Oil pressure sending unit

Hi, I am trying to diagnose a fluctuating oil pressure problem:

1) Does anyone know of an easy way to connect an oil pressure tester? I have
this fancy oil pressure gauge made by K-D Tools, but you need to screw the
end with the adaptors into the crankcase, in place of the sending unit. But
there is a 6' long neoprene hose with dial gauge attached to the adaptors,
so it's going to be kind of awkward screwing in the adapter while all that
stuff is still attached, especially in the tight confines I will be working
in (back of engine from underneath, under the intake manifold, above drive
axle), all without managing to slam the gauge into something while it is
turning clockwise with the hose.

2) I can't find a torque listed anywhere for the oil pressure sending unit,
even in the official GM shop manual.

3) The correct pressure for my car is supposed to be 56 PSI at 150 degrees F
(3000 RPM). How do I know when my engine has hit 3,000 RPM if I don't have a
tachometer in my dash? I do have a separate testing tachometer, but do I
really need to hook that up too just to test oil pressure?

4) If I leave the gauge on for too long while my engine is running, is oil
going to creep up the inside of the hose and contaminate the dial gauge?

5) IF the oil pressure checks out, then the problem must be either with the
in-dash gauge or the sending unit. Can I rule out the in-dash gauge by
simply connecting the prongs of its electrical connector, and see if the
gauge goes to full?

Thanks for any help!

Julie

Sometimes they will give you a right angle adapter so you can get a
straight spin on the hose and gauge. Otherwise, it just flops
around....

You should hook up the tach to get the proper baseline reading.
'Usually' engines are listed as X psi for every 1000 rpm. I normally
see something like 10 psi per thousand rpm depending on the engine as
the lower 'safe' wear limit. 56 psi at 3000 would be for a new engine
with a fresh oil change likely.

I do notice my oil psi drops when the oil gets old.

My Jeep runs a mechanical pressure gauge and it swings from about 15 psi
at idle to 50 or so on the highway. This fluctuation is perfectly
normal with a mechanical gauge.

Your new test gauge should be a sealed unit so oil can't get where it
isn't supposed to be.

Grounding the wire to the gauge should make it pin out either high or
low depending on the system. Opposite of unplugged anyway.... If it
moves smoothly across the range it might be ok, if it is jerky across
the range, you likely have found a/the problem. I think I would do this
step first.

Also check the plug itself. If dirty or loose it can give shaky
readings.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Aug./05 http://www.imagestation.com/album/in...?id=2120343242
(More Off Road album links at bottom of the view page)

"Julie P." wrote:
>
> Hi, I am trying to diagnose a fluctuating oil pressure problem:
>
> 1) Does anyone know of an easy way to connect an oil pressure tester? I have
> this fancy oil pressure gauge made by K-D Tools, but you need to screw the
> end with the adaptors into the crankcase, in place of the sending unit. But
> there is a 6' long neoprene hose with dial gauge attached to the adaptors,
> so it's going to be kind of awkward screwing in the adapter while all that
> stuff is still attached, especially in the tight confines I will be working
> in (back of engine from underneath, under the intake manifold, above drive
> axle), all without managing to slam the gauge into something while it is
> turning clockwise with the hose.
>
> 2) I can't find a torque listed anywhere for the oil pressure sending unit,
> even in the official GM shop manual.
>
> 3) The correct pressure for my car is supposed to be 56 PSI at 150 degrees F
> (3000 RPM). How do I know when my engine has hit 3,000 RPM if I don't have a
> tachometer in my dash? I do have a separate testing tachometer, but do I
> really need to hook that up too just to test oil pressure?
>
> 4) If I leave the gauge on for too long while my engine is running, is oil
> going to creep up the inside of the hose and contaminate the dial gauge?
>
> 5) IF the oil pressure checks out, then the problem must be either with the
> in-dash gauge or the sending unit. Can I rule out the in-dash gauge by
> simply connecting the prongs of its electrical connector, and see if the
> gauge goes to full?
>
> Thanks for any help!
>
> Julie

"Mike Romain" > wrote in message
...
> Sometimes they will give you a right angle adapter so you can get a
> straight spin on the hose and gauge. Otherwise, it just flops
> around....
>

Ah, that's it! I didn't even think of that! I first tried screwing off the
gauge and adapter connected to the hose, but that didn't work (wrench just
kept spinning repeatedly with no progress). Hope I didn't damage any teflon
sealing tape by doing so.

