Merc 260 I/O overheat

[Hikerboater]

1986 Mercruiser 260 Alpha 1 Chevy 5.7l is overheating.
Have replaced:
-Impeller and outdrive pump assembly (twice)
-thermostat
-thermostat housing
-all out drive boots
-engine circulating pump

have back flushed out all hoses, inc the power sterring fluid cooler.

Runs at about 145? at 1500rpm
When on plane, temp rockets up to near 200? within 10 sec.
Have spent $1000, no resolution

Suggested mechanic recheck the outdrive pump to see if it's sucking exhaust, perhaps by attaching clear raw water hose.

 

[Hikerboater]

Re: Merc 260 I/O overheat

Also... this is a freshwater boat, always trailered, occassional use.

 

[seaphase]

Re: Merc 260 I/O overheat

Check to make sure the water hose on the outdrive is not kinking when you have the drive in the full down position.

 

[Hikerboater]

Re: Merc 260 I/O overheat

My mechanic thinks he found the problem with this overheating. His assistant put a waterpump assbly gasket in wrong allowing the impeller to suck exhaust and flow to be restricted. Stay tuned to see if this IS the fix.

 

[Hikerboater]

Re: Merc 260 I/O overheat

Amazing. The mechanic's assistant put a water pump gasket in wrong and that was the difference. It's fixed!! Can't believe how much difference on simple gasket can make.

 

[VeeSporty]

Re: Merc 260 I/O overheat

Mr. Hikerboater,
I am having a problem identical to what you've described - engine temp is fine until I hit about 2800 rpm and then the temp starts climbing. Please post a little more detail about this gasket - sits between what and what, part number, ordered from who?
Thanks,
VeeSporty

 

[dubs283]

Re: Merc 260 I/O overheat

always replace the base assy and gasket on alpha one, r/mr, I drives

be sure to clean the gearcase where the gasket goes between the base and case - use perfect seal to ensure good sealing

 

[Hikerboater]

Re: Merc 260 I/O overheat

I don't know what gasket was improperly installed but he said it was put in 'upside down' and caused the impeller to suck exhaust and not water.

Now the temp stays right around 145? on plane, 130? at idle which is about normal.