How to test oil pressure when stock gauge/sender doubtful

[Old Henry]

Just posted this on the low oil pressure in my 59AB thread as tool and method to check actual oil pressure when stock gauge and/or sender are doubtful.

Get a cheap mechanical gauge such as this one from AutoZone for $18.00 here: http://www.autozone.com/autozone/acc...ier=267574_0_0_:

And temporarily screw it in place of your oil sender:


Run the tube up the firewall


And under the hood. Then hang it on the windeshield wiper temorarily


And read it through the windshield while driving around to see what the real pressure is cold to hot, stopped to high speed.


By this method I just found out that my oil pressure that has never read higher than 16 psi on my dash gauge was actually just great - 40-50 psi cold, 30-40 hot, and no lower than 13 psi hot idling (usually went to 0 on my dash gauge). Good news. That means my sender is bad since two NOS gauges both read the same off of it.

[David J]

In my book that reaches the REALLY GOOD NEWS level . Congrats

[Brian]

Actually, I wouldn't be too hasty in condemning your sender unit as being faulty. There are two different sender units, one rated at 50 lbs, the other at 80 lbs. If you run an 80 lb sender unit with the 50 lb gauge, the gauge will always register a lower than actual pressure. I know this for a fact in my 35. I know you have one of those post war Ford offerings, so don't know for certain how those 46-48 oil gauges are calibrated, but while you have your [faulty?] sender out, check the sides of the brass square and see if it is stamped. I don't know if any or all 80 lb senders are stamped, however, I am sure that all 50 lb senders are. If your sender is not stamped with a 50 on one of the flats of the square, I suggest you find and install one that is, then recheck the readings of your NOS gauge and see how it compares , now you have determined the real pressure.

[Old Henry]

46-48's are all 80 lb sender and gauge.

That's what mine are. My sender is not very old, like a couple of years. I got it from C&G and it is rated at 80 lbs. (Here: https://secure435.hostgator.com/~dlv...&g=79&t=597&tn= Their listing is a little wrong 'cause they list the 80 lb sender for 35-53.)

'35-'42's were 50 lb.


Tomorrow I'm going to try my gauges on my neighbor's 47 sender on his engine. His gauge reads in the same range as my mechanical one. If my gauge reads the same as his gauge on his sender on his engine then I'll have even more evidence that it's not the gauge but the sender. I may even try his sender in my car to see if I get accurate readings on my gauge with his sender. All of that before ordering a new sender.

[TomO]

Henry, you need to match the sending unit to the oil pump and relief valve. If you have a 50# system, you need a 50# sender, if you have the 80# system, you need the 80# sender.

Your mechanical gauge readings seem right for the 50# system. 50# sending units are hard to come by.

[Old Henry]

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Originally Posted by TomO

Henry, you need to match the sending unit to the oil pump and relief valve. If you have a 50# system, you need a 50# sender, if you have the 80# system, you need the 80# sender.

Your mechanical gauge readings seem right for the 50# system. 50# sending units are hard to come by.

I have 80# pump, sender, and gauge.

[ken ct]

Originally Posted by TomO

Henry, you need to match the sending unit to the oil pump and relief valve. If you have a 50# system, you need a 50# sender, if you have the 80# system, you need the 80# sender.

Your mechanical gauge readings seem right for the 50# system. 50# sending units are hard to come by.

You bet on that Tom,real hard to find not repoed. Jeep makes one 50# but its quite a bit taller and requires a adaptor fitting i believe. ken ct.

[Old Henry]

Tested my gauge on neighbors car today. Worked perfect. That leaves the sender as the culprit. Ordered one today. Hope it works.

[Old Henry]

Sure enough! Got the new sender in today and Voilà! Pressure sits right on 30 lbs. just like it's supposed to. It's nice to have the gauge telling what it should be telling. When it was saying the pressure was low, even though I knew it wasn't, it was kinda like having a nagging pain somewhere that you know nothing is wrong. It's still hard to ignore. Now it's fixed so I can worry about something else other than oil pressure.

