advice on water pump change

vetstudent · Nov 12, 2004

I have a 96' 40 hp, 4cyl mercury tracker that I bought used about four years ago. I noticed the last few times I took it out the water output from the "peehole" gauge was pretty weak but sufficient to keep it cool while running (moving anyway). Well with duck and deer season approaching I decided I should replace the water pump. I have a few questions that I was wondering if ya'll could answer. First off I have no idea of the maintainance of the motor before I got it. In all likelyhood the water pump on it is original (96). Also I'm a full time veterinary student that is VERY POOR!!! I spend money if I need to but try to be economical!!! The questions are as follows: 1) Should I just replace the impeller or get the whole kit? (impeller $9, kit $57) Of course I'd like to get away with just the impeller but if it will likely fail sooner because I failed to get the whole kit I won't like that in the long run. 2) Do I need a manual to do it? I am fairly good with motors (carbs and all the upper unit stuff) but I've never messed with a lower unit. I really don't think I need one personally... anybody do it without one??? 3) What other things should I do while I'm in there. Obviously I'll be changing the lower gear lube, but will I need to replace any other gaskets that will be removed to get to the pump? I don't want to skimp on a $.50 gasket or drain plug!!! I'm sure I'll have other questions but I think I've covered a lot so far. Thanks! Brent

Laddies · Nov 12, 2004

Re: advice on water pump change

9 bucks sounds cheap for the imp, but most places sell an imp. kit that comes with the gaskets and wear plate water pump repair is simple, just make sure the shift shafts are in the same gear when replacing thr unit

Laddies · Nov 12, 2004

Re: advice on water pump change

PS mark the trim tab and remove it they hide a bolt under it---bob

vetstudent · Nov 12, 2004

Re: advice on water pump change

Thanks for the quick response! I just noticed that Sierra made two kits for the water pump. One just doesn't include the base of the pump. Is the base something that doesn't wear much? The kit without the base is $27 cheaper! I remember reading somewhere that the merc kit didn't include the base anyway... Is that true? Thanks Brent

wilde1j · Nov 15, 2004

Re: advice on water pump change

Always use the complete kit. The impeller only is not enough, especially given the labor involved. The slightest wear in the pump body or wear plate will drastically reduce the pump output. By the way, the complete OEM Merc kit for my 150's is $32.67 each through Mercury Parts Express (on-line). I would be careful using non-OEM parts, as there have been some issues over time with non Merc impellers.

vetstudent · Nov 15, 2004

Re: advice on water pump change

Jim, Thanks for the response. Unfortunately I have already ordered the parts for it (Yesterday.) I wasn't aware of differences in the off-brand and OEM parts. The kit I ordered was from Sierra. It was $15 and included a new impeller and all gaskets and rings. Before I ordered it I took the lower unit off and removed the H2O pump. When I took it apart the impeller was terrible... it kept its flexed shaped when I pulled it... There weren't any pieces missing though. I inspected the upper housing which the impeller fit into and it looked and felt like new (no scars or scratches and perfectly smooth.) That's why I opted to buy just the impeller and gaskets. BTW the kit for my water pump on "parts express" was $85. If the new impeller and gaskets doesn't fix my problem for this year I'll be sure to get the whole kit next time. Antother question... I plan on doing a decarb with seafoam on the engine as well as replace the spark plugs. Should I replace plugs before or after the decard??? Also: What's a good recommended lower unit oil??? Does it really matter? Are synthetics worth the extra $.

dka1ser · Nov 15, 2004

Re: advice on water pump change

I would probably wait to change the plugs until after your run the seafoam through it. However, check the condition of the plugs before you replace them, they might not need it. Waiting until after you run them allows you to also inspect the combustion chamber and see what condition everything is in. I have always run standard non-synthetic gear oil. I don't think its worth the extra money unless you are running a really high performance outboard, going high speed for long time. Just replace the standard lube once a year. Just my 2 cents. -Dennis

b20 · Nov 15, 2004

Re: advice on water pump change

just be sure to use a 'marine' gearlube.i find the merc high-performance is the best around,but it is a bit more expensive.worth the money though.

