PA oil pressure question

[broker-len]

Bin posting my progress last few months on my 4 cylinder PA   the car is together and running well   except this--------------------------when my motor is dead cold my oil pressure is almost 60  when hot    not quite 30     running 10w30 oil        my 36 plymouth is more constant---- pressure goes down only very slightly        the pump has new gears and mains were done in 70s with not many miles            checked pressure relieve valve a few times      any advise ?     if you have a PA  how does your oil gage read----------------------thanks

[keiser31]

In my opinion, 30psi is excellent! You do not need 60psi all of the time. It sounds like your gauge is reading exactly what it should when it should. Sometimes, you will only get 15psi while driving and that is OK. 15psi is about the minimum for efficiency.

Edited October 31, 2017 by keiser31 (see edit history)

[broker-len]

thanks for info

[broker-len]

I was concerned since the specs call for 30 to 40       and that is with straight weight I am using multi grade

[keiser31]

51 minutes ago, broker-len said:

I was concerned since the specs call for 30 to 40       and that is with straight weight I am using multi grade

Others may certainly educate me if I am wrong. Sounds like you are good if it is 30.

[hchris]

30 hot is fine, as a general rule for older cars, 10psi per 1000 revs is the bench mark when at normal operating temps.

 

60 cold would seem to be on the high side, what grade oil are you using ?

[broker-len]

right now  10w30                  I would think the pressure relief valve would prevent it getting to high      took it apart a few times 

[C Carl]

Almost 60 stone cold , 30 hot on 10W/30 sounds good to me.  I know where you are going with this , mult grade oil should have a relatively flatter temp-viscosity curve. I have been running multi grade oil for many decades , and I see no reason for alarm. IIRC , recommended viscosity on my Maserati 3500 was 40 , or 50. On startup , it pumped 160# , 80# fully warm. I hope that helps.   - Carl

[broker-len]

thanks     C Carl      this car has pored bearings        have a 36 Plymouth with bering inserts      use the same oil      has has a flat   temp-viscsity curve-----could it be because of the tighter specs on bearings

[fraso]

Oil pumps are positive displacement, which means the oil flow they produce is directly proportional to the pump speed.

 

 

Pressure rises with the square of flow so a pressure relief valve (PRV) is used to prevent dangerously high pressure.  The PRV keeps the pressure from becoming too high by allowing some oil to bleed back to the sump.  If your oil pressure relief valve is working properly, your oil pressure should never exceed the PRV's rating.  If it reaches 60 psi when cold but doesn't get higher with increasing revs, then it looks like you have a 60 psi PRV spring in your oil pump.  Your 36 Plymouth appears to have a 30 psi PRV spring.

 

 

A 10W-30 multigrade oil means that it has the viscosity of a 10W-grade oil when cold  and a 30-grade oil when hot.  All 30-grade oils (ie, SAE 30, 0W-30, 5W-30, 10W-30) have the same hot viscosity range (rating is at 100°C/212°F).  See SAE Viscosity Grades for Engine Oils.  If you're concerned that your cold oil pressure is too high, the simplest thing would be to switch to a 5W-30 or 0W-30 engine oil.

[ArticiferTom]

My book of instr. for my truck ,which has the same PA engine . States SAE 40 summer , 50 for heavy duty service and extreme warm weather . Winter SAE 20 under freeze and above zero . So I use 15W-40 Diesel rated . It also says relief is set to trigger at 40psi , normal appox 30-40 lbs. with warm engine , driving . More concerned with no pressure on gauge in Winter . I do notice gage fluctuates with throttling .

Edited November 1, 2017 by ArticiferTom
coma and throttle (see edit history)

[broker-len]

Tom    thanks for responding----------let me asking you------------what oil are you running,,,when you start the motor from dead cold where is the pressure ???           --------------when hot  ...where is the pressure -----------------------thanks

[Grimy]

For what it may be worth, as I have no knowledge of Plymouth 4s, Pierce-Arrows through 1928 produce VERY high oil pressure at cold start, which rapidly diminishes to normal within five minutes or so of running.  In fact, beginning in 1918 Pierce installed 100 psi oil pressure gauges (vs earlier 50 psi gauges) for that reason, per engineering documents published by the Pierce-Arrow Society.  I *suspect* that Pressure Relief Valve technology improved throughout the industry circa 1930 or so, although all these Pierces were so equipped.

 

By way of example, my 1918 Pierce running 15W-40 will have 65 psi at cold start and fast idle, and drop to the published spec of 35 psi @ 40 mph as the oil warms.  My 1925 with very loose engine running 20W-50 will push 75 psi this time of year on cold start. then drop to an acceptable 20-25 psi at hot run.

