Water pump housing hole out of round

Merc90HPnewbie · Aug 9, 2003

On Merc 90 HP straight 6 from 1985; The tell-tale goes from stream at low RPMs to spray/mist at high RPMs. I figured impeller might be the problem. Opened up water pump and impeller looks fine! Only thing I noticed is that the top housing, the metal inner part, not the plastic outer part- the hole in the top for the driveshaft is no longer round. Does this mean that the driveshaft is in the wrong position? I dont want to think about that

Here's a picture http://www.freepicturehosting.com/g/123976_1.jpg Ran to the marina to get a pump kit (only had an impeller and gaskets before). It's got lots of pins and seals that I dont know what they are. Not finding Seloc manual too helpful, for all it's wordiness...

Thanks for any adivce you all may have- what parts should I check. what should I look for? Or is this not really a big problem? THANKS

alcan · Aug 9, 2003

Re: Water pump housing hole out of round

I can't see anything that looks out of the ordinary in the picture. I don't belive there is anything wrong with your driveshaft. The pumps work on an excentric so the driveshaft will not be centered in the pump housing. Just replace all the parts removed. Be sure to replace the o-ring on the splines and the thicker rubber O-ring/band (the slinger) atop the pump housing. Now keep in mind that your manual covers many years and models, also the pump kit you purchessed will cover many different models or years. So, all the parts that are in the box may not be needed for your application. The more expirence you have at working on outboards the more you will realize they are all the same, just a little different.

Merc90HPnewbie · Aug 9, 2003

Re: Water pump housing hole out of round

Hi! I put up another picture which more clearly shows how the hole is round. http://www.freepicturehosting.com/g/123980_1.jpg I agree that the pump looks like it would still work fine with the shaft out of center. But I am still wondering what is causing my problem though (no tell tale output at higher RPMS). I wonder if there is a leak caused by the driveshaft enlarging the hole at the top of the pump. The marina guy suggested maybe ehaust might be getting in there, breaking up the water flow - but that would require another problem to exist too I think. *Is there supposed to be a seal or grommet of any kind between the upper plastic pump housing and the inner metal housing? In the one I just took off, there is some ground away metal that looks like it might have been a seal at one time. I dont see anything in the kit that would perform this function though* You said:

"Be sure to replace the o-ring on the splines and the thicker rubber O-ring/band (the slinger) atop the pump housing. "

I removed the thicker O-ring (I don't see why it's called a slinger- slinger reminds me of the paddle that slings oil in my lawnmower engine) and found a new one in the kit. However I don't know what you mean about the O ring on the splines. Do you mean at the base of the shift shaft splines? Also the kit contains a while bunch of stuff beyond this. There's some really big O rings that I dont know what to do with. The kit only comes with the upper pump housing, not the lower. Thanks for your help

robalofish · Aug 10, 2003

Re: Water pump housing hole out of round

Why not get the whole pump kit including the upper housing, and lower housing. (oops just read that you did) then you don't have to worry about the out of roundness. By the way I do see what your talking about. Could have been caused by a previous impeller going bad. added

lower housing plate is also available you may want to lookup parts on Mercurys web site. RFish

mellowyellow · Aug 10, 2003

Re: Water pump housing hole out of round

did you have any water in the oil when drained lower unit?

Merc90HPnewbie · Aug 10, 2003

Re: Water pump housing hole out of round

I just did the lower unit oil change, the oil looked really good, honey yellow with a small splotch of black stuff that glooped out into the pan at the beginning. There might have been a drop or two of water (milky cloudy stuff) but I dont think water entry into the LU is a problem in this case. If I could find out from the Seloc manual what path the cooling water takes I could try to back flush it but I have no idea! The driveshaft has a shallow groove in it now due to rubbing against the metal inside of the pump's top cover! Is there supposed to be a seal or O ring between the top cover and the driveshaft?? Thanks!!

mellowyellow · Aug 10, 2003

Re: Water pump housing hole out of round

if was a problem, I think water would be leaking from pump into lower unit???

