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View Full Version : Question About Mercury 9.8 Outboards

08-22-2010, 08:14 PM
I have an older (early-70's) Mercury 9.8hp outboard. It starts and runs normally, but almost no water comes out the "tell-tale" outlet just under the cowling, like maybe 4 or 5 drops a minute, and that is all...no more. When I put my finger under this meager stream, the water that comes out is not warm to the touch, but seems just as cold as the water in the tank the motor is setting in. I am somewhat scared to run it for extended periods of time (more than a few minutes) for fear of overheating it.

Q: Is this an indicator of a problem with the motor? Shouldn't there be more of a visual flow of cooling water, or is this just a normal characteristic of Mercury's? Or is there some sort of built-in thermostat where nothing much is going to flow until the motor reaches a certain temperature?
Could it be that the impellor is shot, and maybe that is the reason for the very poor water flow? If it is an impellor problem, where would I find it located? I'm stymied: what do you'all think I should do next?

Ok...just came back to edit post, because I found a motor on YouTube exactly like mine. In the video clip, you can plainly see a stream of water shooting out the bottem of the cowling, out the "tell-tale". Not 4 or 5 drops, but a steady stream. There's something wrong with my water-pump...


Nick Olzenak
08-23-2010, 11:21 AM

Your on the right track the first thing that would lead to is a failed water pump. In most cases these are a fairly easy replacement and typically come in kit form at your local Mercury dealer.

Good luck!

Steve Herschbach
08-23-2010, 01:52 PM
Hi Marshall,

Not familiar with a 1970 Merc per se, but check the water intake or intakes on the lower unit below water line to make sure they are not plugged. Also, a little compressed air applied to where the water comes out (blowing air backwards through the system) will dislodge any debris that might be plugging the system. Cheap and easy, so try this first.

If still weak, it is most likely a worn water pump impellar although it could be a thermostat stuck closed. Follow the tell-tale hose up to near the top of the block - the thermostat should be located under a cover the hose attaches to. The proper way to check a thermostat is in what is basically a slow cooker than can be set for a specific temperature to see if the mechanism opens at the right temperature. Might be easier to just replace it as they only cost around $15.

The water pump is normally on top of the lower unit around the drive shaft, so you have to drop the lower unit off to get to it. Usually just some bolts to take out, but pay particular attention to the shift linkage which may also have to be disconnected. An impellar alone will be around $15-$20. Due to the age it may be that is all you need to replace as it may not be worn out so much as just aged. If worn out from silt then you may need to replace the housing/liner also.

Be sure if you go to get parts that you have the model and serial number!

08-15-2011, 10:17 AM
On the gulf coast mud divers and other bug move in or clog thes holes. Clean tube. If bolts are not froze water pump impeller is easy fix. Down hear people replace impeller ever 2 or 3 years to be safe.