 

I suggest keeping a cold engine at relatively low RPM until the oil warms up.  Your 30 psi hot at speed seems very adequate to me.  I wouldn't worry about it at all.

[fraso]

2 hours ago, ArticiferTom said:

My book of instr. for my truck ,which has the same PA engine . States SAE 40 summer , 50 for heavy duty service and extreme warm weather . Winter SAE 20 under freeze and above zero . So I use 15W-40 Diesel rated . It also says relief is set to trigger at 40psi , normal appox 30-40 lbs. with warm engine , driving . More concerned with no pressure on gauge in Winter . I do notice gage fluctuates with throttling .

That sounds to me like your engine oil is too viscous to pump in cold temperatures.  See Engine Wear.

[Spinneyhill]

3 hours ago, ArticiferTom said:

My book of instr. for my truck ,which has the same PA engine . States SAE 40 summer , 50 for heavy duty service and extreme warm weather . Winter SAE 20 under freeze and above zero

 

Remember that the oil in 1931 was devoid of pretty much all the additives we take for granted today. It had a very steep drop-off in viscosity with increasing temperature, so they started with a thicker oil to finish with a reasonable viscosity at temperature. Nowadays, we can pretty much use one oil all year round because of the smaller changes in viscosity with temperature - the effect of the additive packages. Have a look at http://www.widman.biz/Corvair/English/Links/Oil.html

 

6 hours ago, fraso said:

Pressure rises with the square of flow

 

Well, yes, but.... Bernoulli's Equation relates the three parts of pressure in a fluid: velocity of flow, pressure, and absolute head (i.e. height above datum). The sum of these parts is a constant (with compatible units). The third part is constant for our purposes so we ignore it. Basically, it says that the square of velocity (divided by 2g) equals the pressure. So if the flow speed increases (e.g. as the oil thins with temperature) the pressure drops. The additives in oil try to make the oil viscosity stable so the flow velocity and pressure are fairly constant against operating (oil) temperature. The particular times this matters most are at startup (i.e. cold) and under load.

 

6 hours ago, fraso said:

If you're concerned that your cold oil pressure is too high, the simplest thing would be to switch to a 5W-30 or 0W-30 engine oil.

 

Yes, flatten that viscosity vs temperature even more and increase cold startup oil flow.

 

I have been through 20W-50, 15W-40 and 5W-30 in my Dodge 8. The gauges fluctuates least on the 5W-30. I think the first two are too viscous, as fraso says. It is not true that just because it is old it is loose and needs thick oil.

[ArticiferTom]

Ok, went out this evening and started her up . It is rainy and mid forties cool . Started and gauge showed 52 at high idle for minutes then as dropped idle to medium with choke still, went down to 48 . On rev. it would go up to 56 highest . my engine is a 90's rebuild with very limited mileage on it . Multi -grade been used by me and PO . My Zenith Carb does not idle down to low with out hiccupping and stall , unless engine is hot . Never got to that point . Would have to drive . But I know it goes down in 30's and twenties idle low . I do not know why reads above what should be  by-pass , other then oil viscosity . My truck is a fair weather drive with it's wood board floor and no heater .

   Fraso ; on the statement about Winter , I could have it wrote it better . It was not what I thought , but what the book warned of ,no pressure on gage in Winter .

oilp.pdf

[broker-len]

thank you tom        I would like to see more pressure when hot     maybe check oil pump in spring

[fraso]

 

21 hours ago, Spinneyhill said:

Well, yes, but.... Bernoulli's Equation relates the three parts of pressure in a fluid: velocity of flow, pressure, and absolute head (i.e. height above datum). The sum of these parts is a constant (with compatible units). The third part is constant for our purposes so we ignore it. Basically, it says that the square of velocity (divided by 2g) equals the pressure. So if the flow speed increases (e.g. as the oil thins with temperature) the pressure drops. The additives in oil try to make the oil viscosity stable so the flow velocity and pressure are fairly constant against operating (oil) temperature. The particular times this matters most are at startup (i.e. cold) and under load.

 

I was trying to avoid making my explanation too wordy.  The point I was trying to make was that at any given temperature, the pressure developed by the oil pump varies with the square of oil flow but I should have been clearer.

