~ And now, on to my own problems:
~
~ I was reminded of an issue with my Harvey over the weekend. Oil. First, what
~ kind are we using in our A-Series engines? I've been using 20W50, but this I
~ think is wrong. With the 20W50, however, my oil pressure gets a little
~ creative. At hot idle, it's about 30-40 psi, no problem. Off-idle hot, it's
~ a little over 60 psi, no problem. But if I'm braking heavily (i.e. not too
~ terribly much force, but as much as the crap tires on the car can handle) in
~ neutral (at idle speed), the O.P. gauge plummets to zero, then works back up
~ to 30-40 after I stop. If I'm braking heavily in gear and the RPM's are above
~ about 1500, then this doesn't happen. I'm assuming the oil in the head
~ gallery is slogging to the front, starving the gauge, but at higher speeds,
~ the flow is great enough to avoid this. Is this normal? Am I harming my
~ engine by braking hard in neutral? Can I install some baffle or other boffo
~ trick to avert this icky situation?
You can avoid running the car with low oil level. That's almost
certainly what is causing this symptom, not the weight of oil.
20W-50 is a fine weight for many temperature conditions; that's not
even a possible cause, as near as I can tell, much less a probable
one. Actual probable causes, in order, include:
- Low oil level. The only "sloshing" that goes on under braking
(or cornering) is in the oil pan. The B series engine is
notorious for having oil problems when you're as little as 1
quart low, particularly when you make high-G manoeuvers. If
memory serves, the oil-pressure pickup on the A Series is at
the rear of the block, not in the head. Oil pressure drops to
zero because there's no oil at the pickup; the gauge measures
oil under pressure, and even 30 psi is enough to ensure that
it can't "slog" to the front. (That's two atmospheres, for
reference.)
- Something loose inside the motor, either a piece of something
that slides around and occludes the pickup or something worse.
If for some reason there's a loose drive in the pump, for
instance (which is at the back of the camshaft), you might
run into trouble, but I've never heard of that.
- A bad gauge or gauge connection. Is it an electric gauge?
Could you have a short to the brake lights that's blowing
your gauge away when you hit the brakes? (Try it standing
still, just for fun.)
I've actually experienced problems #1 and #3, admittedly on a B
Series engine, but they're largely similar (oil pumps are quite
different, of course, but the pickups and pans are alike, if I
remember correctly). I would recommend carefully checking not
simply the oil level, but the dipstick itself, and the dipstick
tube. There should be a little plastic trumpet sticking about 2"
up from the bottom of the engine block; if that trumpet isn't
there, you'll be two quarts low even when the stick says you're
full. (Been there, done THAT.)
My money's on oil level; that's really common in BMC motors of
at least the A and B varieties. I can't imagine any way that
oil viscosity would cause the problem you describe. If you
were running oil too *thick*, you can sometimes have oil pressure
fluctuation on acceleration, but not on braking; that's almost
always level-related, not viscosity-related.
--Scott
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