1995 Johnson 115 hp overheat alarm

[Randall in wilmington]

At low speeds and when up on plane my engine runs fine. When I go to full throttle , after a while one or two minutes I get an overheat alarm. I usually go to idle quickly and wait and it apparantly cools off and the alarm stops. A mechanic looked at it and said the water pump is fine.
I removed the thermostat sometime back because I was told in they are not that important if I only run in southern NC warmer waters and it's just one more thing to get clogged up in the saltwater.
Looking at the motor from inside the boat it is only the starboard side that overheats. I was able to proove this by several tests including an infa-red temp probe that shows me whwere the heat is. The mechanic gave me a head gasket and said to look under the head for two little rubber things that divert the water properly. I looked at them and they don't look all that bad . Should I order 2 new ones? Put the head back on without them as an experiment ? Are they critical? Should I try to back flush the system with the head off to see if there is a blockage? Can anyone chime in on this. One mechanic said the guy that told me this was grabbing for straws when he suggested these deflectors are part of the problem. Can someone enlighten Randall in wilmington NC

 

[jonesg]

Re: 1995 Johnson 115 hp overheat alarm

They are important, I wouldn't remove them and I would try backflushing.
Hit any sandbanks lately?

 

[Randall in wilmington]

Re: 1995 Johnson 115 hp overheat alarm

I do operate in tidal creeks and I have run aground a few times. Maybe there is a blockage preventing flow. Regaurdless , it is really great to get feedback from you and others.

 

[emdsapmgr]

Re: 1995 Johnson 115 hp overheat alarm

Bad thermostats cause overheats at idle. When on plane, the pressure relief valves should open and flood the block with extra cooling water. You need to check to be sure the overheat side pressure relief valve is functioning properly. If it was ever overheated, they can deform and stick-restricting water flow. If the valves are functioning properly, I'd look for a water restriction in the powerhead. An easy place to start is the cylinder head cover. If you find any debris in the head cover area, you should pull the head and check the passages in the block. I'd run with thermostats. Engines that don't run stats tend to run colder and that promotes poor combustion and carbon around the rings.

 

[ezeke]

Re: 1995 Johnson 115 hp overheat alarm

One other concern is the water intake screen on the gearcase; it must be in place and in good condition to prevent particles from flowing into the cooling system or particles will block the passages mentioned above. The screens also allow the proper water flow.

BTW, You may also want to check that the water intake is indeed in the water when you are at WOT if you have your motor trimmed too high or set up too high.

 

[Randall in wilmington]

Re: 1995 Johnson 115 hp overheat alarm

I really want to thank all of the folks who are being so helpful. Can I figure out how to trouble shoot the relieif valves by looking at a nomenclature on line or is it always best to by the OMC repair manual for any motor I own

 

[XTCNRED]

Re: 1995 Johnson 115 hp overheat alarm

Randall, keep me posted on your trouble shoot progress. I have a 94 115hp doing the exact same thing and it has new water pump, impeller and thermostat. My next move is check the fuel primer bulb. After that, the overheat side pressure valve - can someone tell me how to do this? I will post my updates as well.

 

[emdsapmgr]

Re: 1995 Johnson 115 hp overheat alarm

A factory manual is the only one to get. Contact Ken Cook co., in Milwaukee. They are the original publisher and will sent you an original model-specific one for your engine.

 

[XTCNRED]

Re: 1995 Johnson 115 hp overheat alarm

Infrared temp gun shows cylinder head temperatures at 190 degrees with muffs on. The factory service manual pointed me looking at the water deflectors located behind the cylinder heads. There are 4 and can best be described as a one inch long piece of rubber shaped like straw. The first two on the starboard side cylinder head were completely corroded shut and oblong in shape rather than round. Working on the other side this week-end and will keep you posted.

 

[jmerchant]

Re: 1995 Johnson 115 hp overheat alarm

Mine is doing the same thing, I have a 1990 115 johnson, i can run it at 3/4 throttle all day long but when i go to fullt throttle it will over heat within a minute or 2, it looks like it loses its prime and quits pumping water. Did you figure out what your problem was ? Im frustrated ready for a new boat!! i have spent 800 bucks with the local yocal part changer here. Thanks Jason

 

[emdsapmgr]

Re: 1995 Johnson 115 hp overheat alarm

The overheat horn will come on at 212 and shut back off at 175. 190 is too hot. I'd replace all 4 of the water diverters in the powerhead. Water has to flow in a circular movement around each cyl in order to cool properly. Follow the service manual diagram for their exact placement when installing. It should idle around 145 to 155 degrees.