Oil Mixing and Viscosity

Nomad Willy · 11-27-2021, 07:54 PM

At times I have mixed 30w and 40w Delo. Usually less than 50-50 as in one quart 40w and 3quarts 30w. For summer use.

But now I am considering mixing 10-30 and 20-50. If the viscosity is linear up and down the scale as one changes vis I think one would come up w 15-40. But I don’t know if this is a linear function.

If 15-40 lube oil is readily available in 15-40 for gasoline road vehicles I’ll be good to go but I don’t think it is. However it would be handy for many of us to mix what viscosity we wanted relative to the variables at hand like low temps and flat land or high temps and mountainous roads. I don’t think 15-40 is available for gas engines. I wonder why but if one can mix per above anyone can mix up 15-50.

Mixing would mostly happen as I mentioned above .. like adding a quart of a different vis. Doing this the vis wouldn’t change enough to need numbers .. IMO. If you have a car in Wash state and the owners manual recommends 5-30 oil from Cali to Wn and in Wn the recommended vis is at max vis (per owners man) just adding a quart of lowest vis per manual should be safe and bring the oil vis up or down to a more desirable overall vis. No need for linear info either.

So is there any chemists aboard that know if one can mix and achieve these vis numbers in a linear way? And as usual I’m open to opinions.

rslifkin · 11-27-2021, 08:27 PM

Many of the diesel rated 15W-40 oils are also rated for gas engines, provided you don't need a specific spec for a Euro car or anything. That's what I run in the 454s in the boat.

Nomad Willy · 11-27-2021, 09:44 PM

rslifkin,
OK good …
But do I dare ask for high millage oil?
The diesel car I’m looking at is a Golf w 350,000miles.

I think I remember reading on the bottle/can that my Chevron Oil was good for cars too.

rslifkin · 11-27-2021, 10:04 PM

Personally I've never worried about high mileage oil as a concept. Just use something of good quality that meets any special needs for the engine in question and is of an appropriate weight for it. If in any doubt, do an oil analysis at the first change with a new oil.

C lectric · 11-27-2021, 11:09 PM

I used to use 15/40 in my two cars although they were 1988 and 1989 s plus my 1999 Ranger 3 L v6.
In fact when I pulled the head off mine 1998 at about 250,000KM there was no sign of the frequent ridge ring at the cylinder top.
Never a lick of trouble.

I'm not so sure I would mess with my boat engine like that though. If I screwed up the cost could be disastrous compared to the cars.

Nomad Willy · 11-28-2021, 05:12 AM

I put high milage oil in my 87 Nissan and it idled better and quit burning oil. Didn’t burn much but enough to notice.
The manufacturers seemed to think it was good. It was a new thing not long ago and I suspect they wanted to get past the “something new” resistance. Remember radial tires? Fuel injection?

I ran 30w oil in the Nissan for several years and the only thing I noticed different was a very slightly lower idle speed at startup. Probably 1/2mpg less gas milage but that’s fly stuff. I was concerned about the MV oil thining out. It probably does …. but not much now. Was a problem early on though I read.

With a car one is much more likely to go out of viscosity range. Not so w a boat. C lectric I don’t see how one could “screw up”. As I put it out one could only go in a beneficial direction w the vis if you thought it out. If you went higher vis in so Cal it would be a benefit or if you went higher vis in Wash it wouldn’t be a problem unless one made big changes in the heavier oil direction. But that would just reduce wear. The’re may be people on this forum that wouldn’t believe that tho.

phillippeterson · 11-28-2021, 07:22 AM

Quote:

Originally Posted by Nomad Willy

Remember radial tires? Fuel injection?

I remember my grandmother flipping out in 1960 at a new car with a tilt steering wheel. She just KNEW it fall off in her lap.

FF · 11-28-2021, 08:40 AM

What changes in oil as it gets "better" or at least newer is mostly the detergent level. All containers are marked with oil detergent style.

There are on line tutorials on the difference between CD ,compression engine , D rated oil and say SD , spark engine D rated oil.(damn little)

Thin oil might help cold starting and mileage , but for long life a single wt. oil still seems to be the champ.

sunchaser · 11-28-2021, 08:46 AM

Here is my oil change story that recently happened -

So I get a notice on my 4 year old gasoline Panamera that the 4 year servicing is due. No big deal on a car with 7,400 miles and only needing an oil change right? Wrong!

