Overheating Merc optimax

[Knotpretty]

looking at a second hand boat with a 2009 135hp merc optimax on it (motor has 65 hrs on the clock). The owner said at 50 hrs he had it serviced and it was overheating. Is this a common problem with mercs opti's. I have just sold my etec and could not go through the pain of another over heating motor again. KP

[LittleSkipper]

Walk away! Don't even bother purchasing someone elses problem, it will only end up causing you grief.

[Knotpretty]

Good advice. Just putting it out there for any one that has knowledge or experience with these motors to comment. KP

[kizza1]

its a bit harsh to say walk away.
there is countless things that can cause an engine to overheat. the good thing about the opti is that it has a gaurdian mode so i can almost garantee the engine will not have been damaged from the overheat. (havent seen an opti damaged from an overheat in 10 years).
firstly you need to find out if it is even still an issue.
it may have been fixed and the owner is just being completely honest of the history.
you can even find out the tempreture it has hit and duration through the mercury diagnostics system. this will also tell you when it happened.

you say it was serviced at 50 hrs and was overheating then. maybe he had some earmuffs fall off while flushing and burnt out the waterpump. or picked up a plastic bag, maybe he picked up a bit of sand and has jammed the thermostat.

if it has been serviced it should have had both the waterpump and the poppet valve replaced as well as the thermostat inspected. more info is needed

[Knotpretty]

Thanks Kizza. Sounds like you know a bit about mercs. I will investigate all reasons why the motor overheated. KP

[Jarrah Jack]

My inclination would be to investigate as Kizza says then if it ok use the info to get a good price.

[kizza1]

no worries,
maybe ask the bloke for the name of the dealership who did the service and ask them what they found.
it would be worth paying for a computer printout if you are looking at going further with the purchase.

[kizza1]

just on your original question. there are no standout problems with cooling of these engines. just little tricks that service people "in the know" will/should know to look for.
things like the poppet valve being jammed open and dumping excess water pressure down the exhaust.
thermostat being jammed closed can cause overheat. usually from sand/gravel or calcium buildup.
new sling on top of w/pump housing "forgotten" to be fitted at service will cause loss of waterpressure.
faceplate damaged and not replaced at service will cause low water pressure.

these are the main causes but not the only causes.

the computer system will tell you if it was just one head or both that was effected by the overheat(port and starboard sensor).

the gaurdian system on this engine is 2 stage. firstly if it reaches a certain temp it will limit the rpm of the engine till it cools down. the second stage if the temp continues to rise it will shut the engine down till it cools enough to restart.