I have a 350 I/O in a 1980 Entertainer. Last year all summer it ran GREAT, but whenever I drop down to idle speed in a no wake zone, the temp creeps up. I have a 160 degree thermostat in it, and everything in the cooling system is new (water manifolds, water pump, thermostat, impeller). All the hoses seem clear, and I can't find any obstructions. SO, yesterday I pulled her out and changed the oil, dropped the lower unit and put yet another impeller in. I was thinking the grommet for the water tube wasn't seated, and under low pressure it wasn't getting enough water. However, after replacing that too, and making sure it seated well, I'm having the same issue? It runs perfectly, and stays right around 150 to 160 degrees, but as soon as I idle in to a marina, it creeps up to 200 degrees or more. I can put it in neutral and rev it to about 1,000 rpms, and it instantly pulls the temp back down. I put a new carburetor on it last year because the one on it was an automotive model, and I replaced it with a marine Rochester 4 barrel. Could the carburetor's adjustment be the problem? I need HELP, I don't want to worry about this for another summer! Thanks,
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Temp problems ... year 2
- Thread starter Jamey
- Start date
I've put three thermostats in it of varying makes. I know at least one was a merc ... no difference. I changed out the water pump on the front of the engine with a new marine pump around the middle of last summer (the one on it was an automotive pump and it was definitely shot) This is really driving me nuts!
Chris E
Well-known member
your water hose from the bell housing to the transom assembly is probably leaking. very common and will cause your problem. the flow is enough at high rpm to keep the engine cool, not so much at low speed. that hose weather checks and leaks. have a very good look at it. another possiblility is the oring from the drive to the bell housing is missing. yank the intake hose from the thermostat and start the motor - briefly - you'll be able to isolate the drive from the engine immediatly. low or no flow will tell you the tale.
I've looked at that hose Chris, and from what I can see I saw no obvious holes, but it is very old and you can only see a little of it. If I were to change that, how do you access it? Does the whole outdrive have to come off, or can you get to it without removing anything? Any special instructions/tools to do the job? Thanks,
Chris E
Well-known member
i have always done it with the drive off - having said that though - i think you could do it with the drive on - just 2 hose clamps hold it on - not a very big job.
daren34
Member
look in your service manual at the section for replacing the drive shaft bellows.
you can do it yourself but plan all weekend
follow the hose from the transom plate to the motor check the inlet side
of the power steering coolerfor obstructions
daren
2springers26
Member
over heat
first Off non EFI Merc i/o's run 140 deg t stats. check your water hose for a kink when trimmed down. this can be seen where the trim sender is( port). ran into this issue also when i was servicing i/o's . the other possibility is the upper watertube gromet In the upper drive shaft housing. it's probbly leaking @ idle where the gasket is blown or got hot @ one time..( you need to spilt the upper & lower gearcase to see this)....kurt
first Off non EFI Merc i/o's run 140 deg t stats. check your water hose for a kink when trimmed down. this can be seen where the trim sender is( port). ran into this issue also when i was servicing i/o's . the other possibility is the upper watertube gromet In the upper drive shaft housing. it's probbly leaking @ idle where the gasket is blown or got hot @ one time..( you need to spilt the upper & lower gearcase to see this)....kurt
happy
Active member
the by pass valves in the thermostat housing cause this problem too.. notably, since you high spped temp is ok, and just you low speed temp is high says that you shouldn't have an air leak problem. a water flow problem would be more likely.. you need to take engine temps along your manifolds, block , heads, risers, and tstat housing and determine where your heating up. once that is known, your diagnosis can go from there..
Big Red
Well-known member
Maybe the same Certified Merc man with over 35 years exp. that worked on my boat worked on yours to. He put my pickup hose on backwards so when I trimmed up, it would kink and started to heat. Talking about a crap load of time and money wasted trying to figure out why mine would only heat sometimes.