exhast manifold rust, winterizing

[nick_vw]

About a month ago I took it out of the bay and removed the four drain plugs on the 4.3L (mine is a 1990 model year),

Today I went and stuck a pick inside the drain holes and broke though rust causing all the water to come out from each manifold so they were plugged as they often are. . The block was dry. I removed the water inlet hose from the bottoom of each manifold and one was completley clogged with rust, had to dig it out with a screwdriver. I dont think this happened overnight, but I ran the boat all last season presumably with this water inlet clogged. The upper water inlet for the riser was not clogged. Everything still seems fine,, but now I am wondering what kind of damage may have been caused by this being plugged up? Im thinking of filling it with automotive antifreeze this year just for the corrosion protection, making sure to wash it out before I get on the lake next spring.

 

[81 Checkmate]

Salt water will cause more corrosion than freash water. If you didnt notice it getting hot last time out.... id say your ok. Proy better off useing the pink stuff instead of the auto - anti freeze...Unless you are going to catch the auto-freeze when you drain it. It's toxic ya-know.

Pull off all your hoses and check them for clogs..install back on......pour pink stuff in the themo opening if you are worried about corrosion.

 

[Scott Danforth]

they are 25 year old manifolds. they will also rust in fresh water after a while.

 

[garbageguy]

Everything still seems fine,, but now I am wondering what kind of damage may have been caused by this being plugged up? Im thinking of filling it with automotive antifreeze this year just for the corrosion protection, making sure to wash it out before I get on the lake next spring.

Assuming you didn't overheat this season (ran at normal temperature?), I doubt it caused any damage. However, a fair amount of corrosion has apparently already occurred, and corrosion protection may not do much good at this point. It could have corroded to the point where you have some very thin spots, and/or the loose material could clog things up at any time. You may have dodged a bullet, for now...

 

[Starcraft5834]

damage? probably none...long as it's running ok and not over heating...... corrosion happens.......complete blockage... hmmmmmm good you found it.. ive got an 87 3.0 they are pretty rugged.......kind of like a Timex.... takes a licking and keeps on ticking

 

[BRG25]

Mercruiser sez...

8. After seawater section of cooling system has been drained completely:

a. Install all drain plugs and tighten securely.
b. Reconnect hoses and tighten all hose clamps securely.
c. If NOT equipped with seacock: Seawater inlet hose must remain disconnected and plugged until engine is to be restarted.

IMPORTANT: Mercury MerCruiser recommends that propylene glycol antifreeze (nontoxic and biodegradable) be used in seawater section of the cooling system for cold weather or extended storage. Make sure that the propylene glycol antifreeze contains a rust inhibitor and is recommended for use in marine engines. Be certain to follow the propylene glycol manufacturer’s recommendations.

9. For additional assurance against freezing and corrosion in the internal water passages:

a. Remove the thermostat cover and thermostat.
b. Fill the engine seawater cooling system with a mixture of antifreeze and tap water mixed to manufacturer’s recommendation to protect engine to the lowest temperature to which it will be exposed during cold weather or extended storage.
c. Using a new gasket, reinstall thermostat and cover. Tighten cover bolts to 30 lb-ft (41 Nm).

 

[nick_vw]

thanks for the input guys. No, it didnt overheat ,exept once it got close to 200 after extended idle, cooled off once i bumped the rpm's slightly. (That was probably the impeller as its on its 4th and final season) My concern was the lower part of the manifold wasnt getting any cooling, and perhaps it warped/cracked although no indication it has. My guess is the rubbers on the exhaust didnt melt because the riser was getting properly cooled.. I took off the riser, seen some rust but not too bad down in the cooling jackets, no sign of rust in the exhaust ports. New gasket and now some marine -50 pink stuff and we will play again in april after the lakes thaw (thats a depressing thought!!)

 

[HT32BSX115]

thanks for the input guys. No, it didnt overheat ,exept once it got close to 200 after extended idle, cooled off once i bumped the rpm's slightly. (That was probably the impeller as its on its 4th and final season)

Sounds like you're going a leeetle bit too far with maintenance intervals there........

I would suggest you not go more than 2-3 years on the raw water pump replacement......

As for your manifolds, using anti-freeze, you're a little late to make any difference now.



25 years on risers and manifolds is a pretty good run!


I would suggest thinking about replacing the risers and manifolds soon.....

If you get a crack or a riser gasket leak and the boat sits for an extended period of time, you'll be replacing the engine as well.....


The next set or manifolds and risers will probably outlive you!

Regards,


Rick

 

[nick_vw]

the manifolds look good now that I had a closer look inside, I suspect they have been replaced at least once in their life. I think some of what was clogged in the inlet elbow was sand from an encounter with a sandbar this past july, likely ground up the impeller a bit as well allowing for the oveheat at idle. I live in Canada, And realistically I find impellers are good for at least 4 seasons, considering our seasons are only 4 months average, with many only gettng out a few weekends in july and august. I guess it all depends on the hours we put on the boat, for most its not many