Low Oil Pressure

[Don St Peter]

My 40 Ply. engine runs great but oil pressure drops from about 40 PSI ( guage reading cold engine) to near zero after warmed up. I use 30W non detergent oil. It does not smoke much at all. Should I be concerned about the low pressure and do something as a precaution.

Thanks in Advance

Don

[Normspeed]

Hi Don, maybe someone here could verify this, I believe it could be a weak or broken spring in the oil pressure relief valve or a stuck piston in the valve. Or maybe just good old bearing wear on the mains. I would think if the mains were that loose, you'd be hearing some pretty heavy knocking though. Just my shade tree opinion.

[Lou Earle]

I - do not have it handy -but service manual says if it will drop to 10 lbs at idle that is fine and should run 30 to 50 on road. Now if it is at 10 or lees at say 25mph you have problems. I would go ahead and run the car on your present oil and then switch to 15- 40 weight or 20 w 40 or something in the neighborhood. Unless your engine has just been rebuilt any good oil is fine rebuilt engines cal of 20 wt in the beginning I believe. On one engine in particular I ran 20 w 50 and it did fine quited the thing down and reduced some the oil burning.

[james curl]

I would pull the oil pressure relief cover and check that the spring has not fatigued and broken releiving the pressure on the piston that controls the oil pressure. Mine broke into four pieces and I had to cut down a new spring from Fastenal co. because a new MOPAR spring cannot be found.

[Don St Peter]

Thanks for the input. I checked my oil pressure relief valve spring and it appears to be in good shape. The service manual mentions different color springs and cautions to replace with like color. My spring is not colored so I am going to assume it is the right one.

Jim mentioned that a broken spring in his case was relieving the pressure on the piston that controls the oil pressure. Is there some way to check to insure that the piston itself is free to move and not stuck?

Can someone explain to me how this relief valve system works as my manuals do not go into it? I did add an oil filter to my car as it did not have that option installed. I am certain that it is installed properly.

Thank You

Don

[Lou Earle]

Please answer this question- Waht is the oil pressure on warm engien at 25 to 30 mph? We do not know if your low pressure is at idle or at speed and that is critical in diagnosis.

I removed my valve by running a pick up magnet up intot the hole I think u can also just crakn the engine a couple of times and it will shoot out withthe plug removed.

Again waht pressure at 25 mph?

[Don St Peter]

Lou:

I followed your tip on using a pick up magnet and it worked like a charm. I now also better understand (after seeing the piston) how the relief system works. Unfortunately the low oil pressure persists at all speeds after the engine is warm. At 25 to 30 MPH it registers about 1/2 way to the 20 PSI mark on the oil guage. As I do not know the guage accuracy, I'm guessing maybe less than 10 PSI. I can tell you that the needle base is painted red and the red shows through the small viewing window.

Thanks for your continued good input on all subjects!

Don

[Lou Earle]

2 things:

1- remove the oil pressure line to the Gage (the flexible line at the firewall )and see if it is pumping oil . Then get another Gage and attach it to the line and see what it reads.

Also just pour in a quart or pint of stp in your present oil- or the store brand knock off and see what happens.

If the Gage is off all is OK if new Gage -auto zone type - shows low pressure say at 1500 rpm I would guess worn mains. But all is not lost get some 20- w 50 and see how the pressure does on that oil. I know some folks who run 20/50 in their newly rebuilt engines and swear by it. So I am sure it will not hurt your engine. One other question did you have this low problem before u installed the oil filter?

Lou

[Lou Earle]

One other thing: check your oil to see if gas has entered it somehow- you can usually smell the gas on the dipstick and you can sometimes light the oil and the gs Will spark a bit. If oil on stick is watery thin you have gas there and need to change it. If it is gas in oil causing low pressure -oil to thin- need a compression check and we can go from there

Lou

[Don St Peter]

Lou:

I'm satisfied that fuel is not present in oil.

When I bought the car about 5 years ago I replaced a blown head gasket, but for reasons I won't bore you with, I did not check or do other engine work as the engine started and ran and did not sound bad. I did not even do compression checks.

Low oil pressure was noted once I got it otherwise up and running with new points, plugs, condenser, distributor, carb, fuel system, etc. and all guages installed. I know for a fact that after installing the NOS oil guage, that the line attached directly to the back of the instrument panel monted guage was shooting oil to the guage good.

It was about a year ago that I found and installed an oil filter. At the time it seemed the already low oil pressure was still low by about the same amount.

Sounds as if I should do an oil change to 20 W 50 and monitor things. I'm in Florida and the car will operate here in warmer weather most all the time.

In your opinion should I add a quart of STP, or equilivant to my 30W oil now to see what happens before changing oil. I've been told adding such stuff could cause old carbon dsposits to break loose, cause smoking, burn more oil, etc. Sounds like old wives tales from your experience. I do not recalling seeing 20W50 oil on the shelves around here, but intend to find out.

Sounds like I should delay a fairly long trip with the car until I better know the condition.

Thanks for the Help.

Don

[Normspeed]

I'd guess you will see some increase in pressure with a heavier oil. I run 15W40 and I've seen 20w50 at Wal Mart. I think you would be fine with either of those in your climate. Not familiar with the markings on the 1940 oil pressure gauge. On the later ones there is a mark at the 0 lb point and a mark at the 80 lb point, with intermediate marks the low and high safe ranges. The high safe mark is 40 lbs. I believe the low safe mark is 10 lbs.

