overheating 260 hp mercruiser

[JBF 1962]

The engine on my '85 Thundercraft Magnum seems to want to overheat on me now (350 V8/260 alpha I)
The outdrive was rebuilt by the marina in for the p.o. before I took delivery in the spring (gimble/bellows/impeller/alignment etc) and its been running amazing. A copule of weeks ago, I took it out and the temp needle spiked, so I stopped, reversed the engine and continued on (its a weedy lake, a common occurance) and the temp resumed its usual reading. Last week I went to take it out and the temp climbed to the top before I even got out of the harbour, so I immediately returned to dock, engine was extremely hot, cooling hoses were not, so I changed the thermostat (142 degrees, per the manual)
This changed nothing and I've noticed that the exhaust is bubbling at the transom rather than through the prop.
I know that I'm going to have to arrange tp have my boat pulled from the water, but in the meantime, anyone have ideas?
Thanks
John

 

[alamantia]

Re: overheating 260 hp mercruiser

I am new to boating so I am hesitant to offering up any suggestions but I can tell you of my personal experiance if you want to hear it... I too have a 260/350 with an alpha 1 which I just bought over the winter. I had the outdrive serviced in the spring and brought it home and put it on and ran it with the muffs and all seemed ok. I replaced the thermostat with a fresh 160, I also replaced some old looking hoses and both belts as a precaution. It still ran around 220 on the water under power, but I thought that the gauge could have been off. I did try and figure it out by pulling the rizers off and sand blasting them out. It still ran over 220. I heard that the circulation pump impellor could have rotted if it was not stainless. I had a small block chevy pump so I swapped it out. Still ran over 220. I kept noticing that the bilege would fill up with a puddle of water when I ran the boat. But I would mop up the water at the end of the weekend and go back to the marina the following weekend to find the bilege bone dry. Get that, a 25 year old boat doesnt leak a drop over a week of sitting there and when i run the engine a puddle forms in the bilege. Strange on both accounts right? Turns out the power steering pump cooler was the culpret. My guess is that the previous owner never drained it and it froze and cracked. So I removed the cooler and bypassed it. Upon removing the cooler I noticed there was some sea weed looking depris clogged in the cooler. Now th eboat runs at 180 stead no matter what RPM. One of these days I will probably buy a new cooler and place it back. But it seemd like some debris somehow got lodged in the cooler and was restricying water flow. I dont exactly know how it got passed the impellor but it seemed to. Thats my personal experiance. Not saying thats what is happening on yours. But if your inlette hose is easily accessable perhaps its worth checking. May be easier than pulling the drive? I know on my boat it was a ***** getting it out because it was mounted behind the port engine mount. Good luck.

 

[wellcraft_zach]

Re: overheating 260 hp mercruiser

I had a similar situation with my 5.7L. In the water i would overheat but in the yard with the muffs on it would not.. ended up being the impeller in the out drive, $40 for a rebuild kit and i was on my way.

 

[JBF 1962]

Re: overheating 260 hp mercruiser

Thanks for the tips, I'm heading up to the lake today to work on it, see what happens
What kind of Wellcraft do you have Zach?

 

[rjenbody]

Re: overheating 260 hp mercruiser

Impeller, most likely. Too bad you didn't get it out of the harbor. If you did and she cooled down when you got up to speed, you would know it's the impeller. I've got the same motor and stern drive and change the impeller more often than the oil. You can do it yourself in less than an hour with basic tools.

 

[JBF 1962]

Re: overheating 260 hp mercruiser

well, as it turns out, after hauling out the boat, incompetence was the cause, Fenelon Falls Marine on Cameron Lake in Fenelon Falls, Ontario, serviced the outdrive before the boat went in this year and didn't see fit to tighten the gear clamps that, among other things, held the fresh water hose that runs from the impellor pump. (they also neglected to tighten the clamp on the exhaust bellows) This is on top of damaging the hull when they took it off the blocks, they claim they didn't do it, but when the boat was surveyed in April, the surveyor didn't notice it...
Anyway, incompetence reigns supreme, no wonder I prefer to do things myself.
Word to the wise for anyone who boats in the Kawartha Lakes, avoid the clowns at FENELON FALLS MARINE
Happy boating!