The maintenance mgr at the dealership says the manual calls for new plugs, serpentine belt, transmission, all filters and Mobil 1. All to the tune of over $2,000. Further, next year all new tires as at five years the speed rating is voided by government decree.

He said all the work could be done in three weeks as they are very busy. So I walked over to the sales manager's office and asked if they are offering really good deals on new cars. Hah! He says sales are up and inventories way down.

Well what the heck, what would you offer for my "new" car. He goes out and looks and then pulls it up on the computer.. We quickly arrived at a surprisingly good offer and I got a check. The car is whisked into the shop and all work commenced as I wait for the dealer's runner to give me a ride home. The next day the car is for sale at 90% of what I paid for it.

I also note Hertz is buying used cars as insufficient new ones can be found. These are amazing times Eric, your Rabbit may well be worth double what you bought it for, clean oil or not.

catalinajack · 11-28-2021, 09:52 AM

Quote:

Originally Posted by FF

What changes in oil as it gets "better" or at least newer is mostly the detergent level. All containers are marked with oil detergent style.

There are on line tutorials on the difference between CD ,compression engine , D rated oil and say SD , spark engine D rated oil.(damn little)

Thin oil might help cold starting and mileage , but for long life a single wt. oil still seems to be the champ.

Straight weight, multi-weight, it doesn't matter a wit as to engine longevity as long as the oil is changed when recommended.

rslifkin · 11-28-2021, 10:00 AM

Quote:

Originally Posted by catalinajack

Straight weight, multi-weight, it doesn't matter a wit as to engine longevity as long as the oil is changed when recommended.

Pretty much, yeah. As long as the oil meets the basic needs of the engine in question (some engines have more specific needs than others and some engines are more abusive to oil than others) and you change it before the oil is sheared too thin, diluted with too much fuel, too dirty, or the additives are too worn out, then you're in good shape.

KnotYet · 11-28-2021, 11:22 AM

Quote:

Originally Posted by Nomad Willy

rslifkin,
OK good …
But do I dare ask for high millage oil?
The diesel car I’m looking at is a Golf w 350,000miles.

I think I remember reading on the bottle/can that my Chevron Oil was good for cars too.

In my VW diesel I've used Shell Rotella T-6 with very good results. It is 5-40 weight.
Oil change intervals are 10,000 miles per Volkwagen. T6 would be fine in any diesel.

I would never consider mixing oils to achieve some imagined benefit since the oil
manufacturers have already provided a myriad of choices to fit most any situation.

Interestingly, the engine builder of my 425 HP Ford V-8 gas engine recommended
Rotella T5 in that engine from day 1. So that's what I use. It is 15-40 weight.

Nomad Willy · 11-28-2021, 02:23 PM

Quote:

Originally Posted by Nomad Willy

At times I have mixed 30w and 40w Delo. Usually less than 50-50 as in one quart 40w and 3quarts 30w. For summer use.

But now I am considering mixing 10-30 and 20-50. If the viscosity is linear up and down the scale as one changes vis I think one would come up w 15-40. But I don’t know if this is a linear function.

If 15-40 lube oil is readily available in 15-40 for gasoline road vehicles I’ll be good to go but I don’t think it is. However it would be handy for many of us to mix what viscosity we wanted relative to the variables at hand like low temps and flat land or high temps and mountainous roads. I don’t think 15-40 is available for gas engines. I wonder why but if one can mix per above anyone can mix up 15-50.

Mixing would mostly happen as I mentioned above .. like adding a quart of a different vis. Doing this the vis wouldn’t change enough to need numbers .. IMO. If you have a car in Wash state and the owners manual recommends 5-30 oil from Cali to Wn and in Wn the recommended vis is at max vis (per owners man) just adding a quart of lowest vis per manual should be safe and bring the oil vis up or down to a more desirable overall vis. No need for linear info either.

So is there any chemists aboard that know if one can mix and achieve these vis numbers in a linear way? And as usual I’m open to opinions.

Quote:

Originally Posted by catalinajack

Straight weight, multi-weight, it doesn't matter a wit as to engine longevity as long as the oil is changed when recommended.

