Oil pressure drop with synthetic oil

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Marchboom

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Got a 2009 Dodge Ram, 5.7 Hemi with 15,000 miles. Have been running Q.S. Advanced Durability dino oil, 15w-20. Changed to Pennzoil Platinum, 15w-20 and now the oil pressure dropped from 58 to 53 lbs immediately after start up. When it warms up, it only dropped from 49 to 48 lbs. Filter is the same...MC.

What would be the cause of this drop?
 
Slightly lower operating viscosity due to a different oil. Unless there is any issue with drivability I wouldn't worry about it.

Some 20wts are on the thicker side, some thinner.

Don't sweat it.

You also mean 5w20 I presume.
 
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Oil pressure numbers you are stating are still very good! Some oils flow a little better, it probably has less to do with synthetic, and more to do with one oil being slightly thinner than the other. oil pumps don't produce pressure, they produce oil flow. The oil is still flowing nicely and isn't a problem.
 
That's still plenty of pressure, and nothing to worry about. As they said, one oil is probably just a little thinner than the other.
 
As other mentioned, not all oils of the same weight are created equal. PP is a rather thin oil. The 5W-30 is almost a 20wt, and the 20 is pretty thin too, at the lower end of the spectrum iirc. Also, the 5W-20/5W-30 essentially act like 0W-20/30 oils. Excellent for cold weather areas.
 
Originally Posted By: Marchboom
Got a 2009 Dodge Ram, 5.7 Hemi with 15,000 miles. Have been running Q.S. Advanced Durability dino oil, 15w-20. Changed to Pennzoil Platinum, 15w-20 and now the oil pressure dropped from 58 to 53 lbs immediately after start up. When it warms up, it only dropped from 49 to 48 lbs. Filter is the same...MC.

What would be the cause of this drop?


Many, many years ago when I switched from dino oil to Mobil 1 I noticed the same thing. I called Mobil and asked why. The answer I got was the oil flows better, and with less pressure. I'll never forget that answer, that was decades before Bitog was even dreamed of. Oil flow lubricates an engine, not pressure. You are still in the safe zone, nothing to worry about. The flip side is when it is the dead of winter and the engine is stone cold, that synthetic oil is flowing faster when the engine first starts up. Assuming you live where cold temps are an issue.
 
I noticed the same sort of thing, only in reverse. I used 10W30 Napa brand conventional oil for a few years then on my last oil change I switched to 10W30 QS Advanced Durability. I noticed a slight icrease in my oil pressure. The Napa oil is a bit thinner than the QS, so I get a little higher oil pressure reading with the QS.

Like the others said here, it's nothing to worry about.
 
The lower start-up OP with PP is due to it's higher Viscosity Index (VI) which is a good thing. It's still slightly lower at normal operating temps because your oil temps likely don't hit 100C.

BTW, at what rpm are you taking your OP readings?
 
March - It's simply because of minor variances in the oil's thickness.
There is no need for concern. Variances are normal and expected.

Also, old oil will probably shear and thin a bit, with resultant lower oil pressure.
 
Originally Posted By: LargeCarManX2
Oil pressure is not alway's the cats...meow. oil volume is where it's at! Less pressure could mean more oil (volume) is going through the engine. This is good.
There is more to it than that.
 
Hi,
Marchboom - IME I have found that even allowing for variance within the J300 viscosity ranges a synthetic lubricant of similar viscosity to a mineral lubricant will show a slight drop in OP. This is usually more evident at idle. It may even alarm some people!!

I have found that it is due to the better flow characteristics of the synthetic lubricant - a benefit in real terms
 
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Originally Posted By: Steve S
Originally Posted By: LargeCarManX2
Oil pressure is not alway's the cats...meow. oil volume is where it's at! Less pressure could mean more oil (volume) is going through the engine. This is good.
There is more to it than that.


Please enlighten us. Most people think less pressure equals more flow. However, some engines seem to like 60Psi when driving doen the road, or the thinking is the oil, particularly a thin one, will just "Splash around" and not really lubricate anything, as its not maintaining a film..

Then again, the kink in the garden hose example comes to mind.