[Lou Earle]

To much oil in the oil pressure line- that might be your problem- oil could have gotten into the oil gage. I remember reading that the line needs AIR pressure to make the gage work properly . Before you go further attach another guage to the line and check that out. If you have been running the car It sounds like a guage problem. Another thing to do run the car 20 or so miles and check the oil filter if hot oil is going thru and according to the book you need 30 pounds of pressure to have oil flowing to the filter.

It also sounds like you installed the oil gage with oil right at the gage- thsi might be it .

Lou

[Lou Earle]

Also I just detach my oil gage line at the firewall when changing engiens and the re attach there . I do not do anything but attach and there is surely air inthe upper line to the gage. Also when I attached a new gage to sons mustang with copper line I did not fill it with oil just attached it and let it go.

So please check gage firs.

AS to addatives- well I personally have not had that happen and don't know anyone who can prove that happened to tham.

However stp is not a cleaner it is a thickener.

I would note if I were u I would drop that pand and clean it - it probably does have sludge having no filter fro over 50 years!!

Lou

[Don St Peter]

Interesting observations!

Lou- On my 40 Ply (P-9), the oil pressure line from the engine block to the guage is direct. There is no firewall connection like you mention. This design is of concern to me since I have now installed a new interior and am always concerned about an oil leak at the back of the guage where the line connects. I recall squirting oil all over the place the time I installed the NOS oil guage and forgot to make the line to guage connection. Thank God that was before the interior. A good steady stream of oil was present at that time.

The direct connection is also a pain when dropping down the instrument cluster.

As for hot oil flowing through the filter, I can attest to the fact it does because about 300 miles ago I did an oil change and new filter element and like an idiot loosened the filter body top with the engine running and sprayed hot oil all over the engine compartment. Both of the mentioned incidents indicates perhaps adequate oil pressure now that I talk about it, yet the guage indicates a strong 40 PSI with engine cold and barely 10 PSI after warm and doing 25 to 30 MPH.

You make a good point about the pan cleaning. I did that at the time of filter installation and the pan had at least 1/2" of crud in it.

????

Don

[Lou Earle]

I don't think that the direct line is the right line my 41 has a flexible connection between 2 lines and so do all my other Chrysler cars- including 46 and 34 so I am almost positive your connection is a replacement. If I were in your position I would remove that line and replace it with the proper 2 lines and joint and I would use the new easy bend brake lines sold at Napa and elsewhere they are great.

If you cannot find a flexible joint I can send u one

Lou

[Lou Earle]

I Really Think Yoru Guage Is Bad

[Normspeed]

Just throwing out possibilities here, but another thing it could be is simply a worn oil pump. As the oil gets warm and viscosity drops, more oil escapes around the pump rotors/end plate, less pressure to motor. Relatively cheap fix if its that.

[Don St Peter]

Thats it!

I'm convinced my configuration is screwed up and that I need the flexible joint you mention Lou, and I no doubt need an oil pressure guage at this point since I have plumbed the oil line directly to the guage and it apparently is air pressure driven from the firewall to the guage. I would appreciate your calling me at 316 304 3650 or E Mail at dstpeter1@thevillages.net to let me know how much to send you and your mailing address. I'm anxious to learn, but obviously have a long ways to go. Once I get this thing sorted out, I will let the fourm know of the outcome.

Thank You very much for the education.

Don

[Guest bizzycoupe]

I have a 46 dodge and mine connected straight to gauge, am I suppossed to have a connection at fire wall too. It seems to work ok

[Guest bizzycoupe]

Thanks, Does this flex line connect to the fire wall to gauge and then too staight line too block? If you have one, tell me the price and I'll buy it from you , thank you

[Plymouthy Adams]

The flex piece is there to prevent breakage of the line as the enigne rock left to right on acceleration due to torque. The lines were steel and thus would work harden if this rubber piece is not used. IF you run a later style hard nylon style hose, the flex of this line is such that you can eliminate the rubber connector.

[PatS....]

How about trying to replace the spring with one of a different resistance to see if that changes the oil pressure. If it does and you know the guage is accurate, then you could just try a couple until the pressure is where you want it.

[Lou Earle]

Probably the spring is just fine why? Becasue he said after a run he went to change oil filter and the oil in the cannister was hot. Well' that cannister cannot get hot unless oil is running thru it and since the realese valve only lets oil to the filter if the pressure goes above20 to 30 we know oil is flowing to the cannister because it is hot therefore the valve is working.

My reasoning anyway.

[Tim Frank]

Don, You mentioned that you use non-detergent oil.

I have always thought that n-d oils were more often used in applications such as compressors, transmissions, and a few types of transfer cases. The good folks in here can now set one (or both) of us straight on this....

Any comments on non detergent oil? Rgds, Tim

[greg g]

Well since no one has mentioned it, the service manual states that it is not uncommon and normal for oil pressure to be low (even to the point of not registering) at idle on a hot engine. As long as it idles quietly, and increases to normal at driving speed, you might be making Mount Molehill out of this issue. From the manual;

IMPERTANT NOTE

"Any pressure indicating oil flow at idle speed is satisfactory, providing the pressure rises to normal (30 to 50 lbs) at 30 mph and higher, when the engine is at normal operating temperature."