What matters is viscosity. Higher vis means longer life. And more residual oil is on the to be lubed parts at start up. A heavy synthetic clings to metal best but viscosity is king re wear.

Nomad Willy · 11-28-2021, 02:36 PM

KnotYet wrote;
“ Interestingly, the engine builder of my 425 HP Ford V-8 gas engine recommended
Rotella T5 in that engine from day 1. So that's what I use. It is 15-40 weight.
________________

I like the 15-40 oil in MV. Thanks for the comment. I’ll take it to the bank .. er garage.
So you use oli manufactured for diesel engines in your gas engine. What does your “builder” think about additive packages meant for diesel engines in gas engines? That’s something I wouldn’t do … normally but w his reco stacked on top of yours holds a lot of water .. or is it oil .. in my book.

Nomad Willy · 11-28-2021, 02:39 PM

Sunchaser wrote;
“I also note Hertz is buying used cars as insufficient new ones can be found. These are amazing times Eric, your Rabbit may well be worth double what you bought it for, clean oil or not.”

Golf actually .. and not this one that I sold.
The one I have now is silver w a 2.Ltr engine.

mike66 · 11-28-2021, 03:12 PM

https://bobistheoilguy.com/motor-oil-101/
A lot of stuff on viscosity, temp, etc. Good read.

rslifkin · 11-28-2021, 04:48 PM

Quote:

Originally Posted by Nomad Willy

What matters is viscosity. Higher vis means longer life. And more residual oil is on the to be lubed parts at start up. A heavy synthetic clings to metal best but viscosity is king re wear.

Thicker oil protects better, but only up to a point. An oil too thick relative to what the engine was designed for may lead to issues if there are any small passages where you may get insufficient flow. Some engine designs are pretty fussy about oil weight, others will tolerate anything within a pretty wide range.

Of course, there's also concern for viscosity at cold start (and resulting wear from poor flow right at startup if oil is too thick). With the same engines I've got in the boat, I'd be running 5W-40 instead of 15W-40 if they were in an application that saw cold weather use.

Ski in NC · 11-28-2021, 04:54 PM

I too drive a diesel Jetta, yr 2001, 1.9ltr, 288k miles. Rotella T6 5-40 for last 200k miles. No issues.

Don't get too hung up with viscosity. Oil viscosity varies a LOT with temperature, whether a single grade or multi-vis. Between the two types of oil, the multi-vis changes less, but between cold and hot engine the vis difference is HUGE.

Don't worry about it. What ever oil you use the car will be a POS before the engine suffers a lube related failure.

I stick with T6 so the "hot" turbo does not coke the oil on hot shutdown. Original turbo still doing fine, so it is working. My Cummins 450 with water cooled turbo gets dino oil (T4).

fgarriso · 11-28-2021, 05:09 PM

Just ask VW

Nomad Willy · 11-28-2021, 05:23 PM

Ski wrote;
“Don't get too hung up with viscosity. Oil viscosity varies a LOT with temperature, whether a single grade or multi-vis. Between the two types of oil, the multi-vis changes less, but between cold and hot engine the vis difference is HUGE.”

Thank you much Ski. Took a long time to come out but this is very important. Oil coolers are golden I’m think’in. And running 30w in my little car with very little difference in idle speed (cold to hot) shows that even w “huge” difference in vis there’s almost no difference in how it runs.

Another thing that’s just a notion w me .. I’m going to mention.
If one started at the recommended vis and went (in vis) both ways the same amount I’ll bet running extra thick oil is FAR better than running extra thin. This is assuming plenty of warm up time running. Re this I’m inclined to think that small changes in vis are also more likely to be good or bad. And if you run just outside the range of recommended vis it’s better to be on the higher vis end. And if you have cold start running issues in mind just warm up longer.

Ski,
How is power (low to mid range) tween the Jetta 1.9 and the 2 Ltr. gas engine. Mine may have issues as it has two flat spots. One low-mid range and the other next to the top end. When I put my foot in it it has more power when I pull my foot back a bit. A NA engine shouldn’t do that I’m think’in. Most people wouldn’t notice … not as noticeable as the flat spot w the 1.8 turbo … usually called “turbo lag”.