1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffled.

[Beaches of Cheyenne]

I just bought a neat old '77 Lund with a '77 Merc 500/50hp serial number 470XXXX. I have a water circulation problem that I can't seem to find any further info about in the SELOC service manual. I posted on another recent thread but now think this is a different problem and best to start another. Anyone have any thoughts or ideas? Let me explain where I'm at the best I can for a mechanically inclined outboard novice...

The impeller was pulverized and the water pump upper housing was also damaged. I put on a new water pump, reinstalled the lower unit and still no tell tale stream. With the lower unit back off I ran compressed into water intake tube and from the other direction, into the tell tale. I noticed air whistling inside the drive shaft housing at the upper end. I connected a water hose to the intake tube. At high pressure I get a stream out of the tell tale, at low pressure I don't. Water instead comes out just where I heard the whistling, the path of least resistance, and runs down the inside of the drive shaft housing. This is at the upper end of the housing just under the powerhead on the port side. Looking up in there I cannot see the exact opening but it's left of the intake tube and drive shaft coupler. Is this normal, some kind of overflow maybe, or do I have a bigger problem?

Anyone have any advice or thoughts? Me and my frustration would really appreciate it.

 

[narvlebenoit]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl

Are you running i t with ears or in a barrel.

 

[Beaches of Cheyenne]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl

Thanks for reply. Both ears and submerged. I first noticed no stream when I backed it into the lake this week. Pulled the intake screens and found impeller parts. Back home and pulled lower unit and new water pump. Lower unit back on and used ears, no stream. lower unit back off and hose connected directly to tube and tell tale stream at high pressure but not low. At low pressure water comes out location described.

 

[narvlebenoit]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl

dont care for the ears .you say you put new water pump I take it that means housing and all.

 

[Beaches of Cheyenne]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl

New housing and all.
Is it a closed system from the intake tube to the tell tale or is there some pressure valve or something of the sort under the powerhead? Does this motor have a thermostat? If not I must have a crack or bad gasket or something allowing water to drain back down from the top of the drive shaft housing on the inside. My manual doesn't seem to be to much help on the subject.
I'm going to put back together and run in a bucket and watch how it heats up. Will it by chance start a tell tale stream after warming?

 

[narvlebenoit]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl

check for a bad gasket and the little half moon key it should take maybe 15 seconds after starting to pee put the cold start to about 1500 rpms in a barrel not on ears.

 

[Beaches of Cheyenne]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl


Thanks for the advice, I'm sold on the barrel!
I rechecked all the new water pump just in case. Pulled brass tube and inspected. Ran weedeater line up through the tell tale. Put lower unit back on and into barrel, not ears. Fired her up and vwa-la. Good pee stream, nice cool head. The water I was seeing out of inside top of drive shaft housing must be normal. Same as dribbles spray out of 2 rectangular exhaust ports below head when put together?
I'm giddy and can't wait to get her on the water, sea trials part 2. I think I'm gonna love her!
Thanks again for the input, and...getting me off the ears.

 

[narvlebenoit]

Re: 1977 500/50 Merc with cooling circulation problem, no tell tale stream. I'm baffl

gladyou got her going I have a 90 inline six it wont pump water with the ears good luck on the water.