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

[herwawan]

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!

 

[spasm3]

The 0w makes little sense to me , as it will have a viscosity like other 5w and 10w oils, until you get below zero. What part of the country will this engine be operated ?

 

[HankHill]

That's an interesting mix, pretty specific formula. Was that just the break in oil spec, or did he say the blend was for everyday usage? Do you track the car ever, was this engine built for track use, or just an everyday runabout car?


https://www.m3post.com/forums/showthread.php?t=1291941

I know you didn't ask, but if I were you, I'd only use the blend he suggested...

 

[Dave1027]

You can find the viscosity of both oils then average them. You would end up with something like a 7.5W-45 oil.

I run a mix of two different oil in all my vehicles. The mix varies depending on each vehicle's viscosity needs.

 

[spasm3]

You can find the viscosity of both oils then average them. You would end up with something like a 7.5W-45 oil.

I run a mix of two different oil in all my vehicles. The mix varies depending on each vehicle's viscosity needs.

There is no 7.5w. The oil is either 5w or 10w.

Viscosity Charts - Bob is the Oil Guy

Viscosities can be related horizontally only Viscosities based on 96 VI single grade oils. ISO are specified at 40°C AGMA are specified at 40°C SAE 75w, 80w, 85, 5w, & 10w specified at low temperature. Equivalent viscosities for 100° & 210°F are shown SAE 90 to 250 and 20 to 50 specified at...

bobistheoilguy.com

 

[930.engineering]

Mixing oil - what is the purpose?

IMHO there is no purpose. I'd just run a proper 5W-40 or 10W-50.

how to measure effectiveness?

There's probably no other way to measure effectiveness without running
a dozen of engines for weeks, disassemble them and determine wear.
.

 

[herwawan]

The 0w makes little sense to me , as it will have a viscosity like other 5w and 10w oils, until you get below zero. What part of the country will this engine be operated ?

California. I think the colder I've seen where I live was in the 40F.

That's an interesting mix, pretty specific formula. Was that just the break in oil spec, or did he say the blend was for everyday usage? Do you track the car ever, was this engine built for track use, or just an everyday runabout car?


https://www.m3post.com/forums/showthread.php?t=1291941

I know you didn't ask, but if I were you, I'd only use the blend he suggested...

A specific oil was used for the break-in (SAE 30). The blend is for everyday usage moving forward. The engine was built to be dual purpose (road & track) with reliability as the main goal. I haven't had a chance to talk with the builder yet about what kind of oil he recommends on the track.

You can find the viscosity of both oils then average them. You would end up with something like a 7.5W-45 oil.

I run a mix of two different oil in all my vehicles. The mix varies depending on each vehicle's viscosity needs.

There is no 7.5w. The oil is either 5w or 10w.

Viscosity Charts - Bob is the Oil Guy

Viscosities can be related horizontally only Viscosities based on 96 VI single grade oils. ISO are specified at 40°C AGMA are specified at 40°C SAE 75w, 80w, 85, 5w, & 10w specified at low temperature. Equivalent viscosities for 100° & 210°F are shown SAE 90 to 250 and 20 to 50 specified at...

bobistheoilguy.com

So my understanding without going into specific numbers is that the goal would be to have a thicker oil than regular 0/5/10W40 and thinner than 15/50? Is there a gap in between that isn't filled by other specialty oil on the market?

IMHO there is no purpose. I'd just run a proper 5W-40 or 10W-50.




There's probably no other way to measure effectiveness without running
a dozen of engines for weeks, disassemble them and determine wear.
.

I called Driven Racing Oil the other day out of curiosity. Based on the clearances I gave them, they recommended running their 5W40.

 

[OVERKILL]

You can find the viscosity of both oils then average them. You would end up with something like a 7.5W-45 oil.

I run a mix of two different oil in all my vehicles. The mix varies depending on each vehicle's viscosity needs.

No you can't. You just made up two grades that don't exist in J300:

The oil, at 50/50, would have the following characteristics:
KV40: 93.58cSt
KV100: 15.19cSt
VI: 172

That makes it an xW-40, likely a 10w-40, though it may squeak in as a 5w-40.

Also, playing home chemist without any lab equipment means you have no idea what characteristics of the lubricant you've now compromised over each of the fully formulated products on their own.

 

[OVERKILL]

I called Driven Racing Oil the other day out of curiosity. Based on the clearances I gave them, they recommended running their 5W40.

Which makes sense, the 100C visc of the mix is 15.19cSt, which is on the upper end of the xW-40 range.

The closest product to that viscosity in the Mobil 1 product range is their High Mileage 10w-40, which is 15.3cSt @ 100C.

