Merc 1 I/O Overheating

[NYBOATGUY]

Have a 1974 Merc I/O with a 1985 Merc 260 which starts to overheat every now and then with no appearent pattern. I can shut down, wait ten minutes, restart and temp starts dropping. Also, other day when temp starting rising I shifted into neutral, then back into forward and temp started dropping. Boat is in salt water with open colling system. Also boat was stored for 4 years with no use. The impeller was replaces 4 yeasrs ago but the boat was stored since then. Any Help???

 

[12Footer]

Re: Merc 1 I/O Overheating

Look for barnacles clogging the intake, and even the intake hose. Put a new tstat in. They have a tendancy to stick.<br />But make sure you get the marine tstat replacement. One from the auto store wont last 3 days (sometimes).

 

[cham22]

Re: Merc 1 I/O Overheating

Smart suggestion on the thermostat..Marine thermostats are made to open at higher temps so an auto one will overheat the motor. Know from personal experience :0

 

[MarkC]

Re: Merc 1 I/O Overheating

Don't you mean at lower temps? Marine engines run much cooler than auto ones. Even my 120 Chevy (Mercruiser) is supposed to run cool enough to put your hand on it (unlike when it's in a car).

 

[NYBOATGUY]

Re: Merc 1 I/O Overheating

12 footer you are on the money, when I pulled the boat out the entire outdrive was loaded with baracles. Replaced the lower pump while it was out since it was several yrs and now she runs at 120 degrees all day long!!!!!!!!

 

[Chum Slick]

Re: Merc 1 I/O Overheating

What outdrive do you have. I'm not familiar with OMC drives but the Mercruiser I/Os have a lower water pump impeller in the lower unit and also a water pump in the engine. Both need to be checked and/or replaced routinely.<br /><br />Bait in the slick....