> You should hook up the tach to get the proper baseline reading.
> 'Usually' engines are listed as X psi for every 1000 rpm. I normally
> see something like 10 psi per thousand rpm depending on the engine as
> the lower 'safe' wear limit. 56 psi at 3000 would be for a new engine
> with a fresh oil change likely.
>

Well, I just did do the oil change last week, but the car has 190,000 miles
on it!

> I do notice my oil psi drops when the oil gets old.
>

Mine drops when mine gets hot.

> My Jeep runs a mechanical pressure gauge and it swings from about 15 psi
> at idle to 50 or so on the highway. This fluctuation is perfectly
> normal with a mechanical gauge.

My gauge starts out pretty high, but it continually drops, so after about
10-15 minutes of driving, the gauge reads at 0 or near 0 when idling and the
warning light comes on. Pressing the accelerator makes the needle go higher,
as does travelling at any speed. And if you stop the engine for a half an
hour then restart, the oil pressure goes back up. A regular poster here by
the name of "sdlomi" has an ingenious solution to this problem that doesn't
involve expensive repairs to fix low pressure, and I am trying to contact
him. He hinted at this solution in 2003 on this newsgroup. (I'll make
another post about that).

>
> Your new test gauge should be a sealed unit so oil can't get where it
> isn't supposed to be.

Ok, good, assuming I didn't ruin that my trying to unscrew the adapter at
the end of the hose.

>
> Grounding the wire to the gauge should make it pin out either high or
> low depending on the system. Opposite of unplugged anyway.... If it
> moves smoothly across the range it might be ok, if it is jerky across
> the range, you likely have found a/the problem. I think I would do this
> step first.

Thanks. Would connecting the positive and ground prongs of the connector do
the same thing (so I would be completing the curcuit then)? Also, for some
reason, the connector has three prongs! I know the tan wire is supposed to
be positive though. The problem is I have been having trouble with jumper
wires. Not sure what the problem is. I need to find a way to securely attach
a jumper wire terminal to the pins of the electrical connector, so I can
crawl out from under the car and then watch the in-dash oil gauge. But then
that may be too late to see any needle movement!

The other day I bought 100' of 14-gauge thin stranded wire (black), as well
as 100- and 30-watt soldering guns/irons, 1/2 pound of rosin core solder,
alligator clamps of various sizes, and various terminals, including 2 banana
plugs (useless, since most alligator clips and terminals won't fit over
them). I still need to learn to solder though. I also bought 8 jumper wires
with alligator clips on each end already, each 40 in. long at Radio Shack.
So I might be able to make one long jumper wire by clipping alligator clip
to alligator clip to alligator clip.

Otherwise, my plan is to make the following

3 ft, 8 ft, and 10 ft jumper wires with alligator clips on each end, to be
able to connect the battery to flat type electrical prongs.

Then I will open the clips and insert a paper clip in between the jaws to be
able to test pin type electrical connectors. But I still don't know how to
make the paper clip stay securely in place while I go to start the car or
whatever.

>
> Also check the plug itself. If dirty or loose it can give shaky
> readings.

Yep, oil is everywhere! UI should have use Teflon tape when I originally
installed the sending unit. Or maybe a better quality one (AC Delco).

thanks Mike,

Julie

> My gauge starts out pretty high, but it continually drops, so after about
> 10-15 minutes of driving, the gauge reads at 0 or near 0 when idling and
> the warning light comes on. Pressing the accelerator makes the needle go
> higher, as does travelling at any speed. And if you stop the engine for a
> half an hour then restart, the oil pressure goes back up. A regular poster
> here by the name of "sdlomi" has an ingenious solution to this problem
> that doesn't involve expensive repairs to fix low pressure, and I am
> trying to contact him. He hinted at this solution in 2003 on this
> newsgroup. (I'll make another post about that).
>

