Discharge Water "Issue"- cold port, warm starboard?

[Woody-jh]

1995 4.3 Mercruiser LX
Engine Serial OF421280
I had a rebuilt engine installed two years ago, not sure if the "problem" I will describe existed before that (old engine hydralocked twice)
"Problem" (I think)
While running on muffs, I have good water flow out the exhaust at the stern drive. However, the discharge water on the port side is always cold, while the discharge water on the starboard side warms up nicely.
Question: Why is the water temperature any different? They take parallel paths through the motor, and should mix in the wye pipe.
Comment: I checked the circulation sketch in my Seloc manual, and can't see any difference in flows, unless one side or the other goes through the power steering cooler.
I pulled the thermostat housing, and the stat was in properly, sealed and had good spring action (140 deg stat)
Question: Could the starboard side have a damaged exhaust shutter that is blocking water discharge, thereby allowing the starboard side to heat up. If so, I would like to change the shutters before I launch for the year. I would have to pull the exhaust elbows to get to the shutters due to tight space, but no big deal if that is the right move.
PS: My temp gauge has not worked since the engine swap, so I don't know what temp I'm getting. Last year the boat ran fine, but I would like to make fine into great for once.

 

[Bondo]

Re: Discharge Water "Issue"- cold port, warm starboard?

Ayuh,....

Even though the graphics look exactly the same on both sides,....
They're Not.... And water takes the path of least resistence......

If you've Ever run the motor with questionable waterflow,....??....
There's a darn good chance the Flappers were Fried....
Without seeing Your boat,... How much you need to take apart is yet to be known....

And,..... Get the Temp Gauge Fixed...... Ground out the Wire, at the Sender to see if it's the Gauge, or the sender....
A Dead Ground should Peg the Gauge.....

 

[Woody-jh]

Re: Discharge Water "Issue"- cold port, warm starboard?

Thanks, Bondo, the marine mech at my parts store took the time to explain how to test the sender/alarm. As far as I know, I have not had any circulation issues- I have only had warm to hot water, not scalding. Since I have been sensitive to this "problem," I check the temp on muffs and in the water.

By the way, the same mechanic showed me the "new" Mercruiser shutters- all rubber now, different design, instead of that dreaded brass affair with the swing pin that wears like crazy. Price for the new shutters is $100 per pair, plus two manifold to elbow gaskets.

 

[Woody-jh]

Re: Discharge Water "Issue"- cold port, warm starboard?

Bondo, you got me thinking with your comment "water will take the path of least resistance." I checked the thermostat (OK), and the Temp Sender OK- first by shorting it out like you said, then I put a hot air gun on the sender inside the t-stat. The ohms changed very rapidly downward, so I took the chance that it was OK. Next I put the t-stat back on, and when I hooked up the hoses, I discovered that the rebuild shop had mixed up two hoses on the starboard side!!
I know that because I marked everything before taking them apart, and then I checked against the diagram in my manual after re-assembly. Feeling confident, I flowed water (muffs) and started the engine. Both sides of the outdrive exhaust are now the same water temperature, and the gauge went to about 140 degF like it should. Next is the inwater test...hopefully this ends a two year problem, that being that my engine has run cold for two years- I used to check the water discharge temp in the lake quite often since my gauge was "not working."

 

[Bondo]

Re: Discharge Water "Issue"- cold port, warm starboard?

I discovered that the rebuild shop had mixed up two hoses on the starboard side!!

Ayuh,..... Sounds like you might be onto something....

Good Luck...