1965 911 Engine Pressure Reading

[bonzer5]

Hi Guys,

I'm quite the lurker, great forum and thank you to all the contributors!

There seems to be a few threads about oil pressure might be often, so I apologize if this is a duplicate and I'm boring you, but I can't find any info explaining my readings so I thought I'd ask. A keen mechanic would know but I'm starting here as many of you are keen as well.

Let's assume the gauge and sending unit are good. I understand 10PSI per 1000RPM is acceptable. From what I gather 4.0-5.5 bar (58-80PSI) @ 5000RPM is acceptable. Warmed up idling pressure on the very early engines will be low, like 5 PSI, maybe even Zero. Correct any of this if I'm wrong. These are the guidelines I've found.

Here's what I am seeing which I'm unsure of. Any analysis will be much appreciated and I thank you in advance.

When the engine is cold, the usual higher pressures are present on the gauge.

When engine is at least 180F:
Needle hits the 0 PSI mark at idle
Maintaining 3000RPM in gear cruising = Oil Pressure is roughly 19PSI
Accelerating 1/2 throttle @ 5000RPM = 65 maybe 70PSI (Hey this is good! )
Accelerating 3/4 to full throttle past 5500RPM = The gauge is pinned at 140PSI

Are these readings a problem? are they normal? 140PSI doesn't seem right and the 19PSI at 3000RPM cruising is not right according to the rule of thumb.

The engine runs like a champ and barely ever smokes during 1 out of 20 cold starts.

Thanks again guys!

[edmayo]

I suspect you may have a mismatched gauge/sender combo. The pressure at cruise is too low in relation to the 140 you see at 5500. The best way to resolve this is to temporarily install a mechanical gauge at the engine. Now you can compare the two gauge readings. With the mechanical gauge all electric foolishness is by-passed.

[bonzer5]

Thanks edmayo! You're right to suspect the sender and measuring mechanically would be wise. Thank you. The sender says 5/65 on it so I doubt it's mismatched but it is almost 49 years old and maybe not working properly. Same goes for the gauge.

[304065]

What Ed said (I should put that in my signature line!)

Do it like this:

[bonzer5]

Geez, a picture is worth a thousand words. I was thinking a fancy set up was needed. Thanks Irish! Probably $15 from McMastercar and I'll be good to go. I really wouldn't have know how to set it up so thank you.

And is that original sound proofing I see?! Right on dude!

[304065]

The gauge is a Wika 0-200 bottom mount pressure gauge, really cheap (like under ten bucks) and German-made besides, with an 1/8" NPT thread. Don't tell Wika they will raise the price.

Below that is a VDO 1/8" NPT female to M10x1.0 male adapter fiting with copper crush washer to seal it to the factory union. This is ridiculously expensive for a little piece of brass, like eight bucks. VDO part number 42-901.

I used teflon tape on the threads. You aren't supposed to do this, it will raise interest rates and cause your cat to spontaneously combust. So far nothing bad has happened.

The factory union is M10x1.0 female to M18x1.5 male and it goes in with an aluminum A18 crush washer. This should already be present in your car though.

[bonzer5]

Thanks a million dude! Painting by numbers now! This will hopefully help some others in the future. Serious karma points for ya!