I googled this group to find an answer to my oil pressure problem, and this
is what I found: here is sdlomi's post from 2003:

http://groups.google.com/group/rec.a...1a336b1c914619

Sounds you want to know 'what' and 'why' and then desire to
fix it yourself. If so:::::You may find that your oil pump or pump pickup
strainer is clogged up, with 160,000 miles of grime. This would be
manifested by the engine running relatively quietly 1st time started in the
mornings; then after driving it a short distance, the oil press. lite comes
on and the lifters start clacking (metal tapping metal due to lack of oil
pressure); a noticeable loss of power as the hydraulic lifters quit
functioning & hence dis-allow the valves to open and close efficiently; and
then the only way to quieten it back down is to let it sit and cool
completely down. These exact symptoms, in the order stated, could indicate
decent oil pressure at first, when cold; lower/lost oil pressure after it
runs a little and picks up grime from the lower part of the oil pan, and
lost circulation thru whatever openings were clogged up as the grime 'tried'
to flow; and then as it cools, it 'lets go' of the suction (& grime) it had
developed on the non-flowing oil, and allows the grime to fall back down
into the bottom of the pan. Now, some of those few openings are open once
again, just enough to allow oil to flow for a short while until the cycle
begins again. But the key is quiet at first with no oil press. lite
burning; noisy and oil press. lite on after driving it a short
distance(maybe even several miles); after cooling down(maybe a few minutes,
maybe a couple of hours) it again runs quietly with the light no longer
burning; probably starts same cycle before you get right back home.
If this is the scenario, email me, and I'll give you a simple enough
cure that has saved me $thousands--I'm retired from the automobile business
where I enjoyed applying both engineering principles AND common sense to
operate more effectively and efficiently.
Hope I can help & good luck. sdlomi
*If you wish to email, you may have to remove an obvious 4-letter word (NOT
a dirty one, mind you!).

[end quote]

My problem is similar to the one sdlomi describes above: my oil pressure is
decent when first starting up, but then slowly declines after driving for 15
minutes or so, sometimes to the point where the warning light comes on for
no oil pressure. The longer I idle in traffic, the worse it gets. Letting
the car sit with the engine off for a while temporarily solves this. And
when I accelerate, or drive at a continuous speed, this also increases the
oil pressure. Idling decreases the pressure.

So I emailed sdlomi a few days ago, but no response yet. I hope he still
posts here! He gives good advice!

Julie

"Julie P." wrote:
>
> Yep, oil is everywhere! UI should have use Teflon tape when I originally
> installed the sending unit. Or maybe a better quality one (AC Delco).
>
> thanks Mike,
>
> Julie

Ya got teflon tape on the sending unit???

On some sending units, this can mess up the ground signal so the gauge
reads 0 or jumps all over creation.... So if the pressure is ok on the
mechanical gauge then that could be the problem....

On the wiring, I hook jumpers together or usually use booster cables to
get power close then short alligator clip jumpers from them. A second
person comes in handy when doing this so you can probe with a pin into
the wire or plug and have them see the gauge....

On the plug, 'usually' only one wire goes to the gauge, the other two
are for a no oil pressure safety switch so the vehicle shouldn't start
with 0 oil pressure. One would be power in, one would be power out with
the switch in the sender unit or it could be a ground tag using the
sending unit as a switch.

So normally it is only the one wire to the gauge that needs to be
grounded. I would make sure there is no power in the wire first before
grounding anything.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Aug./05 http://www.imagestation.com/album/in...?id=2120343242
(More Off Road album links at bottom of the view page)

"Mike Romain" > wrote in message
...
> "Julie P." wrote:
>>
>> Yep, oil is everywhere! UI should have use Teflon tape when I originally
>> installed the sending unit. Or maybe a better quality one (AC Delco).
>>
>> thanks Mike,
>>
>> Julie
>
> Ya got teflon tape on the sending unit???
>

No, no tape, but I read somewhere you are supposed to use tape when
installing the sending unit. But now I know better. (Except there is oil
everywhere. Would help if my shop manual had the porper torque!)

> On some sending units, this can mess up the ground signal so the gauge
> reads 0 or jumps all over creation.... So if the pressure is ok on the
> mechanical gauge then that could be the problem....
>

I tried your advice re the right-angle adaptor. No luck. The problem is the
bore for the adapter is so recessed (it's above the tranny, under and to the
left of the intake manifold) that the hose is going to have to bend anyway,
even with the right-angle adapter installed. And this is with the 2 inch
extension adapter I used--it's still too recessed. It is just too difficult
to connect the hose, given I am working on my back in limited space.

