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MCM 165 overheating

H

Hydro Therapy

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My 1987 Sea Ray with twin Mercruiser MCM 165's has a slight overheating problem with the starboard motor. Port runs at 160 where it should, starboard gets up around 195 degrees under load. It cools down at slower speeds/rpms, it's fine at idle. On the ground they both seemed to be equal as far as water discharge while idling, hooked up to a hose. I was thinking thermostat as the former owner, (I just bought the boat), says he just had the impellers done. Looking in there the bellows were like new so it appeared as though it had been worked on. I checked it with a heat gun and the motor was hot, 194 degrees. it did however cool right down when I kept the rpms below 2200. Any thoughts?
 
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Higher rpm temps typically are due to lack of incoming water flow
For an alpha drive that would point to the impeller as the cause.

The other two issues could be low out put flow thru elbow or bad thermostat.
Typically these would show higher temps ni matter what the rpm is. "Typically'....
.
I would start with NEW impeller assembly.

Running on a hose will not always show input flow problem as hose connection is pressure vs impeller suction.
 
One more point: You should measure the temps with an infrared temp gun to see if the numbers are correct.

Gages lie.

Jeff
 
Thank you, I will replace both impellers, this will hopefully fix the problem and give me a point of reference as to when they will be due again. I had already ordered two thermostats and gaskets, thinking I will replace them as well being that I will have the parts. I looked at the parts diagram here on Marine engine and it's a little vague as to where they go. I spoke with a guy here that has done some repairs for me and he said they go under the coolant reservoir on top. If this is accurate then it looks like I will need the gaskets for the reservoir as well. Does this sound accurate to you? Thanks again, truly appreciate the help........

Dan.....
 
Attached is a pic from manual.

I would suggest that you pay attention to orientation and gasket location.

Also the image of the thermostat itself is a older brass design. if you have the new and standard stainless steel design just make sure you orientate it just like the brass design. Use the "top" of the thermostat as the point of orientation. In the image below the thermostat top is pointing down. This may or may not be correct so pay attention to the way yours is when you take it apart

U.png
 
Okay, so a little bringing up to speed. Changed both impellers, (thought it was good to have them on the same schedule), still running hot, took the manifold/riser off, was a little plugged, really not that bad, cleaned it out and it appears to have very good water flow now, reinstall, still running hot. Pulled the t-stat, looked like new. I took the power steering oil cooler off and checked it, no obstruction there either. Took the heat exchanger off, checked it, the fresh water side is as clear as can be. Pulled the drain plug for the antifreeze, found a bunch of crud in there but it's a small opening, thought maybe the rest is plugged up as well so I ordered a new heat exchanger. I plan to flush out the old exchanger and keep it for a spare if it seems to come clear after the flushing. My new question is:
Should I flush the whole system and do those flushes really work? Bear in mind that when the engines are at temp, starboard is hot, or hotter then the port engine, when shooting the inbound and outbound temps on the exchanger(s) the temp going in is the pretty much the same, coming out the starboard is some 30 degrees warmer. Feels like the obstruction is in the exchanger. I have no aversion to flushing the whole system, just wondering what the general consensus is as to whether or not those flushes actually work or if it seems warranted in this situation? I'm not 100% certain as to the pros and cons of flushing the cooling system, according to the internet, (yes, I know I'm there right now), it's a mixed bag as to whether or not it will help or possible further complicate my problem.
Thanks in advance for any help offered........
 
Hydro Therapy said:
Okay, so a little bringing up to speed. Changed both impellers, (thought it was good to have them on the same schedule), still running hot, took the manifold/riser off, was a little plugged, really not that bad, cleaned it out and it appears to have very good water flow now, reinstall, still running hot. Pulled the t-stat, looked like new. I took the power steering oil cooler off and checked it, no obstruction there either. Took the heat exchanger off, checked it, the fresh water side is as clear as can be. Pulled the drain plug for the antifreeze, found a bunch of crud in there but it's a small opening, thought maybe the rest is plugged up as well so I ordered a new heat exchanger. I plan to flush out the old exchanger and keep it for a spare if it seems to come clear after the flushing. My new question is:
Should I flush the whole system and do those flushes really work? Bear in mind that when the engines are at temp, starboard is hot, or hotter then the port engine, when shooting the inbound and outbound temps on the exchanger(s) the temp going in is the pretty much the same, coming out the starboard is some 30 degrees warmer. Feels like the obstruction is in the exchanger. I have no aversion to flushing the whole system, just wondering what the general consensus is as to whether or not those flushes actually work or if it seems warranted in this situation? I'm not 100% certain as to the pros and cons of flushing the cooling system, according to the internet, (yes, I know I'm there right now), it's a mixed bag as to whether or not it will help or possible further complicate my problem.
Thanks in advance for any help offered........
Click to expand...

By freshwater side you mean the raw water Im assuming from your comments on the AF side. I've never had a closed cooling system on boat , but on my '65 GTO which doesnt get used much, I ran this through my system twice-

https://www.amazon.com/gp/product/B00R74I5UY/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

I was chasing an over heat that I couldnt fix, drained the block and got muddy chunks out. This dropped my running temp by 15-20 degrees. Was a pain to do and had to keep blowing air/wire into the drain ports cause they clogged.... Each time I left it in the system a couple days drove it a bit and flushed with water repeatedly.
 
dunno what kind of heat exchanger you have but generally the end caps can be removed and the tubes "rodded" out with a coat hanger wire or even a little bore brush if you care to be that particular. Then you put the end caps back on with new gaskets and o-rings and you're good to go.
 
Well......I'm gaining on this a bit I think, or at least feel like I made a discovery as to why this engine is running dangerously close to overheating. After reinstalling the heat exchanger, I took the boat for a ride. It was better, only reaching high 180 degree/lower 190 degree temps when up on plane. Neither of my trim gauges work, so trimming the outdrives is a bit of a crap shoot for right now. I had trimmed up, actually too far on the starboard engine as it was starting to cavitate but the temp went down dramatically to the same temp as the port engine. When I trimmed back down the temp went up again. I'm guessing the water hose that goes from the outdrive to the bell housing is getting kinked when the drive is down. My new question is can this hose be changed with the drive on or does it have to come off again? In looking at the parts blowup it appears to be either a 5/8 or 3/4 inch hose. Also, is there a molded hose replacement? I had a mobile boat mechanic come out, he did the impellers and a shift cable and he mentioned something about a kit that included a molded hose to keep it from getting kinked. He did not have one of those kits the day he did the work, I now wish I had paid closer attention to what he was saying. Anyway, can this hose be changed with the outdrive still on the boat?
 
The water inlet where the molded hose attaches could be plugged with corrosion. Remove the hose inside the engine bay to see if it is clogged. Someone may have put a replacement hose on wrong causing a kink and low water flow.
 
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