Optimum Water PSI
 

Not trying to look stupid but what should be my optimum PSI at idle and WOT for a 502 NA

Thanks
Bryan

At idle, the guage will barely move.
Ideally at WOT, you would want 20psi or so.

Thanks... I am going to run a gauge at the block and one at the manifold and was curious what I should see

Brand new impeller gives about 1 psi@idle on EFI engines with low rpm [600] idle . 20-25 psi WOT or about 5000rpm. When pressure readings start to fall under 20psi @WOT, it's an indication of an impeller getting tired. Once it falls under 15psi at WOT, it's definitely the time for replacement. Mercruiser recommends to replace the impeller once a year or at 100hrs.

That is one thing I always do is replace the impeller every year (Previous boat) The guy I bought this boat from hadn't changed it out in 3 yrs (had the mentality "if it ain't broke don't fix it) Got a new impeller and housing this year (housing was thrashed), thanks for the info, I know now where I should be.
What is considered to much PSI (concerned about head gasket failure)

Don't mean to hi jack a thread here but my procharged EFI 502 only makes about 13 psi at wot. Had a new sea pump about 30 hrs ago.. Probably no T stat in it.. I'm thinking I need a restrictor in the t stat housing?

I would be more concerned about the water flow than pressure. With no thermostat, our water pressure is about 10 lbs at speed with a max of 100-110 temp.

Any readings of PSI and or pressure is a measure of restriction. Just because you have a ton of pressure doesn't mean you have the correct amount of volume needed. There is always a happy medium of balance between pressure and flow and volume.

A lot of times proper flow volumes also can not be obtained even with high measured pressure readings as water pressure, water flow and water volume are 3 separate issues. Anyways my point is Mercruiser has specific water volume output tests along with the measurement specs to make sure your motor recieves the proper volume of cooling water flowing into the motor or heat exchanger.

525EFI, approx 3.5 psi @idle, 30 PSI mechanical gauge is pegged at WOT. Smartcraft says around 35 PSI.

Most efi smartcraft engines I've checked with diacom at idle are more along the lines of 1 psi +/- . A little under 1 psi to less than 2 psi at warm idle