69 Merc 500, questions about lower unit and coolant line

[rabbit121]

I recently picked up an old boat with a 69 Merc 500. The guy that had it had bought it with the lower unit cracked in half and located a new one but never installed it because the bolt holes were slightly off. We got the unit installed and working fine but I suspect something is missing where the cooling line comes down and meets the lower units impeller housing. the line coming down the shaft looks like a copper pipe, and the impeller housing has a tube coming up with a bit of a slot cut out of the side. the tube extending off the impeller housing seems a bit larger diameter than the copper pipe going into it and fits loosely. so I'm pretty sure any water being pumped is not being forced up the tube...

Am I missing a part or could it be that the pump housing is just different than the one that would have been in the original unit?

 

[green4themoney]

Re: 69 Merc 500, questions about lower unit and coolant line

this is just the water tube guide, its to help line up the water pipe with the pump housing when re-installing the lower unit, the water tube is initially sealed lower in the pump housing with a water tube seal that is a very good seal to the water tube, the guid will fit loosely around the water tube, but thats not what seals the tube to the pump, just guides it in when re-installing the lower unit... everything is normal.

 

[rabbit121]

Re: 69 Merc 500, questions about lower unit and coolant line

thanks for the reply.

Another thing I noticed is the impeller itself fits extremely tight in the housing. the fins must be curled to fit it in the housing..

is this normal as well?

 

[green4themoney]

Re: 69 Merc 500, questions about lower unit and coolant line

yes, the veins on the impeller curl into the pump housing, this is how they pump, they are placed on an offset and as it rotates it intakes water when then veins are almost straight and it compresses the water and pumps it up through the housing when they are bent, here is a very basic and knowledgable explanation of the cooling system on outboard motors

http://www.ankn.uaf.edu/publications/VS/cooling.html

 

[green4themoney]

Re: 69 Merc 500, questions about lower unit and coolant line

and remember, never under any circumstance run the pump or engine without any water supply, just 5 seconds without water can burn your impeller, it needs water from all the friction of rubbing against the pump housing, and water does a fine job of lubricating and cooling it

 

[rabbit121]

Re: 69 Merc 500, questions about lower unit and coolant line

ok thanks!

I was speaking to somebody that said there is supposed to be a grommet that fits into the guide extending off the pump housing. he said the groove in the side of tube on the pump housing is to hold the grommet up.

I think this may be why no water is getting pumped.



Also... I found the exit where the coolant is being "peed" out of the head is completely blocked and it looks like it has been for a while. Is it possible this engine can still be cooling ok and just spit the water out the exaust?

The motor sounds fine and the only difference between now and last time it was run is the new lower unit I installed. so I can only assume it has been cooling up until now or it would have been most likely seized up, right?

 

[green4themoney]

Re: 69 Merc 500, questions about lower unit and coolant line

well if the indicator hole was blocked and your pump is still working, then yes your engine was still being cooled properly.... but is it pumping now? that you've cleared the blockage? thats the main concern, as long as it was still pumping you will be fine but if the indicator was blocked and your pump isnt working then thats bad news, the block fills up with water and the indicator usually comes off the top of the block to let us know the block is filling up with water and pumping it.