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Mercruser 4.5 250 HP Bravo 3

Chris I have been chasing a problem with the help of a mercruser tech. engine has a smartcraft gauge that shows block pressure. Starting out 3 psi block pressure at idle this is ok and constant. At 3ooo rpms starts out at 14 to 20 and as the day goes on 1 or 2 hours of running the pressure starts to fall. Has gone into guarding mode several times saying low block pressure. Only 60 hrs on motor in salt / brackish water. Seem only to do this after a long run . Pressure does get to 5 sometimes at 3000 RPMS. Drives me crazy. Running out of ideas was thinking stuck thermostat as temp never gets above 149 ...HEEEEELP lol And thanks for the help. Kenny
 
Took this thing out today runs great temp never above 147, Block pressure good at 14 to 16 fro about 30 min. Then after running threw a now wake zone slow . Speeding back up never above 7 to 8 psi. After it sets for a couple hours it good again for about 30 min and starts to fall . did not go into guard mode today. Has to be haunted.
 
K Stephens said:
Merc tech in WIS are saying maybe worn impeller or pump case. Rubber gets weak at temp causing less ability to move water
Click to expand...

That is ridiculous. Maybe time to find a better TECH.


The impeller is always in cold water and unless the impeller is missing pieces it is probably fine and so is the housing. We get about 6 years out of a housing here at the Jersey Shore. The front bearing usually fails before the wear surface.

Did you get the pic I posted for you on FB for the pop it?
 
w/ lot of sand, I'd think about a new raw water impeller and possible complete pump rebuild kit.... and not beaching/unbeaching the boat under power.
 
Poppit valve done new water pump new thermostat. Holds 17 psi block pressure on a run of about 4 miles at 3000 rpms. Then pull back to go through no wake zones. Then back to 3000 rpms only up to about 8 to 10 psi. No alarm this time but just cant figure why pressure is dropping. never above 147 on water temp.
 
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