I could try angling the right-angle adapter upwards diagonally, and shoot
the hose in from the top of the engine, but I still would have to actually
screw it in from below, which would then require someone on top turning the
hose and gauge in unison with my turns of the adapter.

They really need to make a oil pressure tester where the hose can disconnect
from the adaptors without needing to screw the hose and attached adapter on.
Maybe a quick connect system??

So right now I have no way of checking my oil pressure! I'm stuck with
testing the gauge and sender unit only and hoping that works. If not, then I
must assume I have bad oil pressure and go from there. This sucks!

Maybe I can cut the hose of the tester, and then use a larger diameter hose
to connect the two pieces, thereby making my own quick-connect system???

> On the wiring, I hook jumpers together or usually use booster cables to
> get power close then short alligator clip jumpers from them. A second
> person comes in handy when doing this so you can probe with a pin into
> the wire or plug and have them see the gauge....
>
> On the plug, 'usually' only one wire goes to the gauge, the other two
> are for a no oil pressure safety switch so the vehicle shouldn't start
> with 0 oil pressure. One would be power in, one would be power out with
> the switch in the sender unit or it could be a ground tag using the
> sending unit as a switch.
>

Ok, I did check, and the problem is the wires have so much oil on them, you
can no longer easily tell the colors. One is pinkish red, and the other two
are tannish yellow. Maybe I will need to try each one?

And an idea that comes to mind so I don't need an extra person, is to ground
the wire from inside the car, while I am watching the in-dash gauge. I need
to find a ground somewhere though.


> So normally it is only the one wire to the gauge that needs to be
> grounded. I would make sure there is no power in the wire first before
> grounding anything.
>

Why?

Thanks again Mike!

Julie

"Julie P." > wrote in message
news:kMqdf.8967$w85.2460@trnddc02...
>

> Ok, I did check, and the problem is the wires have so much oil on them,
> you can no longer easily tell the colors. One is pinkish red, and the
> other two are tannish yellow. Maybe I will need to try each one?
>
> And an idea that comes to mind so I don't need an extra person, is to
> ground the wire from inside the car, while I am watching the in-dash
> gauge. I need to find a ground somewhere though.

When you turn the key to "on" in my car, the gauge smoothly goes from 0 to
80. This is without the connector connected to the sending unit, and not
jumping anything.

So do I still need to test the gauge with jumper wires? I am sorry to ask so
many questions. Anyone can answer if they wish.

If so, where is a good place to ground the wire from within the car? On a
side window regulator? Or somewhere under the dash on an unpainted metal
surface?

Also, I was able to securely stick a paper clip into one of the pin
terminals in the connector, and I set up a string of jumper wires with
alligator clips.

Julie

Quick question.

Was there oil all over when you started this?

If yes, the sending unit has failed.

