94' OMC 115 loses power after first 5 minutes

[CrazyJ]

After the first 5 minutes of the day cruising on full throttle (which is needed to even plane on a bw rage 15 jet), my engine revs drop from around 5200 to 4700 RPM. After the initial drop it seems like every 2 minutes or so I get the short boost of power backup to 5200 RPM but then quickly drops to 4700 again. Unfortunately with this little power I can't even plane out with 4-5 people in the boat!<br /><br />I am thinking it is a cold/warm temperature/thermostat issue. A couple more things that might help:<br /><br />-- yesterday after we had cut the engine and been sitting around for 30-40 minutes, I turned the key and got the continuous overheating horn, when the engine was obviously not overheated. After turning the key back and forth I got it to operate normally. Weird! We quickly motored back to launch ramp.<br /><br />-- I think the "temperature switch" is located around the heads on the starboard side of the engine. Coming out of the harness there is a orange wire that goes into the head. There is also a black wire coming out of the harness that has a connector, but isn't connected! Is there supposed to be another wire coming out of the head for this to connect to?<br /><br />Anyone have any ideas or suggestions on how to attack this one? Thanks in advance!

 

[Solittle]

Re: 94' OMC 115 loses power after first 5 minutes

This post is rather puzzeling. You indicate that "every 2 minutes or so I get the short boost of power backup to 5200 RPM but then quickly drops to 4700 again." You did not indicate that the horn or buzzer was going off as this happened. Normally when a motor is getting real hot it will slow down as the metal heats up and it starts to bind. It won't operate as you describe. Yet later in your post you talk about the horn going off?? <br /><br />I don't know your 94 as I have a couple of 87s. On mine the heat sensor is mounted in the heads (both) and has a brown wire comming out of it. The brown wire is fairly short and runs into a connector. To test the sensor disconnect the connector and ground the wire going to the front of the boat. The horn should go off.<br /><br />If you have not changed the impeller or thermostats in a couple of years, now ir the time. I would not run the motor very much until you are sure that the problem is solved.

 

[CrazyJ]

Re: 94' OMC 115 loses power after first 5 minutes

Sorry to be confusing! I don't think the engine is actually overheating. It does not seem excessively hot and I do not smell any type of oil burning.<br /><br />The overheating horn has never sounded during operation. It sounded as I turned the ignition key after we had been powered down for quite a while. If it is indicating overheating, and not another sort of sensor issue, it is obviously malfunctioning.<br /><br />I am going to attempt to test the thermostats like you said. And maybe adjust the impeller, although it looks like it is in great shape from my novice eye.<br /><br />Just for reference, are the thermostats and "temperature switch" (as it is refered to in the manual) the same thing?<br /><br />Thanks!

 

[Solittle]

Re: 94' OMC 115 loses power after first 5 minutes

There is no adjustment for the impeller. If you do not know how long it has been since it was replaced - now is the time. A visual inspection will not tell you much.<br /><br />I don't know what the temperature switch is. There is a sending unit in each head for the guage. The thermostats control the water flow and open or close based on water temp.

 

[CrazyJ]

Re: 94' OMC 115 loses power after first 5 minutes

Well the thermostats obviously can't immediately control engine speed, can they?<br /><br />It seems it is being regulated by something electrical the way it adjusts so quickly. Do the temperature switches strictly give warnings or do they adjust engine speed?

 

[Sherman]

Re: 94' OMC 115 loses power after first 5 minutes

I would make sure your fuel tank is vent is not plugged.