Merc90HPnewbie · Aug 10, 2003

Re: Water pump housing hole out of round

Hm, good point. But how come my tell-tale goes away at higher RPMs if the impeller looks fine?

mellowyellow · Aug 10, 2003

Re: Water pump housing hole out of round

u try compressed air through peehole? old impeller, while not broken, may be weak. the blades should be straight, not curved when removed. maybe something (like a piece of old impeller) is floating around in there and only blocks exit tube when pressure is real strong. good luck, M.Y.

profish00 · Aug 10, 2003

Re: Water pump housing hole out of round

Is this thing out of round OR just offset to one side????the offset is normal the impeller rides to one side of the houseing rather than the center, or on my 1993 150 blackmax it is offseted. Check the path to the tell-tale it just may be bypassed at high RPM moveing too fast to make the turn. water flows the path of leist resistance

briannh1234 · Aug 10, 2003

Re: Water pump housing hole out of round

Some of the extra part's in the water pump kit are seals and gaskets that go under the water pump base. If you suspect that water is going into your lower unit oil from under the base, then replacing the seals is the first thing to try. You already have the parts, put them on. Also, among the part's in the kit you will find 2 new seals for your vent and fill holes for the gear oil in your lower unit. Next time you change the oil, put those new seals on as well. You don't need to worry about the t-stat's in your motor - it does not have any t-stat's at all. I have never seen a motor stop peeing at high speed unless it was trimmed to far out of the water. Try back flushing it with low pressure water thru the pee-hole while the lower unit is off.

Merc90HPnewbie · Aug 10, 2003

Re: Water pump housing hole out of round

I thought some of the orange O rings were for the lower unit oil holes but they looked too small...maybe they spread out under pressure or something. I reused the old seals but I will use these next time... I was going to try to look at the lower pump base but as I was prying it up the plastic lip began to fracture so I stopped because the pump kit only had the upper housing. You are the first person to say I dont have thermostats.... even the Seloc book says I have them (it just wont tell me where they are). The engine was not trimmed up too high at the time (the first thing I checked

). And it wasnt a plastic bag because it happened every time I tried to throttle up.. I went in reverse a few times to clear the holes in case there was a bag or some seaweed. I tried blowing in the telltale (I dont have an air compressor or any cans of air) and there was no resistance, however I didnt particularly feel anything coming out of the water pump hose (the lower unit was off) or the square exhaust ports on the leg. P.S. My old impeller was in good shape-no parts missing. Of course, maybe the previous owner just changed it and the one before that is in pieces in the head

PS Profish: The impeller is offset, and that's OK, but the hole in the pump cover where the driveshaft comes down is mangled, the driveshaft rubbed away one side of the hole. Check the picture above, it shows the hole 'stretched' out a little to one side. Thanks!

alcan · Aug 10, 2003

Re: Water pump housing hole out of round

Hi Merc It would be hard for me to say, but your driveshaft may be bent,I can't see it so I don't know. I would sooner bet that the pump housing was not torqued down properly at some time and allowed this wear you are worried about. I also suspect this my still be your problem. You may also have more of a crack in the pump base than you think, I don't know. The splines I refered to are the crankshaft splines. The slinger deal sould be self explanitary. This is just a simple centrifical water pump. The only reason a water pump doesn't work is because it's getting air some how. I'm not tring to belittle you here, just tring to keep this simple and help you sort out the problem.

alcan · Aug 10, 2003

Re: Water pump housing hole out of round

I just took another look at both pics. Great job by the way. I still don't see anything that looks real bad. The first pic does appear to have a little chewing look to it how ever. This looks to me like it could have been caused by the empeller hub. The hub is the bronze center of the empeller that the rubber is attached to. This rubbing/chewwing could be do to too much torque, too little torque or just a delaminated empeller,etc.

