53FordF100

I am in the process of working out a few bugs on a 1999 29' Powerquest running twin 7.4L MPI engines. I have about "0" engine experience when it comes to marine engines so here goes: My Port engine runs between 40 and 60 psi oil pressure (40 at idle, 60 at WOT) with an engine temp of 170 degrees at all RPM's. (On the maiden voyage I had no temp reading on this engine, I replaced the thermostat and now she comes right up to 170 deg.)

My Starboard engine runs 40 psi oil pressure and 150 degrees engine temp, stable at all RPM's.

One of the short blocks is new and I don't know which one, however I am curious why the starboard engine is so stable at all RPM levels.
The original engine has 170 hrs. the new engine has 30. All readings are off the gages.

My thought is that the Port engine is the new short-block, its still tight and breaking in, thus creating more friction and more internal heat. This may also explain the higher oil pressure.
Should I be concerned about the difference between the two motors? Any advice is appreciated.

Thanks, Nate

mcollinstn

A) Factory electric temp gauges and pressure gauges, along with their accompanying electric sending units are held to a fairly wide range of calibration. Unless you have used "known" calibrated mechanical temp and pressure gauges, you can't know for sure what your "real" temp and pressures are. What you CAN do, though, is to buy a set of inexpensive mechanical temp gauges and put the probes in a pan of water on the stove and heat till boiling. The gauges should follow each other very closely. Then install them (temporarily) to double check your electric gauges. Whichever one is way off, swap the wires on the dash from the two senders to see if the trouble follows the gauge of the sender. Replace the out of spec sender or gauge.

Pressurewise, hotter oil means thinner oil and usually lower oil pressure. Hotter also means different thermal expansion in your engine components. This can affect oil pressure.

I believe low spec for oil pressure is somewhere around 7psi per thousand rpm? They don't have to match, and if one short block has been replaced, it may very well be equipped with a higher volume or higher pressure oil pump or be built to different clearances which will affect oil pressure. I wouldn't get too bent over it.