I just said this in another message but I've been meaning to post
my results to the list for a while.

Any chance he can, Dennis Haynes quietly points out that you should not
fill your oil to the upper line on the dipstick.  Dennis, who (as usual)
knows what he's talking about, should be shouting from the rooftops!

With oil at the "full" level, the crankshaft whips it into foam. (mmm,
foam!)  The oil pump is then pumping oil and air, not just oil.

I accidentally verified this:

Our oil pressure, at HOT cruise (>3500RPM for 30 minutes at the very least)
was around 32 PSI with our UH (Unknown History) 2.1 engine, oil level at
the halfway point.  With our van parked on a slight slope, I checked the
oil.  It was down to "min" so I filled it to the halfway point.  After that,
our oil pressure in the same conditions was perhaps 28 PSI.  Freaked me right out!

I checked the oil level in a flat parking lot and sure enough it was
at "MAX".  Oops.  Since we were on a trip, I had to get a bit creative.  To
lower the oil level, I removed one valve cover and let the engine idle.  The
oil dripped out of the head into the valve cover + newspaper I'd put on the
ground below the head .  I disposed of the oil in a crystal clear sparkling
mountain stream and put the cover back on.  (I removed ~400mL, but the level
as indicated by the dipstick was juuuust under "MAX". So the dipstick evidently
does not read in a linear fashion.)  Anyway, my pressure went back where it had been.

Want a bit more oil pressure for free?  Lower your oil level to halfway,
while measured on FLAT ground.

tabe johnson/87 westy