15W/40 Diesel oil in cars

[tradosaurus]

Can anyone answer why I can use for the last few years Mobil 1 Delvac 15W/40 Diesel oil in 4 cylinder, 6 cylinder and 8 cylinder cars with no issues and no MPG loss?

I decided to do an experiment on an older 4 cylinder car of mine after reading an article about a guy who has studied MPG improvements for 30 years. He recommend 15W/40 for all cars.

Right now I am using 15W/40 oil on my 6 cylinder Ford Freestyle and have been doing so for the last 3 years. Also I used it on a 8 cylinder Ford E350 before I sold it to upgrade (or downgrade) to the Freestyle.

I have wondered for the last few years if these oil viscosity recommendations that vary from car to car is nothing but a money making gimmic for the oil companies?

 

[Craig750]

The oil weight is important for plain bearing clearances. If the motor is designed to run thinner oils then the design specs for clearances should be tighter.

Plus the main reason for lighter oils is the push for emission reductions from regulators.

Gimmic, I don't think.

 

[tradosaurus]

So you believe a 8 cylinder Ford E350 (calling for 5W/20)has tighter bearing clearances than a 4 cylinder Mazda 626 (calling for 10W/30)?

Yes, let's put our faith in the oil companies that have given us the likes of the gulf oil spill and billions of dollars in profits. Watch the documentary "Who killed the Electric Car" to understand that oil companies are just as crooked as pharmacuetical companies.

Yet I have PROVEN the oil recommendations wrong!

 

[IndyIan]

Originally Posted By: Craig750
The oil weight is important for plain bearing clearances. If the motor is designed to run thinner oils then the design specs for clearances should be tighter.

But if its the same engine with same bearing clearances in Oz as in the US why are different oils spec'd?
Corporate average fuel economy...

Like the OP I run 15W40 HDEO in the summer in everything, no significant reduction in fuel economy and I'm averaging 36mpg with a 16 year old 3 speed auto Neon.

 

[Cup of Joe]

I have read the article you are refering too. The articles basic reasoning is that a higher viscosity actually lubricates better thus providing better MPG. On short trips obviously that will not be true since the oil never reachs operating termperature. The mpg difference between 20wt and 30wt is .9-2.3%. At most the difference then from 20wt to 40wt could possibly be 5%. If you get 26 mpg and saw a 5% reduction in fuel economy thats a total loss of 1.3 mpg or within the normal variance for most drivers.

 

[Lurch]

Would Rotella T6 5w40 synth work good in my car? I have 3 gallons of it but I'd like to run Rotella 15-40 in my bike and the T6 in my car.

 

[mechanicx]

+1. Also what the OP might not be appreciating is that the thinner oil might cause such a small increase in fuel milage as to be unnoticable on the individual level. But add that up over millions of cars and it makes a sizable reduction. Especially for short trips in colder areas. I'm not particualrly a thn oil fan but keep in mind there are many engines with 200K or much more miles running 20 and 30 grade oil. I'm still waiting on the proof that other countries' engines last longer with their thicker oil recommendation.

 

[440Magnum]

Originally Posted By: Craig750
The oil weight is important for plain bearing clearances. If the motor is designed to run thinner oils then the design specs for clearances should be tighter.


Not always. Bearing rod and main bearing design clearances have remained pretty static for decades. The new wave of "thin oil" engines may have a few tighter clearances, but the main thing is that they have higher volume oil pumps to keep the clearances full of oil. There's also been a steady improvement in manufacturing consistency so there's less variation from bearing to bearing and engine to engine, but the target clearances aren't usually all that different between now and back in 1960.


Quote:
Plus the main reason for lighter oils is the push for emission reductions from regulators.


The only way lighter oil would reduce emissions is if lighter oil INCREASES fuel efficiency. That's exactly NOT what the original poster is seeing. I'm agreeing with you in principle, but the OP is asking why he's not observing any difference.

My answer is that there IS a difference, but its a fraction of an MPG. It adds up when you think of it either over the lifespan of the car, or over a few million copies of that car. But its usually not something you notice in your own vehicle. The savings is smaller on a per-tank basis than the errors in your odometer, the gas pump accuracy, and your ability to re-fill your tank to EXACTLY the same level each time.

 

[tig1]

Originally Posted By: tradosaurus
So you believe a 8 cylinder Ford E350 (calling for 5W/20)has tighter bearing clearances than a 4 cylinder Mazda 626 (calling for 10W/30)?

Yes, let's put our faith in the oil companies that have given us the likes of the gulf oil spill and billions of dollars in profits. Watch the documentary "Who killed the Electric Car" to understand that oil companies are just as crooked as pharmacuetical companies.

Yet I have PROVEN the oil recommendations wrong!
Well you just won't listen to anything so why ask in the first place.