 

More precisely, the flow rate (gpm, litres/sec, etc) of a positive displacement pump is directly proportional to pump speed (allowing for seal leakage) regardless of viscosity (ie oil temperature).  Since oil is incompressible, the oil pump can develop extremely high pressures from the downstream flow restriction and the viscosity of the oil affects the resulting pressure loss in the engine's oil system (galleries & bearings).  Hot oil is less viscous so the pressure loss is less than that of cold oil, which is why the oil pressure gauge at the outlet of the oil pump shows less pressure at a given engine RPM with hot oil compared with cold oil.

 

See YouTube: The Difference Between Pressure and Flow

 

If the PRV has an adjustable setting, setting it somewhat higher than the normal oil pressure developed in a hot engine will ensure that very little oil is bypassed back to the sump.

 

16 hours ago, ArticiferTom said:

Ok, went out this evening and started her up . It is rainy and mid forties cool . Started and gauge showed 52 at high idle for minutes then as dropped idle to medium with choke still, went down to 48 . On rev. it would go up to 56 highest . my engine is a 90's rebuild with very limited mileage on it . Multi -grade been used by me and PO . My Zenith Carb does not idle down to low with out hiccupping and stall , unless engine is hot . Never got to that point . Would have to drive . But I know it goes down in 30's and twenties idle low . I do not know why reads above what should be  by-pass , other then oil viscosity . My truck is a fair weather drive with it's wood board floor and no heater .

   Fraso ; on the statement about Winter , I could have it wrote it better . It was not what I thought , but what the book warned of ,no pressure on gage in Winter .

oilp.pdf

 

It looks like your PRV is set to relieve at 56 psi if this is the highest pressure you will ever see no matter how high you rev your engine.

 

The warning in the manual about watching for zero oil pressure particularly in the winter appears to be about the pump sucking air (or vortexing) from excessively thick oil.  See YouTube: Submergence level and vortex formation

 

4 hours ago, broker-len said:

I would like to see more pressure when hot     maybe check oil pump in spring

 

My Motor manual goes back to 1935 and I believe the Plymouth PA is a 1932 model. The 1935-1953 oil pressure specs in my book show either 45 psi @ 30 mph or 40 psi @ 20 mph so your 30 psi seems slightly low (unless it's at idle).  The recommended summer grade (+32°F) for all engines from 1935 to 1948 is SAE 20. I would expect a 1932 model to have similar specs.

 

Since your PRV is already set higher (60 psi) than your normal hot oil pressure (30 psi), adjusting the PRV setting will not increase the hot oil pressure.  You need to need to increase the pressure loss in the oil gallery either with thicker oil (going from a 30-grade to a 40-grade) or with more flow (less worn pump or higher volume oil pump).  Counterintuitively, using a more viscous oil can reduce oil flow to the bearings if the added pressure loss causes the developed pressure to be higher than the PRV setting.

 

Thicker oil does provide a thicker hydrodynamic wedge and this is affected by the oil's HTHS Rating.  Excessive viscosity causes additional fluid friction losses (reduced fuel economy) and higher oil temperatures (from the fluid friction).  It can also put unnecessary load on the oil pump gears (see SL6 Oil Pump Gear Failure and Oil System Information)

 

See YouTube: Hydrodynamic Bearings

[broker-len]

thank you all for the advise---------------------------the reason for my post is that my plymouth, which was rebuil by a    " PROFESSIONAL SHOP "    has oil pressure characteristics I am not happy with          Book calls for 30--40     get 60 at start up cold    not quite 30 down the road     trying to learn the pressure curve on other PAs in the AACA world--------to see if mine needs some investigation or I am OK----thank you all again ------------BR

[ArticiferTom]

So fraso , The manual calls for 40 summer on my 31 , 32 engine and winter 20 and thinned if below zero . Perhaps I should lower PVR setting in to 40's . It does not seem to cause any leaks . at this higher setting . Which is something they say to watch and tighten gaskets .  On the spec 's I do not know at which point these engine when from these low compression to high compression in the thirties  or what effect that has on your spec for latter engines . Book states lube is spray to rod and such . Also would need to verify gage accuracy before changing . My current oil change cycle is 500miles , above what is called for but a cheap do , since these motors have no filters .

   Thanks for all your input , I watched the vortex video  . Neat stuff . But all this makes my head hurt LOL . We got to be doing better then the original clay base oils used then .

           Tom

[fraso]

If your manual has specific recommendations, I would go with those rather than what is listed in my Motor manual especially since it's more in agreement with the Chrysler Oil Recommendations I came across. If your manual calls for 40-grade oil for summer driving and your oil pressure is normally 30-40 psi when fully warm, I think you are doing fine.

 

I would leave the PVR setting where it is and I don't think there would be any benefit to reducing it.

