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My experience is mechanical oil gages will fail either of two ways: 1 – They indicate HIGHER pressure than actual (and usually the gage hand does not return to 0 when shut down) . 2 – They fail to indicate at all (accompanied usually with the gage face filling up with oil). I have never encountered one that reads lower than actual, though I suppose it is possible. Gage replacement is simple – just unscrew the old one and screw in the new. Like Hal says there should be a square wrench flat on the nipple to turn it with. (Don’t turn it by grabbing the OD of the gage with big pliers or a pipe wrench – you may regret it later!) Tip: Before installing the new gage check it against a known accurate gage using air pressure. I’ve found that gages from Tisco, AutoZone, etc. generally don’t begin move move off “0” until the actual pressure is about 5 – 7 psi. And they read lower than actual until pressure reaches about 20 psi actual. --- Low oil pressure can be caused by several things – and usually is a combination of things. Could be as simple as sludge clogging up the pump suction screen. (Not uncommon when non-detergent oil has been used for many years). Oil pump wear is another. But most often the cause is worn main, rod and cam bearings. I’d first drop the pan to and clean the pump screen and bottom of the pan (an easy job – all you need is new pan gasket). Sometimes you’ll find the oil pump gasket gets partially blown out or the pump cover is slightly warped. Again not a difficult job to disassemble and replace the pump gasket once the pan’s off. Bearings get a little more complicated. Mains and rod bearings can be replaced from below after dropping the pan. Cam bearings however require disassembly of the engine. One other “fix” that works for lightly used (i.e. show and parade) tractors with low oil pressure: Change to 15W-40 oil. It flows easily enough for good cold starting, yet it’s high temperature viscosity helps maintain higher oil pressures when warm.
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