 

[StevieC]

My dad's Windstar rated for 5w20 that has run on this it's whole life is doing just fine at it's current 300K+ Km's (180K Miles).

It burns or leaks no oil and passes emissions with flying colours.


I think clean oil via regular oil changes with decent filters and other regular maintenance of the vehicle is way more important than brand or weight in 99% of cases.

 

[440Magnum]

Originally Posted By: Lurch
Would Rotella T6 5w40 synth work good in my car? I have 3 gallons of it but I'd like to run Rotella 15-40 in my bike and the T6 in my car.


Wouldn't you consider the bike a more stressful application than the car? I'd run the stronger/better oil (RT6) in the bike. The plain Rotella 15w40 should be OK in the bike, but RT6 would be better assuming its compatible with any wet-clutch issues (though you'd have the same issue with 15w40). The car should be fine with garden-variety 5w30.

 

[purelux]

Agreed, plus he seems to be confusing actions largely responsible due to corporate level decisions with recomendations by engineers at those companies. Also 2 or 3 vehicles driven in a static driving pattern is not a very good study for a wide range of drivers to follow.

 

[Steve S]

Originally Posted By: IndyIan
Originally Posted By: Craig750
The oil weight is important for plain bearing clearances. If the motor is designed to run thinner oils then the design specs for clearances should be tighter.

But if its the same engine with same bearing clearances in Oz as in the US why are different oils spec'd?
Corporate average fuel economy...

Like the OP I run 15W40 HDEO in the summer in everything, no significant reduction in fuel economy and I'm averaging 36mpg with a 16 year old 3 speed auto Neon.
Everything is Oz is upside down. That changes everything.

 

[StevieC]

So you want a thick oil then because otherwise it slips past the piston rings if the engine is upside down... I get it now!

 

[addyguy]

Climate is also an important consideration. In Canada and the Northern US, you'd have real problems some mornings getting a car started 'comfortably' on a 15W-40 mineral oil.

'Maybe' 15W-40's ARE better oils, but it doesn't matter, I, and many others, will take the easier winter starts in exchange for a better oil.

However, in Texas, or a similar climate where cold starts are a mute point, 15W-40 might well be a good choice - it usually has a higher TBN, is more shear-stable, and in quantity, is often less expensive than regular PCMO's.

 

[Cup of Joe]

Why is there this claim of a change in tolerance.

Do not over look the fact that manufacturers like Ford back spec'd 5w-20 for use in vehicles built in the 90's that where originally filled with 30wts from the factory. There have been no changes made either internally or externally on these engine. Ford simply states as of this date your engine may now run on 20wt oil year round regardless of temperature. The engines did not improve internally, rather the oil improved to a point that this was proven possible and still provides more then adequate protection for many thousands of miles.

 

[HTSS_TR]

Originally Posted By: tradosaurus
So you believe a 8 cylinder Ford E350 (calling for 5W/20)has tighter bearing clearances than a 4 cylinder Mazda 626 (calling for 10W/30)?

Yes, let's put our faith in the oil companies that have given us the likes of the gulf oil spill and billions of dollars in profits. Watch the documentary "Who killed the Electric Car" to understand that oil companies are just as crooked as pharmacuetical companies.

Yet I have PROVEN the oil recommendations wrong


The oil weight of any car/truck is recommended from the car manufactures, not the oil companies. What is the interest of car manufactures ? You, the customers are the ones they like to come back to buy their cars/trucks. If you are not satisfied with their products for recommending wrong oil weight that caused the engine broke down after few years, you will not go back to buy another one.

The oil companies are working with car manufactures to provide the best product for your particular car/truck, believe it and use the recommended oil weight in the owner manual with confidence.

 

[Chris142]

Originally Posted By: 440Magnum
Originally Posted By: Craig750
The oil weight is important for plain bearing clearances. If the motor is designed to run thinner oils then the design specs for clearances should be tighter.


Not always. Bearing rod and main bearing design clearances have remained pretty static for decades.








I agree and I've been saying this for years. Main and rod bearing clearances have been around .002-.004 forever regardles of engine size or manufacturer. You cant get much "tighter' than these specs.

 

[Craig750]

Originally Posted By: IndyIan
Originally Posted By: Craig750
The oil weight is important for plain bearing clearances. If the motor is designed to run thinner oils then the design specs for clearances should be tighter.

But if its the same engine with same bearing clearances in Oz as in the US why are different oils spec'd?
Corporate average fuel economy...

Like the OP I run 15W40 HDEO in the summer in everything, no significant reduction in fuel economy and I'm averaging 36mpg with a 16 year old 3 speed auto Neon.


Good point. I wasn't aware of that issue, same engine different oil spec for different regions. Not a big shift in weight, but enough to make someone cynical as to the intent.

 

[mechtech2]

I'll bet that internet guy was the hypermiler who extolled the virtues of acetone in gasoline.
I read that sometime ago [using 40].
It's wrong.