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post #1 of 5 (permalink) Old 09-08-09, 08:56 AM Thread Starter
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confused oil pressure drops

85 f150 302. The engine has about 31,000 miles on it. It just started loosing oil pressure after it warms up. I removed the sending unit and installed a pressure guage. At start the guage reads 50 pounds. After driving 2 miles it drops to 40 pounds. Driving 10 miles it drops to 25 pounds while driving at highway speed and idles at 10 pounds. I did notice that when it is at 25 pounds and I let off the gas the pressure will raise to 35 and then go back down again. I checked for oil leaks and found none.

Any ideas?

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post #2 of 5 (permalink) Old 09-08-09, 09:11 AM
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Re: oil pressure drops

I bought an E150 several years ago and the oil pressure would drop when cruising at highway speeds. I took the oil pan off and found the pickup screen for the oil pump plugged with sludge. Evidently the previous owner didn't change the oil regularly. I cleaned it, put it back together, ran some engine cleaner through it and drove it another 30k miles before I sold it. The oil pressure stayed up then. Not sure if this is your situation or not.
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post #3 of 5 (permalink) Old 09-10-09, 10:20 AM
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Re: oil pressure drops

An '85 with only 31K??? How about 231K, or 310K?

How much oil is in it? What weight? How many miles on the oil? How many on the PCV valve & breather? I agree on the sludge - the easiest way to check is to pull the engine to drop the pan.
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post #4 of 5 (permalink) Old 02-04-10, 06:21 PM
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Re: oil pressure drops

Pull that dipstick boy!
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post #5 of 5 (permalink) Old 02-06-10, 10:34 AM
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Re: oil pressure drops

Mileage isn't everything. At the local Babcox & Wilcox plant, they get a new 1/2 ton every few years. It only gets 8-10K during that time, as it's primarily driven around the plant, but it's ALWAYS running, so 12+ hours or idling time in the winter days and 8+ in the summer. The last truck they had, idled to death ('05 F150 4.6L) and it was just over three years old. Neglected maintenance was found to be the cause. If it didn't log the hours idling, but driving, it would have over 250K on it.

I picked up an old 1932 Ford Model B pick-up several years ago. As soon as I attempted to drive it up the hill outside the garage, it would stall out and I'd roll it back down. Turned out, after I took the engine apart that I could literally PULL gobs of built up oil out of the engine. Only about 1/2 quart of oil was liquefied, the rest was jell-o. Cleaned it all out, and it actually run like a champ, albeit smoked like crazy.

'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
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