1985 Mercury 7.5 water pump

[douglasjett]

I decided to replace water pump in Mercury 7.5 and it went together pretty easy.. But, still no water pumping? Does the water travel to the top of the shaft in the copper shifting tube? could this be plugged? I'm just missing something here. The good news is I got the motor for $150 and it runs like a top...

Any advise?

 

[pointandshoot]

Re: 1985 Mercury 7.5 water pump

yes, the copper tube carries the water up to the powerhead and the lower end has to be installed with this tube sticking into the water pump. also the tell tale (pee hole) sometimes gets clogged up with debries and needs to be cleared up by sticking weed whacker or mechanics wire in there to free in up. was it pumping before you took it apart? how did the old impeller look? also the impeller veins can sometimes break off and get lodged in wierd places. check the t-stat also, if its old or corroded replacing it might not be a bad idea. there isn't a huge by-pass for the water around the t-stat and i find i have to wait for mine to warm up pretty good before a solid strem starts to come out.

 

[Mi duckdown]

Re: 1985 Mercury 7.5 water pump

The copper tube has nothing to due about shifting. It has to be inserted in the head and the lower unit. can be trickey to do so.

 

[douglasjett]

Re: 1985 Mercury 7.5 water pump

the pump was not working when I got the motor so I 'assumed' it was the impeller. It looked pretty good when I took it out dry but not cracked or coming apart. I"ll bet the thing is just clogged. I'll take a look tomorrow. Thanks for the tips. Sounds like I might have replaced a perfectly good impeller.

 

[pointandshoot]

Re: 1985 Mercury 7.5 water pump

Sounds like I might have replaced a perfectly good impeller.

i highly doubt it, some guys replace them every few years or after a certain amount of hrs even if the water stream is still strong and the impeller itself looks fine. lets face it, an impeller is only going to fail at a bad time (like when your on the other side of the lake with the wind going the wrong direction, or even worse you don't realize you motor's stopped pissing and your wondering why you smell burning and the motor won't turn over). sounds like $15 well spent.

 

[jeremyfowler]

Re: 1985 Mercury 7.5 water pump

maybe you put the impeller in backwards, where your fins are facing the wrong direction?

 

[douglasjett]

Re: 1985 Mercury 7.5 water pump

OK, so finally dropped lower unit again to see what was up. What was up was mudd dobbers, copper tube was plugged between intake and pump. Guess I should have checked that first! OK, so one more question. There is no gasket or o-ring plate on the pump housing or where the lower end joins the engine.. should I seal these with marine silicone or something, or was this by design?

Thanks

 

[pointandshoot]

Re: 1985 Mercury 7.5 water pump

no seal, no goop. just stick 'er in.

 

[douglasjett]

Re: 1985 Mercury 7.5 water pump

Well, I'm embarraced. I stuck er in and the thing still does not pump any water?? So, intake is clear.. Impeller is new, uptake pipe is clear and hose from head to pee hole is clear..

Thanks for any last minute help I'll be taking this thing to the shop in the next couple days

 

[pointandshoot]

Re: 1985 Mercury 7.5 water pump

did you check to see if the tell tale is clear? does it feel like air is coming threw? any spitting? how long are you running it before you shut it down? like i mentioned in my first post, mine takes a little while before it heats up and the t-stat opens up. have you popped the cover to the t-start and inspected it? also, if your testing in a bucket, how far is the leg in the water? if you visualize where the water pump would be, the water line should be above the water pump. there really isn't much going on to go wrong...i would really check the tell tale, maybe even unhook the tube that plugs into the t-stat housing and see if she puked out of the housing (with the cover off of coarse).

ohhh, two last things...you did reinstall with the woodruff key right? also, i do think they made 2 different sized drive shafts for these motors. i'm not sure which is more popular but the impeller should fit tight to the shaft, make sense?

 

[douglasjett]

Re: 1985 Mercury 7.5 water pump

I could have gotten wrong impeller? with lower unit off, I could spin it wrong way and impeller blades would go wrong way, at least 1 or 2? So, how sensitive is the whole thing cuz I also blew water out of pump housing when presure testing?? Im starting to think that I need new pump housing and.... I may have gotten wrong impeller.... and....

 

[douglasjett]

Re: 1985 Mercury 7.5 water pump

thanks pointandshoot very cool. I will take another look before the shop... cheers

 

[pointandshoot]

Re: 1985 Mercury 7.5 water pump

i'm not sure what you mean by water blew out while pressure testing...you mean with the lower unit off you stuck the hose to the copper tube and water came out of the tell tale? http://www.boats.net/parts/search/Merc/Mercury/1985/1007225/GEAR HOUSING (DRIVE SHAFT)/parts.html# here's a link to a parts diagram, do you have #26? its a flat silver disc that separates the pump into 2 different halves, i'm pretty sure its impossible to install it wrong, but the slotted hole should be positioned under where the pump outlet is. i really don't think the impeller can be installed backwards, like you said the veins just flip flop around depending on which way to turn the drive shaft but i think clockwise is the proper direction. it could be that you have a cracked housing from someone over tightening it. i really need to know where the water is coming from and what you mean. with the lower unit off you could try holding the garden hose to the copper up tube to see if water passes threw, you might have to remove the t-stat (easy to do with a flat head screwdriver). it would let you know if the problem is up top or down below, might want to wrap the connection with a rag or t-shirt to help build pressure and not get sprayed in the face.

 

[douglasjett]

Re: 1985 Mercury 7.5 water pump

water came out of the housing at the conection between 18 and 27. Yes I have #26, came with the impeller kit. I will try the hose thing next time I drop the lower unit.

 

[pointandshoot]

Re: 1985 Mercury 7.5 water pump

any updates there douglas jett?