15w-40 vs 10-30/40?

[Jackrabbit41]

I know this is probably just a debate topic, but I'm curious to hear peoples opinions on running 10-30/10-40 compared to 15-40. I've always ran 10-30 and 10-40 but recently I switched to 15-40. Same oil i put in my cummins. My jeep has the original motor with 250,000+ miles on it (1987 Comanche, 4.0l) so I feel like that thicker oil is a lot better due to the larger clearances present in the motor after so many miles on stock internals. And I also hated how I used to drain my oil and the 10-30 just looks so thin, almost like water, draining out. Whereas the diesel oil looks so much better. Ever since I started running it, I haven't  noticed any differences, as i would have thought, but it just gives me peace of mind. 

[Eagle]

With a multi-weight (multi-viscosity) oil, the first number is the cold viscosity and the second number is the hot viscosity. A thinner oil (lower number) provides better cold flow and, thus, better lubrication at start-up. If the second number is "40," the performance at operating temperature is the same. To get an oil that's thicker at operating temperature, you'll need to look for an oil graded ##W-50. Which is just about impossible to find these days. Both Mobil-1 and Castrol Syntex used to offer oil with 50 in the second place, but I haven't seen it on the shelves for several years.

[Dzimm]

I spent a lot of time looking into this topic and there is no "proof" of any oil being better than the other.   It's all here-say based on peoples opinions.  In reality the "thicker oil trick" is leftover from the mechanics of the old days when engine tolerances changed a great deal over time.  Nowadays those tolerances don't change nearly as much (even on the 4.0L), and if the tolerances on this engine are to the point of needing thicker oil, it's time for a rebuild anyway, the thicker oil is just a bandaid to limp it along and mask the terrible noises.  

 

The engineers of this engine say to run 10w-30 in the 4.0L so that's what I do, but I use a GOOD quality oil.  As long as the engine runs good and you aren't leaking oil out if every possible place on the engine, it isn't too thin.   I wouldn't recommend running full synthetic in these engines though because it is slightly thinner and seems to thin out over time.  Conventional oil is thicker and what was available when this engine was built so that's what the engineers built it based on.  I personally have always used a synthetic blend and never had issues.  

 

In summary it all comes down to proper maintenance and using a good quality oil.  If the engine is still running strong, you've been doing something right, why change it? 

[75sv1]

Basically, what Eagle wrote. Rotella does make a 10W-30 oil. I have used it in my XJs and my MB240D (colder temps).  I am running Rotella 5W-40 T6. I do not see a pressing need to run synthetic in this engine though. Also, convention oils have come a long way from when this engine was designed.

[Jeep Driver]

22 minutes ago, Eagle said:

With a multi-weight (multi-viscosity) oil, the first number is the cold viscosity and the second number is the hot viscosity. A thinner oil (lower number) provides better cold flow and, thus, better lubrication at start-up. If the second number is "40," the performance at operating temperature is the same. To get an oil that's thicker at operating temperature, you'll need to look for an oil graded ##W-50. Which is just about impossible to find these days. Both Mobil-1 and Castrol Syntex used to offer oil with 50 in the second place, but I haven't seen it on the shelves for several years.

https://www.amsoil.com/shop/by-product/motor-oil/gasoline/premium-protection-20w-50-synthetic-motor-oil/

 

The more I seek quality, the less I even go into an auto parts store. 

 

I still get my oil at Walmart though. 

[tugalo]

Some time back there was a site named bobistheoilguy.com.  It was started as a forum by and for petroleum engineers in Houston.  If the site is still up, they will teach you in minute detail, everything you ever wanted to know about oil and filters.

[Marine1Texas]

here in N.E Texas I use mobile 1 15W50 for more then 20 years on my 87 4.0. For me I find that the oil pressure stays higher then when I used 10w30 and 10w40. I like cruising with a 65 to 70 psi oil pressure. It allows my oil pressure to idle around 38 when it is 100 plus out side and 43 when it is in cooler weather.

 

The higher the number like 2nd number 50 means it will stay thicker when hotter. the lower number the 1st one is mainly for start up. If you live in a very cold climate like Canada or places that stay below freezing you want to stay with the 0 to 5 range. If you live in a area that see's 32 and down to mid 20's you can stay with 10.  15 weight is good right down to above freezing.

 

with the 4 trucks I have I used the 15w50 and works great with not excess pressure and no big impact on mpg. In my 2006 super duty I use the 5w20. It has a oil cooler and also that is factory oem oil weight. with 210k on it still running strong, so I stay with the 5w20. The one time I use 10w40 I seem to loose about 1.5 mpg.

 

I say to most people just follow what the OEM says. Here in Texas no need to go below 10w on cold side however unless factory specs say so. Now on high side w40 it is not going to harm anything by going to a higher number. The higher number w40 or w50 is because oil is getting thin due to heat. On older cars the tolerances were much higher so thicker oil was needed. now on newer motors like 4.0 no need to go so thick unless your needing it for heat purposes.

 

The 4.0 in my 87 jeep has 460k on it with out being rebuilt yet. I have done mods however renix original on the inside and still holding strong. no blow by and still  getting above 140 on 5 cylinders, one getting 135 psi on number 4.

 

I do oil a change at 7500 miles with the mobile 1 15w50 for at least 20 years now. Works for me.

[johnj92131]

IMHO,  better oil is the major reason car engines run longer than they did in the 1960's.  Diesel spec oils get a lot of attention because diesel engines are just harder on every part of the engine.  Modern oil lasts longer and protects better because of the additive packages.  There is also the fact that the base stock is better because of improved refinery process.

Another change that has helped cars last longer is the newer formulations for gasoline.  Gas is a much more uniform product than it was before auto emissions.  Back then, gas had a different formulation, depending on what ever product/component of the mix was cheapest.

I run 10-40 oil in my cars.  But I live in Southern California and all but my Comanche are in the garage at night. 

 

Noriyori's experience and advice are well worth listening to.  He needs his equipment to run and needs to keep his cost under control.

 

[WahooSteeler]

A couple of years ago someone on here suggested 5W/50 Castrol as Eagle also mentioned above. My local Advance Auto has it in stock, @$6-7/qt.  

[DirtyComanche]

On 11/15/2017 at 8:04 AM, johnj92131 said:

IMHO,  better oil is the major reason car engines run longer than they did in the 1960's.

 

I'd say it's solidly worth about 20% of the difference.  Lots of things changed, but yes, oil got a lot better.

 

 

I run 10w30, or maybe 5w30 if I do an oil change when it's cold and the 5w30 is on sale.  Synthetic only.  After reading a lot about it I do not believe in using diesel oils.  I do not believe in using thicker oil to increase the indicated oil pressure.  I do not believe in additives.  I do not mix types.