 

My Motor manual has a section about Oil Pressure Regulator, 1935-1953 in Plymouth.  Of interest is this:

Quote

Do not use a heavier spring or a steel ball or washers to raise the oil pressure.  If oil pressure is low, check the fit of crankshaft bearings or look for other causes of possible loss of oil pressure.

 

[broker-len]

when my motor was cold I adjusted the PCV valve at 45LBS-------considering for recommended pressure is 30 to 40          it was at 60 so I know my oil system can get that high---------------------when motor get HOT    can not get quite at 30       ------either pump or bearings or gage-----ANY THOUGHTS ?

[fraso]

I don't think 60 psi is excessive for a PRV setting.  Reducing it to 45 would cause more oil to bypass back to the sump, thereby reducing flow to the bearings when the engine is cold.  I believe the main risk of running high pressure is undue stress/wear on the pump's drive gear.  You could also potentially blow out the oil filter but modern filters are designed to withstand much higher pressures than normally experienced in a oil system that is in good working order.  The burst pressure on the Wix 51515 is 290 psi for example.

 

See Fram: Over-Pressurized Lube Oil Filters

[broker-len]

I wanted to make sure my PRV  was working   there is no need for the 60 LBS since in goes down quick with heat  the motor has no filter    the thing that has me confused      if the clearance of bearings and oil pump  are good enough to produce at least 60 LBs when cold    why can't I keep a pressure when hot  above 30 LBs   I guess I will check the gage, pump and clearance of bearings   though because these are pored in block   don't think I am going to pull motor AGAIN

Edited November 4, 2017 by broker-len (see edit history)

[fraso]

You're confusing flow with pressure.  Your PRV is working because it limits the pressure developed by the pump to a maximum of 60 psi by diverting some of the flow through a low-resistance path to back to the sump.  As the oil warms, it has less flow resistance in the oil system so the PRV closes and all the oil pump's output goes to the bearings.

 

Think of it this way:  imagine you have a mouthful of a liquid and have to blow it out through a straw in 10 seconds.  If the liquid were honey, you'd have to blow a lot harder than if you had a mouthful of water.  In either case, you are blowing a mouthful of a liquid through a straw in 10 seconds but effort required is much higher for the thicker liquid and some of the extra pressure in your mouth would leak out from your lips.

 

It is good to check all those things but if your gauge is accurate and your pump is not worn, then either your viscosity is too low or your bearings have too much clearance.  There are others here who are far more knowledgeable with your engine than me.

 

The easiest way to improve your hot oil pressure would be switch to a 15W-40 heavy duty engine oil like ArtificerTom uses .  This would give your bearings additional protection from a 40-grade's higher HTHS viscosity and a HDEO"s higher ZDDP additive levels.

[ArticiferTom]

broker-Len  one thing you may want to do first is preform these test looking for the 30+ psi , with a straight non-d 30 wt oil . That how the numbers where developed  . I believe mine to act the same as yours , when warm . It may the lube characteristics or todays oil and be fine for multi-grade .

   Book talks of clogged screen , leaky or broke tube , loose bearing and to heavy of body of oil .

Edited November 5, 2017 by ArticiferTom (see edit history)

[broker-len]

I tried straight 30 and it was no better

[broker-len]

I have a 36 Plymouth with a rebuilt motor     running 10W 30---  has a 10 LB oil curve   not to high and not to low   --guess I am comparing my PA to that------I under stand that because of the bearings pored in block it is up to the rebuilder and how he line board the mains   I am real anal about this stuff which is why I don't buy any more cars

[fraso]

It could very well be that your gauge is inaccurate.  Have you tried measuring the pressure with a gauge of known accuracy?

 

All 30-grade oils (ie, SAE 30, 0W-30, 5W-30, 10W-30) fall within the same hot (measured at 100°C) viscosity range (ie 9.3 to <12.5 cSt).  See SAE Viscosity Grades for Engine Oils.  Some 30-grade oils are on the more viscous side of the range like the Petro-Canada Duron SHP 10W-30 that I'm using, which is 12.0 cSt @ 100°C.  If my car weren't burning some oil, I'd be using synthetic Mobil Delvac Elite 222 0W-30, which is 12.2 cSt @ 100°C.

 

Once the shafts are rotating, metal to metal contact is prevented by the hydrodynamic wedge between the shaft and the bearing.  See YouTube: Hydrodynamic Bearings.

 

ArtificerTom's Plymouth owner's manual recommends 40-grade oils for summer use.  If your gauge is accurate, try a 15W-40 HDEO (preferably dual-rated API CK-4/SN or CJ-4/SM) to raise your oil pressure.

[ArticiferTom]