[ChikaFreak]

Originally Posted by Old Henry

And temporarily screw it in place of your oil sender:

Sorry to dig up such an old thread! Henry can you tell me what the function is of the fitting and line that are hooked up NEXT TO the brass fitting that you installed above? On my '41 there is an oil pressure gauge that is hooked up to that line and I want to know what its real purpose is!

Thanks,

Chris

[Lawson Cox]

You can hook up the oil pressure sending unit to either place.

[Old Henry]

Originally Posted by ChikaFreak

Sorry to dig up such an old thread! Henry can you tell me what the function is of the fitting and line that are hooked up NEXT TO the brass fitting that you installed above? On my '41 there is an oil pressure gauge that is hooked up to that line and I want to know what its real purpose is!

Thanks,

Chris

On my 59AB engine that is the oil line that goes to the oil filter then down to the oil pan. It's only a partial filter system, sort of like a swimming pool filter. When the oil pump pumps the oil out of the oil pan it pumps it to this point where most of the oil goes through the engine to lubricate it and some goes through this line to filter it then back to the oil pan. Not the greatest but better than nothing I guess.

As Lawson said, the same oil pressure that is in the socket where the sender is normally installed is also in that line so your gauge will be reading the same pressure as if it were installed in the designated socket. You could actually run your stock gauge from a sender in the socket and a mechanical gauge from the T in your oil line.

Hope this answers your question.

[fottyjs]

The 80 senders have an 80 above the thread on the square portion of the connection...I have also seen the 80 on the can....Jack

[George/Maine]

I had a bad experience with those plastic lines, can un done and burned up engine.
I don't, use gauge you will know when you have no pressure.
If anything use copper line.

[ChikaFreak]

Originally Posted by Old Henry

As Lawson said, the same oil pressure that is in the socket where the sender is normally installed is also in that line so your gauge will be reading the same pressure as if it were installed in the designated socket. You could actually run your stock gauge from a sender in the socket and a mechanical gauge from the T in your oil line.

Hope this answers your question.

Thanks Henry and Lawson that does answer my question! Looks like my engine is missing the oil filter, although it does not sound like a crucial loss. Something to keep an eye out for in the future.

Thanks!

[Old Henry]

Originally Posted by ChikaFreak

Thanks Henry and Lawson that does answer my question! Looks like my engine is missing the oil filter, although it does not sound like a crucial loss. Something to keep an eye out for in the future.

Thanks!

Where does your oil line go if not to an oil filter?
If that line does not dead end or have a restriction in it if it goes back to the oil pan you won't have any oil pressure in the lubrication system of the engine.

[Ross F-1]

Originally Posted by George/Maine

I had a bad experience with those plastic lines, can un done and burned up engine.
I don't, use gauge you will know when you have no pressure.
If anything use copper line.

Copper will harden and crack long before the teflon tubing dies, as long as you keep the teflon supported and away from heat.

My dash gauge was suspect too, so I hooked up a cheap gauge just as Prof. did. It showed a little more pressure, but not much. Then I came into a brand new $150 +/- Ashcroft gauge, an industrial quality piece, brand new. Hooked it up and it showed 50 psi where the dash said near 10, and the cheapo said 30. Gauges are only any good if they can be trusted.

[Talkwrench]

I would still good copper over that cheap tubing, the VDO stuff would be ok.

Agreed.. only as good if they can be trusted. Im sure there is more than a few "autometer" gauges out there that are miles off.

[Brendan]

I put a Stewart warner temp gauge and a oil pressure gauge in my pickup when I first got it. I do that in all my cars. and I run the mechanical gauge, I do not trust electrical gauges

[ChikaFreak]

Originally Posted by Old Henry

Where does your oil line go if not to an oil filter?
If that line does not dead end or have a restriction in it if it goes back to the oil pan you won't have any oil pressure in the lubrication system of the engine.

I have a mechanical oil gauge hooked up there right now. It has started to leak and I couldn't figure out what component originally went there.