitting here flushing this motor out, wondering about my next move. If I want to run this motor again, it is going to require new manifold and riser for at least one side just to discover whether my 11 year old motor is worth salvaging.
Ahhh????

Bushwacker · #7 11-26-2010, 04:07 PM

It sounds like you need new exhaust manifolds anyway, even if you buy a new long block, so I wouldn't sweat that! A compression test will tell you if you have any sticking valves or rings without even running it, so I'd do that first, before even buying new manifolds. If a cylinder is down in compression, squirt some oil in that cylinder and test again. If compression comes up it's a stuck ring or scored cylinder, indicating major overhaul required (or new short block!). If compression doesn't improve with oil in cylinder, it's a sticking or leaky valve or possibly a blown head gasket, especially if 2 adjacent cylinders are low. Requires pulling heads and having a valve job done.

If you got water in the oil, best thing to do is change the oil & filter and get it running asap and get it up to temperature for awhile to evaporate any remaining moisture. I would be a little concerned about rust on the cam if the engine got a lot of water in it, as the Chevy's use pretty small diameter lifters so there is a lot of stress on the cam lobe/lifter surfaces. If there is much distress there, the cam lobe will wear off pretty quick. If you can run the engine for a bit with fresh oil in it, get an oil analysis kit, which includes a syringe and tubing to pull an ounce or two of oil from dipstick tube, and have it checked for high levels of wear metals. This is a routine check on all aircraft engines. If wear levels are low, you're good to go. If levels are high, then you'll have to make a decision on how much work/time you want to invest on a rebuild or spend more $/less time on a new or rebuilt short or long block.

If you have a factory service manual, and decent mechanical skills, teardown and rebuild of a 1950's technology OHV auto engine really isn't that difficult, especially if it only involves pulling the heads or changing a cam & lifters. Could do either of those jobs with engine in boat. Toughest part of the job is probably pulling the rusted exhaust manifold bolts/studs! A read thru the service manual will give you a good feel for what's involved. Hope this input helps. Denny

lost2a6 · #8 11-27-2010, 09:51 AM

Don't sweat it, change the oil, replace the manifolds and get it running ASAP. The important thing is you need to run the engine very soon and get rid of the moisture. At the bare minimum (as of right now) I would change the oil, remove the water supply hoses going to the manifolds, hook up the muffs, and start the engine letting the coolant water run into the bilge until the manifolds start to get hot, then shut it down before you melt the big exhaust hoses. Do this for now until you get your new manifolds installed. Then once your new manifolds are on, take the boat out and run it easy for the first hour or so. Take your oil cap off and look for moisture, milky oil, etc. If none is present, then your good to go.

abl1111 · #9 11-27-2010, 05:33 PM

SH*T !

I have the same motor, 2001, 350 300hp Mag MPI ( fresh water cooled. With original elbows, manifolds and risers... 450 hours. Salt water use... I never flush after each use.

I have a few questions - obviously my manifolds are older than (6) years.

(3) years ago I had my mechanic replace the gaskets at the risers joint - he said the manifolds from that point looked great...

My motor runs cool as she ever has - Should I replace the manifolds, elbows and risers if all seems OK ?

BTW - If I were in your predicament, not being as mech inclined as many of the above - I would do a few oil changes w/ marvel mystery oil in there. Run and dump oil. Get moisture out. Compression test to make sure is OK, 'pickle it' fuel side and oil. Then get new manifolds and install - start her up ASAP, run for a awhile, then winterize again...

Good luck...

Another LI'er...

oldfielder · #10 11-27-2010, 05:41 PM

I'm all over it and praying while I'm at it.
Dude-my boat never ever came close to overheating. they were clogged-they failed-manifolds.
All of the guys on boatered preach changing them as routine maintenance-do yourself a favor and do it now-this is a freakin' nightmare-especially while the bass are chewing hard on herring out east and in mtk-my favorite time of year. I had no warnings.
You can get a pretty good deal on the whole kit locally. Shoot me a pm if you need it.
Don't wait-it totally sucks. i'm just glad it happened in a pretty benign place and not out in some big rip.
BTW-I can help you do the swap-it's not hard at all and worth saving the coin and doing yourself.