How long can I go with these oils?

[Torquejumper]

How long can I go with these oils before my next oil change? Both cars are driven on the highway 90% of the time.

-2003 Nissan Sentra Ser Spec V (Rotella T6 synthetic 5w-40 with supertech oil filter) *This car burns oil, 1qt per ~1800-2000 miles*

-1998 Nissan Maxima GLE (Supertech conventional 5w30 with fram oil filter)

 

[azsynthetic]

I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself. On the Maxima, every 5K is safe.

 

[Kuato]

Originally Posted By: azsynthetic
I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself. On the Maxima, every 5K is safe.



Depends on the capacity of the Sentra, doesn't it? If it's 4 quarts, it's almost like changing every 8k. Torquejumper if you decide on this pattern, don't forget to change the oil filter every 5k or so.

With Supertech on the '98, personally I'd do a 3000-3500 miles UOA on it before I went out too far, although as azsynthetic said 5k is probably ok. (I just like to be sure)

 

[Scienceman]

Senta...once a year to change any dirt and the oilfilter. I would start using a better quality one. As far as the Maxima..with what oil and filter combo I would say 3000 miles.

 

[hate2work]

Originally Posted By: azsynthetic
I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself.


This is not true, don't do this.

OP, 4-5k on the Maxima is fine. On the Sentra, change it every 6-8k.

 

[d00df00d]

Originally Posted By: azsynthetic
I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself.

No.

If the oil is being leaked, you might be adding fresh stuff but there's always a little of the old stuff in there. If there are contaminants, they may build up over time. This is basic grade school science class stuff.

If the oil is being burned, you have that problem PLUS the fact that the combustion doesn't burn all parts of the oil evenly and is likely leaving byproducts behind. This might even require SHORTER oil change intervals than if it weren't burning.

 

[Scienceman]

Originally Posted By: DT466E_bus
Senta...once a year to change any dirt and the oilfilter. I would start using a better quality one. As far as the Maxima..with what oil and filter combo I would say 3000 miles.
Originally Posted By: hate2work
Originally Posted By: azsynthetic
I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself.


This is not true, don't do this.

OP, 4-5k on the Maxima is fine. On the Sentra, change it every 6-8k.
Agreed. The filter has to be changed after a certain amount of time.

 

[sangyup81]

Originally Posted By: azsynthetic
I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself. On the Maxima, every 5K is safe.

I say at least change it out every time you change the filter

 

[chubbs1]

Listen, there can be no staight answers here, we are takin this stuff with little info to go by...

First go by your car manufacturers requested interval for normal service. That is the safe "err on the side of caution answer"

Second: after you have done your said run. get a used oil analysis on both cars and see if the said oils are performing the way they should and extend your OCI's from there.

That is the safe and sound way to do it, rather than guesswork and conjecture, we have no idea what shape those engines are in. And they might not be that good if you use a fram filter...POW...ZING. Just had to get that jab at ya, welcome

 

[azsynthetic]

Originally Posted By: d00df00d

If the oil is being leaked, you might be adding fresh stuff but there's always a little of the old stuff in there. If there are contaminants, they may build up over time. This is basic grade school science class stuff.


No one teaches oil leak in grade school so apparently you are just dreaming. Contaminants builds up over time, hahaha, now that is funny. Contaminants always build up over time no matter what, but you are getting rid of it at a 20-25% rate every 2K which is better than keeping it in there for the whole OCI duration.

Originally Posted By: d00df00d
If the oil is being burned, you have that problem PLUS the fact that the combustion doesn't burn all parts of the oil evenly and is likely leaving byproducts behind. This might even require SHORTER oil change intervals than if it weren't burning.


There is no if about it, the OP said the car burns oil. At the rate of consumption it is no worse than the oil or MMO that I and others have added to our gas tanks every fillup for better mileage. No vehicle has 100% combustion capability so that is why they invented the EGR system. You just worry too much about nothing.

 

[Triple_Se7en]

I would run conventional oil in both vehicles and switch from Fram / Supertech filters to Purolator Classics.

