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TR2/3/3A Oil pressure: the gauge?

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M

mmgwhite

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1959 TR3 with original oil pressure gauge.
Oil pressure starts out at about 70 psi but after driving for a while will drop into the 30s.
All else seems normal.
I dropped the oil pan and inspected the pickup screen. Seems fine.
Haven't sleuthed any further.
Suggestions how to proceed please
Thanks
 
I assume you're talking about at idle. The owner's manual even mentions that low oil pressure may be shown when idling or running at low speeds, "this is quite normal". Typically a fresh engine won't show much drop if any, but as the bearings (and oil pump etc) wear, the drop becomes more pronounced. Using multiweight or heavier oil may help, but when it gets severe enough, it's time to replace the bearings and perhaps regrind the crank journals. The general rule of thumb for "enough" is 10 psi per 1000 rpm, so 30 psi at idle should be no problem at all.

It's fairly easy to change the rod bearings with the engine still in the car; in fact I believe it's the Haynes manual suggests doing it as a matter of periodic maintenance every 30,000 miles. That will usually pull the oil pressure back up quite a bit.
 
That all sounds Normal to me also, but I would get a second opinion before I went into major surgery. I have a collection of original gauges and one gauge I have shows correct oil pressure for about the first hour and then drops to zero at idle, and another one pretty much stays at 50 psi when cold, but drops down to 25 when the engine gets totally warm and comes back to 45psi when the idle increases . Anyways you can plumb in a new gauge for a while to double check the system. In addition there is a small gasket, I think made of leather to seal the old gauge, so if you do test out with a different gauge make sure you have one in place when you put the old gauge back because they can a big mess, I know.
 
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