I had the same problem with HP500 EFI motors
(sand blocking up the tube tapped into the block) I moved the water preasure pickup tube to the side plate on the oil cooler (had to drill and tap a hole) has not pluged up since!!!

I was probably misstating the facts in my case.....it probably is not sand but heavy sediment (like iron,rust, etc) in the block not real sand. I say that because I have no sediment in my intercooler. I had already pulled it off to check it. Remember, it does not take much to stop up a 1/8" tube. Maybe (has anyone tried this???) I could install a filter (like a fuel filter) in the block port. Would this work????
I have never had an overheat problem. I am very cool! I have tried thermostats (140 deg) & restrictors & still show no pressure. go figure???

93Formula, Do you have the Merc Thermostat housing with the Check-balls for the exhaust manifold feed hoses? Without those. you won't have any presure. Or if the spring is missing. It will bypass most of the water to the exhaust manifolds. resulting in no block presure. Just a suggestion.

I have mine installed vertical at rear of intake,you will need 15 to 18 pounds of water presure.

kanookster,
yes, I do have the Mercruiser housing with the balls & spring. Mine is a rough cast bronze "T" out of the housing (not black like most Mercruiser stuff).. Is this stock or after market item? Possibly the spring is weak? How would you test it?
The place I originally tried was at the Thermostat housing & put a "T" with the temp sensor. It did not work there, but that is on the "out" side of the thermostat, if I remember correctly. Would it show pressure before the thermostat opens (it's drilled like Procharger says to do)???
This really is a big help guys, & I get the feeling there are others out there with this same problem. Help & info is appreciated!

93Formula I agree that it seems no one really understandw the best place to put the Oil temp and Water Preasure sender as there are so many opinions on it.

Maybe a week spring 93Formula. I have my presure pickup in the Intake Manifold water passage, before the thermostat. After the thermostat you prob. won't see any presure. There's no resistance there, because it flows out the exhaust manifolds. Check the presure in the heads, or Intake, but not after the thermostat.

Thanks for all the help & suggestions guys....everyone works as a "team" here....this is good...very, very GOOD !!

93

What type of outdrive is it. I know an alpha I gen 2 will show no pressure. Any bravo type will show pressure.

Mine comes off the intake manifold. It goes vertical for about two inches. I have tried several different locations and the pressure readings have been very close. I like it there because if it leaks I will see it. My biggest concern is too much pressure and blowing my intake manifold gaskets and filling my motor with water.

If you have an alpha i gen 2 let me know and I can tell you the theory.