: Yearly engine oil changes really necessary?



tateos
07-06-09, 10:06 PM
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
07-06-09, 10:19 PM
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
07-06-09, 10:22 PM
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
07-06-09, 10:38 PM
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
07-06-09, 10:39 PM
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
07-07-09, 11:44 AM
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
07-07-09, 01:49 PM
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
07-07-09, 05:23 PM
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
07-07-09, 06:58 PM
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
07-08-09, 02:59 PM
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
07-09-09, 06:42 PM
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
07-15-09, 02:59 AM
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
07-15-09, 10:36 AM
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
07-15-09, 11:36 AM
Oil is cheap insurance.... Cheap cheap cheap.

Why look for trouble??

tateos
07-15-09, 04:40 PM
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
07-15-09, 04:43 PM
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
07-15-09, 04:52 PM
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
07-15-09, 09:10 PM
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
07-15-09, 10:02 PM
Even before 5K oil changes, wasn't it "3K or 12 months"?

Submariner409
07-15-09, 10:03 PM
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........).

zonie77
07-16-09, 04:04 PM
I wonder what the cost to do a full chemical evaluation on an oil sample is. Not just ph but a full test of all the additives. Probably more than a few oil changes! LOL:stirpot:

tateos
07-16-09, 06:51 PM
zonie - how much condensation can we really have here in the desert with 8 percent humidity? OK, in the monsoon it could jump up to 30%!

Bigdadcad
07-16-09, 07:11 PM
I was a lubrication engineer for two oil companies for 24 years. The best way to determine oil change intervals is to submit a sample to an oil analysis lab on a periodic basis. As an independent consumer you would probably pay over $25 for this analysis. Half the cost of an oil change for sythetic.

All of the above posts are valid, but just consider that anything can happen over time, such as a coolant leak, which is often catastrophic and an oil analysis may not predict. With a proven synthetic like Mobil 1, oxidation is usually not a factor. It has an excellent additive package which is not normally depleted.

The benefits of sythetics are numerous, even at 4 to 5 times the cost. In cold climates the oil feeds the upper engine more rapidly than mineral based oils. In hot climates oil degradation is much less than its mineral based counterparts.

In my opinion, miles, and how they are driven, are more important than time when determining an oil change. I put 287,000 miles on an 87 pathfinder, 3.0L, used Mobil 1, and changed oil every 20,000 miles. Average mileage was 3500 miles per month. This was the optimum oil change interval when contaminants and wear metals started to approach oil change limits. I never had a physical oil condition, such as viscosity increase/decrease, oxidation, contamination, or additive concerns. I submitted an oil sample about every two months, 6-7000miles.

Filters are also a factor. Buy the best you can. They can deteriorate under high viscosity loads, high contaminant loads, etc. Once you blow a filter and create a bypass condition, all bets are off. You will notice decreased oil pressure if you have a pressure gauge.

Hope this helps. It is hard to make a general recommendation due to the variety of conditions an oil is susceptible to experiencing.

Submariner409
07-16-09, 09:16 PM
Blackstone Labs charges about $25 + your sample postage for spectral analysis, additives, solids, a couple of others. Plenty of info for the average gasoline engine test analysis.

zonie77
07-16-09, 11:02 PM
zonie - how much condensation can we really have here in the desert with 8 percent humidity? OK, in the monsoon it could jump up to 30%!


I agree, my point was how does time affect the other components in the additive package? I don't know and I'm not paying to find out so I just change oil more often.

codewize
07-16-09, 11:40 PM
The crankcase is not sealed, far from it actually.

On the other hand it sounds like if you just drive your cars more this wouldn't be an issue. go ahead and put 15k a year on the car then there wont' be any question about why or when to change the oil.

Submariner409
07-21-09, 06:42 PM
Lots of ideas, but maybe a Moderator will move this into a new thread titled "Exhaust system for 1997 STS ?"

If you go into a running thread with questions far removed from the topic that's "hijacking" - not bitching, just informing.

Ranger
07-21-09, 11:06 PM
Unable to move it, but I'll PM him with a copy so he can repost.

rlphbgby
07-23-09, 03:42 PM
OK now I'm lost. I thought your suppose to change your oil every 3,000 miles? Is this not true?

Ranger
07-23-09, 05:31 PM
3000 miles! That is 1960's advice. Jiffy Lube will still tell you that for obvious reasons. With today's oils and engine technology you can go much longer. Your car (and most) have an oil life monitor that will tell you when to change oil based on your driving conditions. It is very accurate and has a 100% safety margin built into it. Pre 2000's where capped at 7500 miles and the 2000+ is capped at 12,500. You can trust it. Do a search for OLM or Oil Life Monitor and read up. 3000 mile changes are a waste of time, money and oil.

Submariner409
07-23-09, 07:11 PM
riph, Have you ever toggled through the DIC messages to look at your OLM ? If not, who is resetting it at these 3,000 mile ( :eek: ) oil changes ??

As Ranger posted, we're a long way from "Kendall, the 2,000 mile oil !".