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Can’t figure it out!

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Carrpelll
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Can’t figure it out!

Post by Carrpelll » Tue Jul 27, 2021 9:44 pm

I have a “W” engine that has 30 lbs oil pressure at start up.
It does a crazy thing and drops to about 10 lbs when I get under way - at 1200 to 1800 rpm but if I keep driving, after about 4 or 5 minutes the oil pressure goes back up. Then it acts like it should meaning the higher RPM the higher the oil pressure. But it’s that first few minutes that has me puzzled and concerned. Why would the oil pressure drop with higher RPMs then go back up at lower RPMs during the initial warm up. Seems backwards and only during the first few minutes while underway. Any ideas? I thought maybe a plugged pick-up screen??
1948 - CC 25' Sportsman Sedan
1953 - CC 18' Riviera
1957 - CC 17' Sportsman
1952 chevy pick up

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Bilge Rat
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Re: Can’t figure it out!

Post by Bilge Rat » Wed Jul 28, 2021 6:30 am

As a process of elimination, temporarily try a known good pressure gauge connected at the engine gauge port. An easy first thing to check before opening up the crankcase.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

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mbigpops
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Re: Can’t figure it out!

Post by mbigpops » Wed Jul 28, 2021 9:29 am

I am not going to hijack this post but I have the same exact issue. So far I have tested my gauge (good), blew the copper line out, and dialed the oil pump up to 40 lbs via the access plate.

My next move end of season is to pull the engine and replace the oil pump as it is the only engine part that I never addressed during engine rebuild.

Mark
1953 CC Rocket Runabout "Rocket Man"

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Carrpelll
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Re: Can’t figure it out!

Post by Carrpelll » Wed Jul 28, 2021 10:52 am

Yeah. I will try a different pressure gauge.
Maybe sending unit is temperature sensitive but I am thinking that’s not it. Worth a try though.
1948 - CC 25' Sportsman Sedan
1953 - CC 18' Riviera
1957 - CC 17' Sportsman
1952 chevy pick up

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mbigpops
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Re: Can’t figure it out!

Post by mbigpops » Wed Aug 18, 2021 6:51 pm

Well mine is solved. I added a half quart of oil and went out and the gauge started swinging between 25 and 35 lbs which was an improvement. After that I added another quarter quart and it went right to 40 lbs and stayed there solid.

My theory is the oil pump running full pressure at startup but when the oil was pumped into the crankcase the pump was starved for oil.

You may want to try the same thing.

Mark
1953 CC Rocket Runabout "Rocket Man"

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Carrpelll
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Re: Can’t figure it out!

Post by Carrpelll » Wed Aug 18, 2021 8:08 pm

That’s exactly what the problem was here too. The dip stick showed enough oil but when I did an oil change I only sucked 4 quarts out, including the reverse gear. I added 6 fresh quarts and it’s right where it should be. Thanks for the input.
1948 - CC 25' Sportsman Sedan
1953 - CC 18' Riviera
1957 - CC 17' Sportsman
1952 chevy pick up

davewann
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Re: Can’t figure it out!

Post by davewann » Mon Aug 28, 2023 7:38 pm

Good Evening I have a similar problem, I believe... I have a 1964 Constellation 30 Ft. with (2) Flywheel Forward, Small Block Chevs. I changed the oil with both dip sticks FULL and had only 2-1/2 quarts in each engine.

My Question - Regardless of the Dip Stick, what are the minimum quarts of oil per engine? I would suspect at least (5).

I appreciate any help at all!!

THANKS

davidvn
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Re: Can’t figure it out!

Post by davidvn » Thu Nov 09, 2023 2:54 am

I realize this is an old post, however, as a general rule, if you increase your rpm and your oil pressure drops that means it you’re low on oil. Another indicator is if you pull back on the throttle quickly if your oil pressure drops, it means that the oil is running away from the pick up and when it flies back, your oil pressure will be restored.

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