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Jim
Grant has been working in the automotive industry for over twenty
years. In addition, Jim is an ASE Master Technician with advanced
L/1 certification. He works as manager and technician in his
family's automotive business in New Hampshire. He writes weekly
automotive consumer columns and is editor of an automotive newsletter
that is circulated throughout North America. |
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Jim Grant's Tech Tips
’00
Jeep Grand Cherokee, Oil Pressure up and down
Q:
I was driving down the interstate in my ’00 6 cylinder
Jeep Grand Cherokee and I stopped at a station. When I started
the engine there was no oil pressure. After checking the
oil & everything else it came back. Now about once a
week the “check gauges” light comes on “no
oil pressure” after it runs a little while it comes
back. I changed the oil pump and the sending unit, oil and
filter but it has not helped. The idle pressure is not as
good as it once was but it’s okay. Seems to be a ghost.
Is there such a thing as an oil switch on this model? I
only know about sending units..
ED
A:
The first
thing you should know is that the oil pressure gauge along
with just about every part of your instrument display is
computer generated. That’s right it is not real. It
is only the result of a computers interpretation of data
that is then displayed on the instrument panel. The only
hard wired (stuff that is connected to what is it’s
displaying) is the 4 wheel drive indicator, left and right
turn signal indicators and the brake warning light. Maybe
they didn’t trust the computer with that type of information,
who really knows? An oil pump is a mechanical device and
when worn, loose or with a restricted pick-up screen can
be erratic. If the engine has worn bearings then oil pressure
will be low all of the time and not just once a week. You’ve
done all of the right things with replacing the oil pump,
etc. I hope the oil pan was cleaned and the pick-up tube
& screen were replaced with the new oil pump. But now
there’s a question of was the oil pump really the
problem? Well the oil pressure gauge said there was a problem.
But was it? Replacing an engine in today’s vehicles
is big money and having that engine fail some place other
than in a garage driveway causes more money and aggravation.
Here’s what I would do. I would install a mechanical
type oil pressure gauge. The type that has a line that takes
oil right from the engine to the gauge for the pressure
reading. You could do it 2 ways, just monkey it in as a
temporary device or install it neatly for the long haul.
Then just drive the vehicle and compare the dash display
oil pressure to the gauge pressure. If there is a disagreement
I would trust the mechanical gauge over the computer’s
interpretation. If the oil pressure really does drop on
both gauges, then you’d better be looking more closely
at the engine’s lubrication system. If it goes the
other way? Don’t you just love computers!
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