I bought a new Acura RSX about six months ago. The manufacturer’s book swears I only need to change the oil every 10,000 miles, regardless of how long it takes me to get there. However, I have been told by the dealership at various times to change it every 7,500, 5,000, or 3,750 miles. Of course, both the dealership and the manufacturer are biased here, so I come to you looking for unbiased opinion. Also, if it matters, I put fewer miles on the car per month than most people do. In six months, I’ve driven just over 4,000 miles.
Look at the definition for ‘extreme’ driving conditions. I don’t exactly recall from my friend’s RSX manual but I distinctly remember him easily falling under that category.
‘Extreme’ conditions warrented 5000 miles/oil change I believe.
I’m not sure why you think the manufacturer is biased, it is in their best interest for your car to run well for many years. Nobody buys cars based on the time between oil changes, so there’s no reason for them to recommend too infrequent changes. Dealerships and shops have a clear reason to recommend more frequent changes.
Follow the manual, and check it closely for extreme or severe driving conditions, things like idling in traffic for a long time count as extreme.
Well for every car there’s an annual $ amount that the dealership, on average, expects as their service income from non-warranty service. A dealership probably takes that into consideration when deciding which car to push onto the vict…err… customer.
This has been discussed to death on the SDMB and always ends up (or should) in GD territory.
The only thing I’ll say about your specific situation is that the car did not come from the factory with synthetic oil, so the recommended change interval should not be presumed to be predicated on the continued use of synthetic oil.
Several points I’d like to make here:
- Dealer service departments tend to push excessive levels of maintenance to fatten their bottom line. Your car will be well-maintained if you listen to them, but you’ll be wasting a little money.
- Modern oils are much more robust than older oils, and the latest standards (ILSAC GF-4 and API SM) ensure that your oil can survive under conditions no passenger car will ever see.
- Honda, the manufacturer of Acura products, defines severe service as:
“SEVERE SERVICE - When most trips are less than ten miles or outside temperatures remain below freezing. When most trips include extended idling or frequent low speed operation … When towing a trailer or driving rough or muddy roads. When operating in areas with road salt or other corrosive materials.” [1] - My observation is that in most cases, if you don’t have a drive to work over 15 minutes or if less than 75% of your drive to work is on freeways or highways, you’re in severe service.
- Most of the world runs longer oil change intervals than Americans do. Most of the world runs thicker oils, too.
- Based on following a web site [2] that has quite a few chemical analyses of used motor oil on it, a lot of drivers have no need for the “3 months or 3,000 miles” interval we’re being sold on. 90% of the analyses I’ve seen show oil that will make it to 7500 miles or beyong with no harm to the engine. The other 10% were engines with leaks, bad seals, or other defects that dated to before their current oil fill.
- The ONLY exception to the above rule was a soccer mom driving a minivan who apparently never drove more than 2 miles at a stretch and spent lots of time idling the car to stay cool with her kids in it. Based on evidence, her oil should have been changed at 2000 miles and would probably have failed at 4000 miles.
- Synthetic base oils are not needed to practice extended oil drain intervals. What is really needed is a strong additive package that will not deplete until you’ve gone 15000 to 30000 miles. You can actually formulate a non-synthetic to last quite a while, but the oil marketplace is mostly divided between “cheap” oils at under $2.50 a quart and “synthetic” oils at around $5.50 per quart. You could actually get additive packages similar to what you see in synthetics by buying oils formulated for semi truck diesel engine operation, like Shell Rotella T.
[1] http://www.hondaautomotiveparts.com/maintain.htm
[2] http://theoildrop.server101.com/cgi/ultimatebb.cgi?
Don’t get me wrong, I understand the underlying reasons, but I find it funny that they classify driving slowly, idling alot and 5 minute drive times as extreme driving. I never thought of the little old blue haired grandma down the block as an extreme driver.
Its all about heat, baby. Granny is running wicked HOT!
Oil cooled engines don’t suffer from low speeds as much as air cooled (such as Porche’s 911 engines up until just a few years ago). However, they still rely on airflow to cool the oil, which short trips and low speeds don’t allow enough of.
