I noticed the same thing in my Jeep. It has higher pressures using Mobil 1 5w30 than using a thick Castrol GTX 10w30. Thinner oil is better and flows btter to build pressure. Thick oil is too hard to pump, and can only build so much pressure as it flows much slowere than thin oil. I like the thin stuff.
Viscosity vs Pressure
- Thread starter JonS
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You've got it backwards. Thinner oil flows out the bearings more easily and dissipates pressure.
I have no idea why the lighter oil in this case will show more pressure except maybe it doesn't flow as well in the oil passages due to its fluid flow properties other than viscosity...just a guess.
Ken
Someone is confusing pressure with flow.
I guess it really matters at which point you measure the pressure. A thinner oil flows easier so the pressure distribution in the engine is different. The further from the pump the less pressure drop and the higher pressure reading despite slightly higher oil leakage through the bearings (even this may not be true because a thicker oil runs hotter in the bearings). Right after the pump the pressure must be higher with a thicker oil. What you need is the highest pressure at the bearings. Not at the pump.
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Absolutely. The flow, at least under most circumstances, is identical for both oils. The thinner oil should have less pressure at the sending unit (and anywhere else) since it flows easier when all other things are equal.
When someone says "it flows better" they really mean easier. The gpm is the same for the oil pump and engine in question at a specified rpm (bypass limits not breached).
There's no apparent reason for higher oil pressure in the presence of valve train noise that I can figure. The valve train noise would be a result of too little pressure due to the design restrictions on the lifters to retain oil. In a hydraulic lifter ...the lifter draws the available oil on the downstroke at the base of the bore. If it's too thin and escapes too easily from the lifter ...you'll have noise. The same noise happens when it can fully draw oil into itself due to a plugged access hole or being stuck in a limited range of motion internally. I would assume that this would be the same for a hydraulic OHC follower that was supplied directly from an oil galley. If the stuff bleeds off too quickly ..it's going to tick.
If the pressure is too little at that point in the engine ...it should be lower everywhere else as well.
Does the vavle train noise go away with increased rpm??
MolaKule
Staff member
Most likely the Synergyn is a very high viscosity fluid and the 30 weight starting viscosity is high as well.
The Schaeffer's oil has a much higher starting viscosity, but has a lower Viscosity Index than does the Synergyn.
An oil with a large VI will show better oil pressure over the temp range than one with a lower VI.
Are you sure the Vette's noise isn't piston slap instead of valve train noise?
The Schaeffer's oil has a much higher starting viscosity, but has a lower Viscosity Index than does the Synergyn.
An oil with a large VI will show better oil pressure over the temp range than one with a lower VI.
Are you sure the Vette's noise isn't piston slap instead of valve train noise?
I Also have noticed a change in oil pressure in my 7,4l gas engine. I switched from Castrol GTX 5w30 to M! and saw an increase in oil pressure with the M1. I am using the PF1218 oil filter. Just thought that the M1 flowed better.
obviously there's a factor i'm missing here, but i thought i'd share an odd phenomenon i'm seeing.
i was using synergyn lts 0w30 in my 396 lt4 vette (UOA on the way). i was surprised at how much oil pressure the oil maintained even when hot. all the way up to 250 degrees, the idle pressure didn't really drop below 30-35psi.
i put the same oil in my girlfriend's civic, and immediately noticed valvetrain noise. my vette was also noisy, which i had just accepted as a function of the rockers i'm using. but after what happened with the civic, i switched to schaeffer's 15w40 in the vette.
the valvetrain noise is significantly reduced, which made me happy. however, even though this oil is supposedly thicker, it doesn't maintain as much pressure.
cold it maxes at 70psi, whereas the synergyn made it to almost 80, and it hot idles at 30psi when the oil is only at 210 degrees (versus 40-45 for the lts at the same temp).
could it be that the synergyn batch i bought was actually thicker than it was supposed to be? (i double-checked the pail, it definitely is labeled as LTS 0W30.) all else equal, including the type/brand of filter, i can't think of what else could be causing this.
no big deal, it doesn't worry me, just thought it was interesting.
-michael
i was using synergyn lts 0w30 in my 396 lt4 vette (UOA on the way). i was surprised at how much oil pressure the oil maintained even when hot. all the way up to 250 degrees, the idle pressure didn't really drop below 30-35psi.
i put the same oil in my girlfriend's civic, and immediately noticed valvetrain noise. my vette was also noisy, which i had just accepted as a function of the rockers i'm using. but after what happened with the civic, i switched to schaeffer's 15w40 in the vette.
the valvetrain noise is significantly reduced, which made me happy. however, even though this oil is supposedly thicker, it doesn't maintain as much pressure.
cold it maxes at 70psi, whereas the synergyn made it to almost 80, and it hot idles at 30psi when the oil is only at 210 degrees (versus 40-45 for the lts at the same temp).
could it be that the synergyn batch i bought was actually thicker than it was supposed to be? (i double-checked the pail, it definitely is labeled as LTS 0W30.) all else equal, including the type/brand of filter, i can't think of what else could be causing this.
no big deal, it doesn't worry me, just thought it was interesting.
-michael
Very interesting! Might explain why I got lower oil pressure (just a few psi) from Citgo Superguard 10w40 than I got from Maxlife 10w40, even thought the Citgo is listed as having about half a cSt higher viscosity than the Maxlife.
i had an auto-x yesterday. after the first run the pressure went back to "normal." now it does indeed appear as if the schaeffer's has higher viscosity, it's maintaining ~5psi more than the synergyn in varying conditions.
i can only assume that there was some debris, either in the filter, or that i introduced during the oil change, that was temporarily hung up in the passage to the sending unit (or maybe in the pump's bypass valve). which doesn't make me feel very good, but all appears to be well now.
thanks much for the input.
on the valvetrain noise, at higher rpm the engine exhaust is so loud that i cannot tell whether or not the valvetrain noise goes away. we're talking close to 500hp with no catcons and straight through mufflers. i am using the comp cams magnum lifters, and all aftermarket valvetrain, so none of it is made to pass OEM noise levels.
it never really bothered me, it's not much more than when the engine was stock, but it did quiet down a bit with the schaeffer's.
-michael
i can only assume that there was some debris, either in the filter, or that i introduced during the oil change, that was temporarily hung up in the passage to the sending unit (or maybe in the pump's bypass valve). which doesn't make me feel very good, but all appears to be well now.
thanks much for the input.
on the valvetrain noise, at higher rpm the engine exhaust is so loud that i cannot tell whether or not the valvetrain noise goes away. we're talking close to 500hp with no catcons and straight through mufflers. i am using the comp cams magnum lifters, and all aftermarket valvetrain, so none of it is made to pass OEM noise levels.
it never really bothered me, it's not much more than when the engine was stock, but it did quiet down a bit with the schaeffer's.
-michael
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