What say you, Stevie!
thumbsup2.gif
 
Harley ..pressure and flow, to that limited dimension, are exchangeable. By that I mean that a given volume at a given visc through a given resistance ..will produce a given pressure.

At all times, if you are below the relief threshold for the oil pump..flow will never be altered. Never. The pressure will go up or down with visc and rpms ..but the flow ..for the most part and ignoring the given "trivials" ..will be in command of all that you see with the needle moving.
 
Originally Posted By: Gary Allan
Harley ..pressure and flow, to that limited dimension, are exchangeable. By that I mean that a given volume at a given visc through a given resistance ..will produce a given pressure.

At all times, if you are below the relief threshold for the oil pump..flow will never be altered. Never. The pressure will go up or down with visc and rpms ..but the flow ..for the most part and ignoring the given "trivials" ..will be in command of all that you see with the needle moving.


Hi Gary,

Hate to disagree but oil flow through an engine, below the relief threshold, increases with the drop in viscosity as the oil heats up and decreases as it cools down and thickens. That's why the oil back pressure that an oil pressure gauge measures, drops as the oil heats up, because the resuling thinner oil is flowing faster through the bearings and the engine generally.
The faster the oil flows the better subject to the minimum oil pressure spec's for the engine.
 
Originally Posted By: CATERHAM
Originally Posted By: Gary Allan
Harley ..pressure and flow, to that limited dimension, are exchangeable. By that I mean that a given volume at a given visc through a given resistance ..will produce a given pressure.

At all times, if you are below the relief threshold for the oil pump..flow will never be altered. Never. The pressure will go up or down with visc and rpms ..but the flow ..for the most part and ignoring the given "trivials" ..will be in command of all that you see with the needle moving.



Hi Gary,

Hate to disagree but oil flow through an engine, below the relief threshold, increases with the drop in viscosity as the oil heats up and decreases as it cools down and thickens. That's why the oil back pressure that an oil pressure gauge measures, drops as the oil heats up, because the resuling thinner oil is flowing faster through the bearings and the engine generally.
The faster the oil flows the better subject to the minimum oil pressure spec's for the engine.


Reread what I posted ..and I don't think you'll be in conflict with it.

..or get your glasses checked
grin2.gif


or do you know how to have a given visc (however you define it) manage to NOT produce a given pressure through a fixed restriction at a given volume (whatever volume you choose at the moment)??

Educate me on that one
thumbsup2.gif
 
I think what Gary is saying is that while the pressure may go up and down to some extent the oil flow is more of a constant.The reason being,the by-pass pressure valve will allow anything over a certain pressure to just flow back into the oil sump and the remaining oil will flow to the motor.The pump is just that,a pump.It moves the oil at a constant for the most part,it doesnt make the pressure,it just moves the oil.The engine makes the pressure by restricting the flow to some extent because it has to move through the motor.If an engine pump can only pump 10 gallons per minute,that is what it will pump regardless of RPM and pressure,anything over the set pressure will be diverted by the by-pass and be of no effect and unless the pump is failing the flow should remain the same or very close to it.
 
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Okay ...now I see where I'm misunderstood.


"the flow will not be altered".

You're reading this as "the flow will not vary".

BIG DIFFERENCE.


Put "100% of the sensible flow of the pump will go to the engine" in its place ..as in it won't "diverge". It will remain 100% of the sensible pump output. Not a % of it.


..and back to what I was responding to (follow the thread)..it will not "flow faster" ..it will not flow slower. It will flow what it flow ..period ..REGARDLESS OF ITS (CURRENT) VISC ...as long as the pump is not in relief. Thin ..thick ..whatever (and sure, obscure and limited conditions and restrictions apply).

..and CATERMAN ..
31.gif
you offend me to even entertain that I don't understand this fundamental principle. (no, you don't/aren't)
 
To the op - you're asking about a 1 psi difference (hot) between two oils? Cold pressure isn't really a fair comparison due to superior cold flow of the synthetic.

To motorguy222 I'm sure there are exceptions but I believe the relief valve only relieves excess back to the pump chamber. I know this because I was doing some research on melling's web site.
 
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