Grease as an air sealant?

[srah1953]

A mechanic once told me to put grease on the threads on the screw-in cap on the sea water strainer to make it air tight. I had a leak on the cover of the strainer to the pressurised water pump. As part of my investigations I put white universal marine grease on the threads of the cover and water spewed out all around the threads.
I won't be inclined to put grease on such things in the future but I would be interested in any thoughts as to what happened.
Many thanks

 

[NormanS]

Grease or Vaseline or similar is normal on the cap of many water strainers. What I do find curious is that water spewed out. It depends on how your pump and strainer are plumbed, but it is more common for air to leak in to many strainers, which tends to make the pump "lose suction".

 

[TradewindSailor]

Your water leak sounds like a problem with the seal ..... that on most filters sits in the lid. The threads don't seal .... they just provide the pressure for the top of the filter housing to mate with the seal, and the seal to the lid. Applying grease just reduces the friction between the threads, and the seal and the mating surface to allow the lid to be tightened more. Be careful though because overtightening can not only damage the seal but the lid can crack too.

 

[cryan]

The grease is just to make it easier to remove/ loosen the threads at a later date. It lubricates the threads and protects from corrosion. In the marine environment you should never put threads together dry unless the manual specifically states it for torque purposes. Even then it might sllow for a thin mix of anti seize and lub oil.
Air getting in is down to either the gasket/seal or poor mating surfaces.

 

[srah1953]

Excellent. Very many thanks. I'm wondering, if this conceivable, that a large dollop of grease made it harder to screw the cap tight, or else, I was just being too cautious as the acrylic cover was cracked, possibly from someone screwing it too tight previously (as suggested). I'm separately trying to seal the cracks but that's a different question.

 

[ghostlymoron]

If the cover is cracked, it needs replacing as it will let air in which may affect cooling and damage the pump.