andrewkafp · Nov 15, 2004

Re: advice on water pump change

As a minimum, do the base plate (metal) and the impeller. Search on here for the technique for your motor. They are all basically the same, but there are always a few good tips for re-assembly and trouble shooting in the posts.

dolluper · Nov 16, 2004

Re: advice on water pump change

once you have done it a couple of times it's only parts cost becomes second nature for maintaining your fun time

Elmer Fudge · Nov 16, 2004

Re: advice on water pump change

Lots of good advice so far, a good service manual is an invaluable tool to have. If you are in need of one,they can be found at the bottom left of this page, good luck and keep posting

vetstudent · Nov 16, 2004

Re: advice on water pump change

Thanks, Thanks, and Thanks! Removing the lower unit was easy and I don't forsee and problem replacing the pump and putting it back on! By the way I was looking at getting a manual but didn't know where to look... I had no idea it was so close

Brent

vetstudent · Nov 18, 2004

Re: advice on water pump change

OK, I have an update... I initially changed the pump and let me tell you... I had a very difficult time taking on/off the base of the water pump. I actually tore the base gasket trying to get the base down. I went ahead and tried it anyway and I quickly got water in the lower unit. I took it back off and again had a difficult time removing and replacing the base. The second time I made my own gasket out of a little tougher material that I got from carquest. It had an adhesive side so it made it a lot easier to get fit right. It finally dawned on me what I thought was the problem. Please tell me if this could be an issue. When I drained the lower unit I replaced the drain and vent screws. I think I was fighting air pressure in replacing the pump base!!! To verify my theory I loosened the vent screw and a nice little squeek of air came out... Maybe this wasn't the cause of my troubles but it seems possible. Anyway I added a little blue RTV to the base gasket to give it a little extra seal. I'll try it again in the AM. Anybody have any thoughts on the air pressure issue??? Thanks Brent

andrewkafp · Nov 18, 2004

Re: advice on water pump change

It's rare that the pump base needs replacement. Usually only the impeller, base plate and sometimes the upper housing. Be careful with that pump base and refer to the manual. Some have pre-load requirements and there is a specific procedure to follow.

rodbolt · Nov 18, 2004

Re: advice on water pump change

hello take it back apart and clean the blue goo it will leak silly cone has very very limited use in a marine application. if you need a sealant on the base gasket use perfect seal or omc gasket maker. and the proper gaskets are availble seperatly. sometimes the gasket is a specified thickness and yes if all the plugs are in you will fight air pressure

see how much you have learned so far

vetstudent · Nov 19, 2004

Re: advice on water pump change

rodbolt, So the blue RTV will for sure leak??? It said it was a "gasket maker." I'm pretty sure nearly all of it was squeezed out anyway. I figured it would seal any imperfections the gasket might miss??? Is it something that will leak imediately or over time??? I've tightened it down pretty good right now. I hate to take it apart again but if it will likely leak in the near future its better now than later. Also, I didn't replace the pump bottom but when I took the upper housing off the gaskets were very brittle and pretty much fell apart. I just figured the bottom gasket was just as bad so I took the base off to replace it too. It did fall apart just as the upper gaskets did but I guess it was doing a fine job before I took it apart...... I'm thinking now I should have left it alone!?!?! Oh well, had it leaked I'd be saying "I should have just replaced it when I had it apart the 1st time." I think the real problem lies in the design of the pump base. The rim around the base is too darn narrow. The majority of the "rim" is about 1/16-1/8". There's enough room to have put a wider rim on the base and given a little more area for the gasket to seal. Unicorn: what is meant by "Pre-load"? And yes I have learned a ton of information so far!!! This site has been a great help! My manual should come in the mail today so I'll have some directions to go by! hehe Thanks!

