engine oil pressure drops

[not2old]

At start-up oil pressure is normal @ 45psi, but once warmed up starts to drop @ idle to 20psi. I have changed oil and used 10w40. Engine is 351C 4bbl. and idles about 800 in D. I can hear aslight engine knock in bottom end, but have doc's that previous owner changed pistons and bored 30 over. I'm I looking to replace crank bearings and upgrade to high volume oil pump. This car is a weekend cruiser and am not looking to rebuild. What's my best choice?

Thanks NOT2OLD

 

[cobra3073]

Not2Old,

You are taking me back to my "Cleveland" days when I was always concerned about oil pressure with my .030 over '73 351CJ motor. I had the restrictor kit, high volume pump and all the goodies and it still would go down to about 20 PSI at idle (900 RPM) when warmed up.

Finally had an ole Funny car racer break it down to me. He noted that if the engine is not using oil and if you have 10 PSI for every 1000 RPM at idle, you are good to go. I stopped worrying about it and ran that puppy until I swapped it out with a 428CJ. When I tore the 351CJ down, everything looked good.

So, the question for you is, have you notice any oil usage? If not and you are staying at 20 PSI at idle (under 2000 RPM) after the engine warms up, you are probably fine.

Hope this helps.

BT

 

[Nance]

Both of mine my 71 and the 72 stay around 30psi . I am like cobra 3073 drive it.and enjoy.

 

[droptop73]

I would be way more concerned about the knock than the oil pressure. Get with someone who knows engines and have them listen to it before putting many miles on it. If you hurt the crank or rods due to a bad bearing you've increased your repair costs greatly. Best wishes I hope the knock is nothing.

 

[cobra3073]

Yes, I agree - - if it is a "knock", it needs to be checked out.

You might get a piece of water hose or rubber tubing and try and isolate the sound by holding the tubing to your ear and moving it around the motor, while it is running.

Hopefully, you will be able to determine from where the "sound" is actually coming. Often times, sounds are not coming from where we think they are coming.

Hope this helps.

BT