 

[kcfx4]

Ill get beat on for this im sure, but if my vehicle were using oil, id try a thicker oil

 

[ronrackley]

Originally Posted By: Torquejumper
How long can I go with these oils before my next oil change? Both cars are driven on the highway 90% of the time.


If you are in an area where you do not have to start the car with the outside temperature below about, oh, 20 - 30 degrees F, I'd switch the Sentra over to Rotella conventional 15w40. Both it and the synthetic 5w40 Rotella are excellent oils. The conventional will not leak as much if a leaking seal or gasket is the problem.

Adding oil regularly does tend to replenish the additives, which could give you added confidence in extending the drain interval a bit, but I'd still change it and the filter on schedule to get rid of contaminates. [My schedule with Rotella is normally 5,000 miles - except I've recently gone to 10,000 on my Cadillac Northstars because they hold 7.5 quarts instead of the normal 5 and used oil analysis show them to be easy on oil.]

 

[d00df00d]

Originally Posted By: azsynthetic
No one teaches oil leak in grade school so apparently you are just dreaming. Contaminants builds up over time, hahaha, now that is funny. Contaminants always build up over time no matter what, but you are getting rid of it at a 20-25% rate every 2K which is better than keeping it in there for the whole OCI duration.

Looks like the school system is in worse shape than I thought. Not your fault.


Here's how it works. The day you put the oil in, you have 4 fresh quarts. Let's say every 2,000 miles, 1/4 of the sump leaks out, and you add a quart.

At 2,000 miles, 3 qts are 2k miles old, and 1 qt is fresh (from top-off.)

Every 2,000 miles after that, you multiply each number by 0.75, and add one fresh quart.

So, at 4,000 miles, 2.25 qts are 4k miles old, 0.75 qt is 2k miles old, 1 qt is fresh.

At 6,000 miles: 1.69 qts are 6k miles old, 0.56 qt is 4k miles old, 0.75 qts is 2k miles old, 1 qt is fresh.

And so on.


See how that works? At all times, the majority of the oil in the engine is old. The oldest part gets smaller and smaller but it never goes away. This is why you eventually have to change the oil, even if it is leaking/burning and getting topped off. You could definitely run longer than if you weren't leaking and topping off, but you couldn't run forever.

 

[Geonerd]

Originally Posted By: d00df00d
Originally Posted By: azsynthetic
No one teaches oil leak in grade school so apparently you are just dreaming. Contaminants builds up over time, hahaha, now that is funny. Contaminants always build up over time no matter what, but you are getting rid of it at a 20-25% rate every 2K which is better than keeping it in there for the whole OCI duration.

Looks like the school system is in worse shape than I thought. Not your fault.

Here's how it works. The day you put the oil in, you have 4 fresh quarts. Let's say every 2,000 miles, 1/4 of the sump leaks out, and you add a quart.

At 2,000 miles, 3 qts are 2k miles old, and 1 qt is fresh (from top-off.)

Every 2,000 miles after that, you multiply each number by 0.75, and add one fresh quart.

So, at 4,000 miles, 2.25 qts are 4k miles old, 0.75 qt is 2k miles old, 1 qt is fresh.

At 6,000 miles: 1.69 qts are 6k miles old, 0.56 qt is 4k miles old, 0.75 qts is 2k miles old, 1 qt is fresh.

And so on.


See how that works? At all times, the majority of the oil in the engine is old. The oldest part gets smaller and smaller but it never goes away. This is why you eventually have to change the oil, even if it is leaking/burning and getting topped off. You could definitely run longer than if you weren't leaking and topping off, but you couldn't run forever.


Coping a snotty attitude isn't helping your case, mister.
After enough iterations, the system will eventually reach a stable balance, with the very 'old' oil making up a vanishingly small percent of the total. With good filtration and a constant influx of new oil to fortify the TBN, etc., the oil may never reach a point where it us unusable. There will certainly be no further 'build up of contaminants.' If the oil is serviceable at that point, something best determined by UOA, the OP would be fully justified in never changing the oil again.

 

[ronrackley]

Originally Posted By: Geonerd
Originally Posted By: d00df00d
Originally Posted By: azsynthetic
No one teaches oil leak in grade school so apparently you are just dreaming. Contaminants builds up over time, hahaha, now that is funny. Contaminants always build up over time no matter what, but you are getting rid of it at a 20-25% rate every 2K which is better than keeping it in there for the whole OCI duration.

