OMC Raw water pump issue.

[KRH1326]

Hey Guys,

This one is a bit aggrevating and frusterating.
Best to start at the beginning, so not to miss anything.
1976 OMC 235 HP Electric shift. This past winter as part of restore job, I installed all new seals and gaskets in both the upper and lower units, as well as the intermediate housing. Included in this work was a brand new impeller and housing.
When I disassembled the unit, the pump pick up tube was rotted away and almost completely gone. According to "aftermarket manuals" ( I have recently located and purchased an original OMC factory manual, just waiting for it to get here.) some models had the tube routed down to the underside of the cav plate, and located right near the prop blade tip, while some models had the tubing routed down to the cav plate and actually drawing water in through the hollow rudder, which is aft of the blade tips.
My cav plate had a hole and screen at both of these locations. From what was left of my original tube, it really looked like it hit the port right above the prop tips, so I fabbed a new tube from copper pipe, and firmly fitted it to pump housing and that port.
This having been my first "wet" season with boat, since rebuilding engine, outdrive etc., I have spent this current season working the bugs out and finding and fixing various problems that have popped up out the blue. All this time, I have had an intermitant over heating issue. I would see the temp climb and chop throttle, would cool off then off I go again. Now I am addressing this problem.

I have noticed that it is happening when I am powered up and climbing out on a plane. Usually at and above 3000 rpm. It was suggested here in these forums that it has to do with the outdrive rising out of the water and maybe losing "suction".

I went through alot of the usual suspects, new thermostat, removed and examined both manifolds and risers. I have GREAT flow through manifolds and risers. So I am suspecting something amiss with the new impeller and housing, or pick up location.

At an idle and under 3000 rpm, I do have copious amounts of raw water coming in. As I am mostly alone, I haven't been able to check above 3000 or out on plane.

As is, this engine does run cool. It hovers between 100 and 140 below 2500. usually 140-160 out to around 3000 and up. Sometimes it stays there, sometimes the heat goes wild.

Just for fun, this morning I hooked up a crank mounted water pump. I just tee'd it into the water coming from the outdrive, heading for the tstat housing assembly. It ran just fine, actually it ran a touch cooler than usual. Didn't break 140 until I was trying to plane. Then it hovered around 140 up to 3500 rpm. At that point , now more confused than ever, I cruised back to mooring.

Now I am sure that it is a prob from pump and housing and down.
Can a pump work fine at lower rpms then crap out at higher rpms? What do you think of water pick up location? Am I missing a place or thing to look at?

Thanks Guys

 

[BLDFW]

Re: OMC Raw water pump issue.

Hey, long time no post!

First, if you haven't done so already, I recommend swapping out the water intake hoses from the intermediate unit to the exhaust manifolds with clear hoses so you can tell at a glance whether you have a clear column of water in each hose. You'll need help but when you get the RPM's up above the problematic point, you can do a visual on the hoses to see if air bubbles are being introduced to the flow. Since there's no heat on those hoses there's no danger of them rupturing.

Did you replace both the upper and lower seals as well as the gasket the lines the inset at the bottom of the exhaust housing that the the upper unit slips down into? It sounds like you may indeed have leak caused by higher water intake suction pressure at higher RPM's. It could be sucking exhaust gases in around the above mentioned seals if they weren't replaced.

I had the same problem with mine until I replaced all the seals and those where the upper unit mates to the lower unit.

Thoughts?

 

[KRH1326]

Re: OMC Raw water pump issue.

I bought the upper and lower sierra gasket kits, and made sure that I used every one. I can't remember off the top of my head each one in particular, but that is an awesome point.

I can't believe I didn't think of the clear hoses. Duh!!! I even HAVE a roll of 3/4 in my shop. Duh again!

I am going to swap those tommorrow. I plan on pulling the boat for the season in November, pending the stiper action. Then will get to anylize the out drive again.

What do you think about running the crank pump along with the outdrive pump for now, untill boat is pulled? Can it cause damage, over pressurization problems?

What do you think of the actual pick up locations?


Good to see you BLDFW, did you figure out your steering cable stuff?

 

[BLDFW]

Re: OMC Raw water pump issue.

See the attached pic on the seals I was referring to where the upper and lower units mate. That's a possible source where the exhaust gases can slip past the seals and into the water stream coming up from the water inlet. You recall replacing those seals?

I'm not familiar with the crank pump you're referring to. Not sure how that connects. It would have to feed the two hoses to the exhaust manifolds. How/where does it hook up?

In anycase, before circumventing the normal cooling flow I'd first validate the water flow via the clear hoses. It could be you don't have a pump issue but perhaps a blockage issue somewhere in the manifolds.

