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1979 351 PCM overheating issue

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I recently replaced the impeller in my 1979 351 PCM Ski Supreme, because it was overheating; the impeller which was replaced had all fins broken off. The placement of the new impeller has NOT corrected the problem. When I used 'Add-A-Lake' to test, I had the opportunity to visually inspect the new running impeller, and it was turning; however, there was absolutely no water in the pump or lines. I then disconnected, inspected, and s***** all water intake hoses from the intake grate to the water pump. No obstructions were found. The boat was also put back into the actual lake and started, only to be met again with overheating. What other issues can cause no water uptake and overheating? With the limited knowledge that I have, it would seem that if there is a new working impeller and no obstructions in the incoming water lines, that there should be no problem with the cooling water intake system; BUT I COULD WRONG . :rolleyes: THANK YOU !!
 
Did you lube the new impeller?

a closed sea cock has killed many 'new' impellers...improper pump overhaul will prevent water flow as will a worn one - there's more to check than just the impeller...loose hose clamps will let the pump suck air and air doesn't cool very well...closed or leaking strainers, too, are high on the list... with the age, if original, the hoses themselves could be leaking
 
My boat doesn't have a sea cock or a strainer . I unhooked the pick up line from the water pump and hooked up a 10 " hose straight to a bucket of water . Still - no water coming out of the outbound side of pump . When I put the new impeller in , I didn't overhaul it ( bad me but didn't know that you could ) , thought that with a new impeller I would be good to go . By researching I see that I can buy them for my pump . Still can't comprehend what the rebuild kit will do though - figured with a new impeller , I should have excellent suction . Maybe I'm missing something . I have a feeling that my next plan of attack is rebuilding the water pump . The water pump doesn't need to be pre primed does it ? I never do that in the Spring time coming out of Winterization . To your original question - no I didn't lube the new impeller . Do you just put grease on the impeller blades ?
 
The rebuild kit (major overhaul kit) replaces the wear items expected to be "worn out" after 5 seasons (or so).

The "sealing surfaces" of the housing need to be smooth so a wet impeller makes a seal at all of its contact points...any roughness (irregularity deep enough to catch your fingernail in) will let air leak and impact the pump's operation. The Cam needs to provide sufficient deflection of the vanes...

they don't need to be "primed" but a new impeller should be lubed - not with grease but a water based friction reducer that won't attack the impeller's material. I use a water based silicone gel and apply it to the housing before the impeller.

finally, your impeller will last many seasons if you can find the time to remove it before winter storage...

BTW, how did you determine the direction to spin the impeller when it when in?
 
I'd also suggest getting the overhaul directions from the sherwood www site. There are comprehensive but usually target an experienced audience...
 
  1. the impeller which was replaced had all fins broken off.
  2. The placement of the new impeller has NOT corrected the problem.
  3. however, there was absolutely no water in the pump or lines. I then disconnected, inspected, and s***** all water intake hoses from the intake grate to the water pump.
  4. No obstructions were found.
  5. What other issues can cause no water uptake and overheating?

First and foremost..... which sea water pump is this? Belt driven Sherwood style, or crankshaft pump?

  1. You'll want to do your forensic work, and retrieve all of these broken impeller peices. These pieces can block and restrict coolant flow.
  2. OK.... if this is a belt driven Sherwood pump, did you orientate the pump body correctly?
    These pumps are ambidextrous, and it's very easy to re-install one incorrectly.
    (see images below)
  3. See above.
  4. Agian, you need to retrieve the missing impeller fins.
  5. Whether belt driven or crankshaft style pump, the correct inlet/outlet suction/supply hose connection is critical.


If crankshaft pump, this may help you.

Sherwood's crankshaft pump to the left.......... Johnson's crankshaft pump to the right.
.................



This would be as though installed on a Std LH rotation engine. Note the inlet and outlet ports.
(BTW, this pump is ambidextrous.... ports swap functions when reversed)






If belt driven sea water pump...... this first image would represent a correct installation for a Standard LH rotation engine.
Second image shows the same.

Third image would represent a correct installation for a Reverse RH rotation engine.
 

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  • Sherwood impeller Direction LH.jpg
    Sherwood impeller Direction LH.jpg
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  • Sherwood pump for LH engine.jpg
    Sherwood pump for LH engine.jpg
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  • Sherwood pump for RH engine.jpg
    Sherwood pump for RH engine.jpg
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It's a Sherwood belt driven pump . Marked the pump before disassembling it . Hopefully overhaul kit will arrive tomorrow . Bummed out that it didn't come today . Bad U.S. mail . Bad bad U.S. postal service .
 
Can't believe that I did this - but yes , I installed the water pump in backwards . Installed it correctly ( even though it looks backwards to me - LOL ) , and presto - water pump is pumping water like a faucet !! Ok , here it goes . BAD me . BAD BAD me !!
 
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