1973 trisonic 165 hp merc


Old 10-31-01, 03:49 AM
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We bought a boat back in April, first time buyers, and don't know a whole lot about boats. I replaced the prop, not sure which pitch, replaced the plug wires and plugs, and fuel pump, however, i can only pull about 35mph out of my motor. what can i do? is this motor no good? Is this as fast as it should go? Also, as the summer progressed, my boat started overheating. Here in Texas the summers usually reach 95-105 degrees. We're on the lake as often as we can be, usually every weekend. The boat runs great, cranks right up, everything is fine except it starts to overheat. Ive noticed if i have about 5-6 people in the boat or a heavier person in the boat, it starts to overheat. Also when we're pulling someone on the tube, we have to stop for a little while in between. If we're just idling, changing tubers, it will start to overheat. It wasn't like this when we bought the boat, but again, that was back in April when the temp here is around 85. I dont know if the outside temperature raising 20-25 degrees will make it do that or not. Again, we know very little about boats and would be very greatful if someone could help us with this. Also no familiar with all the technical names so when explaining it would help if you could use the most basic boat terminology possible........Thank you.
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Old 11-01-01, 06:27 PM
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Hi there,
lets get started with the engine type,horsepower and year if possible. Then we will talk about changing the water pump. Then we can move on to getting some of your friend out of the boat. Or maybe just a prop change.
How big a boat is it?
we should have you back on the water in no time.
Old 11-02-01, 03:01 AM
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Hi. OK, Im not sure ill have all the answers, but let me try. Its a 1973 18' 165 hp mercruiser. From my understanding, the motor is something like a 255 old Chevrolet motor. Don't hold me to that though. I was told that by some of the friends we're gonna throw overboard. I know I definitly need a new prop. Between being a new boat owner and a loose fitting for the trim, my prop is pretty well beat up.lol. (I didnt know about the loose fitting, so there for i was losing oil and my trim would not come up or stay up.) Laugh at me now, but we were gonna play with this boat regardless. Well, hopefully Ive provided you with the info to get something started.

p.s. There is a little black rubber ribbed piece under my trim, not sure what it is or what it does, but it has a gash in it, or a hole. Was just wondering if that may have anything to do with the overheating.........thanks.....Sam
Old 11-03-01, 12:31 PM
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Sam, first.. the ribbed hoses are very important.
But the lower one not so much. it directs the exhaust flow.
When you run it on the garden hose adapter, And do not ever run it without water, does it have a good abount of water coming out the prop?
You have a good reliable package there. It may just need a pump or impeller. If the water flow is not great and the engine is getting hot, the w/p in the drive is bad.
Old 11-03-01, 04:21 PM
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My Two Cents

Hi: Sam

If the engine begins to run hot or run close to hot, Scott is most likely correct regarding the water pump or impeller. He's the pro here. I'm only adding 2 cents...

The over heating may be caused by a restricted cooling system and or a defective thermostat. Another thought may be a collapsing water hose or restricted water port in the engine block or any type of water flow restriction elsewhere in the cooling system.

An old water hose can become restricted internally. The entries and exists where the hoses connect can become restricted.

Old water hoses can also collapse under excelleration loads, etc. All hoses should be checked and or replaced, if there is any doubts regarding there conditions.

Scott is also correct about verifying the volume amount of water exiting the prop exhaust. It has to match the intake volume.

Wondering if restricted exhausts could be all or part of the problem??? Any thoughts on this or anything above Scott?

Also wondering about engine timing as a possible problem? The engine may start and run fine but run hot from a too lean fuel setting or incorrect timing advance??? Your thoughts Scott?

And there you have it..."My Two Cents"...

Regards and Good Luck Sam
Hi Scott
Tom B
Old 11-04-01, 11:20 AM
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Well guys, I appreciate the help. Just as soon as I can get a chance I'll start trying to check out some of these things. I'll let you guys know what I find and what I did. Being that I'm in North Texas, the winters aren't the coldest, what do I need to do about winterizing? I will probably have to do most of it myself, seeming how the economy's fall has taken effect on my pocketbook as well as others.(Hopefully it's pretty easy too!) Thanks again for the advice........Sam
Old 11-04-01, 08:45 PM
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Again Tom has the Golden Cents.
The exhaust system is the second most common cause of overheating. Good tips on updating the hoses too.
Makes me want to change the ones on my 165.
Timing is very important especially with the unleaded fuels.
Lets keep it down to 6" btdc. The thermostat should be relplaced every two years. Good insurance for a trouble free vacation.
Thanks all. scott

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