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Old 06-28-2005, 01:59 PM
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mechanical oil gauge bleeding?

I just put a mechanical oil gauge on the rat project (bone stock 351M - no overhaul/about a gazzilion miles) and have encountered a problem. At cold start up the gauge will register between 35 and 50 lbs pressure. As the engine warms up, however, the pressure at the gauge slowly drops and by the time the 190 degree thermostat opens, my oil pressure shows virtually zero at the gauge when at idle (and only a couple of lbs. if I open the throttle).

I'd be interested in ANY troubleshooting tips but my major question has to do with the gauge itself. When I start the engine I can see the oil push up the plastic line toward the gauge. However, I can also see a whole bunch of air bubbles that remain in the line and do not go away as the engine runs. When I shut the car off, I can see the oil drain back down the plastic line and the line is filled with air. Should I disconnect this line at the gauge and start up the engine to bleed out the air or are those air bubbles normal in a mechanical gauge?

Dewey

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Old 06-28-2005, 02:39 PM
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Air bubbles are normal and have NO affect on the accuracy of the guage reading. If it really bugs you, you can loosen the fitting on the guage and start it up and "bleed" the line, but the readings will be the same.

Sounds like your bazillion mile engine needs some rebuilding.
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Old 06-28-2005, 04:34 PM
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I have a 70's truck with about 300k miles in dire need of a rebuild. Its just used for transporting junk. I encounted the same exact problem. I put some WD50 oil in it, stright 50, not that 20wd50 crap. And a bottle of lucas oil stablizer, i got about a 25% increase in pressure.. Good enough for me
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Old 06-28-2005, 04:48 PM
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check line

make sure there is no splinter in the line. The air might be an indication of it sucking air into the gauge. Just cause there is no oil leaking out, doesnt mean the line could not be kinked, or have a micro size hole in it sucking air.

Or gauge could be bad too.
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Old 06-28-2005, 05:00 PM
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Quote:
Originally Posted by Jmark
Sounds like your bazillion mile engine needs some rebuilding.
Unfortunately, you are probably right. But is there anything specific that might cause the oil pressure to drop like that as the engine gets hot or is that symptom indicative of a very tired engine in general.
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Old 06-28-2005, 05:37 PM
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Spring in the oil pump could have lost tension due to age.Might be worth putting an oil pump in it.
I had a 350 that did the same thing 60 cold idle 80 cold driving,55 hot driving but only 15psi idle.I tried bleeding the line and it gave me like 2psi so not really an acuracy problem.
I'd say try an oil pump,if the motor don't have lifter ticks and smoke problems.
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