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I have a390 from a 66 T-Bird in my truck and it can't seem to maintain oil pressure. When you first start it the pressure is almost past the normal range on the factory gauge but when the motor warms up it drops to about a 1/3 up the gauge or less. Is it normal for the pressure to fluxuate that much? It never dropps out of the "normal" range but it just seems wierd to me that it fluxuates that much. The motor has a fresh rebuild and a new HV oil pump. Is this an common FE problem? Every FE engine I've ever had held terrible oil pressure and I don't want this engine to deteriorate to that point.

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In general, that's normal. When cold, the oil is thicker and you're also on the fast idle cam raising the rpm.

I've never really held too much stock in factory gauges and sending units. These are mass produced and calibration isn't check and questionable at best. I don't know why everyone assumes the readings from these are gospel!

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
 
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Yeah i don't think you have anything to worry about. Last July I put a new 390 in a pickup I have and that's the way it is also. With gauge [Stewart Warner] reading 40 or so cold, after it's warmed up it drops to about ten or twelve at stoplights. My Mustang is the same way. As long as it doesn't drop off while your at speed I think you're okay. Too high of an oil pressure is not necessarily a good thing.
Steve

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