Mechanics

OIL PRESSURE DROPS THEN COMES UP

1994 Ford Thunderbird • 213,839 miles

My oil pressure drops to nil, then comes back up when I rev up the engine to 2000 plus rpm's. The motor is a 3.8L non super charged engine.
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Demoguy1073
January 13, 2012.




Is the engine knocking? Replace the oil pressure switch first


Cadieman
Jan 13, 2012.
THIS MAY NOT BE SERIOUS. OR IT COULD BE!

IF YOU ARE EXPERIENCING FUNNY NOISES OR KNOCKING AT LOW PRESSURE FOR SURE, IT IS SERIOUS

SOMETHING NOT MENTIONED HERE, IS HAVE YOU CHECKED YOUR OIL LEVEL?

WHAT I MEAN IS "YOU"---NOT "DAVE" DOWN AT THE "SUPER DOOPER LUBE" TWO MONTHS AGO!

IT IS IMPORTANT TO CHECK IT AT MINIMUM, "WEEKLY" AS PROBABLY PRESCRIBED IN YOUR OWNERS MANUAL. AND ALSO IF YOU SUSPECT A PROBLEM OR YOUR GAUGE OR LIGHT SAYS YOU HAVE A PROBLEM! ANYTHING COULD HAPPEN WITHIN SECONDS, YOUR OIL PLUG FALLS OUT (INSTALLED WRONG) OR ROAD DEBRIS KNOCKS A HOLE IN YOUR PAN. IF OIL IS THE ISSUE, IMMEDIATELY SHUT IT DOWN!

EVEN IF YOU "HAVE OIL"---YOUR OIL PUMP MAY NOT BE WORKING!

HAVE YOU KEPT UP WITH SCHEDULED CHANGES?

USING THE CORRECT OIL?

THIS IS WHAT YOU NEED TO DO NOW

REMOVE YOUR OIL SENDER AND INSTALL A MECHANICAL OIL PRESSURE GAUGE---THIS WILL GIVE YOU AN ACCURATE READING AS TO WHAT YOUR ACTUAL OIL PRESSURE IS.

ONE SET UP LIKE MINE, OR AN AFTERMARKET UNDER THE DASH MOUNT (USED AS A PORTABLE) WILL ALLOW IT TO BE RUN OUT FROM UNDER THE HOOD AND INTO YOUR WINDOW, SO YOU CAN WATCH IT AS YOU DRIVE.

IF IT SAYS EVERYTHING IS A-OKAY WITH THE MECHANICAL GAUGE

YOUR SENDER IS MOST LIKELY DEFECTIVE (NORMALLY THE PROBLEM IN CASES LIKE YOURS)---THEN THE ACTUAL GAUGE IN THE DASH WOULD BE THE SECOND GUESS AS TO BEING BAD

SOME PEOPLE JUST CHANGE THE SENDER AS THEIR "TEST"---I LIKE TO KNOW WHAT THE "REAL DEAL IS".I CAN'T AFFORD A NEW ENGINE EITHER

SEE MY PIC BELOW OF MY GAUGE

SEND YOUR RESULTS

THE MEDIC
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CJ MEDEVAC
Jan 13, 2012.
New oil and Wix filter. The gauge is mechanical and works fine otherwise. What is the bypass mode my engine builder friend mentioned and how can this be corrected? The same thing happened with previous filter.


Tiny
Rehabber1
Dec 8, 2014.
I DON'T THINK HE WAS TALKING ABOUT THE FILTER ITSELF "BY-PASSING"

THE FIXTURE THE OIL FILTER SCREWS ONTO HAS A SPRING AND BALL/ PLATE/ POINTY DEVICE INCORPORATED INTO IT

THIS IS CALLED THE RELIEF VALVE

THE SYSTEM USUALLY "BY-PASSES" THE FILTER AT PRE-DETERMINED SPRING PRESSURE

ON MY '77 CJ-5, THE SPRING PRESSURE IS 75 PSI

IF MY EVERYDAY OIL PRESSURE EXCEEDS THAT, THE RELIEF VALVE IS PUSHED OPEN AND THE EXCESS PRESSURE DUMPS BACK INTO THE INLET SIDE OF MY "OIL PUMP" (SORTA LIKE JUST DUMPING IT BACK INTO THE OIL PAN)

BASICALLY IT'S A PRESSURE SAFETY VALVE

I'VE SEEN "STUCK" PRESSURE RELIEFS, AND STOPPED UP OIL FILTERS, SORTA ARTILLERY THE "CAN" PORTION OF AN OIL FILTER OFF OF THE ENGINE AT THE CRIMP, BUT LEAVING THE ROUND SCREW ON PORTION STILL SCREWED ON

I WATCHED A FELLER PUT 3 NEW ONES ON IN A ROW, JUST TO WATCH 'EM BLOW OFF, THEN HE DECIDED IT HAT TO BE A STUCK RELIEF VALVE!

MAYBE I'M NOT UP TO SNUFF ON SOME OF THIS NEWER STUFF, I JUST DON'T SEE THE RELIEF VALVE "KICKING IN" AND PERFORMING A "TASK" AT LOWER PRESSURES, IT MIGHT BE POSSIBLE THE SPRING IS WEAK, BUT THERE AGAIN, I'D THINK PRESSURE WOULD REMAIN CONSTANT, JUST AT LOWER PRESSURE

I'M GONNA SEE IF I COULD BE IGNORANT ON THIS, I'LL SEE IF THERE IS A DIAGRAM IN "PRODEMAND"

THE MEDIC


CJ MEDEVAC
Dec 8, 2014.
Hi guys. Excuse me for butting in, but I have a question. It was stated the oil pressure gauge is mechanical. Does that mean it is an aftermarket installation to compliment the factory warning light, or does the car have an original gauge? Some people call original gauges "mechanical" because they have a pointer, but in reality they are electronic circuits. Nothing should be assumed with only a factory gauge. A adapter needs to be installed temporarily, then a truly mechanical test gauge should be used to see exactly what the pressure is at all times.

Factory electrical gauges often don't respond fast enough to get some of the useful observations. For example, when the pressure comes back when raising engine speed, how long does it stay up after speed is reduced back to idle? If the pressure drops immediately, I'd suspect worn engine bearings, especially at the mileage listed. The additional clue is pressure will be higher when the engine is cold and if higher-viscosity oil is used.

If the pressure drops slowly within a few seconds of coming back to idle, I'd consider debris blocking the oil pickup screen. There's a bypass valve for that but it only opens when there's enough suction on the inlet pipe, and that may not occur at low speeds.

Gotta go for now. Racing against a dying laptop battery.


Caradiodoc
Dec 8, 2014.
Thanx for all ur input.I'm suspecting it's a weak relief valve. The car is now under wraps for the winter so nothing will be done until next spring. The gauge is mechanical and is ok. It's a newly built motor. The previous owner had it built for drag racing his 67 Impala, but after4 runs decided it wasn't fast enough so I bought it for my car. Thanx again.


Tiny
Rehabber1
Dec 9, 2014.

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