mercruiser 120 overheating at speed

[johnguz76]

Have a older bayliner{1968} if you saw the boat it looks showroom new.It has a 4cly mercruiser chevy 2 engine in it.Impleller water pump theromastat hoses and everything assosiated with cooling have been replaced.Outdrive has been serviced and the motor has great compression given it;s age.Problem is that the temp guage goes up into the red when cruising at speed.I can run all day at lower speed with no problems.Just at 3,000 rpm and above i encounter the overheating issue.Can anyone give me some solutions to look at please.I;m stumped here.I;m told by a friend of mine to check a heat riser but i have no clue as to what that is.

 

[tommays]

Re: mercruiser 120 overheating at speed

you friend sounds right he is talking about the manifold and riser as they become old they clog and restrict water flow<br /><br /><br />

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<br /><br /><br />if there cloged the repiar is to replace them<br /><br /><br />tommays

 

[achris]

Re: mercruiser 120 overheating at speed

The elbow is item #14 in the diagram......<br /><br />

 

[johnguz76]

Re: mercruiser 120 overheating at speed

Ok i found it.I will remove this part to check it out.Why would the boat run at normal temps at lower speed though..

 

[tommays]

Re: mercruiser 120 overheating at speed

it doesent require as much water flow because the engine is not working as hard<br /><br />tommays