Looks like the school system is in worse shape than I thought. Not your fault.

Here's how it works. The day you put the oil in, you have 4 fresh quarts. Let's say every 2,000 miles, 1/4 of the sump leaks out, and you add a quart.

At 2,000 miles, 3 qts are 2k miles old, and 1 qt is fresh (from top-off.)

Every 2,000 miles after that, you multiply each number by 0.75, and add one fresh quart.

So, at 4,000 miles, 2.25 qts are 4k miles old, 0.75 qt is 2k miles old, 1 qt is fresh.

At 6,000 miles: 1.69 qts are 6k miles old, 0.56 qt is 4k miles old, 0.75 qts is 2k miles old, 1 qt is fresh.

And so on.


See how that works? At all times, the majority of the oil in the engine is old. The oldest part gets smaller and smaller but it never goes away. This is why you eventually have to change the oil, even if it is leaking/burning and getting topped off. You could definitely run longer than if you weren't leaking and topping off, but you couldn't run forever.


Coping a snotty attitude isn't helping your case, mister.
After enough iterations, the system will eventually reach a stable balance, with the very 'old' oil making up a vanishingly small percent of the total. With good filtration and a constant influx of new oil to fortify the TBN, etc., the oil may never reach a point where it us unusable. There will certainly be no further 'build up of contaminants.' If the oil is serviceable at that point, something best determined by UOA, the OP would be fully justified in never changing the oil again.


Actually, for rigorous analysis using classical mathematics instead of an iterative numerical solution you need differential equations - and that's taught in the second year of engineering school.

The contaminate level would follow what is called a sigmoid curve and over time asymptotically approach a level lower than would be the case if no oil were being replaced - how much lower depending on the rate of replinishment.

 

[AzFireGuy79]

You are "speculating" with alot of "maybes" and "ideal" scenarios. I'm going to assume this topic is beyond your qualifications or pay grade, if you will. I'm in no way trying to insult you, its just much too common place for people here to make statements based on what should work.

 

[d00df00d]

Originally Posted By: Geonerd
After enough iterations, the system will eventually reach a stable balance, with the very 'old' oil making up a vanishingly small percent of the total. With good filtration and a constant influx of new oil to fortify the TBN, etc., the oil may never reach a point where it us unusable.

Theoretically, sure.

Now, in order for that to support a statement like...
Originally Posted By: azsynthetic
I would not change oil at all in the Sentra. A quart burned every 2K is an oil change by itself.

...at least one of the following must be true. Either:

A. azsynthetic has deep insight into all the variables involved, has run the right math, and is qualified to make that determination; and/or
B. The possible outcome you are suggesting is vastly more likely than not to play out in the majority of cases.

I wouldn't take either bet, frankly. But that may be a difference of opinion.

 

[Kuato]

Good discussion!


Both analyses of what happens to oil over time are correct; not changing increases the amount of old oil in the sump AND eventually (with consistent OCI) the level of old vs new will stabilize, or nearly so (approaching stability, for those with math background)


However one possibility that has been overlooked is the chance that the oil is getting burned off, but the contaminants are not. In this case, the contaminants would in fact get more and more concentrated over time. With this sort of possibility, it would be advisable to have a used oil analysis done periodically to insure this was not happening, before never changing the oil again.

 

[TFB1]

Originally Posted By: fredjacksonsan
Good discussion!
However one possibility that has been overlooked is the chance that the oil is getting burned off, but the contaminants are not.

True, but from a country boy perspective, I'd think the contaminants suspended within the oil are mostly going out the tail pipe... No doubt the remaining oil in the crank case is continually building contaminants but at some point, there will be a equalization where the ratio after the top off will nearly same after each add... Whether the oil is still suited for service, only a used oil analysis before the add can tell...

If the oil is being used because of failing valve stem seals or a leak, there won't be nearly as much oil contamination as there would be from worn piston rings that were allowing blow by into the crankcase... Sooo as already pointed out, without more info this is defiantly not a one solution fits all condition...