Merc 500 water pee question, is my impeller shot already?

[hotrod53]

My '77 Merc 500 4 cylinder was peeing fine when I moth balled last year. Yesterday I hooked up the muffs and fired it up ... no pee. I pulled the block plug by the spark plugs and it was dry, I also snaked the pee hole. Today I blew compressed air thru the drain plug and I could hear air in the intakes on the lower unit. I hooked up the muffs again and the water ran for probably 3 minutes when I realized that I had water coming out of the exhaust in the center of the prop. I started the motor and I got a pee stream. It was almost zero at idle, but I had a needle valve stuck (thanks ethanol), therefore it wasn't idling very fast. At a slightly higher idle, I got a decent stream. I pulled the carbs and put in the new ethanol compliant needles that I have had since last year.

To back up.... this is the start of the 3rd season since I rebuilt the pump, new impeller, seals, and a new impeller cup. I wouldn't think it would be shot yet, and it has only been on the river so it hasn't been ingesting any sand. I use the boat about 8-10 times a season and not long runs, my hours should be pretty low since rebuild. I also have very low water pressure at my house when I'm testing it, only about 38 psi, couple that with the muffs only feeding water in one side, I hope that explains it.

This motor has notoriously been slow to pee on startup, even with a brand new impeller, higher rpm it pees like I would expect. The original owner told me that he never changed the impeller and it lasted for ever.

I guess I won't know anything for sure till I put it in the river... any advice or input?

 

[bgc]

Re: Merc 500 water pee question, is my impeller shot already?

I change impellers every other year. New impeller is cheaper than a new powerhead.
Have you flushed the motor and is the telltail coming from the exhaust side or the top of the block?
During my rebuild I found an excessive amount of sediment and calcium in the passages and block. I used an acid wash (Muratic and water) to remove buildup.

 

[hotrod53]

Re: Merc 500 water pee question, is my impeller shot already?

I have not flushed with anyting but compressed air. I typically keep an eye on the tell tale since it was clogged once.

What is your proceedure for flushing? My motor sat for 13 years before I got it and put it back in the water. At that time the water pump was new, but according to the original owner, it was always slow to pee, and he owned it since the late 70's.

 

[bgc]

Re: Merc 500 water pee question, is my impeller shot already?

Mercury makes a flush adapter, screws into the larger screw hole above the anti cavitation plate, port side.
Undo the plastic fitting the telltail hose is contented to and check for buildup. The hard water from the limestone and sediment in the water builds up over the years.

Use a mild acid in a barrel, Muratic or vinegar. Don't go overboard with the acid, you want to loosen the build up not eat the motor apart. Run for a bit with the prop off. Flush thoroughly with clear water.

 

[hotrod53]

Re: Merc 500 water pee question, is my impeller shot already?

Update: I got the new needles in, set the floats, reinstalled the starter and carbs, pressurized the fuel lines and the lower carb bowl is about as fuel tight as a whiffle ball! I removed the bowl while still on the motor .. who even knew that was possible... I put the hard bowl nut gasket on the outside and the softer paper-like one inside the bowl and its holding its fuel again. Reinstalling the bowl nut with the carb still on the motor is something I don't care to ever have to do again.

It started on 2 carbs and idled nicely, the pee stream was better than the last time, probably because it's hitting on all 4 cylinders and the idle is now a bit higher. Question: if I have a weak pee stream at idle but I have water coming out of the prop, I assume that is an indication that I have enough water flow for cooling, correct?

I took a ride to the river and saw that they put the docks in, Tuesday evening I'll do a maiden voyage and see where I stand.

 

[Laddies]

Re: Merc 500 water pee question, is my impeller shot already?

Your engine has the telltale hooked to the bottom of the exhaust housing, they were really prone to limeing up and mud partly pluging the fittings so if you look at the top of the engine you will see a 1/8 pipe plug remove it and run the telltale hose to the top fitting that's where all the newer engines are hooked. Then on some engines you can get to the original fitting on the exhaust and you can remove it and put a plug in, if you can't get to it easily just plug the old hose and tuck it in the bottom cowling.

 

[Urbina]

Re: Merc 500 water pee question, is my impeller shot already?

clean your hoses one by one spider nest are always plugging mine up

 

[hotrod53]

Re: Merc 500 water pee question, is my impeller shot already?

Laddies... I have removed the 1/8" plug a few times, its around spark plug #2, most recently to blow compressed air thru it. I have not looked to see where the tell tale is connected but I do recall a hose going around the block somewhere. I'll pull it apart and take a look.

UPDATE: OK, I looked down in there and there is a rubber hose that comes from the tell tale, up, loops down, runs across the back of the block way down inside the cowling, and connects to a fitting at the bottom of the block way down in no-man's land. I can see the hose clamp and maybe I can disconnect it, but there is no way to get to the fitting down there. I could cut off the hose in the middle and put in a plug and a clamp on it, then put a 90 degree brass fitting in the 1/8" plug hole. I can barely reach the hose going to the tell tale, it's down under the coil packs.

 

[bgc]

Re: Merc 500 water pee question, is my impeller shot already?

If she's been runnin the Ohio or Mongahela your gonna have silt and calcium. Follow Laddies recommendation and check for set on the impeller. None of this is worth risking the powerhead....trust me I just rebuilt one, what a PITA.

 

[hotrod53]

Re: Merc 500 water pee question, is my impeller shot already?

BGC, I already know if this one goes, it's not getting rebuilt. No power trim, no head, crankshaft comes out the bottom with all of the rods and pistons.

The Monongahela is where 99% of it's hours come from. I'm going to run it Tuesday just to test it, but even if I decide no impeller, it will definately get changed this year or next. The previous owner had never changed the impeller in 15-20 years and he ran it in the MON! I was suprised how good the impeller looked when I pulled it. Sure it was bent a little, but still working last it was run.

I actually have a friend whose family ownes a marine repair shop, he'll give me a hand. I had issues getting the gears right last time. Couple that with this motor having a Bay Mfg shaft extender made it goofy, especially with a missing shift lock rod and not knowing which one was the right one.

 

[Laddies]

Re: Merc 500 water pee question, is my impeller shot already?

You want to hook it to the plug on top of the power head not the one on the water jacket cover so you will probable have to but a new piece of hose. By hooking to the top the power head is completely full of water before any comes out the telltale.

 

[hotrod53]

Re: Merc 500 water pee question, is my impeller shot already?

I ran it Tuesday and it ran great. Like last year, at initial idle there is no pee, just an occasional dribble, rev it once and it pees fine at idle, it does that on every start as if it's filling the block. Running up river it shoots a very strong stream. After being run once, I'm curious to see how it acts next time, it may be back to normal. I am however going to order a new impeller.

 

[Laddies]

Re: Merc 500 water pee question, is my impeller shot already?

A engine that dribbles from the telltale at idle usually has a impeller with a set in it, at idle the rubber impeller is a displacement pump as it wipes the housing but at higher RPM it is a centrifugal pump and the impeller acts as a slinger

 

[bgc]

Re: Merc 500 water pee question, is my impeller shot already?

I ran it Tuesday and it ran great. Like last year, at initial idle there is no pee, just an occasional dribble, rev it once and it pees fine at idle, it does that on every start as if it's filling the block. Running up river it shoots a very strong stream. After being run once, I'm curious to see how it acts next time, it may be back to normal. I am however going to order a new impeller.

Good call, impellers are cheaper than motors.