Common cause of marine engine problems

This is a copy of a recent post on my new blog, but is my own work and not anyone elses. I run a marine parts business and spend all day on the phone discussing marine engine related problems with folks and hopefully convincing them to buy parts from my company, the story below is a very common one

In my experience as an engineer and spare parts supplier, the number one cause of engine problems on older Gas (petrol) marine engines is Exhaust Manifold failure, (mainly on engines used in salt water), the minute an engine starts to misfire or run rough the owner goes through every concieveable option, (plugs, carb,leads, rotor, etc) but usually fail to notice the telltale signs of emulsified creamy deposit in the oil filler cap, and often the creamy oil in the sump, when they finally do accept that there is a more serious problem, they usually have a buddy who is “good with cars” and who instantly diagnoses the problem as a failed head gasket, and procedes to tear the engine apart, then (if you’re lucky and he follows the job through) he refits the heads and inlet manifold declaring the job ” good to go” the poor owner then arrives at the coast with the Wife, Kids (in wetsuits), Dog, skiis, Tube, and picnic baskets and proceeds to slip the boat, the engine often starts fine, runs for a minute or two then as the cooling system fills with water it starts to misfire just as he is reversing away from the dock, it then stalls, will not re-start and he hits another boat. :-(

After a few minutes of cranking the engine and a bit of spluttering, he either gets a tow back to the slip, or paddles (with the skiis, wife on one side, him on the other, have you ever tried that) and puts the boat back on the trailer.

That would be a good scenario and ending, (apart from the thunder faced wife and kids, and the end of a beautiful friendship with the car fixer) it could also be a lot worse, (think coastguard rescue etc). if the car fixing friend knew anything about marine engines he would have gone straight for the exhaust manifolds rather than the head gaskets.

Marine exhaust manifolds are water cooled and most (Mercruiser, Volvo Penta, OMC, etc) Manifolds are cast iron, this material (although great for the job) is porous and spends its life soaking up the salt from the water that passes through it, until ultimately corrosion eventually breaks down the internal walls that separate the exhaust gas from the cooling water, the resulting hole then sprays salt water up into the exhaust ports causing all the associated problems,

for more information paste the following link into your browser

PS, If, as is often the case, the engine is left for a period of time before the correct diagnosis is made, (or even worse, pulled apart and left with the atmosphere getting to it) the corrosion damage (from contaminated oil) to the internal mechanical surfaces of the engine can be catastrophic.


Comments 12 comments

Dale Beaver 7 years ago

454 V8 in 33ft with < 600 hrs does not have power equal to other engine and will not gain any additional speed with throttle fully advanced. Any thoughts on what's wrong?

jim 6 years ago

engine runs good until it reachs 190 degrees then it shuts down.when temperature goes back below 190 it runs good. what's up?

kenyan 5 years ago

i have a yamaha twin v6 engine motor boat that is not starting and any time i try starting it it produces a fault beeping sound, any clue?

Mario 5 years ago

I have a 2005 I/0 mercruiser, and experiencing the same issues described above, starts up fine, but when I give it throttle or put it in gear it starts to sputter, then stalls. I bought a carb kit,changed the gaskets etc. Also changed the fuel water separator filter, and still having the same issues. I only use the boat in freshwater. Could this be an exhaust manifold issue too. if not, what else can it be?

Jeff 5 years ago

I just took my boat out tonite for the first time this year. It started up right away as ususal when I take it out of storage but this time I had no power. I could put it in gear and go all day long in a no wake zone. It idled at about 2000 rpm but when I tried to go faster the outboard vibrated and the rpms spiked so I had to let off the throttle. What's wrong with it.

Jim 5 years ago

Got the boat all clean ready to go. checked oil every thing great. it fires and test runs on the fake lake (baffles) keeping it cool. suddenly the pcv tubes start pouring out this pudding substance. The oil is watery and seems to be getting the crank case filled as it Idled. HELP!!!!!

ramkrishna 5 years ago

iam having diahatsu( ds 22)tug engine.problem is lube oil pressure decreses to alaram level ,when rpm decresing at instently. some one please suggust reason and solution for this problem

scott 4 years ago

Hi I just bought my first boat know nothing on them it has a 3.0 Volvo penta motor inboard trying to get all the info on maintance I can

scott 4 years ago

Hi I just bought my first boat know nothing on them it has a 3.0 Volvo penta motor inboard trying to get all the info on maintance I can

JOHN 2 years ago


dick Bolt 19 months ago

Boat Inboard Engine starts OK, & will idles OK for long time. Backs up in reverse OK. Runs strong at first, but then will not run slow & dies and hard to restart! Will not run slow again , but will run great fast! Not water in gas, cleared all gas out & put new in! Likely fuel control /carburetor? Not fun going into dock in windy day & stalls & cannot restart! Its A 2005 Bayliner 195 with 4 cylinder Mercruiser 3.0 inboard.

brad 17 months ago

Milky oil

    Sign in or sign up and post using a HubPages Network account.

    0 of 8192 characters used
    Post Comment

    No HTML is allowed in comments, but URLs will be hyperlinked. Comments are not for promoting your articles or other sites.

    Click to Rate This Article