Oil Pressure guage

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Can anyone tell me how to fix my oil pressure guage. On idle it reads good pressure, but when the engine

revs up the guage will jump to 80 # then bounce back and forth occasionally to 40-50# and all over.

Is the guage gummed up with krud, or is the oil line going in….or ???

I’m willing to remove it and clean it if there is a recommended way to do that.

I appreciate your group wisdom on this issue…..

(this is on my 1918 Series 4 48)

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Gauges can and do lie, but it may be telling the truth. My advice is to first use a known good gauge of the appropriate pressure range, connect it to the engine, and compare readings. You could possibly have erratic pressure because of a failing pump, a crack in a vital part, tube, etc, or another problem. In the case of oil pressure, it is wise to be sure. Hope this helps!

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Richard,

How high does your oil pressure guage read? The ones on Series 1,Series 2 and Series 3 cars read up to 20 pounds and the one on my C-3 reads in that range when the car is running.I believe the guage on Series 4 and Series 5 reads to 50 pounds and the one for Series 31 and 51 reads to 100 pounds.I would suggest placing a universal engine oil pressure guage in the line,starting the engine and seeing how it reads.If that one jumps around then it may be something in the engine.

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Hi Richard,

Your symptoms sound like oil starvation to the oil pump.

Did you drop the oil pan and clean it when you got the car a year or two ago?

Have you removed the screen and cleaned it? If it’s like the screen on my S31, it’s not a difficult job to remove and clean.

Here is my thinking on this: If your gauge reads the same oil pressure at idle consistently after the gauge has been showing an erratic pressure, and the needle had been bouncing back and forth then the gauge mechanism is not at fault.. The needle’s shaft has a pinion gear that is meshed with a rack that is attached to the ‘Bowden Tube’ . If there was something mechanically wrong with the gauge, the needle would not return to zero and the idling pressure would be inconsistent.

So: if the screen is covered in sludge, there would be a greatly reduced flow of oil through the screen, and as soon as the oil pump pulled all the oil from inside the screen, it would starve for oil to pump, the pump output pressure would drop, then when more oil was able to get through the restricted screen, the pump would show improve oil pressure. This slow-flow through the screen would be worse with cool, thick oil.. And would be lessened when the oil warmed and go thinner..

I agree that installing a second pressure gauge to test to see if your gauge is telling the truth or not is a good first step.

If you have not cleaned the pan or screen, I would recommend doing that regardless of what the problem with the oil pressure indication is.

If you did clean the pan and screen, if the engine did have some sludge adhering to the inside of the crankcase, it is quite likely that fresh oil and running the engine may have washed plenty of sludge down into the pan and it needs to be cleaned again.

I think I remember emphatically recommending removing the oil journal plugs from each rod journal and scraping out the old sludge.. And I think I remember you telling me you had done this important cleaning job..

Please let us know what you find.

Greg Long

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Hi Rich.

I have had the identical symptoms of a steady oil pressure reading at idle, but an erratic reading at above-idle engine speeds.

This was in cool/cold weather, and running 15w-40, or 20w-50 oil. Once the engine warmed up, the erratic pressure readings disappeared.

Since i did run this car a lot in cool/cold weather, I changed oil to 10w-30 for the cold weather. The erratic indications went away with the lighter-weight oil

It’s just hard for the thick oil to get through the thin mexh screen, when the oil is cold..

Greg Long

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