Believe it or not, I only last week finished working out all the bugs I've been dealing with on my Explorer. I've been dealing with charging/electrical issues which I finally was able to resolve. The previous owner had it only partially wired right and I finally was able to figure it out and FINALLY able to conduct a fully successful test run yesterday. Unfortunate that it's the end of the season and possibly no more warm days but at least it will be ready for next year.

I'm still interested in installing the Tru-Course steering and have been meaning to followup with you on that but there wasn't any point until I was sure it would be running! Is that offer still good?

 

[KRH1326]

Re: OMC Raw water pump issue.

Yes, I do believe that I did those. And if I remember correctly, there even was a plastic ring, or collar that went around the exhaust housing as well. That wasn't part of any of the kits, but I got one when I did the work.

Sure the offer is good. Will always be good, as long as I still have the parts. I hope to rebuild that spare this winter. WITH SOME HELP THIS TIME, from an old timer that has worked on these regularly in the past.

Just remember that I don't have the cable. I just have the stuff at the int housing, the stuff from the inside of the upper, and steering wheel with mechanism's attached.

As far as the pump right now, It is a crank mounted "Johnson" pump. you pull the 3 crank pulley bolts, sandwich the pulley to the crank with the pump flange, reinstall 3 longer bolts.

It is drawing off a 1" thru hull fitting that was in the boat when I got it.

On my OMC there is a 3/4" hose that comes from the inter housing (discharge from leg pump) that goes to the thermostat housing. The normal flow splits there. Either it goes to exhaust mani's or it goes through engine if tstat is open, and eventually thru mani's.

All I did was add the crank pump discharge to that 3/4" line. So now both pumps are pumping to tstat housing. Right now, if I lose the drive pump pressure, I still have crank pump pressure coming in.

 

[BLDFW]

Re: OMC Raw water pump issue.

Wow, that pump setup sounds interesting. I'd have to see a picture but I think I get it. It's reassuring to have a secondary source of cooling should there be an impeller failure.

On the seal, the three pieces, the two seal rings and the gasket liner should be enough to seal out exhaust gases but again, the clear hoses will validate that. I believe that's about the only place where air can get into the water flow. It will be interesting to see how it pans out.

On the tru-course, I've been monitoring cables on ebay off and on. I'd only need the fittings at either end. Since it's at the end of the season, there's no hurry but if you've got them handy I guess there'd be no time like the present to talk about it. My old cable/pulley system
bound up on my one time so it's always been in the back of my mind that it could be problematic at the least opportune moment.

 

[KRH1326]

Re: OMC Raw water pump issue.

OK I get the seal issue, and that may very well be the problem.
When I put the clear hose on, I should be able to see if I am sucking air/ ex gas.

But I am thinking about other places that it could come from. I know that I braised the copper joints with silver. I do that for a living and my copper joints hold hundreds of psi easy. BUT, If I did have a leak in it, it could suck there. At lower rpm the leak could be under the water line, and not really be a factor, but as I climb up on plane, could I raise the leak above the water line, and then start sucking?

Plus the fact that it coinsides with higher rpm, I am highly concerned with the location on the cav plate of the water pick up. Did I have the right one? Why did they have two different possible places? Was one better than the other, was one found to be a failure and they went with the other?

 

[BLDFW]

Re: OMC Raw water pump issue.

As I would see it from my rebuild experience, as far as the lower unit goes, the leak could only be in three places, 1) where the tube meets the exhaust housing at the top of the tube, 2) the seal of that particular housing under the previously mentioned sleeve, or 3) the sleeve itself. Once you are above that, now your into the upper unit and the pump itself. You might have a breech somewhere in the lower part of the upper unit but not sure what you'd look for at that point (ie; a screw hole, a crack, etc).

As for the braised connection, even if it leaked, I would think it would be insufficient to cause the water to run out and no longer pump. It would probably be represented by a pinpoint bubble stream in the water hoses. I tend to think it would not be that particular source but it would have to be checked. The tell-tail bubble stream in the clear hoses are going to provide the biggest insight into the volume of air getting into the system so until you can run it at full RPM and watch the hoses, it's all guesswork.

 

[KRH1326]

Re: OMC Raw water pump issue.

Yes I see your point. Will replace hoses tomorrow.

I will post back what I find.

Thanks again for your help.

 

[BLDFW]

Re: OMC Raw water pump issue.

Cool. Looking forward to hearing the outcome. It's definitely something of interest to me!

I'll ping ya offline via PM on the tru-course stuff!