Short trips don’t let the engine heat up. Chronic short trips actually breed water contamination. Oil that gets up to full temp tends to burn off water contamination.
The engine oil doesn’t warm up to real operating temperatures on less than a half hour trip, and barely heats up at all in a five minute trip.
Note that your temperature gauge in your car, 9 times out of 10, is gauging COOLANT temperature, not oil temperature. The coolant gets hotter quicker than the oil. Certain more-gadgety cars display both temperatures.
Most modern cars have fan systems on the radiator that allow your car’s cooling system to handle pretty impressive outside temperatures in traffic or idling with the AC up. However, YMMV, and your car might just blow up if you try idling all day in the sun with the AC cranked all the way up in a black car in Texas in the middle of summer.
Conventional motor oils are OKAY as long as your crankcase oil stays under 300 degrees fahrenheit. Past 300 you’ll need to add more cooling or run a good synthetic, as conventional won’t make it 3000 miles in these conditions without sludging up on you.
The most common two ways to get past 300 are multiple-lap racing events (autocross and drag racing won’t generally do it) or the kind of trailering where you spend most of your time with the throttle past the 50% mark. That, or maybe just having neglected radiator maintenance.
What exactly is happening chemically or physically when an oil “fails”.
The shorter interval for low speed/frequent idling also accounts for the amount of engine operating time per mile driven. 60 miles at highway speed is 1 hour of engine time. 60 miles at town speeds is 3 hours of engine time. 60 miles with lots of idling is ?? hours of engine time.
Cars don’t have an “hours” gauge for engine use, only the odometer, so this is a way to get the car in for an oil change at the right time.
Water is a byproduct of combustion and can get past the rings and into the oil. If a car is only used for short trips, the oil doesn’t get hot enough to vaporize the water and the water will oxidize the oil.
Beyond that, the lighter fractions of the oil vaporize and/or burn as the car is driven, causing the oil to increase in viscosity and/or become contaminated with burnt oil; carbon from the cylinders and dirt from the incoming air get past the rings and also contaminate the oil, and the oil molecules can be sheared at they move through the engine (though I have really only heard of this being a problem in motorcycles where the engine and transmission share a common oil sump.) Finally, the additive package “wears out”, though I have no idea what that entails.
I made a post in this thread discussing various ways in which motor oils reach the condemnation limits agreed upon by automakers and oil blenders.
Cheesesteak: as a point of trivia, Ford Motors has indicated that it thinks that one hour of idling is worth 33 miles of driving, at least for purposes of calculating when to change your oil.
Cornflakes, good summary. About additive packages wearing out, what happens there is that the chemicals used as additives in motor oil wear out for largely the same reasons that the base oils wear out as cited in your post. I know that among other reactions, an additive named ZDDP can break down into its constituent elements, which lack its positive traits in the fields of antiwear and antioxidization.
The below quote refers to ZDDP in a hydraulic fluid, but some of the failure modes for the additive are similar [1]:
“Depending on formulation, a common AW hydraulic fluid may contain anywhere from 100 ppm to 500 ppm of ZDDP, as measured by the elemental concentrations of zinc and phosphorus. Subjecting an oil containing ZDDP to high temperatures and high levels of moisture will likely result in significant additive depletion due to hydrolysis - a chemical reaction between the ZDDP molecule and water. Under such circumstances, the ultimate by-products of the hydrolysis reaction will likely be zinc salts and phosphates, which although no longer chemically ZDDP, may remain in solution in the oil.”
[1] http://www.practicingoilanalysis.com/article_detail.asp?articleid=477&relatedbookgroup=Lubrication
I have heard that if a car leaks oil, you can avoid oil changes and simply add oil ad infinitum. I realize you could not really do this indefinitely but could you really just keep adding oil for a long period of time?
pool, you can extend your intervals thanks to a leak, it’s true. Of course, you’ll eventually want to change the oil out.
Some semis actually have designs that intentionally feed motor oil into the combustion process at timed intervals, purely to have the same effect you mention.
If you had a real bad leak, you would probably wind up changing more due to your oil filter’s needs than the oil’s needs. I’ve never seen a credible source suggest the average oil filter is good for more than 15,000 miles, and some sources would lead you to believe they’re only good for 5,000 miles.
