Oil Pressure - 88 Caravan 3.0L 184,000 miles

[Paul A Gigl Jr]

Greetings,

My oil pressure gauge has been reading dangerously low within 3-4
minutes of a cold start. The needle borders the caution zone at idle
and has a tendency to dip into this zone under acceleration. First
couple of minutes it will read fine, but the minute the oil warms up
the pressure dives. Before this started occurring, I had noted a few
random occurrences where the gauge flatlined when accelerating hard
(2.8-3K rpm) from a stop as if it wasn't reading at all. During these
instances, I would immediately back off the throttle and it would
return to normal.

There is a noticeable ticking and given the mileage I would expect
some wear to be part of the cause of a low pressure reading. I've also
run some engine flush through it to help clean out any sludge in the
oil pick-up screen. Looking through the archives, I've noted that
replacing the oil sending unit seems to be a fairly common task for
those with low pressure readings. Where exactly is this located and
what is involved in replacing it? Several old posts state that it is
near the oil filter, but the autozone web site states that it is
located _inside_ the oil filter adapter. There is no reference to it
at all in my Haynes manual. I'm also curious, is this unit simply a
sensor for the gauges?

Aside from the sending unit, are there any other possible causes for
these readings? I assume the pump is fine as the readings are normal
to start. FWIW - I'm running Mobile One Syn 0W-40 and a Purolator Plus
filter.

Thank You,

-Paul

 

[Ted Mittelstaedt]

Greetings,

My oil pressure gauge has been reading dangerously low within 3-4
minutes of a cold start.

typical symptoms of a worn oil pump.

Ted

 

[Geoff]

Greetings,

My oil pressure gauge has been reading dangerously low within 3-4
minutes of a cold start. The needle borders the caution zone at idle
and has a tendency to dip into this zone under acceleration. First
couple of minutes it will read fine, <SNIP>

Correct diagnostic procedure is to connect an external oil pressure gauge to
the engine, usually where the sending unit screws in, and take an *accurate*
measurement of the oil pressure and then compare what you get to the spec in
the FSM. If the pressure is okay, you've got a sending unit problem. If
not, you have engine wear: could be bearings, oil pump, or a clogged pickup
tube.

Anything else is a waste of time, effort and money.

--Geoff

 

[Steve]

Greetings,

My oil pressure gauge has been reading dangerously low within 3-4
minutes of a cold start. The needle borders the caution zone at idle
and has a tendency to dip into this zone under acceleration. First
couple of minutes it will read fine, but the minute the oil warms up
the pressure dives. Before this started occurring, I had noted a few
random occurrences where the gauge flatlined when accelerating hard
(2.8-3K rpm) from a stop as if it wasn't reading at all. During these
instances, I would immediately back off the throttle and it would
return to normal.

That's pretty characteristic of a bad oil pressure sending unit with a
"dead spot" as the pressure swings through a certain zone. Certainly it
would be the first thing I'd check- with a mechanical guage hooked up
instead of the factory electrical guage.

Other possible causes range from simple (collapsed oil filter- hope
you're not using a Fram to severe (bearing clearances opening up so
wide that the crankshaft shifts under heavy acceleration.).

Start little, hope for the best.