Mobil 1 5w50 viscosity

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Hi guys, i have a modified Jeep with a common GM 350 in it, freshly rebuilt, oil pressure was decent , about 40 PSI when cold and 7-10 PSI hot, it's being pretty warm in these days and i've seen gauge go down close to zero at idle, it is non accurate but i measured the pressure with a mechanical one previously so i know that was close to 10 PSI when hot, not sure about how many PSI is now but seems really low.
I'm running a Castrol Magnatec 5w40 plus a Comp Cams break in additive (i have flat tappets), i'm wondering if a Mobil 5w50 would be a better thing when warm compared to the 5w40 or is a waste of time and money.
I'm kinda afraid to use thick oil like 15w50 or even 20w50, i'm obsessed about get a dizzy/cam gear because too much load due to the thick oil...
I can get a 10w60 Bardahl here, what do you think?
Any help would be greatly apprecciated.
 
Welcome to BITOG!

I presume the Jeep is in Italy not BC?

The OP figures you've give are I presume on idle.
Normally for a GM V8 a light 5W-30 if all that's required to maintain more than adequate OP of over 50 psi at elevated rev's.
Even M1 0W-40 would normally be heavier than necessary.

Since you're running Magnetec 5W-40 now I'd check you're hot OP at high rev's and if it's well over 50 psi you don't need to run anything heavier. Also check you by-pass point, (maximum OP at high rev's when cold) to make sure you're below that point when the engine is hot at high rev's.

Since it's a flat tappet engine, another option is a 10W-30 HDEO.
 
Next fill try a dino or synthetic 20w50 motorcycle oil. Actually Brad Penn 20w50 might be a good choice.
 
Last edited:
Originally Posted By: JethroBodine
Next fill try a dino or synthetic 20w50 motorcycle oil. Actually Brad Penn 20w50 might be a good choice.

Yes it would be a good choice if you want your oil pump to stay in by-pass mode 100% of the time!
 
Originally Posted By: CATERHAM
Originally Posted By: JethroBodine
Next fill try a dino or synthetic 20w50 motorcycle oil. Actually Brad Penn 20w50 might be a good choice.

Yes it would be a good choice if you want your oil pump to stay in by-pass mode 100% of the time!


I seriously doubt that, I'm yet to see a hot engine with a crankcase full of 20W-50 produce anywhere nearly the oil pressure it does cold... Yes it may well be in bypass cold, still not a big deal...

In my opinion, nothing but a scare tactic...
 
Of course hot oil produces a much lower OP than cold oil but that's not the point.
Running 3 grades heavier than spec' oil, particularly a low VI 20W-50, you simply will not be able to use high rev's in a Chevy V8 without the oil pump going into by-pass mode.
 
Originally Posted By: Doug Hillary
Hi,
jeepers_creepers - M1 5W-50 is an excellent product and has been part of the Porsche recommendations for a decade or more

It is used as a race oil by some


Doug,

It appears there are two version of Mobil 1 5W-50; Peak Life and Rally Formula. What are the differences between the two? Thanks!
thumbsup2.gif
 
Originally Posted By: CATERHAM
Of course hot oil produces a much lower OP than cold oil but that's not the point.
Running 3 grades heavier than spec' oil, particularly a low VI 20W-50, you simply will not be able to use high rev's in a Chevy V8 without the oil pump going into by-pass mode.


But I still say that isn't going to happen when hot...
 
Originally Posted By: Doug Hillary
Hi,
Falcon_LS - Sorry I can't help with any info - I have no access to it


Hi Doug,

Just got off the phone with Mobil 1 Europe earlier. Turns out the Rally Formula was a PAO based formula and Peak Life is "new" its successor. The RF was sold as a full synthetic in Germany, whereas Peak Life is sold as SHC technology.
 
I think flow is more important than pressure. Pressure is just easier to measure. The size of the engine oil passages are fixed by design, so by increasing viscosity to raise pressure, you decrease flow. Engine designers think about this kind of thing, and that is how recommendations for viscosity are made.

If you think your pressure is low, change the pump. However, a high output pump can get too much oil on top of the engine because the oil can't drain back to the sump as fast as it is being pumped to the top. Stick to OEM specs.
 
Originally Posted By: Georgiadave
I think flow is more important than pressure. Pressure is just easier to measure. The size of the engine oil passages are fixed by design, so by increasing viscosity to raise pressure, you decrease flow. Engine designers think about this kind of thing, and that is how recommendations for viscosity are made.

If you think your pressure is low, change the pump. However, a high output pump can get too much oil on top of the engine because the oil can't drain back to the sump as fast as it is being pumped to the top. Stick to OEM specs.


Agreed. Volume pumped at slightly lower pressure is more desirable then more pressure with less volume.
I laugh now when I read posts from guys going from a 20 grade to 40 grade and are just thrilled with the higher pressure reading not clueing in that the extra pressure is indicating more resistance,and drawing more energy from the engine to drive the pump.
 
If you look back, we calculated that the increase power requirement on the oil pump from higher viscosity was less than turning the headlights on...
 
Originally Posted By: Shannow
If you look back, we calculated that the increase power requirement on the oil pump from higher viscosity was less than turning the headlights on...


Really ?
I'm amazed at the talent this forum consists of. I wouldn't even know where to begin to start trying to calculate the energy required to pump the oil.
Thanks. I'm going to search for that thread.
 
Originally Posted By: Shannow
If you look back, we calculated that the increase power requirement on the oil pump from higher viscosity was less than turning the headlights on...


Oh Gawd, we're gonna have BITOGers riding around in the dark...
 
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