Little to no oil pressure? Or, is my gauge lying?

[Bobs29ModelA]

I am running 40-wt Brad Penn racing oil (with zinc additive) in my stock (but rebuilt a few years before I bought the car) flathead 4-banger. Since I have so far been unable to determine who rebuilt the engine, or if they converted it to bearing inserts (versus babbits), I don't really know much about the quality of the rebuild, other than it is a very strong-pulling engine.

Anyway, I recently decided to put a 0 - 10 PSI oil pressure gauge on the car, to see what it would read-out at, and was shocked to find the following:

When the engine is cold, the needle will peg all the way to the right. Within a few minutes, however, as it warms up, the needle will be somewhere in the middle of the gauge at speed on local roads, but then will drop down to zero at idle. Then, after driving it for a few more minutes, the gauge just reads zero (and that's all)... even while doing 55 mph on the freeway!

Now, I know this engine is getting oil, otherwise it would have blown or siezed years ago! The only other thing I can think of is that either this brand-new gauge is defective, or, there is some kind of unknown minute material inside the capillary feed line that might be moving around and blocking the pressure of the oil from hitting the gauge... although that seems unlikely, since the symptoms (erratic readings) are always consistent under the same conditions as mentioned above. Conversely, I can see the oil thin-out a little bit as it goes from cold to hot, but to make the gauge go from pegging the needle, then down to nothing? None of that makes sense to me.

So, does anybody have any ideas or similar experiences to share, that might shed some light on what might be going on here?

[Bob C]

If it has a stock oiling system there is no oil pressure, it is gravity fed
to the mains and the rods have dippers.

Bob

[PC/SR]

Your gauge is correct for the reasons stated. The oil thins and the pressure drops. Mine reads the same way.

[Terry,NJ]

I felt that same sense of shock when the pressure went 40 PSI, cold to 3 PSI when hot in my 1952 Ford 8N tractor. A little investigation and I found out that early engineers were more concerned with oil just being present, not under pressure. That's why we find archaic technology such as dippers and dipper trays. I never advise anyone to put a oil Pressure gauge on a Mod A for this reason. It's panic striking!
Terry

[C26Pinelake]

I learned the hard way ! I had my car towed 52 miles because all of a sudden I noticed no oil pressure. When the mechanic arrived he said it was not supposed to have any pressure but there was no charge because I had already been punished enough ( towing charge $125 dollars ) for my lack of Model A knowledge.
Wayne

[Bobs29ModelA]

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Wow, I'm feeling a little bit silly right now, and I do thank you all for sharing your expertise and experiences with me. Again, I wasn't really worrying about it, but was thrown for a loop by all this.

So, I guess there's just a couple of nagging questions left:

First, I've both heard and read that the removable plug (under the exhaust manifold) was originally intended as a place for the Ford mechanics to connect an oil pressure gauge, ostensibly for confirming some type of oil pressure or flow there. If there's no real pressure, why did Ford provide access to that spot?

Secondly, just why are these up-to-10-psi gauges being sold all over the place for the Model A, if there's not really any usable "pressure" available to them?

[Mike V. Florida]

Originally Posted by Bobs29ModelA

So, I guess there's just a couple of nagging questions left:

First, I've both heard and read that the removable plug (under the exhaust manifold) was originally intended as a place for the Ford mechanics to connect an oil pressure gauge, ostensibly for confirming some type of oil pressure or flow there. If there's no real pressure, why did Ford provide access to that spot?

Secondly, just why are these up-to-10-psi gauges being sold all over the place for the Model A, if there's not really any usable "pressure" available to them?

First, if that plug is removed you will be able to confirm flow. No Pressure gauge needed.

Second, the 0-10 pressure gauge is not as common as you think and if they will buy it they will sell it. Ford never had an oil gauge in the A.


You happened to buy a car that someone felt it was necessary to have such a gauge. Nothing really wrong with it but like you said almost useless once the engine warms up.

[Tom Wesenberg]

Here's a thought. If the oil line breaks on that gauge you wouldn't know it because the gauge already is reading zero. Your engine could suddenly lock up due to all the oil being pumped out the broken line. Remove the gauge and you have one thing less to worry about.

BTW, could that slotted plug have been put in the block as a neccessary means for the factory to drill the oil passage?

[29 Tudor]

If you add the oil filter that screws onto the valve chamber cover, the gauge will read the pressure going INTO the filter. In my case, when warm I see about 4 PSI when going down the road at 35-40 mph, still zero at idle. It is comforting to see the pressure and KNOW I am getting oil to the engine. Just a thought........

sd

[James Rogers]

A little story. A couple of weeks ago, I decided to pull the motor in my Cabriolet because the new oil pressure gauge wouldn't show pressure except at high speeds. I figured the pump was crappin' out so I would check the bearings and rebuild the pump and do some maintenance. Pulled the motor and mounted it on a stand to begin. I grabbed the adjustable and a gallon jug and pulled the drain plug and almost fell over. The oil came out like water and filled that jug and another one by the time it emptied the pan. What had happened was I am running a Weber and over the winter it had leaked the cylinders full which drained into the pan. The pump was ok but I replaced it with a rebuild and did the maintenance and painted the motor again and installed it in the car. It started on the second turn and the oil pressure needle pegged at 15#. After driving it 40 or 50 miles it will run at 7# steady but if I jam the throttle, it will run 10 or 12 for a second then drop to 0 till I let off. This pump will drain the pan in a second but I don't worry because the oil is where it needs to be.

Lesson, check the oil daily.

[CarlG]

That's another vote for me to put in an electric shut off gas valve

[Bobs29ModelA]

Interesting thoughts; however, the car did not actually come to me with an oil gauge; I happened to have the kit in my box of parts (leftover from an intention to use it on my first Model A, which never happened), and I decided on a whim to hook it up to see what it would say, but only on a temporary basis... which is why its readings (or rather, a lack thereof) really threw me for a loop.

I have since removed the gauge now and am not going to sweat it! I drove about 25 miles on the freeway today at speeds between 55 to 60 mph, and the engine was cruisin' just fine all the way, so no worries...

Also, I am aware that you can remove the plug; however, I also have a special plug that threads in there (in place of the stock plug) that also has another screw in the center of it... and that is the "tool" that is available specifically to be used to hold the pump in place when you drop the oil pan (meaning, the stock plug itself will not hold the pump in place). I used this little tool to hold the pump in place when I dropped the pan on my '31 a few years ago, and it did the trick just fine... but again, it's only for use to hold the pump in place, and you would never leave it in there under driving conditions.