Boat guys - Overheating problem

jorian · 02:22 PM

I have a 31' boat with twin 7.4 liter Mercs. The port side motor runs significantly hotter than the SB side. 160 deg VS 190. at a constant 3100 RPM

I have recently done the following:

cleaned out the intakes (they were pretty gummed up - engine ran 205 degrees prior to cleaning)
new impellers
cleaned risers
checked thermostat

Not sure what to do next.

Here is a picture of the old girl.

nota · 06-24-2009, 02:25 PM

I/O drives? counter rotation?
equal water flow out? [I bet not !!]
you did reverse the impeller on the non-standard motor?
remember if it runs backwards the pump needs to run backwards too

jorian · 06-24-2009, 02:42 PM

Thanks for the reply.

Boat has I/O with counter rotating props.

I guess I would have to check the water outflow with the boat out of the water?
Not sure about the reversing the impeller... I'll check on this.

VincentVega · 06-24-2009, 03:50 PM

I dont know power boat engines, I'll ok with sailboat engines. Have you flushed the block? Vinegar does wonders.

Also, any chance the hot engine is lean? Clogged jet/injector?

jorian · 06-24-2009, 03:53 PM

Quote:

any chance the hot engine is lean? Clogged jet/injector?

Co-incidently one of the carbs was rebuilt recently - I'll check with the mechanic.

VincentVega · 06-24-2009, 04:50 PM

I know a guy that tried to run a car carb on his boat. Even with the fattest jets it melted the pistons. Make sure it's setup right.

JeremyD · JeremyD's Garage

Check the sensors too - they are famous for being off on the mercruisers. That said - I'd check mixtures first. Sea Ray?

dhoward · dhoward's Garage

Impellers are just those rubber-vane guys, right? No right or left when new..
So Bravo3 drives?
Didn't say where you play, lotsa sand?
I/O's are sand vacuums. Pretty easy to pack a motor full...
Pull some of the block and manifold drain plugs and poke a screwdriver up there, any exhaust restrictions?

jorian · 06-25-2009, 08:36 AM

The mechanic is going to look at the mixture today. Not sure where the sensors are but I'll ask him about these too. The boat is a Formula.

Impellers are indeed those rubber vaned deals. No sand where I am.

Thanks again.

JeremyD · JeremyD's Garage

Sensors are on the thermostat housings - at least they are on the 5.7's, I'd also pull your hoses - as I had one that put on that was an auto 1" hose that had partially collapsed - and gave me about the same temp difference.

How about heat exchangers? When were they replaced? or cleaned? You can get them cleaned at a radiator shop - you can also run white vinegar through them that will remove some of the scale. I'd get em cleaned or replaced if they haven't been lately (last 5 years)

Nice looking boat.