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Cooling Problems Mercury 115

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Metallife89

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I have a 1989 Mercury 115 horse 2-stroke outboard, serial Oc106309. Boat is new to me, only two times out. First time out, alarm goes off for the first five or ten minutes and then is off for the rest of the day. Being new to the boating scene I thought it might me some sort of warm up indicator. The next time out the alarm stayed on for most of the day, being on 10 minutes then of for 10 and on for 5...you get the picture. So after browsing around noticed the pisser was not working on the back of the motor and the was a cooling issue. I replaced the impeller thinking for sure my problems would be solved, and they were in part. My alarm never came back on, but there's still no water coming out, only air.

Another interesting thing is that the first time I went out I topped out at about 27 mph on my little deck boat. The second time I couldn't make it past 20-21. I talked to the previous owner and he said it used to run about 35 topped out.

Any help would be greatly appreciated guys. Thanks!
 
At this stage I would start with a compression check,you may have overheated,hope not.
The tell tale may have a bit of dirt in it,poke it with a bit of wire/weed eater string or blow some air through it.
 
I took the hose off the side of the block and blew through it. It was clear.i blew into the fitting itself on the block and there is more resistance but can still be blown through.

When I have the hose and ears hooked up but there is no water coming out of the port, is there supposed to be water coming out at an idle or does it have to be throttled up?
 
Water should come out at idle.Did you allow the engine to reach normal working temperature and the 'stat to open? May take a minute or two
You could pull the 'stat,run it for a minute to see if water reaches the 'stat housing and check the 'stat is working,dip it in boiling water to see if it opens.
 
I read somewhere that the vanes in the new impeller have to be bent in the right direction when pressed into the housing - don't know if that still applies. But, haventaclue has the right ideas.
 
They will go the way they need to go once it's started, are you sure the impeller is working and key didn't slip? Watertube mate up with it's counterpart in midsection? If you've been running it a lot as your describing and no waterflow, compression check is in need before spending anymore on the alarm issue.
 
What the fellas above said; one last tip - never turnover/run the engine without water; the impeller will burn out if you do and then not pump cooling water thru the block.
 
Pulled the lowers off and double checked the impeller. Everything seems to be in order. Pulled the cover off the head and everything accessible is clear and I ran trimmer string anywhere I can. Thermostat is working.

Two things though....looking at my block there is something with a wire running to it completely melted next to the spark plugs. Looked at a diagram and it says it's the temperature sender. Could this be the cause of my alarm and no water issue?

Also when I was looking at the diagram I noticed there is supposed to be a cylindrical rubber seal on top of the pump housing that wasn't there when I pulled my motor apart. Haven't been home yet but unless its smashed in the end of the pipe inside, is this my water issue?
 
I think you are getting close: melted wire; rubber seal missing from pump housing which I think the water tube seats into; is there a seal at the other end of the water pipe?
 
I'm not sure if the seal is stuck in the pipe. I will have to see when I get home. It definitely wasn't one the pump housing when I pulled the lowers off.
 
Temp sender is more than likely the alarm issue. If it's not responding vac advance won't shut off once operating temp is reached and can cause the rough running.

One to add to the tip of the day, don't run your 90's era tracker/merc outboard after jumping it, on a bad battery or no battery without unhooking the stator charge leads. It will fry everything lol. $125 battery could have saved $1250 parts list...
 
So I was not missing the seal top of the pump housing. It was on the pipe.

Put it together and ran it. Had water coming out of the tell tale after I engaged the prop. Stayed going when I put it in neutral. Checked it again today, two days later and can't get water to piss out. There is a lot of water coming out of the center of the prop. Is that normal? Have a new temp sender ordered. Any ideas?

Thanks again guys!
 
So I ended up changing the impeller and temp sender. Checked thermostat function. Changing the impeller and sender for the most part fixed my issues. HOWEVER, it took running it in a barrel to piss properly. Ears and hose weren't cutting it.*

Now I have to make a post about my issue this weekend of the motor not going past 2000 rpm.
 
So, for this problem, you changed the impeller again and that worked better - that is surprising; if you don't mind, did you compare the newest with the previous to see differences?; did you use OE Merc replacement parts?; did you replace only the impeller or the impeller and its housing? Just curious.
 
RickM46 said:
So, for this problem, you changed the impeller again and that worked better - that is surprising; if you don't mind, did you compare the newest with the previous to see differences?; did you use OE Merc replacement parts?; did you replace only the impeller or the impeller and its housing? Just curious.
Click to expand...

Sorry, just to clarify, I only put one new impeller in. A quicksilver one. That fixed my water/overheat issues...I just had to use a barrel instead of a hose to see the results. To fix my alarm issue i changed the temp sender.
 
Cleaned all 4 carbs and replaced both fuel filters. Took it to the lake where it seemed to be running normal but ended up getting stuck at 1500 rpm later in the day and was running very rough.

Trailered it and pulled the plugs, all 4 which were fouled with oil residue. Cleaned them with some carb cleaner and a rag and went back out. Was immediately capped at 3000 rpm with the throttle wide open, so better but still garbage. Called it a day after that.

Any ideas?
 
Plugs fowled with oil is a clue - maybe not burning fuel well? Have you done a compression test, a spark test, checked timing?
 
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