1974 mercruiser 120hp overheating

[ATAPIA2002]

hello all
i recently purchased a 1974 mercruiser 120hp and when i took it out in the water it overheats almost immediately, the first thing that pops into my head is that the pump or impeller are bad>> can somebody give me their opinion on what the problem may be. does it have an impeller and a separate water pump? where are these items located on the boat i am mechanically knowledgable on automobiles but boats are a different story help please

 

[Bondo]

Re: 1974 mercruiser 120hp overheating

or impeller are bad>>

Ayuh,... I agree, that's Always the 1st place to look with an Overheat condition...
It's mounted in the outdrive, at the top of the Lower unit, under the upper unit...

 

[ATAPIA2002]

Re: 1974 mercruiser 120hp overheating

This is the same location for the inboard motor correct?

 

[Bondo]

Re: 1974 mercruiser 120hp overheating

This is the same location for the inboard motor correct?

i recently purchased a 1974 mercruiser 120hp

Ayuh,... I'm Assuming you have a 120hp motor, 'n mercruiser Outdrive bolted to it, 'n Not an Inboard...

If so, the raw water pump, the 1 with the rubber Impeller is mounted In the outdrive as I stated...

If you have a 120hp motor, with a transmission, hooked to an Inboard,...
It's hard to say Where the raw water pump is...

 

[Bluestream]

Re: 1974 mercruiser 120hp overheating

Also, check your water supply hose on the outdrive, they crack with age and cause loss of water pressure to engine

 

[ATAPIA2002]

Re: 1974 mercruiser 120hp overheating

so i changed out the water impeller and took the boat out and it over heated a little less what else should i be looking for or try before taking to a shop?

 

[fishrdan]

Re: 1974 mercruiser 120hp overheating

Did you just change the impeller or the whole water pump? Were there any pieces of the old impeller missing, if so did you find the missing pieces? Missing pieces could cause a restriction.

Thermostat?

Maybe someone used an automotive water pump on the engine and the steel impeller rusted away?

 

[ATAPIA2002]

Re: 1974 mercruiser 120hp overheating

I will check for restrictions and the engines waterpump the impeller was in pieces when it came out so the engine is like a car engine huh? I can work on that!! I will look into it and keep you posted thank u forum...

 

[fishrdan]

Re: 1974 mercruiser 120hp overheating

Hunt down all the missing impeller pieces.

so the engine is like a car engine huh?

The 2.5L 153CI engine was used in the 68 Chevy II and other small vehicles way back,,, well I should say the non-marinized version was. Some (few) parts of your engine are the same as automotive, many of the parts need to be marine spec; ignition, starter, alternator, waterpump, fuel pump, carb, etc, etc...

......don't run down to Autozone to get replacement parts for your engine.