View Full Version : Oil Presure Guage?

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03-03-2005, 05:06 PM
O.K. here's the problem.

Oil pressure reads 60psi cold (just installed a new timing chain; oil pump & rear main seal last week) 50 psi warm & 20 psi @ idle.

The guage works & I replaced the sending unit (electric) due to the fact the oil pressure guage is erratic, sometimes it will read 50 psi then jump to 80 & then back to 40 & then to 20 & today it went to 0 on the hwy & when I got off the hwy it went to 40 then to 20 @ idle.

When it jumps to 80 it will go back to 50 or 40 & stay for a while & today driving home it only did it once.

I found out that there is a pressure switch next to the sending unit (electric) which closes @ 4psi. SINCE I did the nutter etc. does this pressure switch do anything (it is suposed to send info to the computer) & do U think it's the problem?


P.S. I'm gonna try out a mechanical guage.

***Oil Pressure Sender***

This sender is on the engine block and looks like a small 2 X 3 inch filter with one terminal.
The other sender with the two connectors is an oil pressure switch .
It is supposed to close above 4 psi and goes to a dash warning light in some speedometer clusters
and in other models it sends the signal to the engine's computer.

To be sure the problem is not the gauge, you can momentarily short the wire from the output of the Sender to ground. This should show up as 80 psi on your gauge. No resistance at all (full 12 volts).
DO NOT hold it long in this position.
If the needle does not move from ZERO psi then, either the wiring (open circuit) or the gauge is bad.
If it does move, the sender unit is bad.

***Oil Sender Resistance***

These are hard to test but might help choose the correct replacement.
*0 PSI 234-246 ohms
*20 PSI 149-157 ohms
*40 PSI 100.5-105.5 ohms
*60 PSI 65-69 ohms
*80 PSI 32.5-34.5 ohms

03-03-2005, 06:07 PM
That's why I ditched mine and went with a cheapy mechanical guage.

03-03-2005, 06:48 PM
I think that's what I'm gonna do.

03-03-2005, 07:06 PM
I think the one I got was $20 or something. Mine would register all over the place, tried replacing the electric sensor, then tried a fancy guage. Still no worky (although they were compatible), so I figured it was in the wiring harness and went mechanical instead of getting a headache.

03-07-2005, 02:54 AM
Agreed wholeheartedly.

My Jeep had a mechanical gauge (Stewart Warner), but after I rewired the Jeep this last year and installed white vinyl instrument decals I had to change back to the stock electrical sender so the decals would match.

The mechanical pressure guage was always great, but nowthat I have switched with a new sending unit, new wiring and new guage I can't get a good reading. It just plain sux compared to the mechanical!!

Granted I now have low pressure in my motor, but the mechanical gauge was far more accurate and read the lower pressures better.

When I re-do my dash I will be buying new guages and I will be switching back to a mechanical oil pressure guage. Although I hate to lose the big speedo......I have a soft spot for it since it is a Jeep hallmark.

BTWay, the electrical sending units have small orafices and when they get older they need to be changed because they can easilly become blocked. Also, IIRC you can use a thicker tube to attach your oil pressure guage to. It should be the same size as the flexible tubing on your grease gun, or you can just go with braided steel. Either one would reduce the likelyhood of a potential mess since it would be pretty tough to break one of those lines.

03-07-2005, 06:00 PM
I'll look into it.

On my 79' I left the speedo for the same reason U mentioned & installed other guages & it still looked good & the speedo still caught your eye.

04-03-2005, 08:11 PM
I always used the auto meter mech oil pressure gage and had no troble at all -- did you blead the air out of the line to the gage ?

04-03-2005, 08:22 PM
Ya, it's fine now, thanks Fuzz

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