9.8 not pumping water

[AEROCOOK]

My early 80s 9.8 Merc (Canadian model 7176494) isn't pumping water at idle but if I increase RPM I get a weak (and very hot) stream out of the tell tale. I'm running the motor in a barrel with the water level at least as high as it would be if on a boat. I removed the lower unit , disassembled the water pump and can confirm that it's in good shape. I then ran the garden hose directly onto the water pick up tube and got good flow through the motor and strong stream out of the tell tale. I decided to check the thermostat and discovered that there wasn't one installed. I checked the parts catalog and found that not all motors had thermostats? This being said, I have 2 questions... Is there a visual way to tell whether my motor should have a thermostat? Any other ideas as to why it's not pumping water properly?

 

[Scott Danforth]

Change your impeller. You are changing it EVERY 2-3 YEARS RIGHT? You may need a full water pump kit if the housing has gotten warm

 

[AEROCOOK]

There is no sign of overheat on the water pump housing and as mentioned, everything is is good shape, impeller is in excellent shape. Any idea on the thermostat question? If my motor has the removable cover with the spring clamp can I assume that it should have a thermostat?

 

[Scott Danforth]

Yes removable cover with spring clip is a thermostat model. The ones without a thermostat have a different case ( no spring cover)

Regarding the plastic water pump housing, you won't know if it's melted until you get the leg off.

You also can't order an impeller or water pump until you get the leg off and measure the shaft diameter. The small mercs (3.9 - 9.8) of that era were made with one of two posible water pumps. You have to measure the drive shaft diameter to verify.

If the impeller is more than a few years old, change it.

 

[AEROCOOK]

Thanks for the replies. I have already taken the leg off and then completely disassembled the water pump, it's in good shape. The PO told me the impeller was just replaced but when it wasn't pumping well I knew the pump was the first thing to check. No melting, all grommets in place and as mentioned, the impeller is good. I will likely replace it as a matter of routine maintenance. I'm wondering if running without a thermostat in place can cause flow issues?

 

[gm280]

AEROCOOK, have you looked over the inlet port(s) to make sure there was nothing plugging up the inlet to the pump? JMHO!

 

[Scott Danforth]

Is the key still in the impeller?
Was the rubber grommet at top of mid section where the water tube goes replaced?

I woudnt run without a t-stat

 

[AEROCOOK]

I had the inlet tube off when I took the pump apart and it was clear, I made sure the key was in place during reassembly. I tried running it with a thermostat installed and no change (I was surprised to learn that the T stat is the same as my 110 Johnson so I had a few spares) I guess I'll pull the powerhead off and check the grommet at the top of the water tube. If that checks out good, I'll replace the pump assy.
Thanks for the help, I'll post with updates.

 

[AEROCOOK]

I thought I'd provide an update on my progress.
I took the powerhead off and replaced the little ring at the top of the water tube, the old one was deteriorated but still relatively intact, I replaced the base gasket at the same time and also installed the missing thermostat along with a new gasket. I put the motor in the barrel and fired it up and there was no improvement, it just barely spit out the pee hole and what did come out was very hot. I then pulled the lower unit off, and spun the drive shaft with a drill at approx 1500 RPM with the unit submerged and it seemed to pump water quite well. I reinstalled the lower unit and tried running it in the barrel again but no change. At this point, I'm inclined to remove the exhaust cover to inspect the condition of the plate and gaskets, aside from that, I'm running out of ideas.
One thing I did learn along the way was the power of Thunderbolt ignition, worst shock I've had in quite a while.

 

[AEROCOOK]

Well I got the exhaust plate out and it was severely warped, I also managed to break three of the bolts during removal.
In order to maintain what little sanity I have left, I've decided to cut my losses and sell the motor for parts.
Thanks for the help.

 

[gm280]

Well I got the exhaust plate out and it was severely warped, I also managed to break three of the bolts during removal.
In order to maintain what little sanity I have left, I've decided to cut my losses and sell the motor for parts.
Thanks for the help.

AEROCOOK, don't give up. There are ways to solve most every problem with those engines. Post a picture or three of your engine and the exhaust plate in particular. We can offer ideas and suggestion for you to get that engine running and working like it should. That fact that is does run means there is very little to get fixed. JMHO

 

[AEROCOOK]

AEROCOOK, don't give up. There are ways to solve most every problem with those engines. Post a picture or three of your engine and the exhaust plate in particular. We can offer ideas and suggestion for you to get that engine running and working like it should. That fact that is does run means there is very little to get fixed. JMHO

I really appreciate the support and I'm sure the motor could have been repaired but I just didnt have the time or desire to see it through. To be honest, I'm more of a "Johnnyrude" guy and I've got several of those to keep me busy.
Thanks till next time.