2.5 L Mercruiser over heating

[GasCan II]

I am working on a 1989 2.5L raw water cooled MerCruiser.
1. New thermostat
2. checked circulating pump
3. new impeller in drive, and verified it is pumping
4. cleaned exhaust manifold and checked with 65 psi. water pressure.
5.cleaned riser
6.installed new exhaust flapper
This engine still over heats but, not all the time and only at 3000 rpms or more.
Any Ideas ? Did I over look anything ?
Thanks for any help !

 

[Bondo]

I am working on a 1989 2.5L raw water cooled MerCruiser.
1. New thermostat
2. checked circulating pump
3. new impeller in drive, and verified it is pumping
4. cleaned exhaust manifold and checked with 65 psi. water pressure.
5.cleaned riser
6.installed new exhaust flapper
This engine still over heats but, not all the time and only at 3000 rpms or more.
Any Ideas ? Did I over look anything ?
Thanks for any help !

Ayuh,.... Is this a sweetwater boat, or is it run in the brine,..??

 

[GasCan II]

Bondo;
This is a raw water cooled boat run in fresh (river) water. I removed the exhaust manifold and blocked off at the riser flange and put 65 psi. water pressure on it for a good hour and no leaks.Checked for old exhaust flapper in exhaust pipe and found none.Also over heats at times even without thermostat.
Thanks.

 

[Bt Doctur]

you really cant clean the elbows and that's where the cause may be.The second area for hi speed overheats is the water pump base.It warps and sucks exaust instead of water

 

[GasCan II]

Thanks for the ideas.I will look into the pump base.
This one really got me .

Thanks again !

 

[achris]

Exhaust elbow.

Or water pocket cover. Try putting a clear section of hose in the line between the transom plate inlet and the thermostat housing. If you see bubbles, you found you're problem.

 

[Bt Doctur]

water pocket is on the pressure side not the suction side ,achris

 

[achris]

water pocket is on the pressure side not the suction side ,achris

Yep, I know that... Here's a screed I wrote a couple of years ago. Have a read and you'll understand how exhaust gas can get into the 'pressure side'...

http://forums.iboats.com/showthread.php?t=556903&p=3825409&viewfull=1#post3825409

 

[s.hadley81]

I just figured I'd update the post my dad is op(gascan II) we were working on my boat and after installing a clear hose we found air bubbles and sometimes a loss of flow I pulled the drive and found the water pocket leaking like crazy I plugged one side and poured water in and it leaked right out so i guess I get tackle replacing the water pocket gasket it looks like someone replaced it before as the bolts are not stainless but luckily I have another drive so I'm gonna put that one on and tackle the water pocket at my leisure thanks for all the help