[tateos]

2000 DTS - I changed the oil 16 months ago to 5W-30 Mobil One. I've driven it about 6,000 miles and the OLM shows 64% engine oil life remaining. All highway and suburban driving, in the AZ desert. So with 64% life remaining, why do I need to change the oil? I mean, it's not like there's fruit or milk in the oil that's going to go bad - it's just oil, right?

On my '97 ETC I changed the oil most recently at about 5,000 miles and 14 months, and the OLM showed about 20% life - that car has always indicated about a 7,500 mile oil life.

 

[Krashed989]

Combustion blow-by? I figure that no matter how good the oil is, it's still going to get the same amount of contamination from blow-by gasses. So regular oil changes are a must IMHO. I wonder how well little particulates of carbon serve as lube.

 

[tateos]

Combustion blow-by? I figure that no matter how good the oil is, it's still going to get the same amount of contamination from blow-by gasses. So regular oil changes are a must IMHO. I wonder how well little particulates of carbon serve as lube.

Yeah, but that amount of blow-by or any other contamination must be the same whether it is a month or a year or two years, no? I am not arguing - just trying to find a reason for the yearly oil change. Maybe it's for people that make infrequent and short trips? That's not me - most of my trips are 30 miles or more.

 

[Krashed989]

I would think it should be the same... The amount I guess just depends on how you drive and how much you drive. If you left the car in a warehouse for 5 years I dont think the oil would go bad or anything. At the most, just condensation in it from sitting for so long.

At the shop I work at, we have a customer with a chevy s10 that lives kinda far up the mountain. When he comes for an oil change, the first thing that comes out of the pan is about a pint of water. We've tested it for blown headgaskets a few times, but eventually came to the conclusion that it was just condensation (and a lot of it).

I'm not arguing either... mostly just speculating.

 

[Ranger]

Personally I see no reason to change it. I think you are right. The one year thing is for the short tripper, but then the OLM would tell him to do that anyway So I think the one year thing is for older short trip cars without an OLM.

 

[Submariner409]

One reason for the "12,000 miles or annually, whichever occurs first" is that the oil itself is OK - blowby products in a modern engine in good condition are the least of anyone's worries - but the additive and detergent packages contain volatiles which are depleted by not only engine usage but also by the evaporation caused by heat and PCV operation.

Just as in coolant, you change oils primarily to maintain the additive package.

 

[tateos]

That is a good insight, Sub, I appreciate your input, I really do, but isn't the engine pretty much sealed? I mean, how much evaporation could possibly occur? When running, sure, and the OLM takes that into account.

 

[STSS]

I know people are looking for an understanding here, but are we talking about enough money/trouble to not do it? Seems like awful cheap insurance to me.

 

[Submariner409]

Take a SWAG (Scientific Wild-Ass Guess) at what the crankcase temperature and vapor level is at 70 mph, and factor in the staggering amount of air that PCV pulls through the engine, and you'll have an indication of just how much volatile evaporation really occurs.

EVERY time you shut down, 12 months of the year, that crankcase cools and draws air back in - through both ends of the PCV - causing some internal condensation. The one or two open cylinders draw ambient air in from the intake and exhaust, creating some level of condensation in one or two cylinders. (You can literally blow air into either the intake or exhaust of a V-8 and have it come out the opposite: one or two cylinders are always open due to valve overlap.)

PCV is wonderful: It removed the primary cause of "sludge" - no air movement through the crankcase except that provided by blowby forcing crankcase gasses out through the road draft tube. (Which used to be attached to a valve cover, which is why the other valve cover filled with enough crap to cause the rocker arms to carve their own operating channels in the gunk.)

Don't forget that the OLM guidelines in the 2000+ FWD Northstars are "12,000 miles or one year, whichever occurs first". Under normal rural driving my OLM is always above 50% at oil change. A city driver may well see less %. .............and we know from experience and study that the OLM has a large safety factor built in. Somehow, running the same oil in a gasoline engine (without onboard active purification) for a year and a half is heretical. I'm far too anal to try it.

