Intermittent overheat 98 Johnson 115 (J115ELECM)

[midsized johnson]

My outoboard has been overheating only at higher end RPM's but cools off at idle. As long as I don't run wide open, it doesn't overheat. That said, I'm not getting full my full top-end RPM's unless I trim the motor out to the point that it wants to porpoise. I'm thinking the problems are related. I recently replaced the powerpack, optic sensor and timing wheel. It ran good at first (still runs good except for top end), but yesterday I couldn't get upper end RPM's as noted earlier.
Is it possible that I'm slightly out of time causing a bit of lug in the motor? I haven't ruled out fuel delivery issues as it may be a lean condition in one or more carbs.
Any insight is appreciated.

 

[boobie]

Do a cylinder drop test on it to see if it's running on all the cylinders. When's the last time the water pump was serviced ??

 

[midsized johnson]

Are you saying pull a spark plug wire, or block the carbs individually? I did the latter and all were pulling hard and seemed to kill the engine equally. I'm not sure on the terminology, but I noticed that the fuel spray in the carb's throttle body was not equal on all four cylinders. I put my hand over each one and revved the motor. After doing this, they all had a similar spray of fuel. If that's a likely culprit, then I'll overhaul the carbs.
This makes me feel like maybe I had a lean condition on my starboard side cylinders which could cause the overheating at upper end.
As for the water pump, I think it's fine as I've got around 20 lbs of pressure while running at 4500 rpm.

 

[boobie]

Were you doing this testing in the lake or on a flusher ??

 

[midsized johnson]

Was in the driveway, but I see your point. Wanted to go run it after I messed with it, but too cold yesterday!

 

[Bosunsmate]

hows the sparkplug colours, any different?

 

[boobie]

A good way to check the spray in the carbs is to take the air box cover off, get a timing light and then run the motor at WOT on the lake. Put the timing light on each cylinder and then look into the carb throat for that cylinder and check the spray pattern. I have found carb problems using this method.

 

[midsized johnson]

Have not had a chance to do any more to the motor. If I need to clean these carbs, what are the things I need to watch out for? I'm really hesitant as I hear the plastic carbs have a tendency to warp.
I've been wondering if I have a bad cylinder head gasket, but if the plugs aren't clean, that should rule that out, or does it?

 

[Chris1956]

Gee, I would change the waterpump impeller and inspect/replace the thermostats, before blaming the head gasket. I have the 150HPV6 version of that motor. She pegs my 30PSI water pressure gauge at cruising speed.

Your motor probably has O-rings for the cylinder head gasket.

 

[midsized johnson]

Gee, I would change the waterpump impeller and inspect/replace the thermostats, before blaming the head gasket. I have the 150HPV6 version of that motor. She pegs my 30PSI water pressure gauge at cruising speed.

Your motor probably has O-rings for the cylinder head gasket.

I'm not "blaming the head gasket," just wondering out loud as a friend with experience with these outboards mentioned that possibility.
Maybe I'm wrong, but I would think that if my impeller/water pump was bad, I'd be overheating all the time, not just at upper end RPM's.
The thermostats are fine, water pressure is where it's been since the last impeller change, so for now at least, since the motor isn't really running 100%, I'm pretty much thinking the problem is either caused by a lean condition in the carbs or a possible leak in the head gasket as my buddy suggested.

 

[boobie]

Your motor has O-rings, not head gaskets. Rarely have problems with them.

 

[midsized johnson]

Your motor has O-rings, not head gaskets. Rarely have problems with them.

Good to know. Thanks!

 

[Brock O]

Have a read of the below file path, this was posted on my topic....."O" compression, giving what I've just been through and the intermittent alarms I was having even after new thermo's and water pump, id pull the heads off and check you water galleys and diverter's. Small job really.....or stay away from WOT for long periods.

http://forums.iboats.com/forum/engin...ng-a-tell-tale

I'm far from a mechanic but that's my thoughts!

Brock

 

[midsized johnson]

UPDATE:
I took out the thermostats and ground off the metal caps at the ends and reinstalled and added Yamaha's Ring Free to the fuel tank. Next time out, ran like a champ. I actually saw it "clean up" as I was running at about 4500 rpms and it edged up to around 4900 without touching anything. I really don't know if I fixed anything, but it's running great (for now, it's an outboard, so who knows how long that will last???).
Anyway, it's got good waterflow, hasn't overheated, and is running great.

 

[Faztbullet]

It now maybe running to cold and you run risk of piston seizure!!! Cutting tops of t-stats off didn't fix anything as that heads not getting to temp, you now have 2 problems....

 

[midsized johnson]

"It now maybe running to cold and you run risk of piston seizure!!! Cutting tops of t-stats off didn't fix anything as that heads not getting to temp, you now have 2 problems.... "

Definitely a concern, but running in saltwater, the first set of thermo's I put in had locked up and the new ones were suspect. I needed to eliminate the thermostat as a possible cause, because I wanted to see if it would run at upper end without overheating. I know it's not getting up to optimum running temp, but the takeaway is that it won't burn up because of a seized thermostat.

 

[racerone]

Are you saying that you run the motor to 4500 / 5000 RPM in the driveway and testing in neutral ???

 

[Faztbullet]

Being in salt water you need to use the newer Ficht saltshaker style t-stat housings and install the S/S t-stats and also run it in a tank of salt away as you have a restriction in water flow..

 

[midsized johnson]

"Are you saying that you run the motor to 4500 / 5000 RPM in the driveway and testing in neutral ??? "
Haha! Good question! I guess I come off sounding dumber than I thought. Nope, not doing that.

 

[midsized johnson]

Being in salt water you need to use the newer Ficht saltshaker style t-stat housings and install the S/S t-stats and also run it in a tank of salt away as you have a restriction in water flow..

I suppose that was what is in there. The old ones quit rattling, so I replaced them. The new ones still had the overheat issue at the same RPM's which is why I took the ends off. Still restricting flow, but definitely not getting as hot as it should for preventing carbon buildup.