Mercruiser 350 engine life advice

[Modi]

I am interested in buying a boat with Mercruiser 350 MAG mpi., ran for 300h, good service history. the engine is 10 years old (2008 model) however i dont have previous experience with Sterndrive engines.
I have requested Mercury to run inspection and computer diagnostics for engine health check.

Is 10 years old engine a bit too old for an engine? whats the expected life span of such engines ? when would an engine become too old and require replacement? any other tips would be appreciated
cheers

[Ruffryder]

300 hrs is low for an engine that is 10 yrs old. Heck I put that in one season .
while those hours can give you a good base line... all depends on how she was maintained and what kind of RPM range this thing ran. How much fuel went thru that engine is more important than its hours.
don't trust that engine hour meter ... see if you can find a dealer with a Rinda Mercruiser scan tool to be certain.
a good properly maintained marine gas engine shouldn't have any problems up to 2000 hours or more.
many boating yrs left on that engine, especially if you are only putting 30 hrs annually LoL

[Modi]

Many thanks
I have booked it with Mercury to do CDS the computer disgnostic test and some other inspections by their mechanics . this is all the test they can do in Dubai
Is it possible to tamper with the hours meter ? if yes , is there a way to tell?

[Ruffryder]

Anytime & welcome to the club!
anybody can tamper an hour meter easily & nope no way you can tell.
get it scanned,
perform a compression test,
sea trial is a must, ensure she will reach her recommended WOT... propped properly ,
send in her oil sample to be analyzed .

[iceclimber]

My 1987 305's are original and running fine. The low hours make the maintenance that much more important.

[2850Bounty]

I am interested in buying a boat with Mercruiser 350 MAG mpi., ran for 300h, good service history. the engine is 10 years old (2008 model) however i dont have previous experience with Sterndrive engines.
I have requested Mercury to run inspection and computer diagnostics for engine health check.

Is 10 years old engine a bit too old for an engine? whats the expected life span of such engines ? when would an engine become too old and require replacement? any other tips would be appreciated
cheers

You will see three types of cooling systems:
.....Raw Water Cooled
.....Half Closed Cooling System (exhaust manifolds not included)
.....Full Closed Cooling System (exhaust manifolds included)

If ten years old and Raw Water Cooled, and if operated in Ocean water, I would be concerned..... even at only 300 hours!


.

[Modi]

many thanks
it is raw water cooled
Mercruiser did full inspection and CDS test
they commented that cooling system is running cold at 140F instead of 150-170F is that a problem?
they also reported that block water sensor needs replacement - no reading
any advices?

[88fourwinns]

That cold running could be nothing more than a thermostat that does not close all the way (common in open cooling systems due to rust flakes and sand/grit getting stuck in the thermostat, keeping it open a bit.
HOWEVER....raw water cooled....if in SALT water....the exhaust system needs regular maintenance checks at 5 years, and may well need to be replaced at 5-7 years, due to salt water corrosion. If this was done, then fine the engine could have a lot of life left in it but if not, there is the risk of salt water leaking inside defective exhaust manifolds or elbows and getting into cylinders via an open exhaust valve. This causes corrosion of exhaust valves and can in extreme situations cause cyl wall rusting.
Was the engine used in salt or fresh? Its a big difference in the possible problems you can face.
I would make sure you do a good water test and make sure that it reaches it's specified max rpm, pulls the load of the boat well, the outdrive shifts properly, does not jump out of gear, make odd noises, etc. Check the bilge and transom mount area carefully for leaks.

I still think you'd be better off by far with an outboard boat, with an engine that is supported in your location. Take it from someone who owns a boat with a drive system most mechanics won't work on (OMC Cobra). It has been very good to me with minimal problems but out of production for a long time. Most mechanics here only work on Mercruiser and newer Volvo. Anything else and you have to search around for someone or do it yourself.

