425 Oil Pressure

**64RIV** · 07-05-2006, 01:24 PM

I just had may 425 nailhead completely rebuilt. I have been following my rebuilder's engine break-in procedure/advice and am being perhaps a little over cautious along the way. After I fired the engine up the first time, I monitored oil pressure and temperature @~1200 rpm. When cold, the pressure was right at 40 psi, per the specs. However after coming up to about 160 degrees the pressure dropped roughly half (~ 19 psi). I was running 10W30 castrol. I called my rebuilder and asked if this was something I should be concerned about. He advised me to switch to straight 30W and try again. With 30 W the pressure held up better but it still dropped to ~28 psi and looked as though it still hadn't bottomed out yet. Can anyone comment on the expected oil pressure in this engine i.e. what should I expect the pressure to be for various temperatures, oil viscosity and engine RPMs? What is the lowest pressure I should start being concerned with at idle (and for now 1200 rpm)? Any advice is much appreciated.

Thanks in advance

Jim

**telriv** · 07-05-2006, 03:23 PM

Jim, NailHeads do not require gobs of oil pressure. Average oil pressure is 35PSI@ 35MPH. You could idle all day at 5PSI if need be. The most important thing is when you touch the go pedal that the pressure starts to immediately rise & settle out at it's max at around 1500-2000RPM's.

Tom T.

**howpeculiar** · 07-06-2006, 08:12 AM

As a general rule of thumb, and some engines will vary from this, you want to see 10# per 1000 rpm. If your pressure never changes from the 28# once its warm and you increase the pump speed (increase rpm), then you should be concerned. You didn't mention whether or not the pressure inceases at higher speeds, but so long as you are getting 40# at 4000 rpm, you should have a healthy oiling capacity.

**telriv** · 07-06-2006, 06:06 PM

Don't mean to sound sarcastic or anything, but a NailHead doesn't, normally, follow the general rule of thumb. In this case, oil pressure, is NOT one of them.

Tom T.

**64RIV** · 07-06-2006, 06:23 PM

Thanks for the replies guys.
I feel more at ease now.
So far all my data gathering has been in the driveway.
I hope to get this beast on the road this weekend (barring any other issues.) I'll let you know how it goes.

Regards,
Jim

**howpeculiar** · 07-06-2006, 07:04 PM

Telriv,
I didn't hear any sarcasm. I have very little experience with the Nailhead, this 364 is the first I have played with. Had I known the parts costs I would have thought twice though! Like I said before, it is a general rule for most engines, and has never failed me.
Aaron