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ljpcool67 04-03-2019 05:13 PM

Oil pressure drop
 
I have a 351W and have a pretty big oil pressure drop from when it is cold to when it is hot. When cold it is between 60 to 50 then once hot and idling at stop sign (700 rpm) it drops to about 10. Once I start moving the pressure goes up with the rpms. I am just concerned by the low oil pressure at idle. Should I be concerned if so what can I do to improve the oil pressure?

Update: after reviewing other threads I noticed some advice and some questions other threads were asking. I actually have a mechanical gauge under hood and an electric gauge inside. It seems like a different oil might help. I can't remember what weight I put in last but I know I was told to put performance oil with zinc added. I have been messing with adjusting carb. Perhaps flooding could add to the problem. The engine was rebuilt about 5000 miles ago.

RAGGAREN 04-03-2019 10:31 PM

Re: Oil pressure drop
 
sometimes worn cam bearings will show same signs..
good pressure cold but as it heats up pressure drops



was cam bearing replaced in rebuild or was motor just freshened up
with a hone new rings, crank and connecting rod bearings... ??

1964Fastback 04-04-2019 03:16 AM

Re: Oil pressure drop
 
What is the hot pressure if you turn the idle up to 800-850 or so?


Pat

ljpcool67 04-04-2019 04:45 PM

Re: Oil pressure drop
 
yes everything was gone through. Complete tear down plane and rebuild.

ljpcool67 04-04-2019 04:56 PM

Re: Oil pressure drop
 
Hello Pat

"What is the hot pressure if you turn the idle up to 800-850 or so?"

Answer: I is normally about 15. If I turn it up above 900 it gets run on. The bad part is that the idle will very day to day by about 100 to 200 rpm. So I have to set it close to 700 to allow for the days (or times of the day) when it wants to run a little faster. If I turn it up to 850 or so and it steps up to about 1000 (when idle and not in gear) then I have to leave it in gear so it bogs the engine down to below 900. Don't know if this helps. Perhaps the idle is a whole other thread issue. I would prefer for it to idle closer to 800. pressure is better, voltage is better. Currently there is about a 150 rpm drop when put in gear. So it is idle in park @ 750-800 then drops to 600-750 in gear.When I drive at 1500 rpmI can get around 25-30 psi. Temp normally runs around 180 f.

Maybe this will help.

1964Fastback 04-04-2019 05:30 PM

Re: Oil pressure drop
 
I don't think that's too bad for pressure. They say 10 PSI per 1000 RPMs I think. Too bad it runs on when you turn it up more. 600-750 seems a little on the low side in gear but I'm not that familiar with autos.


Pat

galaxiex 04-04-2019 05:40 PM

Re: Oil pressure drop
 
Hot engine 10 psi per 1000 rpm is considered "normal" for most stock (ie: non-racing) engines.

So if you have approx 30 psi at 3000 rpm, and approx 60 psi at 6000 rpm, I wouldn't worry.

My 428CJ with Melling high volume oil pump, and oiling system mods ran 70-75 psi cold at idle.

Hot idle dropped to ~ 15-20 psi.

Hot running at 3000 rpm was ~ 30-35 psi.

6000 rpm ~ 65-70 psi.

I never ran it cold at 6000 rpm but I suspect it would still show approx 75 psi,
as that is likely where the pressure relief would open.

RAGGAREN 04-04-2019 06:55 PM

Re: Oil pressure drop
 
i dont know ..
still seems low to me for a for a fairly freshly rebuilt windsor..
on re-build, I would expect at least 30 at idle.


FE's seems more common with lower pressure readings
more variable's like worn rocker assembly's for example,

but that can remedied with oil restricted oil port in head..

galaxiex 04-04-2019 07:17 PM

Re: Oil pressure drop
 
Quote:

Originally Posted by RAGGAREN (Post 1629578463)
i dont know ..
still seems low to me for a for a fairly freshly rebuilt windsor..
on re-build, I would expect at least 30 at idle.


FE's seems more common with lower pressure readings
more variable's like worn rocker assembly's for example,

but that can remedied with oil restricted oil port in head..

Ya, true dat. :)

Been a long time since I had a vehicle with a Windsor and an oil pressure gauge...

Used to have a 65 Mustang with a well worn 289 and if I recall... it ran maybe 10-12 psi at idle hot.

I still don't think 10 psi at hot idle is bad.
There is very little load on the engine at idle,
and he says the pressure comes up with rpm, as you would expect, so I still don't think it's a concern.

Now if the pressure stayed low, then I would worry.

Edit; for the record... I have had numerous "other brand" engines that had hot idle pressure ~ 10 psi and never a problem.

The 10 psi at hot idle seems normal to me.

70XL 04-05-2019 11:03 AM

Re: Oil pressure drop
 
How has this situation changed over time since the rebuild? I concur that 10 PSI at hot idle is not a real problem as long as it has not been a rapid change, or a significant change over a short time.

Marauderjack 04-05-2019 12:44 PM

Re: Oil pressure drop
 
I had the run on problem with my 408W so I installed an AC Solenoid that held the idle up to 850 RPM's at idle but dropped to ZERO with primary butterflies completely closed when I turned the ignition OFF.....worked GREAT!!:wink2:

Give that a whirl if the low OP at idle is bothersome!!:smile2:


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