oil pressure drop

My sons 2001 Ford Explore 6cyl. 4.0 . the problem is when it is driving the
oil pressure is at the half way point on the scale. but during idle at
stops etc. it drops to the low end of scale. regular oil changes.new
filter. what would cause this to happen? the check gauge lite went
on,would a bad oil pump or faulty pressure switch be the culprit or is it
just the oil breaking down i think he uses 10w30 valvoline.

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deafone wrote:
> My sons 2001 Ford Explore 6cyl. 4.0 . the problem is when it is driving the
> oil pressure is at the half way point on the scale. but during idle at
> stops etc. it drops to the low end of scale. regular oil changes.new
> filter. what would cause this to happen? the check gauge lite went
> on,would a bad oil pump or faulty pressure switch be the culprit or is it
> just the oil breaking down i think he uses 10w30 valvoline.
>
> --
> Message posted using http://www.talkaboutautos.com/group/rec.autos.4x4/
> More information at http://www.talkaboutautos.com/faq.html
>

Old age.... The crank main bearings for one wear which radically lowers
the oil pressure.

Or a bad gauge. A test with a mechanical gauge is in order before an
engine teardown.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com

Mike Romain wrote:
> deafone wrote:
>> My sons 2001 Ford Explore 6cyl. 4.0 . the problem is when it is
>> driving the
>> oil pressure is at the half way point on the scale. but during idle at
>> stops etc. it drops to the low end of scale. regular oil changes.new
>> filter. what would cause this to happen? the check gauge lite went
>> on,would a bad oil pump or faulty pressure switch be the culprit or is it
>> just the oil breaking down i think he uses 10w30 valvoline.
>>
>> --
>> Message posted using http://www.talkaboutautos.com/group/rec.autos.4x4/
>> More information at http://www.talkaboutautos.com/faq.html
>>
>
> Old age.... The crank main bearings for one wear which radically lowers
> the oil pressure.
>
> Or a bad gauge. A test with a mechanical gauge is in order before an
> engine teardown.

The oil pump also gets a tad loose, as noted the bearings now have more
clearance and just as often the sensor gets arthritic. If you've seen
an abrupt and drastic change in behavior you might want to check with a
good mechanical guage to see if your sensor has bit the dust. If not,
it could be a sign of something more serious such as a failing pump or
worse. If this has been gradual, the engine is just getting older and
looser. Plus the more modern multigrades are actually a tad thinner at
running temperature in an effort to improve mileage and their lube
qualities are good enough they get away with it. You might want to try
a 10w50 or 20w50 to see if it changes it...I'd doubt it. Or toss in a
can of STP or motor honey. It is typically harmless, contrary to some
of the hype for high mileage motor oils--although STP is good enough
that you can run a desert race with an air cooled motor using only
enough STP to keep the oil pump working.

If you have a trustworthy mechanic, of the variety more prone to keeping
your trust than emptying your bank account, see if they will take a look
at it. There are still a few of those folks around even if they do
appear to be a dying breed--so at least pay them for their opinion.