Oil Pressure appears low - tip - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
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post #1 of 1 (permalink) Old 10-09-05, 07:01 PM
Backyard Mechanic
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Oil Pressure appears low - tip

{I'm asking a question as a hypothetical owner:}

I have a 1989 Ford Tbird with a 1990 Merc Cougar engine 3.8.

And since I changed the engine, the oil pressure is low..

It is higher on idle than with the ign turned on but not running, but on
the road does not ever get to the "Normal Range" though it does go up

I just changed the oil pressure switch not the prob still low oil


Since you changed the engine, I suspect the problem MAY be in the sender
used. Some senders are switches, some are pressure sensing variable

The Cougar being a slightly higher range car may use the variable type
which are more expensive and larger in size, about 1 3/4 to 2 inches in
diameter. Switches are about half that diameter

TBirds and Mustng LX around that time used a switch and resistor in the
gauge circuit so that when there was oil pressure at idle or speed it
would always be in the same place on the gauge... approx mid-normal.

Check the gauge by grounding the lead that connects to sender against
engine with key on.
If it goes to midrange of the word "Normal" it has a resistor in the
gauge circuit, and expects to see a switch - either ground or nothing.

If it goes to top of gauge it doesnt have resistor and a "low" reading IS
low... Whether you have a switch or sender.. So then the problem may be
in the oil pump itself

In 93 or so, the resistr and is on the back of the gauge cluster and if
you have the variable sender you must solder a wire from one side of that
resistor to the other to get normal readings with the variable sender.

If your pressure varies from very low (but higher than ign on) at idle to
just low at speed, then you PROBABLY have a variable sender so check for
that 20 ohm resistor by grounding the sender

I hear on others it may be in the lead at the sender end.
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