wrd1972

iTrader: (12)

I recently switched from Penzoil dino 5w30 to Mobil1 synthetic 5w30 and I have clearly less oil pressure now. I would speculate maybe 5# less at idle and 10# everywhere else. Is this normal?

RamAir95TA

iTrader: (2)

From a good article:

Oil pressure is also directly related to flow volume. Synthetic oil is more uniform in molecular structure and provides less resistance to flow therefore in order to achieve the same flow volume as a petroleum oil, which has a higher frictional resistance to flow, it is possible that under some conditions, such as idling that a slightly lower oil pressure could be noticed, but that the oil flow volume delivered to the engine is adequate for the engine operating RPM and conditions. Synthetic oil has better flow characteristics than petroleum oil and may also cause an engines RPM at idle to increase due to decreased resistance to flow, less internal drag and parasitic losses.

Here’s another way to explain pressure and flow volume: if you have an air tool at requires 90 PSI @12 CFM, you could use a 1 HP air compressor that delivers 90 PSI, however it would not deliver 90 PSI @12 CFM, and would have to work very hard to make the tool operate, however the tool would not operate at maximum capacity due to the lower flow volume. A 10 HP compressor on the other hand would easily provide 90PSI @ 12 CFM and would not have to work very hard to do it. Pressure and flow volume go hand in hand. You can have maximum oil pressure, however if you don’t have the proper flow volume it isn’t going to do you any good. With synthetic oil, and all other engine parameters remaining equal, it takes less oil pressure to achieve an equivalent flow volume of oil than it does with a petroleum oil, and the engine doesn’t have to work as hard to deliver the increased flow volume. Often when changing to a synthetic motor oil the engine RPM may increase at idle due to decreased internal frictional resistance of rotating and sliding components.

At high engine operating temperatures synthetic motor oil will be much more shear stable and will not drop nearly as much as petroleum oil does. I recently had a friend with a jet boat with a 460 cu. in. racing engine. After one mile run across the lake with a 20W-50 petroleum oil the oil pressure went from about 45 psi down to about 15-20 psi. After changing to a premium quality synthetic motor oil and after the same one mile run across the lake the oil pressure only dropped to about 30-35 psi. That is the direct result of the superior high temperature characteristics of synthetic motor oil and its ability to resist the effects of intense shear forces.

Short answer...yes.

pillarpod

you do learn something new every day

96capricemgr

iTrader: (1)

5w-30 is just a RANGE it falls in. I have not kept up on the current specs but M1 oils have typically been at the very thinnest end of the range for each weight. Look on the BITOG forum for the actual viscosity a CST number in the 10-12.x range and I bet you find the Penzoil is actually thicker too.

gregrob

iTrader: (8)

Try casterol syntec 0 -30 made in Germany its as "thick" as most 40 weights.

The base of the oil isn't what causes a pressure drop, its the relative viscosity...

big_bird_93

iTrader: (1)

Good info. Never even thought about it.

thehammer69

iTrader: (2)

Not quite...it's ALMOST as thick as a 40wt that runs it's viscosity on the LOW side of the 40 wt. viscosity spread. German Castrol usually runs around low 12's cSt@212F while the average 40wt used in a car runs around 14's cSt@212F. So basically the average 40wt is gonna be around 2 cSt thicker than German Castrol at operating temp. And just to toss it out there, other oils that also typically run on the thick side of the 30 weight scale are your 30wt High mileage Oils such as Valvoline Maxlife, Mobil-1 High Mileage & Pennzoil High Mileage.

Viscosity Weight scales of oil @ 212F (this is the last number of a multi weights viscosity...otherwords, ignore the 0w, 5w, 10w etc and focus on the number AFTER the hyphen)

20 weights: < 9.3cSt
30 weights: 9.3cSt to < 12.5 cSt
40 weights: 12.5cSt to < 16.3cSt
50 weights: 16.3cSt to < 21.9cSt
60 weights: 21.9cSt to < 26.1cSt

gregrob

iTrader: (8)

Lured

thehammer69

iTrader: (2)

You believed

wrd1972

iTrader: (12)

Thanks guys.
If I understand the CST between the conventional Penzoil 5w30 and the Mobil1 5w30, the M1 should be thicker. My pressure gauge is saying then opposite. My pressure is not really low but I just would sleep better with a bit higher pressure. I am going to put the penzoil back in or maybe try the higher mileage M1.

Cold pressure is the same, hot pressure is just lower.

NewOrleansLT1

It could be your Oil Pressure Sending unit. I changed it on my 94' Silverado and oil pressure shot up like it was a new truck...

wrd1972

iTrader: (12)

The old one did fail and it has been replaced. It nearly matches the mechanical unit under the hood.

96capricemgr

iTrader: (1)

Did you check the UOA CSTs or just the new???

wrd1972

iTrader: (12)

I would say the new. This is new territory for me so I appreciate the heads up. I have been trying to join the Bob is the oil guy boards but I cant yet get logged in to use the search bar. Never got a email to click in order to activate the user name either. Wierd.