1990 Ebbtide 305 Merc overheating

Hi all, new to the forums here. I recently acquired a 90 ebbtide with a 305 alpha one. Plenty of automotive mechanical abilities here and a little on a previous boat or two I've owned years ago.

Impeller looks good, seems to have decent water flow when hooked to the hose. Top water hoses are cold, ones on bottom get hot. The person I got it from had it in the shop for overheating. They replaced the impeller, thermostat, gauge, and water pump and still overheats. The boat is in immaculate condition and worth the time and effort it will take to correct this issue, just not sure where to go from there with it.

I browsed a couple of posts before registering and saw where some were talking about the manifolds possibly being clogged and/or the shaft or bearing out the back needing greased. If anyone has experienced this before I could use all the advice I could get.

Thanks,

HydraulicBanana said:

Hi all, new to the forums here. I recently acquired a 90 ebbtide with a 305 alpha one. Plenty of automotive mechanical abilities here and a little on a previous boat or two I've owned years ago.

Impeller looks good, seems to have decent water flow when hooked to the hose. Top water hoses are cold, ones on bottom get hot. The person I got it from had it in the shop for overheating. They replaced the impeller, thermostat, gauge, and water pump and still overheats. The boat is in immaculate condition and worth the time and effort it will take to correct this issue, just not sure where to go from there with it.

I browsed a couple of posts before registering and saw where some were talking about the manifolds possibly being clogged and/or the shaft or bearing out the back needing greased. If anyone has experienced this before I could use all the advice I could get.

Thanks,

Click to expand...

Assuming that this engine is Raw Water Cooled:

After the seawater has removed engine heat, the "spent" seawater enters the exhaust manifolds, and then exits through "transfer" ports (aka water ports) and into the elbows...... where it then goes on out with the exhaust gasses.
These "transfer" ports can and will become restricted with rust scale.
The rust build up will restrict spent seawater flow causing over-heating.

This is most likely what you were reading about.


Suggestion:
Warm engine, crack the bolts loose and let it cool back down.
Remove the elbows so that you can examine the transfer ports.

They may look like these below.
In many cases they can be successfully cleaned up.




You will occasionally see Spacers/Risers being used.
These too can become rusted and restrictive.




Bottom line.... if the seawater cannot leave the cooling system effectively and with no restrictions, the result will be over-heating.





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