Merc 500 Water Pump Issue

[Solomon Shaffer]

Just bought a '70 Merc 500. It starts and runs fine, but does not pump water.
I took the hose off of the 'pee hole' and blew - it seemed to be blocked.

I removed the lower unit and checked the impeller - no cracks or problems there.

I took a water balloon, hooked it to that hose I had blown on, and water barely trickled out. Soon the blockage or whatever came free and water poured out the bottom...I was very happy thinking that I had solved the problem.

That's when I noticed that the water wasn't coming out of the copper pipe but aroundit. I don't know much of anything about outboards so I put the unit back together to see if I had fixed it (crossing my fingers) and of course I did not.

Any ideas? It seems that between that rubber tube and the copper pipe there is a leak of some kind?? Any help would be appreciated.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

also...it does put some exhaust smoke out of the tell hole and the main exhaust ports on the shaft.

 

[prolinews]

Re: Merc 500 Water Pump Issue

not sure where your from but down south we have dirt daubbers that pack crap in our pee holes. Run a thin wire up hole to clear blockage. Make sure muffs are good and tight.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

Thanks for the reply....that's what most people say. I have taken the water hose off of the 'pee hole' and attached a water balloon to it. Before that, you couldn't blow air through the hose. Now you can - but the air doesn't come out of the copper hose that connects to the water pump at the bottom - it sounds as if it's coming out just below the motor.

If i attach a hose to the copper tube at the bottom, I should get water spitting out of the pee hole, right? I don't - it just acts as if its spilling out of the top of the tube and running back down.

I'd like to know what is in between the copper tube and the rubber hose....

 

[sschefer]

Re: Merc 500 Water Pump Issue

You might get a little but not a full amount until the thermostat opens.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

so an engine this old does have a thermostat?

 

[Aqualift]

Re: Merc 500 Water Pump Issue

Your motor does not have a thermostat. If you can force water back through the tell-tale hose (pee-hole), it will exit out the bottom of the block. It will appear to be running on the outside of the copper inlet tube like you mentioned. That is normal. But, if you don't get water coming out of the tell-tale with water circulating up the copper pipe from either the water pump or a garden hose, you have a blockage or leak in the system.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

Ok, that makes sense & helps. I have taken a video of what happens and I will post it if need be.

I just put a regular garden hose on the copper pipe and still got nothing out of the pee hole. I tried siphoning the top hose and i did get a weak flow. (With water leaking out around the "50hp" signs and pouring out the bottom.) I guess my final test will be to put an exact fitting hose on the copper pipe and see what happens.

If there indeed is a leak, where do I go from here? I have no idea what to tear apart next. It looks like I'm going be taking off a lot of stuff.

 

[Aqualift]

Re: Merc 500 Water Pump Issue

Do you have a plug on the top of the block? If so, remove it and see if water comes out of that opening. Also, when you forced water backwards through the tell-tale hose, did you watch to see if any water was leaking at the fitting where it attaches to the bottom of the block? Is the exhaust cover plate getting nice and cold when you are circulating the water?

I have a 68 Merc 500 powerhead and the passageways were badly corroded and blocked to the tell-tale. It was a lot of work to remove everything and clean them out, but it solved my problem.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

I can't see where the tell tale hose goes into the block. I'm not sure what I need to take off of the engine to actually get in there. I'm no mechanic but I don't want to take this engine to a shop and say "have at it."

 

[Iandayen]

Re: Merc 500 Water Pump Issue

I just finished fixing up a 68 merc 500 thunderbolt.

First off, there is no actual head on these things, the plate around the sparkplugs is a water jacket, and the gaskets for it are like $3 and you might be able to pick one up locally (I did)

I thought I had a problem with mine too, I replaced the impeller and when running on muffs or in a barrel I didn't get any water out of the tell tale, and I got a tiny bit if any when running the garden hose right to it with the lower unit removed.

I did have mud dauber blockage on my pee hole that I had to clear out though.

Your pee hole is on the bottom right side of your lower cover, inside the cover you should see a fitting and a tube coming from that fitting to your block.

A good idea would be to remove that cover, screw your plugs back in, hook the garden hose up and see if you get water up into that area, if so, replace gasket, then find the rubber line and remove/clear it out, try and clear out your fittings and then you should be good.

My peehole doesn't put out any water really until i have been in the water running for a couple minutes, and then it's not a solid nice stream until I'm cruising along, at idle you don't get much out on these motors.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

Iandayen:

The cover you are saying I should remove is that one around the spark plugs, correct? (Just checking before I start tearing.)

I didn't mention that the copper pipe does seem to be loose. It travels quite a bit - I don't know of this is normal or not. There is also a very large rectangular "pipe" that fits into the LU. I'm not sure what that is. (Like I said, I'm new at this!)

I have cleaned the fittings at the tell hole and have run water through the rubber hose that travels around the block to the other (left) side. That's where I lose it tho - I can't see the exact spot where it goes in.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

http://www.youtube.com/watch?v=FGqH4YBlhWQ

Here's the link to show you guys what is going on.

 

[Aqualift]

Re: Merc 500 Water Pump Issue

The rectangular pipe is the exhaust tube.

You clearly have a blockage and/or leak.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

BTW, I saw your boat on you tube - it looks really nice! I hope my Merc runs that good once I get this prob. solved.


I agree - I think it is a leak. What's the next step? I'm thinking I had better get a manual of some kind. Am I correct in thinking that I'm going to have to unbolt the powerhead from the chassis to access this stuff? (If so I'm doomed because I have absolutely no desire to mess with all of that throttle and shift linkage junk.)

 

[Aqualift]

Re: Merc 500 Water Pump Issue

Thanks for the compliment.

Yep, the only way to check any of the passageways or gaskets is to remove the powerhead from from the base and start exploring. Here is a picture of my 68 Merc 500's powerhead after removal and replcement of gaskets. You can see the fitting for the tell-tale at the lower right. It was time consuming and a little difficult, but I was able to do it over the course of a couple a days. I had to replace the exhaust cover, baffle plate and powerhead base gaskets in the process of cleaning up the water passageways.

You might also want to get a better seal with your hose to the inlet tube, so you can make sure your getting enough water pressure into the system. This might magnify any leaks or get more water to come out of the tell-tale hose. You could have a leaky powerhead base gasket, bad inlet tube seal at the base or a bad gasket elsewhere. A possible blockage would be easier to find with the powerhead removed too. That is one reason that I mention you remove the plug from the top of the block to see if water exits from there. (if your model year has that)

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

That's what I was afraid of. I'm definitely going to try to test it again with a better fitting hose.

I'm not sure where this 'plug' on top the block is. What is it made of? (Rubber, metal, etc) It maybe possible that I don't have it.

Thanks for your help...

 

[Aqualift]

Re: Merc 500 Water Pump Issue

The plug is threaded metal. Here is a picture of where it is located on mine. (red circle) Part of it is blocked by the top support cowl. Use a slotted screw driver to remove. There shouldn't be water dripping out of the area near that 50HP decal either.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

Where is the picture?

Somebody told me at church today that it could be that something froze and busted because of improper winterization.

 

[thefairlaneman]

Re: Merc 500 Water Pump Issue

Nice engine.. Heres my 60 merc 300 thunderbolt