[Modi]

much appreciated, thank you
you are right , they said the thermostat is not working

it was run in salt water , water salinity is a bit higher than ocean water.
the computer diagnostics was done ,
reported WOT 3400 rpm. i think thats low for this engine
compression test was between 170-185
oil pressure 507psi at idle

[88fourwinns]

low WOT is a concern, Should be more like 4400-4600. Compression test results are OK. Oil pressure @ idle (think you meant 57?) is usually 40 cold engine but can drop to about 20 with a hot engine, that's still OK.
Concern is the salt water use and as I mentioned was the exhaust system maintained. Good comp test results suggests it probably was. But, after 10 years in very salty water I can tell you this:
I took apart a 4.3 used in moderately salty water for 15 years. The block was fine but the cyl head cooling passages were getting eroded to the point where the machine shop guys felt it was better to install re-man heads than to rebuild these. So you might get 5 more good years if careful. If it was closed cooled I would not be so concerned. However the same holds true for outboards, they get a good 10-15 years in very salty water and after that, on borrowed time.

[Ruffryder]

Mercruiser 350 Mag should be turning 5000 RPM @WOT... so she's been running over propped & that engine has been lugging, who knows how long.
it is extremely critical that your engine is able to reach within the recommend RPM range at WOT.
ECM stored scanned total hours?

[TX H210 SS]

Seems I recall the recommended thermostat temp rating for saltwater use is 140 and freshwater use is 160. Don't take this as gospel, but I believe the 140 temp in salt is because saltwater will crystalize at higher temps.

You may research that issue.

The WOT RPM is off as mentioned....it may be sure to incorrect prop as mentioned.

[builderdude]

What size boat, large cruiser?
As stated the 3400 WOT rpm is super low.
You sure that wasn’t the “cruising” rpm?
Was there marine growth on the hull bottom, outdrive or prop?

[Modi]

the boat is bayliner 245, 24ft , Mercruiser are the ones who did the computer diagnostics test and inspection
They said the temp should be is 150-170 F
I have asked them to confirm if the 3400 rpm is really the WOT or cruising rpm as it is quite low.
the belows and the drive were not inspected as the boat is wet berthed in the marina
but the boat had polish work done 6 months ago with anti fouling and the usual service.
with this in mind and the fact that there is no much support for Mercruiser inboard engine support , i am worried i will get in trouble with it

[88fourwinns]

Agreed. A 10 year old Mercruiser in salt water with unknown service history and no local support, spells trouble to me.

[2850Bounty]

many thanks
it is raw water cooled
Mercruiser did full inspection and CDS test
they commented that cooling system is running cold at 140F instead of 150-170F is that a problem?
they also reported that block water sensor needs replacement - no reading
any advices?

I know of no way to ensure that the inside of the cylinder block has not become compromised due to Raw Water cooling for this long.
Also, operating at 140* is OK for running in Ocean water, it is too cold for running in River/Lake water.

much appreciated, thank you
you are right , they said the thermostat is not working

it was run in salt water , water salinity is a bit higher than ocean water.

All the more reason for walking away...... Or, for planning on a new engine in the not so distant future!

the computer diagnostics was done ,
reported WOT 3400 rpm. i think thats low for this engine
If that is a true and accurate WOT RPM test, this engine has been "Over-Burdened" for who knows how long!!!!

compression test was between 170-185
I would want to verify this myself!

oil pressure 507psi at idle
Must be Typ-O.
If 50 psi, that is excessive for idle RPM.

[Fishtank]

Anytime & welcome to the club!
anybody can tamper an hour meter easily & nope no way you can tell.
get it scanned,
perform a compression test,
sea trial is a must, ensure she will reach her recommended WOT... propped properly ,
send in her oil sample to be analyzed .

This guy is right on the money ^

An hour meter means absolutely nothing! Age also means practically nothing as long it has closed cooling. The unfortunate thing about boats is that people can abuse their engines with poor maintenance or run at WOT all the time, and sometimes you'd never know it after only a few hundred hours.