Why not strictly mileage for oci?

[TxHeat]

Can someone explain why we still use the xx miles or xx months, whichever comes first, formula to set oil change intervals?

Does oil really break down or lose its ability to do its job by just sitting in the crankcase? I suppose there was a time that was true, but is it still with all the new technology being used in the production of modern engine oil?

Shouldn't the oci be decided strictly by mileage, or engine hours if you do a lot of idling?

 

[bullwinkle]

Short trips definitely cause moisture (and acid) buildup, shortening oil life and raising the risk of sludge-BUT, on vehicles that are thoroughly warmed up regularly, just not driven often-I agree to some extent. The age-old BITOG battle between lengthening OCI & engine protection!

 

[d00df00d]

I think the time variable is just to account for the fact that not all miles are equal. 3,000 miles of 5-minute trips are quite different from 3,000 miles of highway driving.

You're right to point out that time is quite a crude measure. Engine hours is much better, IMO; it still doesn't account for differences in HOW the engine is used during its on-time, but at least it accounts for WHETHER the engine is used.

I suspect that this is why OLMs are gaining popularity. They gather data from the engine's computer about how the engine is running; sometimes they also read from actual sensors in the oil pan to get a (VERY) rough idea of how the oil seems to be doing. In theory, this is the best possible kind of OCI indicator. The problem is, many (I'm not sure if it's most) people have a hard time trusting a black box, especially if it tells them they can stretch their OCIs farther than they thought possible (which OLMs frequently do).

 

[GROUCHO MARX]

Hours on the engine differ greatly in low mph situations.

 

[electrolover]

im in agreement with the others, short trips kill your oil thats why the time thing is there. if an old woman just drives to church and the grocery store she needs to change the oil more often than someone who drive a 50 mile commute to work. (miles wise that is) so the easy way is just to say 3 months or 3k which ever comes first rather than try to explain severe service operations to her.

 

[TxHeat]

I missed the 15 minute cutoff for edits by 1 minute!

I wanted to add;

So, is the current xx miles/xx months the best we can do short of used oil analysis, or is there a better method?

As d00df00d pointed out, OLMs may ultimately be the answer. Especially if they become sophisticated enough to actually provide the condition of the oil.

Over fifty years of driving I changed my car's oil every 3000 miles or 3 months whichever came first. Now, thanks to Bitog!, I know I've wasted a lot of oil and filters and money over all those years!

I guess though, on the upside, my wife's 2008 Fusion specs 7500/6 months for normal or 7500/5 months severe service OCIs. So the manufacturers are reflecting today's better oils and better engines in their maintenance specs.

So maybe my question is becoming or has already become moot!

 

[ltslimjim]

^Which you just bring up again the need for application specific regimens, whether it be miles driven/time inside the engine etc. If you started modding the Fusion and took it to the track a couple of times, you'd definitely not want to go 7,500 or 5 months. Depending on how much to the extreme you push your vehicle can change all of that, even the 'severe' service recommendations. I find it's helpful just to re-visit and consider what has the vehicle been through during any current OCI.

 

[FL_Rob]

Ok then, split the difference,3mo or 6000 miles.I know it's generalizing but I think its sound.No?

 

[d00df00d]

Any OCI at a fixed time or mileage, without a good deal of research behind it, is a stab in the dark.

 

[tig1]

For 33 years I have changed oil every 10K regardless of the time of the year, number of months(6-8-10 etc), % of town vs hwy miles driven. In all this time I have put a lot of miles on various type of engines, and never had an engine to show visable signs of wear, or had an engine that looked less than clean through the oil fill hole.

 

[demarpaint]

I did pretty much the same as tig1, only shorter runs. Then I rethought the strategy when I joined Bitog. Then I had to rethink the strategy again when I bought the Jeep, and had a warranty to deal with. My engines were always clean, at least the engines I had to open up to replace a VC gasket, or a pan gasket.

 

[The_Jeff]

The month/mileage rule often assumes you only own one vehicle and if you run out of time first it's because you've been commuting two miles and therefore beating on the oil.

I've had an occasional beater truck or other 3rd/4th vehicle see 18 month OCIs but get warmed up nicely when run.

 

[Malo83]

5K or 6 mos whichever comes first, pay a little now than a lot later

 

[Artem]

I'm personally against the whole X miles or X months baloney.

It would be nice if every car owner was educated enough to use common sense to determine proper OCIs based on driving conditions / oil & filter quality.

^ of course that's just wishful thinking, seeing as 90% of the drivers on the road don't even know the basic car maintenance safety rules of properly inflated tires and overall vehicle condition in general.

 

[ahoier]

My real concern is, does oil actually "break down" simply sitting in the crankcase?

When I purchased my new (to me) Dodge Aries, I went to the ladies house, MMO in hand, having already seen pictures, etc.....so I added the pint of MMO to the engine to "rejuvinate" the "old oil" - the vehicle hadn't been driven for 2+ years. Drove the car around for a good 2 weeks, MMO in the crankcase, and the oil didn't look too bad coming out, wasn't overly "thin" or extremely dirty.

 

[Artem]

Originally Posted By: ahoier
My real concern is, does oil actually "break down" simply sitting in the crankcase?

When I purchased my new (to me) Dodge Aries, I went to the ladies house, MMO in hand, having already seen pictures, etc.....so I added the pint of MMO to the engine to "rejuvinate" the "old oil" - the vehicle hadn't been driven for 2+ years. Drove the car around for a good 2 weeks, MMO in the crankcase, and the oil didn't look too bad coming out, wasn't overly "thin" or extremely dirty.



Technically, yes it does break down over time, as with any organic earthly material.

Once new oil is mixed with some remaining old oil and gets circulated throughout the engine it gets "contaminated" so to speak with combustion byproducts which contain acids, etc, etc.

Those acids will break down the oil in the long run... how long that time frame actually is, is unknown.

I've seen far too many UOA on oils which have been in service for more then a year and the results weren't bad. Of course no TAN count was present, to show the oils acidity but still, wear rates didn't dramatically increase after the 12 month threshold.



P.S. Adding any type of additive in hopes of "rejuvenating" used, old engine oil seems silly to me.

 

[Spector]

in my case, drive the car 17 miles one way, highway speeds but will change oil at 3000-5000 miles in 18 months. Obviously not driven every day.

 

[Ken2]

GM's Oil Life gizmo does it right. The unit is based on a bell shaped curve. Short, cool trips are hard on the oil. Hot & heavy hauling is hard on the oil. Light duty highway or boulevard cruising is easy on the oil.

3 months or 3000 miles is very important...to the profit of the Iffy Lube places.