1999 johnson 150 acting up

so i just got my boat up and running again, starts up first try idles perfect and everything, when i started idling out the water temp light came on and had a constant beep for about 15 seconds, then stopped, light stayed on for about another minute or two, then the water temp light just turned off, the engine gets to about 2000 rpms, and starts rumbling really hard and it wont pick up no more speed, i had water pump changed about 2 years ago, but we have only used it for a total of about 30 hours in those two years, i have talked to a couple people and they say the rumbling is because the engine is putting itself in safe mode. so if anyone could help, i would greatly appreiciate it, so the boat mechanic wont be able to screw me!!!

Re: 1999 johnson 150 acting up

any help, would be helpful!!! thank you

Re: 1999 johnson 150 acting up

A cheap infra red thermometer will show whether its overheating and where.
Yeh safe mode will shut one bank down and cause rough running until the ignition is re-set. Could be thermostats need changing or needs a good flush, de-salt.

Re: 1999 johnson 150 acting up

If the motor is not overheating, the temp sensor could be bad. There are tests for them. The sensors should close at heat reaches 190* or so.