Oil pressure gauge issue

My stock motor with a VDO mechanical gauge runs somewhere near 70 cold and over 60 hot.  Been that way for 35 years.  I have a 350 Chevy also running a mechanical gauge that can barely pump 30 hot.  Never had a problem with either of them.

Also, did you change the type of oil you are running?

I have not changed oil type or viscosity, and change the oil at least once a year. The motor uses almost no oil, except for a very annoying minor leak near the front seal that I aim to fix this winter. The motor was rebuilt about 20 years ago and has about 15000 miles les on it since then.  The puzzling thing is that the pressure creeped up about 15 pounds over the last three years.

has anybody changed the oil pump without pulling the motor? Possibly  the pressure relief valve is sticking.

Curious what oil viscosity you run.  I have always used the Valvoline 20W50 race oil.  I looked on the 351C Facebook group site and the references suggest pretty high pressures on the motor.

Here is one thread you should read from the forum.  It may help:

https://pantera.infopop.cc/topic/oil-pressure

I’ve always run 10w30. It does get quite hot and cold in Virginia

@tomkuester posted:

I have not changed oil type or viscosity, and change the oil at least once a year. The motor uses almost no oil, except for a very annoying minor leak near the front seal that I aim to fix this winter. The motor was rebuilt about 20 years ago and has about 15000 miles les on it since then.  The puzzling thing is that the pressure creeped up about 15 pounds over the last three years.

has anybody changed the oil pump without pulling the motor? Possibly  the pressure relief valve is sticking.

You can change the oil pump without pulling the motor.  The oil pan will have to be dropped.  If your car has the removable crossmember then it is less of an effort.  If the original crossmember is still there then it is a project to convert it to a removal unit.  Chopping out the crossmember is easier if your oil pan is stock.  It was somewhat of a challenge with my 10 quart aluminum oil pan.  I also had to remove the parking brake mount to get my oil pan out.  Once the oil pan is out the oil pump is readily accessible.

I thought so and had removed the cross member more than forty years ago, so that’s not a problem. remounting the oil pan was on the agenda to fix a leak. Is there a trick to holding the dive shaft in place? I may not be using the correct words.

I understand about the drive shaft.  No, it is no problem.  It just comes out with the pump and goes back the same way.  I had the distributor out that may have made it easier to reinstall the shaft and the pump.  

Take note that the shaft should have a friction-fit washer attached to it. Take note of its position and make sure to retain it. It is what keeps the shaft from pulling out of the oil pump should it stick to the distributor hex drive shaft when removing the distributor.

if that happens with a distributor removal, it will necessitate removal of the oil pan to retrieve and reinstall  the shaft 😕

Larry

Something to keep in mind. Thank you

@tomkuester posted:

I have not changed oil type or viscosity, and change the oil at least once a year. The motor uses almost no oil, except for a very annoying minor leak near the front seal that I aim to fix this winter. The motor was rebuilt about 20 years ago and has about 15000 miles les on it since then.  The puzzling thing is that the pressure creeped up about 15 pounds over the last three years.

has anybody changed the oil pump without pulling the motor? Possibly  the pressure relief valve is sticking.

I have changed an oil pump with the engine in the car. You just have to be able to take the oil pan off. Your high oil pressure issue sounds like an oil pump with a stuck relief spring.

I am assuming that the oil pump is working properly, but may have a sticky pressure relief valve. I looked on the internet if that valve  can be cleaned or replaced without removing the pump and it seams that this is possible. Have any of you done this?

I would imagine you would need to have the oil pan removed to get to that valve. At that that point it is only two more bolts to remove the pump and you can examine it in the luxury of your workbench.  It might be more practical to replace the entire pump since the outcome of cleaning or the replacing the valve will not be known until the car is back together.  And, oil pumps are reasonably priced.

You are absolutely right, but I’m concerned about the alignment with the distributor.

This distributor will not move if all you do is remove the pan and oil pump.

The fit of the driveshaft into the pump and the bottom of the distributor shaft is not a difficult NASA precision fit and will pose no difficulty during reassembly.

if you decide to replace the oil pump, the generally agreed pump to purchase is a Mellings, standard pressure, standard volume.

Larry

Tom, realignment of the distributor to the oil pump shaft can be a hassle but it certainly can be done.  Health of the oil pump is more important.  Once you repair or replace the oil pump let us know of any issues with the distributor and we will try to get you on track.

If only DeTomaso had gone with a Chevy motor, the distributor/oil pump alignment would have been so easy, but no he had to go for looks and hid the distributor. Most likely I’ll replace the entire pump once I get started in earnest. I’m just trying to work myself up to the task since I’m 78 years old and don’t have a lift. But I love this stuff.

If you have a reliable mechanical gauge and it is reading 65 lbs., why would you think there is a problem?  Why would you not conclude the old gauge or sender was failing and giving you a false reading?

It may very well be a be a correct reading, and within proper tolerances, but I'm concerned because the pressure has climbed after about 20 years since the motor was rebuilt. Does that not make you wonder. No, I really don't want to go through the trouble of putting in a new pump. I'd rather leave that to the next caretaker.

Ford''s unhappy combination of an Italian Veglia oil gauge and the US pressure sender has always resulted in an inaccurate gauge reading. Gauges & pumps do not increase their reading due to age or wear. The reverse is what normally happens.

Likely the pump is just fine and the connecting wire has loosened a connection, changing the reading. Believe the mechanical gauge- the Veglia is only to tell you if the engine is running.

I just started my stock motor.  Reads 70 stone cold.  As it warms, drops below 70 but not much.  VDO mechanical gauge.

That's good to know. Maybe I'm fretting over nothing. The problem with owning old cars is that you question every sound, smell and change.

For the time being I installed a mechanical gage on a T that also allows the old sending unit to remain in place. It's been so cold here lately, so no test run yet.   

as for hints that the engine is actually running, mine is somewhat noisy and gives it away.

Tom, a few decades ago I colluded with a friend who worked for Ford and borrowed eight (8) brand new 351-C oil pressure sending units.  I tried them one after another in the garage on a thoroughly warmed up Pantera. I got six (6) different answers and none agreed very closely with the SW- mechanical, which is, like yours, on a Tee fitting back by the bell housing. Its still there after 30 years- bothering nothing & no one.

There's a second threaded oil pressure port above the OEM fuel pump that will give MUCH different results, so pay no attention to data from that spot. It is all but impossible to access on a Pantera, anyway

I trust you returned the gages after you were done with the experiment, but we are all benefitting from it.

@bosswrench posted:

Tom, a few decades ago I colluded with a friend who worked for Ford and borrowed eight (8) brand new 351-C oil pressure sending units.  I tried them one after another in the garage on a thoroughly warmed up Pantera. I got six (6) different answers and none agreed very closely with the SW- mechanical, which is, like yours, on a Tee fitting back by the bell housing. Its still there after 30 years- bothering nothing & no one.

There's a second threaded oil pressure port above the OEM fuel pump that will give MUCH different results, so pay no attention to data from that spot. It is all but impossible to access on a Pantera, anyway

Useful for installing a safety pressure switch on the control of the electric fuel pump

The plate on the fuel pump opening is temporary, the final one will be "cleaner".

Yes, even though they were cheap, I splashed the ends in solvent to remove oil from the insides of the pipe threads, and gave them back. My friend was not shocked to hear of the scattered results.