 

[tateos]

Yeah - some good points. We don't have condensation here in Phoenix like you do - it's probably 8% humidity here today! The oil looks and smells great, and it is Mobil One Synthetic, but I guess I'll change it this Fall when it gets cooler here in Phoenix, in spite of what the OLM says

 

[orconn]

All the points Sub makes are very good and valid, so is the one mentioning relative inexpensiveness of an oil change (even with synthetice oil). I think changing the oil every 12 months or 12,000 miles (or when the OLM indicates a need) just makes good sense from an overall car maintnence point of view.

 

[zonie77]

A lot of good points. I used to change oil by 3000 miles, so that was usually every couple of months. Now I go longer because I'm lazy!!!! LOL!!!

I just changed the oil in my pickup tonight and realized it was 7 months! I'm not sure of the mileage but probably less than 6K.

I feel more frequent oil changes with premium dino oil is better than less frequent with synthetic. You cannot tell when the additive package fails and I'm not much of a gambler. Even when I use a full synthetic I don't let it go over a year...just MHO.

Tateos, I changed it at 9:30 PM ....still HOT! I must be crazy.

 

[Submariner409]

Last fall, before a run to Florida and back, I changed the 5W-20 (!) oil in the truck with my usual Pennzoil Platinum synthetic and a WIX 51516 filter (same size as a Northstar filter - tiny). Ran 6,300 miles to two weeks ago and did it again. Sent the clean, clear sample off to Blackstone and it came back Monday - nothing in the oil, wear-wise or coolant-wise, and the additive package was still high. All Shell 87 octane and not one drop of oil used. Not one drop. The truck is amazing.

The next change will be in early March, 2010. Just did the car, too, so it will also go to next March. It ain't like "Kendall, The 2,000 mile oil !" (The fist with 2 fingers logo - that's its meaning.....)

 

[Patrick7997]

Oil is cheap insurance.... Cheap cheap cheap.

Why look for trouble??

 

[tateos]

A lot of good points. I used to change oil by 3000 miles, so that was usually every couple of months. Now I go longer because I'm lazy!!!! LOL!!!

I just changed the oil in my pickup tonight and realized it was 7 months! I'm not sure of the mileage but probably less than 6K.

I feel more frequent oil changes with premium dino oil is better than less frequent with synthetic. You cannot tell when the additive package fails and I'm not much of a gambler. Even when I use a full synthetic I don't let it go over a year...just MHO.

Tateos, I changed it at 9:30 PM ....still HOT! I must be crazy.

Yeah - you are my neighbor, sort of. I am in Fountain Hills - I think you said you are in Cave Creek?

 

[tateos]

I agree with everyone that it's no big deal, bother or cost wise - just looking for a real reason why oil is OK at 11 months and not at 13 months, when the OLM says it's OK.

 

[JohnnyO]

Just an average time factor for the reasons mentioned, and again, it's not like it costs a lot. I change the oil in my mother's '99 once a year in December when they leave for Florida, OLM is typically around 65%. Then it sits for four months until they come back.

P.S. I use Valvoline Max Life even though the car does not have a lot of miles on it. Seems to slow down the oil burning somewhat.

 

[tateos]

I just thought of this: I wonder if GM said 1 year, in case the OLM gets re-set by accident, sometime during the year?

I actually think I may have done that once on my wife's car - it's a Pontiac and different from a Cadillac and easy to do. Maybe that's it.

 

[STSS]

Even before 5K oil changes, wasn't it "3K or 12 months"?

 

[Submariner409]

Suppose you changed the oil/filter yesterday. Drove about 25 miles after, and laid up the car for 10 months. Given the heating and cooling of normal daily temps during that time, a significant amount of condensation may have formed in the engine. BUT, when you once again start the car next May, what does the OLM say ??? And how comfortable are you driving with oil that has been subjected to a LOT of surface area exposure while just sitting in the pan ??

Minimum oil changes are now at or over 7,500.......by the manuals, not the dealer come-ons or your local QuickFlop that makes money by the quart. The national average yearly mileage is currently 12,500 miles/year, so the 3,000 figure has been obsolete since 1946 (and 3,000 was the average for a set of tires........).