9.8 merc hot tell tale

[stevenj]

80/81 mercury 9.8, serial 5794858 , replaced impeller a few years back after
figuring i had an issue with overheat lack of tell tale stream, at that time
I remember finding pieces of the disintegrated impeller in the water tube,was
able to clear tube put back together and run in a barrel. noted that tell tale
stream was flowing intermittently, with t/stat removed. seemed to me to have exhaust gasses mixed in with the stream and getting very warm to the touch (water from tell tale) my hand are very rough and handle hot very well.

Put away and forgot about it .then last season pulled out, started , and was reminded of the issue stated above. put away again and began playing
with a 57 big twin 35, installing a helm and steering components in my
mirro-craft, turned out well to me.

fast forward to today cold dreary rainy and bored and dreaming of getting out fishing,remembered flow issue.


b4 putting away last year, i started with the stat cover off and felt what i feel was exhaust gas coming from the center port of casting hole , time
to order a manual and tear into this.

someone told me that there might be baffles of some sort in the exhaust cover that might be distorted. does this sound possible?

thanks for any and all thoughts.
sorry if i rambled a bit on this
steve

 

[woody66912]

Re: 9.8 merc hot tell tale

this sounds like the classic case of old impeller chunks under the power head.under the power head is also a rubber seal that seals the water tube.if it got really hot this seal will melt and will restrict water flow.in this case you will have to remove the power head.I'm 90% sure this is the case.

 

[emckelvy]

Re: 9.8 merc hot tell tale

Woody, my very thoughts!

Before pulling the powerhead, it might be worthwhile to take off the cyl block water jacket cover (the back cover on the block, over the spark plug holes), and inspect for debris/silt buildup. This can also hamper circulation.

It might be productive to blow air up the water tube or even hook up a water source to the tube, and flush out of the open water jacket. At any rate it'll be a real good indication of water flow (it should literally gush out of there), and if you're not getting it, very likely you've got 'stray' rubber chunks or an issue with the water tube rubber grommet/plastic washer.

HTH & let us know what you find...........ed

 

[stevenj]

Re: 9.8 merc hot tell tale

Thanks guys, I have pulled the cylinder head water jacket plate, do not see
anything in there that would indicate blockage. also pulled exhaust cover and
baffle plate. could tell that gaskets were all intact.will drop lower unit in next few days as time allows.and blow out as suggested.
does any one have a detailed water flow diagram for this motor?
In my mind i'm trying to figure out the exhaust issue in the t/stat inlet.
could it be the water tube o-ring allowing exhaust up into the water jacket.

Am i right in assuming that when the motor is running with no thermostat installed the telltale should have a constant flow and not intermittent and somewhat sputtering?

 

[emckelvy]

Re: 9.8 merc hot tell tale

Am i right in assuming that when the motor is running with no thermostat installed the telltale should have a constant flow and not intermittent and somewhat sputtering?

Yup. Without the 'stat in place there's no reason you shouldn't have a steady flow.

It's very possible the prior overheat has "cooked" the exhaust manifold gaskets, causing them to leak. New gaskets, properly torqued, will fix that issue, I expect.

When you have the powerhead off to check the water tube grommet & washer, also take a look at where water goes out of the block (a slot running perpendicular to the centerline of the powerhead, and you'll see discharge hoes in the slot).

I had a 4HP with an unusual amount of spray out the telltale, and it turned out that was the only place water could exit the motor, due to plugged outlet at the bottom of the block. Pulled powerhead, cleaned it out, and cooling system was restored to normal.

HTH........ed