corm · Aug 10, 2003

Re: Water pump housing hole out of round

Hi, If your upper driveshaft bearing is bad your water pump body will look like the picture,but as has been mentioned you did not have any water in your LU. It might not be a bad idea to pull the lower pump base and look at it anyway. it seems like you have some driveshaft whip. It could have been a used pump body off a different motor to start with, so you maybe chasing nothing,I hope.

bqsburb · Aug 11, 2003

Re: Water pump housing hole out of round

I am having the same problem with a late 70's merc in-line 6 cyl 150 hp. I tried new impeller and housing with no luck. Still strong tell-tale at low rpm, then diminishing with increasing speed to nothing and very hot motor. I have since replace 3 gaskets on powerhead 2 exhaust side and one head cover gasket. That didn't work either, same result. I am going to check the gasket between the powerhead and shafthouse. I am still thinking it might be high exhaust psi taking over the low water psi via a bad gasket. I will let you know if I have any luck, and I am paying close attention to your situation. Let me know if you get it figured out. Good luck. bq

BF · Aug 12, 2003

Re: Water pump housing hole out of round

Hiya, Just wanted to say, that I've replaced impellers on 2 of my outboards this season. Neither motor pumped water adequately. Both impellers "looked fine" when I took them out. A new impeller fixed the problem in both cases. I think the rubber can get a bit hard and not seal well within the casing which will affect their pumping ability, even if it looks like they should still have some sevice left in them. This experience made me a believer in just changing them no matter how they look. They're cheap. BTW, if the leak was out of the top of the pump, you wouldn't get water into the lower unit (as long as the seals around the driveshaft below the pump are OK). So, I'd change the upper pump housing, put in new impeller and see if it fixes it. And no, there isn't a seal or anything above the impeller, inside the pump housing, just the "slinger" sitting on top. Oh, and the O-ring by the splines that someone mentioned, your drive shaft may have a groove on it up near the splined end. An O-ring sits in there to keep water from being flung up the shaft and corroding the driveshaft/crank connection (the splines). When you reassemble, lightly grease the splines, but wipe the grease off the very top of driveshaft, other wise you won't be able to push it in all the way. Good luck. Brent

Merc90HPnewbie · Aug 12, 2003

Re: Water pump housing hole out of round

bqsburb: Seems to be an epidemic on ~20 year old 6 cyl mercury engines... would be nice to find a solution before I have to put thousands into having a mechanic chase the problem down.

alcan · Aug 12, 2003

Re: Water pump housing hole out of round

Hi Merc This situation can happen to all sizes and brands of motors. Believe me I know how frustrating it can be. Espeicaly when you want to go play. Try to keep in mind that usually this is turns out to be something simple. We all tend to get a little worked up and start thinking nucular powered aircraft carrier. I have been hung up the longest and been most frustrated by the simplest, stupid, little problems. All the fellows have offered good suggestions. Sorry, I don't have any more right now for you. I just thought I'd try and toss in a little encourgement. Calmly keep up the trial and error thing, you'll get the problem.

bqsburb · Aug 13, 2003

Re: Water pump housing hole out of round

Good news! Great tell-tale! This old motor had several leaks on the powerhead before gasket replacement(lots of loose bolts). I then resealed the area between the powerhead and the shafthouse, but they looked ok. Not thinking we had found anything unusual I started over with the pump. I put in another new impeller and gaskets. I found a poor seal at the bottom of the pump where the water comes up from inside the lower unit(inlet). The gasket or "boot" that seals the exhaust tube to the lower unit was definately leaking. The two small problems together created the big problem. I'm sure at higher rpm the exhaust gas leaked out right next to the poor seal under the pump. The pump was sucking the exhaust instead of the water. Anyway, there it is in a nutshell. I'm sure you will have to replace your impeller if it ran dry. I know those don't last long without water especially if you feed them hot exhaust gas. I would be happy to give you more detail if you want. I will check back. GOOD LUCK. bq

Water pump housing hole out of round

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