Oil Pressure Goes to Zero when Braking Hard?

Something interesting happened today. The pressure gauge on my 91 dropped
quickly toward zero when I braked hard coming off a freeway exit. The
pressure immediately came back up to normal as soon as I let off the brake.
I kept a close eye on the gauge at the next stop light and it did the same
thing. I checked the oil level when I got home and it was at the low level
mark, so I added a quart. The pressure now stays up where it should be even
under hard braking. I'm guessing that the oil pump lost suction as the oil
sloshed forward in the oil pan. What surprised me was that it would happen
when only a quart low. Thoughts?

Gus (91 BRG)

Gus, when your engine is turning at "freeway speeds", there is over 1/2
of your oil in a spray condition inside your engine. It takes time for
the oil to run back down to the oil pick-up to be pumped again. Don't
drive your car fast, with a low oil reading ! Remember the Miata also
has a "spray oil system" to the piston and cyl, assy's that most other
cars do not have. It will not harm the engine to run with 4 qt's of oil
when you are pushing the engine hard. ( autocross or freeway cross
country ) AND you will find that up to 60% of your engine heat is acting
on the engine oil. ( oil coolers on 94 and on. ) are not there just
because they didn't have anything else to do with them. :-)

Bruce RED '91

Marcio Watanabe > wrote in:

> When full, the oil pan of a 91 takes only 3.5 quarts of oil. "Only a
> quart low" means 30% less oil in the oil pan. That's a significant
> amount. I find that on the track, a Miata needs to be filled full and
> a bit more to prevent oil starvation.

Question: Does someone make a baffled pan for the Miata?

Slightly off topic, but I've noticed that my miata has a slight oil
pressure drop lately. Not severe like this, but running about 20% lower
than normal.
Usually, 3,000 rpm oil pressure is about 45 psi. Lately it's running 35
psi or so, just to the right of the 30 mark. Right now I'm not too
concerned, as the oil pressure is high enough, but I'm expecting it to
get worse. Change oil/filter doesn't help.
I normally run mazda filters and a major brand of dino oil.
Idle pressure is the same, or close enough that I can't tell the
difference.
Start-up pressure is max 45, used to be 65-70 psi.

What are your thoughts as to where to start looking.

wrote:

>Slightly off topic, but I've noticed that my miata has a slight oil
>pressure drop lately. Not severe like this, but running about 20% lower
>than normal.
>Usually, 3,000 rpm oil pressure is about 45 psi. Lately it's running 35
>psi or so, just to the right of the 30 mark. Right now I'm not too
>concerned, as the oil pressure is high enough, but I'm expecting it to
>get worse. Change oil/filter doesn't help.
>I normally run mazda filters and a major brand of dino oil.
>Idle pressure is the same, or close enough that I can't tell the
>difference.
>Start-up pressure is max 45, used to be 65-70 psi.
>
>What are your thoughts as to where to start looking.

Could it be your sender or oil gauge? I believe the oil
pump is a positive displacement unit.

Leon

--
Leon van Dommelen Bozo, the White 96 Sebring Miata .)
REMOVE THE "z"s -> www.dommelen.net

"EXIT THE INTERSTATES" (Jamie Jensen)

I thought about that, the one thing that keeps me from beleiving that
the obvious answer is the right answer, or maybe the easy answer is the
right anwser is the oil pressure takes about a second to come up from a
cold start. This used to be nearly instantanious. And I know the oil
pressure doesn't start for about that long, I can hear the valves
tapping at start-up like there is no oil pressure.
I'm about to do oil change number 2 since this problem started, so I'll
report if anything changes in the next hour after the oil change.