Mike

"Julie P." wrote:
>
> "Mike Romain" > wrote in message
> ...
> > "Julie P." wrote:
> >>
> >> Yep, oil is everywhere! UI should have use Teflon tape when I originally
> >> installed the sending unit. Or maybe a better quality one (AC Delco).
> >>
> >> thanks Mike,
> >>
> >> Julie
> >
> > Ya got teflon tape on the sending unit???
> >
>
> No, no tape, but I read somewhere you are supposed to use tape when
> installing the sending unit. But now I know better. (Except there is oil
> everywhere. Would help if my shop manual had the porper torque!)
>
> > On some sending units, this can mess up the ground signal so the gauge
> > reads 0 or jumps all over creation.... So if the pressure is ok on the
> > mechanical gauge then that could be the problem....
> >
>
> I tried your advice re the right-angle adaptor. No luck. The problem is the
> bore for the adapter is so recessed (it's above the tranny, under and to the
> left of the intake manifold) that the hose is going to have to bend anyway,
> even with the right-angle adapter installed. And this is with the 2 inch
> extension adapter I used--it's still too recessed. It is just too difficult
> to connect the hose, given I am working on my back in limited space.
>
> I could try angling the right-angle adapter upwards diagonally, and shoot
> the hose in from the top of the engine, but I still would have to actually
> screw it in from below, which would then require someone on top turning the
> hose and gauge in unison with my turns of the adapter.
>
> They really need to make a oil pressure tester where the hose can disconnect
> from the adaptors without needing to screw the hose and attached adapter on.
> Maybe a quick connect system??
>
> So right now I have no way of checking my oil pressure! I'm stuck with
> testing the gauge and sender unit only and hoping that works. If not, then I
> must assume I have bad oil pressure and go from there. This sucks!
>
> Maybe I can cut the hose of the tester, and then use a larger diameter hose
> to connect the two pieces, thereby making my own quick-connect system???
>
> > On the wiring, I hook jumpers together or usually use booster cables to
> > get power close then short alligator clip jumpers from them. A second
> > person comes in handy when doing this so you can probe with a pin into
> > the wire or plug and have them see the gauge....
> >
> > On the plug, 'usually' only one wire goes to the gauge, the other two
> > are for a no oil pressure safety switch so the vehicle shouldn't start
> > with 0 oil pressure. One would be power in, one would be power out with
> > the switch in the sender unit or it could be a ground tag using the
> > sending unit as a switch.
> >
>
> Ok, I did check, and the problem is the wires have so much oil on them, you
> can no longer easily tell the colors. One is pinkish red, and the other two
> are tannish yellow. Maybe I will need to try each one?
>
> And an idea that comes to mind so I don't need an extra person, is to ground
> the wire from inside the car, while I am watching the in-dash gauge. I need
> to find a ground somewhere though.
>
> > So normally it is only the one wire to the gauge that needs to be
> > grounded. I would make sure there is no power in the wire first before
> > grounding anything.
> >
>
> Why?
>
> Thanks again Mike!
>
> Julie

"Mike Romain" > wrote in message
...
> Quick question.
>
> Was there oil all over when you started this?
>
> If yes, the sending unit has failed.
>

Yes!

But even when I installed a new sending unit in 2003 (a cheap Sorensen
brand), the oil pressure started out at around 60 psi, then gradually
dropped to around 10 psi after a half hour to 45 minutes of driving, but
only when idling. Now it drops to 5 psi or even 0 psi when idling after
15-20 minutes of driving. So I must have low oil pressure. So I am hoping
sdlomi posts here with his solution he mentioned. Otherwise, I will have
remove the flywheel cover, starter, oil filter arm, oil pan and exhaust pipe
just to check the oil screen for clogging. And I am not sure even if I can
pull the flywheel cover without first removing the engine.

Julie

"Julie P." wrote:
>
> "Mike Romain" > wrote in message
> ...
> > Quick question.
> >
> > Was there oil all over when you started this?
> >
> > If yes, the sending unit has failed.
> >
>
> Yes!
>
> But even when I installed a new sending unit in 2003 (a cheap Sorensen
> brand), the oil pressure started out at around 60 psi, then gradually
> dropped to around 10 psi after a half hour to 45 minutes of driving, but
> only when idling. Now it drops to 5 psi or even 0 psi when idling after
> 15-20 minutes of driving. So I must have low oil pressure. So I am hoping
> sdlomi posts here with his solution he mentioned. Otherwise, I will have
> remove the flywheel cover, starter, oil filter arm, oil pan and exhaust pipe
> just to check the oil screen for clogging. And I am not sure even if I can
> pull the flywheel cover without first removing the engine.
>
> Julie

Well, when lots of them fail they leak oil out the end.

They fail with your exact symptoms.

You also have to think of the mileage. Lower pressure is to be expected
when the engines get worn. It is normally worn main bearings that allow
the oil to flow too easy. Folks sometimes go to a thicker grade of oil,
say 20W40 instead of 10W30 to keep the pressure up a bit. 10 at idle is
still within the drivable range. My engine only has about 50K on it and
when hot at idle runs about 15, sometimes when really hot down lower.

I would change the sender before messing with the oil pickup screen. I
have even filled engines with mineral spirits to flush out filter
screens on the hope of raising the psi back up, but a worn engine is a
worn engine....

Are you starting to get any spits of oil into the air filter yet?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Aug./05 http://www.imagestation.com/album/in...?id=2120343242
(More Off Road album links at bottom of the view page)