andrewkafp · Nov 19, 2004

Re: advice on water pump change

Vet Rodbolt can explain the pre-load.. but if you have not removed the plastic base, it doesn't matter. With a W/P kit, you get the new gaskets and a thin steel plate. Just clean all the goop off and intall the kit. This is a pic of the W/P kit

rodbolt · Nov 19, 2004

Re: advice on water pump change

hello ok lets get some basic terms the plastic part that houses the impeller and insert cup is called the upper housing. the plastic part it sits on is the lower base. the lower base has an oring around it. the gasket goes on first then the oring. then the assy slides down the studs.the lower base also contains the drive shaftseals. the only normal thing that wipes out the lower base is a dry run pump and it melts it. same with the upper housing. any sign of melt at the top of the insert or at the cup edges is a sign of a junk upper housing. after the base is installed place the lower wear plate gasket then the wear plate then the upper wear plate gasket. then the impeller key and impeller. insert a new cup( peferably in a new housing and lubed with dish soap)assy dwn the drive shaft until the cup touches the impeller. then rotate the driveshaft clockwise while pusing down on the housing. the only place I use any sealant is some perfect seal on the lower base oring. preload is a measurent of rolling resistance or static load applied to a beaing or spring or any other object you need all the clearance out of with a specified force. the older merc units used the lower base to preload the upper drive shaft roller bearings by shims under the lower base. the problem with silly cone is oil and water wick underneath it. it probably wont leak imediatly put it will leak. good luck and keep posting

vetstudent · Nov 20, 2004

Re: advice on water pump change

I think I'm understanding all the parts. I need to be a little clearer on what I did. I ordered the exact kit that Unicorn put up a picture of. The only other difference was a few extra rings and gaskets that apparently did not apply to my pump except for the two small gaskets that go under the drain and vent screws. I took off the lower unit and removed the upper housing to replace the gaskets, impeller, and impeller plate. The gaskets were very brittle so I pulled off the lower base to replace it's gasket too (not the base itself). When I put the base back on I wasn't real happy with the kit's gasket as it didn't seem to fit real snug around the diameter. Since I was fighting air pressure putting the base back down I probably buggered up the gasket when I was in the process. I fully assembled the pump..... put it back on and refilled the lower unit. Five minutes of running and I checked the lower unit fluid... It looked like milk so I'm sure it was leaking!!! I took it back off and did the same thing except I cut my own gasket out of a sheet I got at carquest. I was much happier with the fit of my gasket over the kit's gasket. This is probably where I messed up... I thought a little blue rtv would help seal the base gasket a little better. I put it back on tried again. It was very difficult to tell if it leaked but I don't believe it did. I checked the lower unit fluid after running for about 10 minutes and it looked much better. It didn't look like it did when I put it in but had a VERY subtle tint to it. I believe this little bit of "tint" was due to left over oil that was in it when I replaced it the second time. I'm kind of thinking if I was using a lower unit oil that was hydrophobic I might be able to tell if water was getting it a little easier. The water would sit at the bottom wouldn't it??? Sorry about the long post but my current situation is this: All back together and no leak that I know of. However, there is blue RTV under the base gasket. What to do??? BTW, I looked at some old posts and I found one from laddieservice (sp?) It was about replacing a water pump. In his post he said (I'll paraphrase since I can't find it again) put a little "blue" on it and you'll be fine. I believe he was referring to the base gasket at the time. I noticed that his profession was a merc master tech. I'm wondering what he meant by "blue". Thanks for all the help so far!!!

vetstudent · Nov 21, 2004

Re: advice on water pump change

Update: I removed the lower unit again because of the fear that the silicone RTV would cause a leak. Because of the thin rim on the base housing I still didn't feel comfortable with just using a dry gasket. The edge of the lower unit where the gasket would set had some imperfections as well. I knew I didn't want silicone so I went back to the store and got "permatex hylomar hpf gasket dressing." It is supposed to be resistant to all chemicals including gas and oil. It's a non-hardening dressing that should help the gasket to seal a little better. I'm thinking this should work much better than silicone! My water pump has worked great and I'm not worried about it cooling the engine. My main concern is keeping the oil in the lower unit and the water out of the lower unit!!! I'm a little dissappointed in the design of the water pum base. There needs to be more of a lip on the base to seal to the lower unit... I guess I'll have work with what I have! I'll repost when I have a chance to take it out. If anybody has any comments or suggestions on anything I've done I'd be glad to hear about it. You guys have been very helpful and I've learned a ton from this site! Brent

advice on water pump change

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