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What should the water pressure be on a 1999/502 MPI,salt water cooled motor and where is the pest place to but a pressure gauge
 

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On my HP500EFI I see about 3 lbs at idle and in the 10 to 12 lb range at the higher rpm's. My engine came with Mercurys little blue drain plugs on the lower sides of the block, I pulled the brass adapter out of one side, drilled and tapped it, and take my pressure reading from there.

I lost an impeller once due to hydrilla plugging my pickup, that was my reason for installing a pressure gauge.
 

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Any pressure under 25psi should be safe for the engine, but IMO that is the edge. I would not want anything over 21/22 or so.

Year and what you cool it with isn't of any importance, it's a GM Big Block, it's a car engine, like all of them, are designed to run under 25psi coolant pressure.
 

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What should the water pressure be on a 1999/502 MPI,salt water cooled motor and where is the pest place to but a pressure gauge
Range at running speeds should be between 10-25, depending on the water pickup, and where the reading is taken from. 25 is pushing it, but should not create issues. 15-20 is the best range. under this, you may have water issues, and above it, you may start pushing past gaskets.

Best place to mount the fitting for the gauge is in the intake manifold on the large water passage that the Stat housing bolts to. This keeps more junk out of the line to your gauge. You can use the block drains, but there seems to be a lot more issues with rust and garbage plugging lines mounted there.
 
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