2004 Chaparral 4.3 Mercruiser Cooling question

[gergAlicious]

I have noticed in the three trips out this year that my cooling gage never really tops ~165* give or take. This is a 19' boat, I run it about 3900 rpm for six or seven miles (repeated route) and when I look at the engine after running, the tanks above the exhaust manifolds aren't even warm. The connecting hoses in front that go to the center of the engine are not warm either. Obvious that the upper system hasn't flowed not or worm water in it. Engine seems to run fine. It does diesel when I kill it though. Not too hot to touch, or even hold when I kill it. I am wondering if it just hasn't gotten warm enough to open the system completely? Not sure what temp this should run.

Replaced the sea pump about two weeks ago, just preventive maintenance. Ran the engine in the driveway with ears and water got pretty warm, but never hot enough to not hold my hand under the output. I seem to remember the fellow running it for us before we bought it (used, last year) and he made mention of the exhaust note quieting down when the thermostat opened. Maybe just a stuck T-stat now? Oil pressure is just under 60lbs when running. I watch the gages closely, and wanted to take her out today - any thoughts?

Thanks!

 

[Bondo]

that my cooling gage never really tops ~165* give or take.

Ayuh,...... Welcome Aboard,...... Runnin' a 160? t-stat, I don't see a problem,.....

 

[Rick Stephens]

That is how every Merc I ever been in was when the cooling system was clean. Sounds just right.

 

[gergAlicious]

Thanks Bondo! I read that an open system should have a 143* T-stat?

Anyhow, I took a look at a few things just now. I pulled two hoses to verify the check balls weren't open or stuck. They both look fine.

Is it strange or bad that the hoses I am pointing at here NEVER get even warm? Nor the tank above the exhaust they go to?



Appreciate your feedback and knowledge!

This is my first I/O stern drive. I'm used to vintage OMC Big Twins

 

[Bondo]

I am pointing at here NEVER get even warm? Nor the tank above the exhaust they go to?

Ayuh,.... Those hoses carry the excess water from the raw water pump, that the motor don't need, usually cold water,...

The tanks are the risers, that are also are fed water from the manifolds below, 'n the hose, exhaustin' the water into the exhaust stream at the aft end,....

The risers rarely run the exact same temps, starboard usually warmer,....
Cold is good, to hot to touch is not,....

140? t-stats are for raw water cooled saltwater run boats,...
160? for the same, run in freshwater,....

 

[Rick Stephens]

Those hoses dump water into the manifolds. Only a small amount of the fresh cold water actually goes through the thermostat to circulate through the motor. The rest of it is poured through the manifolds and elbows to keep them cool and prevent the rubber exhaust parts from melting.

 

[gergAlicious]

Awesome guys!!!! So I can rest assured the the cooling is fine and has nothing to do with the dieseling.

Any ideas where to look on that? Timing maybe? Sometimes it kills quickly, other times it can diesel for several seconds. . .

 

[Rick Stephens]

Timing, wrong plugs, lean condition. I would check things in that order. Pull a couple spark plugs and see what they look like.

 

[R055]

Awesome guys!!!! So I can rest assured the the cooling is fine and has nothing to do with the dieseling.

Any ideas where to look on that? Timing maybe? Sometimes it kills quickly, other times it can diesel for several seconds. . .

91+ octane might do the trick if you're using 87.