 

[Graham Piccinini]

Plenty of UOAs here show how Mobil1 0W40 (best oil on the planet btw, imho) drops to a "heavy" 30-grade and just stays there for the whole OCI.
This trend also seems to apply to Mobil 1 15W50. It usually drops to a "heavy" 40-grade. In rare cases (air-cooled applications, with or without a shared sump) it could "shear" down to a "heavy" 30-grade.
With all this in mind I'd use M1 15w50, if it's a weekend car and garage stored. Otherwise alternate with M1 15w50 in summer and M1 0w40 in winter. No need to mix both in the crankcase. It doesn't become one strong blend, but rather two weakened blends that just coexist in the crankcase for an OCI.
Realistically either of these oils should do great, as viscosity is only a part of the picture, and additives usually provide a lot more protection than viscosity does. Both of these oils are loaded with good additives in healthy amounts.
Just my couple pennies. Carry on.

 

[Accent Abuser]

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!

Mobil 1 5w50 would probably be a better option, the viscosity would likely be the same as that mix but unlike the 15w50 it will start easily in the winter. Mixing viscosity really only works for operating temperature, it's best to assume whatever the highest winter rating is is the limit for cranking/pumping.

 

[spasm3]

High Perfomance Lubricants, sells a 5w-50 in several lines. I'm thinking about that for my ram.

 

[xgmad]

how higher is the clearance?

 

[herwawan]

The oil, at 50/50, would have the following characteristics:
KV40: 93.58cSt
KV100: 15.19cSt
VI: 172

That makes it an xW-40, likely a 10w-40, though it may squeak in as a 5w-40.

Also, playing home chemist without any lab equipment means you have no idea what characteristics of the lubricant you've now compromised over each of the fully formulated products on their own.

Which makes sense, the 100C visc of the mix is 15.19cSt, which is on the upper end of the xW-40 range.

The closest product to that viscosity in the Mobil 1 product range is their High Mileage 10w-40, which is 15.3cSt @ 100C.

You gave me some homework with the KV40/100/VI & cSt, I'm slowly starting to make sense of it but I still need to read more to fully grasp the implications and meaning of these values!

Plenty of UOAs here show how Mobil1 0W40 (best oil on the planet btw, imho) drops to a "heavy" 30-grade and just stays there for the whole OCI.
This trend also seems to apply to Mobil 1 15W50. It usually drops to a "heavy" 40-grade. In rare cases (air-cooled applications, with or without a shared sump) it could "shear" down to a "heavy" 30-grade.
With all this in mind I'd use M1 15w50, if it's a weekend car and garage stored. Otherwise alternate with M1 15w50 in summer and M1 0w40 in winter. No need to mix both in the crankcase. It doesn't become one strong blend, but rather two weakened blends that just coexist in the crankcase for an OCI.
Realistically either of these oils should do great, as viscosity is only a part of the picture, and additives usually provide a lot more protection than viscosity does. Both of these oils are loaded with good additives in healthy amounts.
Just my couple pennies. Carry on.

Very insightful. I might be wrong but I think one of my builder's main focuses when it comes to the oil grade is the impact on oil pressure. I guess it's a question of balance, avoiding too little pressure but not going ballistic with too much thickness with the adverse effect. Not sure if it is relevant but the engine runs with a dry-sump system.

Mobil 1 5w50 would probably be a better option, the viscosity would likely be the same as that mix but unlike the 15w50 it will start easily in the winter. Mixing viscosity really only works for operating temperature, it's best to assume whatever the highest winter rating is is the limit for cranking/pumping.

High Perfomance Lubricants, sells a 5w-50 in several lines. I'm thinking about that for my ram.

This would make sense, especially considering Vladiator's feedback on the drop.

how higher is the clearance?

The current build clearances are:

Main bearing: .0020"-.0022"
Rod bearing: .0026-.0028"

I was looking at this earlier (I highlighted some areas) on Driven's website, which I thought was interesting.

 

[RooflessVW]

M1 0W-40 and 15W-50 mixed 50-50 is a mix I've seen here and elsewhere. Should be pretty stout.

I'd personally just run M1 5W-50.

 

[mahanddeem]

In many cases (or most) if your wallet is happy you know you have achieved "effectiveness"

 

[ZeeOSix]

You gave me some homework with the KV40/100/VI & cSt, I'm slowly starting to make sense of it but I still need to read more to fully grasp the implications and meaning of these values!

If you want to know the mixed viscosity, use this calculator. You will just need the KV40 and KV100 viscosity (in cSt) from the oil maker's spec sheet usually shown on their website.

Mixing viscosities | Widman International SRL

www.widman.biz

 

[FCD]

Don't really see the point of mixing M1 0W40 and 15W50 when M1 5W-50 is available

 

[kschachn]

IMHO there is no purpose. I'd just run a proper 5W-40 or 10W-50.

There's probably no other way to measure effectiveness without running
a dozen of engines for weeks, disassemble them and determine wear.

This is correct.

And the wear tests are included in SAE J300.

 

[Fauxchemist2009]

The purpose is to get rid of old stock. I mix and match all the time. Especially during the warmer months. I may buy a jug of 0w-16 and that 6 or 7th quart may be 10w40 MA2 oil, if that's what I have on hand.