I’d recommend an oil filter replacement for every oil change. Remember that Fram™ Oil Filter commercial? It shows a mechanic doing some serious work on a car engine. Basically the point of the ad was, why skimp on the price of an oil filter when it could lead to bigger problems later on? The mechanic says "you can pay me now (for an oil filter) or pay me later (for an engine rebuild).
What’s with the new motor oils being sold for “older engines”? They have the same viscosity rating, IIRC, so what’s the difference?
BTW, great posts above.
That depends on the specific motor oil, and isn’t something I’m horribly versed on.
My best summary based on reading is that the “High Mileage” style oils use:
- Increased levels of detergent, anti-wear and anti-oxidant additives.
- Small quantities of esters for cleaning. Some esters can be highly effective at getting the gunk out of your engine, unsticking stuck reings, etc. Esters are technically “Group V synthetics”, and I’ve seen a few high-mileage formulation that used something like 15% of this synthetic oil base stock in their blend. [1]
Interestingly, the best engine flush I’ve seen on the market [2] is a Group V synthetic. There’s anecdotal evidence that the “High Mileage” oil market segment was born after the vendor in my link 2 demonstrated his product to Valvoline in an attempt to sell out his company. Supposedly a year later Valvoline Max-Life was born.
There are 5 market segments passenger car motor oils fit into:
- Wal-Mart’s Supertech. It’s just like the oils in segment 2, but it costs 50 cents less. Around $1-1.10 depending on region.
- Conventional motor oils. Usually ranging from $1.40 to $2.10.
- Synthetic blends. 15% synthetic; the rest of it is usually a blend of various base stocks from Groups I, II and III. Prices in the $2.25 to $2.75 range.
- Low-priced synthetics. This includes Wal-Mart’s store brand synthetic. It’s made primarily from Group III base stock, and ran around $3.00 last time I checked. There’s another oil in this category, Shell Rotella T Synthetic, but it doesn’t really count as it’s a diesel oil.
- Full-priced synthetics. Mobil 1 is the biggest player here. Prices range from $4.75 to $6.50. A couple of brands are around $8, including Redline. The composition of these motor oils varies. Some are basically Group III products, some (like Mobil 1) are a mix of Groups IV and V. Some are engineered for long oil change intervals. Some are engineered to provide really good protection for normal oil change intervals, such as the newer Mobil 1 that doesn’t have “Extended Performance” on the packaging.
Looking at the above list, it’s pretty obvious that most high mileage products fit into my category 3. They’d be labelled synthetic blends, but that wouldn’t be creating another profitable market niche, would it? 
Before you run a high mileage oil in your car, be aware that some automakers feel that raised levels of certain anti-wear adds may be responsible for poisoning catalytic converters. Other people think that if your car doesn’t burn oil, it shouldn’t matter, should it? The automakers that do hold the concerned position here do have somewhat of a point, given the new super-long warranties on emissions equipment they’re being forced to provide. It’s a controversial topic, but I have noted that the new API SM [3] [4] oil spec restricts these additive levels. You’ll also note that even brand new palettes of many (all?) high mileage oils don’t meet API SM. Just something to ponder.
My car doesn’t have 60,000 miles on it yet, so I don’t have a horse in the high mileage oil race at the moment. For background on my previous posts, I’ve never intentionally done an oil change interval past my automaker’s reccomendation. My calculations say that going with the cheapest oil in my category 2 above at my automaker’s reccomended interval is the most cost-effective option.
[1] A good quick summary of the 5 API-recognized categories of motor oil base oils can be found in the Proactive Management section of http://www.plantservices.com/articles/2005/324.html
[2] Auto-Rx is at http://www.auto-rx.com/ . I have no stake in this company and have not used its products, but I’ve seen indepent tests that impressed my socks off with emissions improvements, dyno testing and pictures of dramatically cleaned engine components.
[3] What the heck does API SL, SM, etc mean anyway? http://api-ep.api.org/filelibrary/API_MotorOilGuide_2004.pdf <---- Warning, PDF
[4] The literal specs for API SM are here: Infineum | 404