225 Merc OB overheating
 

I'm not an OB guy but my neighbor has a problem with his motor overheating at cruising speeds. Doesn't appear at idle which suggests a flow restriction. Here's the real problem.

He took it in for repairs at the beginning of summer and this is a condensed summary of the work.
1-replaced (1) coil and wire so that boat could be tested.
2-test and replace pump assembly and thermostat.
2a-Replace 2.4 poppet valve with 3.0 ???.
3-test and spun prop
4-rehub prop and test. Spun prop again. Reason given; overtemp causing rubber deterioration. vendor will not rehub.
5-Sold him a new prop and still overheating.
6-pulled the powerhead and found blown gasket between head and exhaust/gear housing. Area between Water and exhaust.
7-Replace gasket and still overheating.
8-They are now removing the powerhead and are going to remove exhaust tube and water tube looking for corrosion.
9 They want to sell him a new engine !!
Could all this be caused by the infameous Chunk of destroyed impellor lodged somewhere?
WHATCHA THINK GANG ?
Walt

Just a couple of suggestions. Is the motor at the proper height. Perhaps when he is on plane, he is not getting water. Does he have a water pressure guage in the boat? If there is not enough water pressure and the engine and lower unit get too hot, it will make the prop shaft seals flake away as well. Is the mechanic well qualified ? . I have found that if you go to 5 mechanics, you get 5 diff. opinions.

it is rare thatthe impellar get up ther but it is possible. there is also a pop off valve on the right side of the engine. it is there to bleed off pressure. sometimes the fail and the end result is what you described.

also is it a 2.5 or 3 litre. there are 2 stats in the v-6's.
and as stated are there temp and pressure gauges?

Thanks guys, I will try to answer your questions as best I can, the boat not being mine.
The boat and motor combination are not new but have low hours suggesting that motor height has not been changed. As an "old" boat rigger I will double check as this is a possibility but motor is sitting on transom cutout as I remember.
I don't remember a water pressure gauge. The lower unit shaft seals are now leaking after Marina testing.
Poppet valve was replaced with 3.0 valve.
Competency of mechanic (s) definitly a question mark as I worked for a Marina,boat builder and several race teams, so I know that they come in all sizes and shapes. This place is a big outfit, gobbling up smaller nearby businesses to make a High and Dry. Usually there is ONE certified mechanic in the organization that will get involved. They also said that they had been in contacct with Mercury....what ever that means.

WOW
Disapointed that no one has any suggestions. Seems like the Marina might not be as inept and incompetent as I thought.
I tried the Mercuiser site but can't find a way to get to pose the problem to them. Anyone know? Did find out that there is (was) a class action suit on this motor.

Get a water pressure gauge and install it. Without knowing the pressure its anybodies guess.
Jim

Jim,
Agree, but wouldn't you think that the Marina would have done that to trouble shoot? This is not a shade tree mechanic asking for help but a large High and Dry that has had the boat all summer.
I was appealing to someone that might have "special" knowledge of this motor and something that might be unique to the problem.
All the things that they have done are text book and maybe they did hook up a gauge.?? But they haven't found the problem.

These days you can't assume anything. Most overheating happens near idle or wot. Overheating at cruise I would think is related to insufficient water pressure. Is the alarm going off or is it the gauge talking? A new transducer could be the culprit. As for as special knowledge I've been working on them since they were new, have rebuilt them, watched all the early warranty updates and on. I can't even count how many times I've gone behind some else only to find something minor was overlooked done improperly. Assumptions will get you no where. Good luck
Jim

Plus- a compression test should have been one of the first things done.
All summer that sucks. I'd be disappointed too.
Jim

Jim,
Thanks, It's not even my boat. It's the next door neighbors but I am Upset! He hates to pull the plug and go somewhere else and start all over.
I made a compression test before it went to the Marina because he had a problem giving it gas after another mechanic had rebuilt the carbs because of hesitation. The way it acted I was suspectious of a bad cylinder or head gasket but all the cylinders were up and within a few lbs. of each other. Don't remember the exact numbers. He may have them yet but nothing was suspicious. One gunky plug was on the cylinder that the Marina had changed the wire and coil on.( without us telling them what we found) Boat originally went in for that problem. During test they found OVERHEATING?
Could something as basic as TIMING be causing overheating?
Walt