Oil Pressure Question

Hello All:

My 425 in my Wildcat runs about 25 PSI at 1500 RPM. At idle it goes down to around 10 PSI. It doesn't smoke or burn oil. Is this normal pressure for a Nailhead?

 

10 PSI for each 1000 RPM. (and yes, nailheads are typically lower, the "majority" are 20PSI idle warm - 40PSI off idle )

My nailhead starts cold and hits 38-40PSI.

When warm it will run between 15-20PSI, at idle (the hotter, the lower) and still hit 36-38 off idle and steady 38 at highway speed.

I have known some to have idle down around 4-6 PSI, and still rise as RPM goes up.

As long as you see that, you are likely OK.

Like your blood pressure, you should be within "normal" range, know what "your specific pressures" are,and if you see a sizable change from "normal", then stop and investigate that.

 

Thank you very much. I am, sadly, a newcomer to vehicle mechanics. Electronics, that's in my ballpark. But, I am trying to learn.

 

No one here seems to be asking the right questions of you!
First off is this amount of cold and hot oil pressure you post about the way it has been, or is it a recent change that prompted you to ask about it?

 

What weight oil?

Had a guy look at my 67 Riv for sale and he asked what oil I run. I said 10w30 with one or 2 20w50s thrown in depending on season. He said "I run 5w30 in all mine".
I said you can't do that in a 53 yr old car with lots of miles! Maybe in Alaska.....

 

at 2400 rpms it should be 37 psi. questions are, did you change the oil because older cars do get diluted with gas, and what weight oil is in there ?

 

I did change my oil the other day, but that didn't change the readings. I run 10w30 conventional oil. I was told not to run synthetic because of the cork gaskets.

 

This is hot oil pressure. No, there hasn't been any change. I was just reading about oil pressure and wanted to clarify things a little for myself. Thank you all for your responses.

 

Why? Wasn't the oil recommended sae30 (singleweight lawnmower oil)?

I've run 5w30, 10w40 and 15w40 and the oil pressure cold/hot is of cause not the same, but all weights have been fine.. No difference in driveability etc.. I've added zddp each time..

 

I bought an original owners manual and it recommends S.A.E. 10w30 until zero F. below zero, it recommends 5w20. The only thing I won't do is change the every 60 days. It isn't driven all that much. I put on 3000 miles in 8 months. Then I changed the oil. I will pick up the zinc additive today.

 

Most also recommended 10w-40 and 20w-40 above 60deg. Anything with over 100k miles I like to go next heavier weight.

 

I am running a mechanical oil pressure gauge. It was installed for me by my local mechanic Bob. He is the one I trust to work on my girl. Where it is getting the reading from I cannot say. Car is covered for 2 week of bad weather. My baby doesn't go out when it snows, that's what my F150 4x4 is for.

 

The manual calls for 40 lbs of oil pressure at 2400 RPM. Typically any oil pressure at a normal (500-650 RPM) idle is fine. I worked at a place that had a 390 Mercury station wagon as a company car. It idled a 3PSI! It ran fine with about 18-20 PSI at cruise speed and the extremely high mileage big block held together and made no strange noises. I think we ran the thing for about three years before we finally put a set of bearings in it during a slow February. I wouldn't worry about 10 LBS at an idle in the Nailhead. I use Shell Rotella 10W30 in my 425 Nail.

 

Thank you John. I appreciate the insight from all. The article I was reading referred to normal V8's, no mention of the Nailhead, hence my inquiry. In automotive shows I watch they talk about 60 - 80 lb's of pressure during break in period. I know a 55 year old engine that has never been rebuilt(this I know. Ray bought it from original owner and she stated never rebuilt, and not running at that time.). I am no judge of things mechanical, but as I said, I am trying to learn all I can.It now has 105,000 miles on her. I realize that higher pressures in the Nailhead were not typical, but 10 lb's did concern me. I am slowly collecting parts for a refresh of the motor next summer (timing chain and sprocket, complete gaskets, rear main seal, rings, oil pump. fuel pump so far. I acquire as finances allow). I just purchased the Nailhead rebuild book advertised on the site and had the shop manuals. I intend to let my Brother-In-Law oversee, but let me do the work. I've got to learn.

 

Nailhead rule of thumb: 10 lbs of oil pressure for every 1,000 rpm's. Internal parts built to a different standard then later engines.

 

You will NEVER get 60PSI out of a "Nail" oil pump.
6-10pds. hot idle is fine. Of course more is better. Then again you don't want too much as it will cause other problems.
For years in MOST manuals it states 35pds. at 35MPH is normal. The MOST that has been gotten out of a "Nail" oil pump is 55PSI after it having been blueprinted.

Tom T.