'71 Merc 9.8hp not cooling. Need help w/fix.

I am resurrecting my little Mercury after a 10 yr. lay-off. I rebuilt carb and fuel pump. Impeller is in good shape. Replaced short length of hose between engine block and "pee" exit and cleaned out orifice there.

When I started it up, I discovered it was not producing a water stream. I pulled the lower unit and did the drill test to check for sure and water pump is working. I then blew compressed air into tubes from both ends and discovered air is escaping somewhere just below the motor.

Sounds like I'll have to split the motor from the leg below it just to get at this area. This is unfamiliar territory for me but not something I'll shy away from doing. Any advice/info on what to remove and where would be much appreciated.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

First, I'd use water from a hose - force it up the uptake tube as well as back through the tell tale. Then you can see where it comes out.

I'd also remove the thermostat cover and see if water gets forced out there.

If no water is getting through to the thermostat, then it could be that the rubber fitting at the top of the water uptake tube is crimped or out of position.

Maybe others have further advice. It would be great if you didn't have to pull the power head.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

Stoneroller said:

I am resurrecting my little Mercury after a 10 yr. lay-off. Impeller is in good shape. .

Click to expand...

No it isn't lol!

They go bad whether they get used or not.

I just replaced one on my 6hp with one I bought a few years ago and had kicking around my shop. The rubber sheared off the bronze hub within an hour.

They should be replaced every 2 at most 3 years. The pump housing and plate must also be inspected for grooves and replaced if any are found.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

I'll use your method, Rick, to see if I can localize the leak source. I'll report back with results. Obviously, removing the power head will be my last resort.

I see your point, Red. While I've got it off, I should go ahead and replace the impeller and inspect. Cheap insurance.

Thanks, guys!

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

I'm not sure about your engine, but you may have a pressure release feature on the cooling system.

If there is a blockage, the water/air might escape there while you're testing.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

Hmm, don't know Rick, the system does not operate with very much pressure so I don't know if that would be needed. It is more primitive than later models, too, for example, it does not have a thermostat at all in the cooling system.

Incidently, I just ordered a service manual specific to his model and year on CD from a guy in Canada on ebay. Not expensive and says it covers most everything, we'll see.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

Yes, I see your point. Best of luck with getting it working & please post outcome.
cheers

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

Look at 31,32,33 in this picture.

http://www.crowleymarine.com/mercury-outboard/parts/444_11.cfm

Those are supposed to be famous for causing a no water flow issue from my understanding. The pic is of a 7.5, but the 9.8 is the same.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

Yup had the same problem on my 6hp as you.
Started by replacing the impeller(twice!)
Moved on to the baffle cover and plate.
Full of gunk and corrosion.
Cleaned it out but still no go.
Finally I pulled the power head off and found the plate underneath between the block and leg was completely plugged with even more corrosion.
I used a wire brush and some CLR to get the crud off.

I had to use a really long phillips screwdriver to slowly drill away at the corrosion that had built up in the telltail port as a drill wasn't long enough to reach.

Re: '71 Merc 9.8hp not cooling. Need help w/fix.

I had a 7.5 come in this summer that was missing #7

http://www.crowleymarine.com/mercury-outboard/parts/444_18.cfm

I made a seal to go in it's place and then it started pumping, make sure 7 and 31 are in good shape. Also make sure the washer "36" as I call it is on top of the impeller, if it's missing it won't pump either, lot's of little parts that make up this system.