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1985 Yamaha 115 uneven temp

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catman357

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I have a 1985 Yamaha 115 outboard that I bought new and it has been a fantastic outboard with very few problems all these years, it still runs great. Two years ago I developed a overheating problem only while running the boat on the water at 1/2 throttle or better. So I decided to replace the water pump that didn't help so I also replaced the thermostats and that didn't help! After looking the outboard over many times I realized the problem was my stupid mistake of putting the inlet covers on backwards:mad:! The motor runs great but I've noticed that the port side runs around 25 degrees warmer than the starboard side on motor flusher at idle. It's not getting hot, port side reading was 102 degrees while the starboard side was 75 degrees. I've cross switched the thermostats and that changes nothing. Is there something I'm missing? Any help will be greatly appreciated.

Alan
 
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at that age you could have salt/calcium type build up under the cover plates. If you don't find anything else I would look at pulling those off and checking for build up.
 
Agreed with ^^^. When was the last time you pulled the head and head cover? If its been years that's the next step I'd take. My guess is you've got corrosion build up in the water passages, and this is the primary reason you were experiencing the high temp alarm, not the inlet covers installed backwards. The backwards covers I imagine only exacerbated the cooling problem.

And if you follow through with the above then you might as well replace the head and cover gaskets. Be careful unscrewing the head bolts as to not snap one. Also, these bolts absolutely require proper torque. See your manual for the exact lb/ft.
 
I don't have a overheating problem at all just one side of motor seams to not be heating up as it should. It acts like there isn't a thermostat in it or the thermostat is stuck open but its not and I even swapped them to see if the temp difference would follow the thermostats but it didn't change at all. I even swapped the pressure relive valves? I think that's what their called and no change at all. And believe me my overheating problem was the inlet covers installed backwards because I was running it on the river after installing new pump and thermostats and it still overheated. So I put the boat back on the trailer and started looking at the motor and noticed the screens were on backwards, they are designed to channel water into them and with them on backwards at higher speeds they will cause the water to pass around the inlets instead of going into it. I changed the screens around put it back into the river and ran it 2 miles pretty hard and it was fantastic. That was 2 years ago and its never overheated again. So my only concern is the temp differences from one side to the other.
 
I hope this isn't a double post as I tried to post earlier and its not showing. My motor hasn’t overheated in two years since I changed the intake screens around, and 10 minutes before I changed them it was overheating while running on the river. So it was 100% the intake screens and my stupid mistake. This motor has never been in the salt and has great circulation in the cooling system as it did before replacing the 29 year old water pump and thermostats. What I’m trying to figure out is there any explanation as to why the starboard side of the motor is running noticeably cooler than the port side? I've swapped the thermostats around and also the pop off or pressure relief valves. Doing this doesn’t change anything. Like I said before, running on ears in driveway after its run about 5 minutes port side was running 125 degrees on the head and starboard was running 75 degrees. Sorry if I didn’t make myself clear in my first post.

Alan
 
It is not abnormal for one cylinder to be hotter or colder than another cylinder or for one bank of cylinders to be hotter or colder than another bank cylinders. I know the answer you're looking for is WHY, but this is all I can offer.

Also, how are you getting the temp? Sender? When you get into temp problems it's best to check temps with a laser temp gun. Senders and gauges have an "allowable" factory tolerance.

Despite your motor being a freshwater outboard and regularly flushed, water passages can still become corroded over time. Fresh water lakes/rivers have microbes, bacteria. Like salt, over time corrosion can occur with a freshwater outboard. Lastly, if you've got the time and are comfortable removing head bolts, open the port bank and check the passages. Hour labor at most.

 
I’m taking temps with a laser temp gun. Thanks for the reply, yes I’ve read that there is a difference between cylinders or banks of cylinders but this just seems like a bigger difference that I noticed in all the years that I've owned this motor. When I get some gaskets I’ll take your suggestion and open it up to see if there is any restriction in there. My thought process is there is something wrong on the starboard side that its not coming up to temp. Also I've never checked the temps on the water with a laser temp gun while running it at higher RPM and under load to see what kind of difference there is, only felt by hand and could tell there was a difference. My main concern is I don’t want to hurt this motor after the great service its given me all these years.
 
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