Oil pressure sending unit problems...
 

Hey guys, wanted to give a heads up about a problem I just had with my Mercruiser big block. Just built my motor over last winter. Installed a brand new Sierra oil pressure sending unit (bell style). Motor never had great oil pressure from day one. 45 psi cold, 25 psi hot. I wasn't happy, thought a new motor should be better. Used it all season, until last week, pressure started diving off under throttle...took a few years off of my life. I hooked up a mechanical gauge, and it had 60 psi cold, and 45 psi hot!!! Installed a new Merc seding unit...BAM...60 psi. It's getting hard to work with these junk new parts, it can make you crazy!!! Hope this helps somebody.

Does not surprise me, Sierra stuff is mostly junk.

Learned that the hard way!!! lol.

Don't use their exhaust manifold gaskets either. Coooked a set out in less than a season.

sending unit must also be compatable with gauge as well..not all will work together..

Using thread sealant on an electric sender can cause this problem too.

Yah, I'm just glad the motor is healthy!

how do you guys check a mechanical gauge while your up on plane? I've been wanting to try this as well.

Buy a proper length of copper tubing and wire tie the gage so you can see it at WOT.

Or you can just put a mechanical gauge in the dash. One of the fitting companies has a nice cloth braided hose, -4 is the smallest it comes in I think. Or you could have your local Parker store make you up one.