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Drove the daughter's '66 289 C4(45k miles)today and noticed the following:
40 mph stock gauge reads about 2 needle widths above the low end of the bracket(normal range is what I assume the bracket represents)
50 mph about 1 needle width above low end
60-65 mph at or below low end
As soon as speed decreases needle reads higher.
No ticking, oil levels good, running Mobil 1 syn.
I know the sending unit should probably be the first thing to swap out but wanted any thoughts/experiences you guys have. Gauge problem, oil pump(new when rebuilt), sending unit.

Our '92 5.0 AOD(also syn oil) seems to do the same thing.
Could it be the Nor Cal Triangle? :lol:
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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I had something similar happen in my 68 some years ago. Everything was fine until I got on the freeway then psi went to zero. Scared hell out of me. I surprised to see it pop back up as soon as I slowed down. Above something like 50 mph, no oil pressure. Below that It was OK. After the usual checking everything I could think of I got around to pulling the oil pan. And found nothing much. Then I noticed the gasket between the oil pump and block sticking out a bit. The oil pump bolts had loosened just enough that higher oil pressure was pushing the gasket out and the oil was just dumping back into the pan. A new gasket and some LocTite and all was well again.
I thought this was a fairly unusual thing to have happen at the time, but there are some striking similarities to what you have told us of your problem.
The most common cause of this type problem is actually not having enough oil in the pan. At higher rpms the oil can all be in the engine and the oil pump will suck air (cavitation). Roadracers with fairly stock cars will commonly add a "quart too much" oil to their engines before a race to help avoid exactly this problem.
Check the easy stuff first.
 

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If the oil pump pickup screen is mounted to close to the bottom of pan it can cause the pump to cavitate at high RPM and gage will read low oil pressure.
 

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Hi Ted -- first thing you might consider is to establish what PSI you really have. A cheap mechanical gauge might reveal it together with an underhood tach you can see while you spin it up. It could be the sending unit, the gauge or the dash voltage regulator. Sorta sounds like the sending unit.....Once you really know what it's doing you can decide. You can do it all in the driveway and watch the gauge as you spin it up. If you don'thave lifter noise, that's a good sign....Victor
 

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I strongly agree with Victor. Thats the way to go. Ken
 

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P.S. In one of the most recent mags for Ford, can't remember exactly which one, a guy was doing a fairly stock rebuild for a Sunbeam Tiger(289). Anyways, this fella dimpled the area of the block right where the oil pump goes. Said it was to give the gasket something better to grip to and I THINK it was because of this same type of problem. Might be worth a look. I think it was this months Mustangs and Fords.
 

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Hi Ted -- first thing you might consider is to establish what PSI you really have. A cheap mechanical gauge might reveal it together with an underhood tach you can see while you spin it up. It could be the sending unit, the gauge or the dash voltage regulator. Sorta sounds like the sending unit.....Once you really know what it's doing you can decide. You can do it all in the driveway and watch the gauge as you spin it up. If you don'thave lifter noise, that's a good sign....Victor
Exactly!

You also may want to try putting an extra quart of oil in the pan. If the motor has a hi volume pump, it could be emptying the pan and cavitating at high rpms. A look under the valve covers to ensure the returns are clean and sludge free wouldn't hurt.
 

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If consta-volt is bad, the gas gage should allso be doing the same tracking bit under high RPM. Sound advice from Posters above.
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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Dimples do help retain gaskets but in my case they wouldn't have. My problem was caused by bolts loosening up. Dimples would have had no effect except maybe delaying the time of the problem's appearance. My solution was LocTite. I have since noticed that on race engines these two bolts are commonly drilled and safety wired. Normally a bit too hardcore for me but surely the most effective cure.
 
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