Johnson 115hp hot engine light and alarm comes on at full throttle.

We just purchased a used 02 Wellcraft. Test run it ran fine. First day we got it we took it out hit full throttle and the hot engine alarm and light went on. We went back to land looked over engine changed out spark plugs those were bad (not that we thought that was issue). But didn't seen any other signs of trouble. Took boat out today ran great unless we do full throttle once again hot engine light and alarm. Drove the boat before that for hours and no issues but if we try full throttle alarm and hot engine.

What are we looking at for possible issues?

Thank You to anyone that answers. We just bought this boat we love this boat but kinda stressed at the moment over this.

Re: Johnson 115hp hot engine light and alarm comes on at full throttle.

Have you checked the water pump to see what kind of shape it is in?

Re: Johnson 115hp hot engine light and alarm comes on at full throttle.

If you do not know when the water pump was changed, you're overdue.

Re: Johnson 115hp hot engine light and alarm comes on at full throttle.

Daviet said:

Have you checked the water pump to see what kind of shape it is in?

Click to expand...

We didn't check that yet. Thank You for the replies. We want to take boat out tomorrow is it safe to do so and just not go full throttle?

Re: Johnson 115hp hot engine light and alarm comes on at full throttle.

Thats a decision for you to make for sure....its about chance and consequence unfortunately. Your able to tell when it overtemps, by guage or alarm which is good. But what if its a blockage that moves or this gets worse? By the time it alerts you to overtemp--Its pretty hot. Do you want to chance internal damage? It gets pretty expensive and time consuming. Your engine is telling you something, may be a good idea to listen.

Re: Johnson 115hp hot engine light and alarm comes on at full throttle.

I had a problem like this that I chased all over. Finally found out that the problem was my fuel filter/water seperator!! Yea! It would not allow enough fuel through it at high RPM and the engine would start to run lean and hot! Changed out the filter/seperator and it has run great since.

Re: Johnson 115hp hot engine light and alarm comes on at full throttle.

Thanks for all the advice everyone. After everything we read and heard from other people..We did take it out next day and had to get towed in (stupid move). I ordered new thermostats and a water pump kit figuring that would be cheap easy and way to go from everything I've heard and read. Parts finally came this weekend. We changed the thermostats first because thats an easy fix they are in a hard plastic housing so hard to tell if they were damaged but I'm sure they probably were.

Next was the water pump. The impeller was in pieces. Replaced that with a water pump kit and drove the boat like crazy today. We have water pressure, it's shooting out, it's not hot, and no engine alarms.

Thank You so much to everyone that responded. I was in panic mode we just bought this boat and we did test drive it and no issues. Then first day we take it out alarm. We really were thinking the whole here we go BUST OUT ANOTHER THOUSAND. Was cheap to fix and I helped him (well I researched how to replace them..pat on my back). Now we now how to do this in future.

Thank You again everyone.