Mixing oil - what is the purpose and how to measure effectiveness?

[OVERKILL]

if op just ran a regular xw-40 or a 50w, dont think the cst is that big of a difference.

No, I don't think it's a big difference either.

 

[xgmad]

No, I don't think it's a big difference either.

No reason to mix oils then, it won't really make a difference.

 

[herwawan]

A quick update on that one. I did an oil change from the Driven Racing 5w40 to Mobil 1 High Mileage 10w40. I noticed a slight decrease in oil pressure when warm (about 2 psi). I talked to Driven Racing about it out of curiosity and they said it is common considering their blend to see higher pressure than equivalent grade from different brand, and in this case, even with higher grade.

Since my engine already runs with a lower pressure because of the axle oiling lifters, I think I’d rather go with an oil that keeps things on the higher side.

I am quite tempted to try the 5w50 and see how it goes, but I want to make sure I’m understanding things properly - thicker oil should result in higher oil pressure… but at what cost on the rest of the engine? Also it’s getting real hot around here and I wonder if thicker oil helps with oil temperature, or if it’s the opposite. I get confused by this topic.

And last but not least, I’m not sure I see the difference between 5w50 & 15w50 when I compare the viscosity. In most case it’s identical.

 

[OVERKILL]

A quick update on that one. I did an oil change from the Driven Racing 5w40 to Mobil 1 High Mileage 10w40. I noticed a slight decrease in oil pressure when warm (about 2 psi). I talked to Driven Racing about it out of curiosity and they said it is common considering their blend to see higher pressure than equivalent grade from different brand, and in this case, even with higher grade.

Since my engine already runs with a lower pressure because of the axle oiling lifters, I think I’d rather go with an oil that keeps things on the higher side.

I am quite tempted to try the 5w50 and see how it goes, but I want to make sure I’m understanding things properly - thicker oil should result in higher oil pressure… but at what cost on the rest of the engine? Also it’s getting real hot around here and I wonder if thicker oil helps with oil temperature, or if it’s the opposite. I get confused by this topic.

And last but not least, I’m not sure I see the difference between 5w50 & 15w50 when I compare the viscosity. In most case it’s identical.

What pressure figures are we talking here? Different cSt numbers will yield different oil pressures, that's totally normal. As long as it is still within the anticipated and safe range for the engine, it won't have any impact.

 

[herwawan]

What pressure figures are we talking here? Different cSt numbers will yield different oil pressures, that's totally normal. As long as it is still within the anticipated and safe range for the engine, it won't have any impact.

With the previous oil (5w40) I was at 27 psi at idle (200F). With the current oil (10w40), I’m closer to 25 psi in the same conditions. At 1,500 rpm on the highway, I was at roughly 40 psi (200F), now closer to 38 psi in the same conditions.

It is still in the anticipated range for this engine, yes.

 

[gregk24]

I wouldn’t fool with mixing, that is generally not recommended due to the possibility of competing add packs. I’d keep it thick on a build. He says mix a 40 and 50, so I’d go with a 50. 5w50 preferably or 10w50. 15w50 is thicker than I’d personally be comfortable with in the winter months as cold oil viscosity will be significantly higher than a 5w50.

 

[OVERKILL]

With the previous oil (5w40) I was at 27 psi at idle (200F). With the current oil (10w40), I’m closer to 25 psi in the same conditions. At 1,500 rpm on the highway, I was at roughly 40 psi (200F), now closer to 38 psi in the same conditions.

It is still in the anticipated range for this engine, yes.

Then I wouldn't worry about it at all, both of those sound perfectly fine.

 

[Bill_W]

If you did not change the oil pump pressure from before the rebuild that could give you a clue. Find out what pressure is normal for your engine and adjust viscosity to match. Oops… that was just discussed.

 

[herwawan]

If you did not change the oil pump pressure from before the rebuild that could give you a clue. Find out what pressure is normal for your engine and adjust viscosity to match. Oops… that was just discussed.

Yep! I’ve got a higher pressure/volume pump in the build, it was designed that way. We could’ve gone with an even higher pressure pump but then it would be extreme pressure at cold with 100+psi and it’s just wasted resources plus harder on the bearings.

 

[kschachn]

Yep! I’ve got a higher pressure/volume pump in the build, it was designed that way. We could’ve gone with an even higher pressure pump but then it would be extreme pressure at cold with 100+psi and it’s just wasted resources plus harder on the bearings.

What does a high oil pressure get you?

 

[herwawan]

What does a high oil pressure get you?

Not sure I understand your question?

 

[ZeeOSix]

Not sure I understand your question?

What components in the LS7 oiling system require high oil pressure to operate correctly? What operates on pressure where a certain amount of pressure (or higher) is required? Yes, the oil pressure has to be high enough to ensure all brances of the system receive an adequate amount of oil flow volume.

Oil pressure is just a measure of how much force per area is required to move X volume of oil through Y flow restriction of the oiling system. If the pump isn't in pressure relief, then the same volume of oil is going into the oiling system at X RPM regardless if the oil pressure is 38 or 40 or 45 PSI. Oil volume is delivered by pressure. Oil volume is what gives lubrication. High volume oil pumps are to deliver more volume, and the result is higher oil pressure, unless the oiling system's flow resistance has changed - ie, larger journal bearing clearances.

 

[ZeeOSix]

With the previous oil (5w40) I was at 27 psi at idle (200F). With the current oil (10w40), I’m closer to 25 psi in the same conditions. At 1,500 rpm on the highway, I was at roughly 40 psi (200F), now closer to 38 psi in the same conditions.

It is still in the anticipated range for this engine, yes.

What's the oil pump pressure relief valve set to? And what's the oil pressure near redline with the oil at 200F?

 

[53' Stude]

I mix oils when I have quarts to empty and get rid of. Done quite a few “frankenblends” and used them in friends late 80’s Jeep Comanche with 4.0 engine without issues

 

[Schandyman]

Hello everyone,

My engine (LS7) recently went through a complete rebuild with forged internals and other goodies. The bearing clearances are higher than stock so it requires a thicker oil than what these engines when in stock configuration call for (5W30 per Chevy).

Now, the builder of the engine is going with a mix of 0W40 (50%) & 15W50 (50%) using Mobil 1 synthetic oil. I didn't really get more details from him other than the clearances call for this mix.

I am not an expert in oil so I am trying to better understand the purpose of the mix and how to "measure" its effectiveness. I searched "mixing oil" over the forum before creating this thread and it answered a lot of my questions - it is safe, synthetic oils of the same or different brands are compatible, etc. Most threads I read though are asking about using some leftovers in cars that are usually stock.

Let's hear it!

Is it necessary for mixing? I would play with 5w40, 5w50 or 15w50