9.9hp outboard question (water pump?)

Geezle · #1 05-22-2012, 09:08 AM

So I recently had a 1998 9.9 horse Merc given to me. I took it over to mudbug's place and we changed out the leg oil, cleaned up the plugs (got some new ones, but they were the wrong ones) and fired it up. It ran great, so yesterday I took it out for a trial run on Wab. It runs awesome, but it seems like when I've got it at WOT the water coming out will be at a hard spray, then will taper off a little, but it's still a steady stream, and then it picks up and there's more pressure again.

It seems like a regular change of pressure, not intermittent, if that makes sense? The water coming out was pretty warm, but not HOT.

At idle it's more of a trickle.

I *think* it's okay, but I want to be sure...I don't want to kill the thing after I just got it.

Also, although it's 14 years old, the motor has hardly been used, and has been stored for at least the last 5-6 years. It's still got the original plugs from the factory in it even.

Any thoughts from those of you who know these motors?

I took a couple vids of the motor in action with my phone, but neither of them really show the water coming out

RapStaff · #2 05-22-2012, 10:12 AM

I had the same problem with my 9.9 merc and all it happened to be was one fin had broken off the impeller causing water flow issues.
Super easy to change out the impeller PM me and I can walk you through it.
Or I can do it for you for a beer...... LOL

Pixel Shooter · #3 05-22-2012, 10:53 AM

Hard to tell from video, but what you are explaining is common for these Mercury's starting mid 90's Im thinkin. It will spit constantly from overflow, only when it hits 170 degrees or whatever your thermostat is , will the thermostat open that will allow a full stream, then the thermostat will shut off once it cools again. Once your motor is fully warm, will there be a constant stream. I think this time of year with water so cold, it takes much longer for that thermostat to open. My older motors had a constant stream from second it started but technology has changed. Im thinking your ok.....

Geezle · #4 05-22-2012, 11:03 AM

Quote:

Originally Posted by Pixel Shooter

Hard to tell from video, but what you are explaining is common for these Mercury's starting mid 90's Im thinkin. It will spit constantly from overflow, only when it hits 170 degrees or whatever your thermostat is , will the thermostat open that will allow a full stream, then the thermostat will shut off once it cools again. Once your motor is fully warm, will there be a constant stream. I think this time of year with water so cold, it takes much longer for that thermostat to open. My older motors had a constant stream from second it started but technology has changed. Im thinking your ok.....

Interesting...sounds like I may have to do a little more homework on this thing. The way the flow changes it does seem very much controlled, and when we booked it back across the lake at the end of the day it seemed to be coming out pretty steady.

skidderman · #5 05-22-2012, 01:16 PM

New impeller is an easy do it yourself thing and should cost less than a hundred for parts. They should be changed every few years anyway as the rubber hardens over time.

sourdough doug · #6 05-22-2012, 02:47 PM

X 2, skidderman. The rubber impellor is offset in the pump housing and after being stationary in this position for so long, the compressed rubber fingers may not be pumping up to capacity. Not a big deal to DIY, if you are half handy with a tool. Prob. lots of info on U tube....

Dark · #7 05-22-2012, 04:01 PM

Quote:

Originally Posted by Pixel Shooter

Hard to tell from video, but what you are explaining is common for these Mercury's starting mid 90's Im thinkin. It will spit constantly from overflow, only when it hits 170 degrees or whatever your thermostat is , will the thermostat open that will allow a full stream, then the thermostat will shut off once it cools again. Once your motor is fully warm, will there be a constant stream. I think this time of year with water so cold, it takes much longer for that thermostat to open. My older motors had a constant stream from second it started but technology has changed. Im thinking your ok.....

X2

pickrel pat · #8 05-22-2012, 04:09 PM

even if it is normal as pixel suggests, it has been sitting for 5 or 6 years and an impellar is cheap and easy. i would change it.

nicemustang · #9 05-22-2012, 05:38 PM

Impellers are rubber and dry out if not used very easily. They also only last a few years. Easy to change them do it every 4-5 years just to keep it good IMO. I have heard about the thermostat issue to but I'd still change the impeller.

The Fisherman Guy · #10 05-22-2012, 06:12 PM

If your impeller is going, it could fail you far away from the boat launch. If your water pump dies and you don't find out soon enough, you could cook your motor. I would change the impeller no matter what!

skidderman · #11 05-23-2012, 11:51 PM

The trick to getting the bottom end off is the bolt under the steering tab. Take the small bolt and the tab off and you can see the bolt up high. Take the bottom off slowly as you need to pull a plastic tube off first. The bottom end will drop out then and you can get at the pump easily. If you are unsure of reassembly snap a couple of picks first. Use anti seize on the bolts before putting them back. Never run engine without water supply as you can damage the impeller in seconds. Careful not to over tighten the bolts as the aluminium threads can be stripped easily.

Should take an hour or less to do.