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08-15-2020, 03:42 PM | #1 |
Senior Member
Join Date: Dec 2013
Location: Waxahachie, Texas
Posts: 949
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Oil pressure drop
At engine startup on my '40 Ford with stock engine, my oil pressure gauge reads 45+ lbs of pressure on the factory gauge and has done this for quite a few years. After driving for 20-30 minutes and the oil is up to temperature the gauge reads around 10 lbs going down the road and maybe 5 lbs. at idle. My oil pressure sending unit is an old one; maybe the original.
My questions are: - Is the sending unit malfunctioning perhaps due to age? - Is it possibly a weak pressure relief spring playing tricks when the oil gets hot? - Is it a faulty gauge? (it's old too) ...or a combination of the above? I want to make sure I am diagnosing my problem before I order and replace a part unnecessarily. |
08-15-2020, 03:56 PM | #2 |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
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Re: Oil pressure drop
Many would say that these numbers aren't bad for an engine with a lot of miles on it. If you want to verify your oil pressure install a mechanical oil pressure gauged (temporary or permanently) to double check what the pressure is.
The pressure relief spring should not change as the engine warms up. The oil viscosity thins out as it gets hotter and with increased clearance in the bearings the pressure decreases. What viscosity oil are you running? How many miles are on the engine? If you want to read one (of numerus) thread on this topic, this is one currently up:https://www.fordbarn.com/forum/showthread.php?t=283042 Last edited by JSeery; 08-15-2020 at 07:55 PM. |
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08-15-2020, 08:20 PM | #3 |
Senior Member
Join Date: Jan 2014
Location: Orcas Island Washington
Posts: 4,930
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Re: Oil pressure drop
I have 'improved' my oil pressure by removing the sender and squirting carb or brake cleaner into the sending unit more than once. . Give that a try and report back.
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Owner/Operator of 'Jailbar Ranch' on the side of Mt. Pickett. Current stable consists of 1946 1/2 ton pickup turned woodie wagon with FH V8, 1947 Tonner Pickup (red) mostly stock with exception of a cummins 6at turbo diesel, 1946 Tonner Pickup (green) with 226 cu in 6 cyl flathead, 1979 Toyota landcruiser wagon, completely encased in 1947 Ford Jailbar sheet metal. Ok, cornbinder rear fenders..... 'Rusty ol' floorboards, hot on their feet' (Alan Jackson) |
08-15-2020, 08:38 PM | #4 |
Senior Member
Join Date: Dec 2013
Location: Minnesota, Florida Keys
Posts: 10,316
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Re: Oil pressure drop
The first thing you have to do is determine whether you have an engine problem or a gauge problem. Mechanical gauges are relatively easy to install (temporarily), cheap enough, and readily available.
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08-15-2020, 09:04 PM | #5 |
Senior Member
Join Date: Dec 2013
Location: Waxahachie, Texas
Posts: 949
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Re: Oil pressure drop
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Thanks to all! |
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