Engine overheats and wont stay on at idle

[RyanM3]

Finally got the boat out on the water. Idling really low(rpm guage doesn't work). However, stays on. When i run it for about 5 minutes out on the water with half throttle, it overheats.Temp guage stays in middle then quickly jumps. Where do I begin? 1986 3.0l mercruiser gm 4cyl

Noticed exhaust bellow is cracked. Could this be the problem?

 

[SSTKO81]

Re: Engine overheats and wont stay on at idle

Most common culprits are seasonal parts. Start with your thermostat, cause its cheap and easy, then check out the water impeller in the lower unit. OOH, And yeah, that cracked exhaust bellow is and issue. Change it out ASAP.

 

[Bondo]

Re: Engine overheats and wont stay on at idle

Finally got the boat out on the water. Idling really low(rpm guage doesn't work). However, stays on. When i run it for about 5 minutes out on the water with half throttle, it overheats.Temp guage stays in middle then quickly jumps. Where do I begin? 1986 3.0l mercruiser gm 4cyl

Noticed exhaust bellow is cracked. Could this be the problem?

Ayuh,... It should be idlin' at 650/ 700 rpms, in the water, in gear...
(Fix yer tach)

In ANY Overheat situation, the very 1st thing to do is change out the Impeller,...
'n the pump body if it needs it, scoring ruins 'em...

Which exhaust bellow, Outside, or Inside the boat,..??
Inside, it'll sink yer boat...
Outside is more for noise suppression...

 

[RyanM3]

Re: Engine overheats and wont stay on at idle

How do i go about fixing the tachometer, changing the impeller and pump body?..

Also the exhaust bellow is cracked on the outside of the boat. So i take this isn't of much concern. Just makes the boat louder.

I notice when i go into idle from neutral throttle that the oil pressure goes from 40(middle) to 0.. Do i need to adjust the idle mixture on the carb?