oil pressure drop

> wrote:
>oil pressure gauges seems to give erratic readings, not that they are in
>error, but something causes it - aside from temperature / oil level.
>
>I expect a mid-scale reading at highway speed, and at times in stop and
>go city traffic (is there any other kind) it dips - real low.
>
>Why the yo-yo readings?

1. Your sending unit is bad and is intermittently dropping out.

2. Your oil pump is bad and the pressure is dropping considerably at
low RPM.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

wrote:
> oil pressure gauges seems to give erratic readings, not that they are in
> error, but something causes it - aside from temperature / oil level.


Oil level has no effect on oil pressure whatsoever, until the oil is SO
low that you get air sucked into the oil pickup (a bad thing).
>
> I expect a mid-scale reading at highway speed, and at times in stop and
> go city traffic (is there any other kind) it dips - real low.
>
> Why the yo-yo readings?


That sentence doesn't make much sense to me. Oil pressure depends
somewhat on engine RPM, so it *should* drop when the engine drops to
idle. Some engines show much more variation than others.

Some factory "oil pressure" gauges aren't gauges at all. The sending
unit is just a switch that closes at (say for example) 5 PSI, and the
gauge snaps up to a nice happy mid-scale reading and just sits there.
The fluctuating oil pressure that a REAL gauge shows causes idiot
customers to complain that something is wrong, even though its perfectly
normal.

Have a 2002 S Blazer myself auto 4.3 with 4X4. Also have the factory
service manuals right here .

Your OP sender is under the distributor and is a long unit connected
into the oil gallery with an elbow.
The wiring comes directly back off the unit and it has two wires.

Book says 6 psi minimum at 1000rpm 18 at 2000 and 24 at 4000. with 5W30
oil.


--
Steve Williams

"Ken Hilson" > wrote in message
...
>
> "Ken Hilson" > wrote in message
> ...
> While considering options of testing with mechanical gauge, just
changing
> the sender or maybe even testing with another electric sender/gauge
that I
> already have I decided to drop the filter a couple times to get rid of
the
> overfill. I expected to also check the connector on the sender as I
thought
> it would be attached at the filter adapter.I could not see any sender
but
> did see 2 pipes from the adapter to my radiator. I did not realize
that I
> has an oil cooler in the rad. Second and not encouraging was that
there
> appears to be oil around the middle lower bolt that attaches the
tranny to
> the aluminum oil pan. Removing filter put oil on the outer bolt but I
don't
> see how it would wet the centre one, meaning maybe a rear main seal
leak.
> So question is does the rear seal leaking usually cause a drop in
pressure
> and where is the oil pressure sender located on the 2002 4.3? Only
connector
> I can see is on rear left below words "vortec" on the valve cover
which has
> 2 wires. The sender paer says it's 1 blade , so why 2 wires and the
pipe
> thread looks larger than 1/4 (which I thought I saw somewhere as the
fitting
> size)
> Thanks
> > 2002 S10 4.3 with about 38k on it.
> > Noticed last night that oil pressure gauge was reading lower than
normal.
> > Midscale is 275 kpa (39 PSI) and it normally runs about there or
higher
> when
> > hot at highway speed Last night it was down about 1/4 scale at speed
which
> > it normally only would go when at idle stopped. Crawled under and
noticed
> > small amount of oil on the filter but no dripping.
> > Difficult to check oil level when hot and with flashlight so added
about
> 3/4
> > quart and restarted. No real change, so left it until morning.
Checked oil
> > level and it was now actually a bit above max on dip stick so wasn't
> really
> > short of oil. Started it up and it read 2 bars above midpoint (
there are
> 4
> > bars per quarter of gauge range which is pretty normal. Took short
drive
> to
> > store and back. By the time I was back home the reading had gone low
> again.
> > Gauge needle moved more with rev change than last night but still
seemed
> to
> > go to 1/4 point above idle. Read somewhere that senders can go and
oil
> will
> > be in plug. Wonder if that might be the source of oil on filter,
assuming
> > sender is near filter base. Is this a common problem on these
motors?
> Could
> > I be losing pressure hot or maybe sender is now measuring wrong when
hot.
> >
> >
>
>



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Thanks very much., Steve. Those specs are way below what I was getting
before but I am still above them now. I have used 5w30 synthetic since
the 3rd oil change. I might try 10w30 next change. I don't suppose the
manual indicates if the distributor has to be pulled to change the
sender as I can just get a glimpse of the sender? update- Didn't get
to post above earlier today and went off to talk to dealer service
fellow. He printed me out a copy of all the engines specs including the
oil pressures you posted. Sender is apparently difficult to get at. He
asked me if I have lost any coolant. Unfortunately I have an external
leak (again) at the thermostat housing but even with that the coolant
hasn't gone down yet. Reason is that he has seen one of those engines
that had an internal coolant leak into the oil, thinning the oil and
causing a pressure drop. No sign of white slug in the oil fill cap.
Hate to drain away $25 worth of synthetic that I put in just a short
time ago but maybe I'll change it to 10w30 cheaper dino stuff and see
if the pressure returns ( and then goes away again) . One further issue
is that when I changed it and when I just was checking things I noticed
oil on the cooler lines at the crimps. Since the power steering pump
above those hoses was wet I assumed a leaking power steering pump, but
a mechanic at the dealer said it could be the oil from the line blowing
up to the pump.He advised me to clean really good , start it and look
for source of oil or put dye into one of the oils to determine which it
is. He didn't think a leak there, unless real bad, would drop engine
pressure.
Ken