Oil Change interval

[CDW6212R]

As far as engine protection, replacing air filter more often is actually worse than letting it get dirty. An air filter is least efficient when it is new and increases in filtering efficiency as it gets dirty.

Quality air filters don't need to be full/dirty to filter properly. They filter very well all of the time, until the restriction(dirty) affects A/F ratios.

Fabric filters like K&N let too much dirt through, their high airflow is a result of poor filtering. The oil applied helps to hold/attract dirt, and as they get a little dirtier, the filtering is better than new.

The conclusion from all of that should be, don't buy K&N air filters.

I prefer Amsoil EA air filters, which can last up to four years. They are dry, sturdy enough that proper maintenance includes vacuuming them once a year. Unfortunately they stopped making those for OEM applications, they only now come in universal sizes.

I had my 99 SOHC 4.0 running on the same Amsoil Signature oil for over 9,000 miles, with the EA air filter. That oil I checked regularly, every 3-4 weeks etc. It was nearly clear until one day, it was pitch black. I was puzzled, paused to think of why, and then I checked the air filter. I have a Volant air cleaner in that truck, and the EA air filter had fallen off, the clamp was not on tight enough. I stopped using the Amsoil oil at that time, didn't have any on hand that day when I got the black oil out. I will do that again very soon when I get the transmission rebuilt.

That engine didn't use oil to speak of, so extended change intervals is possible given quality oil and air filters, and very little oil consumption.

 

[Odrapnew]

Quality air filters don't need to be full/dirty to filter properly. They filter very well all of the time, until the restriction(dirty) affects A/F ratios.

Fabric filters like K&N let too much dirt through, their high airflow is a result of poor filtering. The oil applied helps to hold/attract dirt, and as they get a little dirtier, the filtering is better than new.

The conclusion from all of that should be, don't buy K&N air filters.

I prefer Amsoil EA air filters, which can last up to four years. They are dry, sturdy enough that proper maintenance includes vacuuming them once a year. Unfortunately they stopped making those for OEM applications, they only now come in universal sizes.

I had my 99 SOHC 4.0 running on the same Amsoil Signature oil for over 9,000 miles, with the EA air filter. That oil I checked regularly, every 3-4 weeks etc. It was nearly clear until one day, it was pitch black. I was puzzled, paused to think of why, and then I checked the air filter. I have a Volant air cleaner in that truck, and the EA air filter had fallen off, the clamp was not on tight enough. I stopped using the Amsoil oil at that time, didn't have any on hand that day when I got the black oil out. I will do that again very soon when I get the transmission rebuilt.

That engine didn't use oil to speak of, so extended change intervals is possible given quality oil and air filters, and very little oil consumption.

Just bolding the 2 responses I have.

I never said a quality filter needs to be dirty to perform well. Just stating a filter is least efficient when it is new. A little dirt on the filter is good for filtering efficiency.

I'm curious at what restriction it would impact air/fuel ratio with fuel injection on a car/truck. My motorcycle(fuel injected) filter was so restricted, it wouldn't run without 1/2 throttle input. It was odd since it ran just fine on a Friday, and wouldn't start the next Monday. The only thing I noticed was a significant power increase when I put a new one in. I saw no impact to fuel mileage when I changed it.

I agree, K&N is terrible for engine protection.

 

[bigdude2468]

A dirty filthy plugged air filter will not affect air fuel ratios. The mass air flow sensor has no idea what an air filter is. All it knows is based on how much air is passing by the engine needs this much fuel to run efficiently/ It can certainly affect performance but not efficiencies or MPG.

 

[CDW6212R]

That is another myth, that the computer magically knows what the best A/F ratio is, and never deviates from that. Wrong, many things affect the actual A/F ratio, and the PCM is not perfect in achieving the ideal ratios or ignition timing. Many things cause the actual fuel and timing to be off from ideal. The computer programming is not perfect to start with. You can take any car from the last 30 years and have the PCM re-tuned. New or old car, the performance and fuel economy will improve. What does that mean, it means the original programming is not ideal. So why is it surprising to think little changes will also effect economy etc?

My comments like most people's, are generalities. The computer is very good, but it's not perfect. Ideally it it, but it is not. Same goes for the air filter, the oil brands, oil filter etc, etc.

Take everything with a grain of salt is the saying, bottom line, use common sense and apply good logic. Just because ideally an air filter cannot affect A/F ratios, is no reason to never change the filter. By that thinking, less air will be injected, and ideally that means the PCM will compensate perfectly, and result in less fuel used, since less air is being consumed.

Thus better fuel economy, by that logic, ... no, that is not how reality works. I live in the world of logic and reality, where smart decisions should result in better outcomes. Change the air filter, as often as you can think of doing it regularly. For some people, that might be twice a year, for others, that could be every 2-3 years. Everyone should write down their maintenance items, when anything is changed. Then you can check that log and figure out what needs to be done next. I used to have a mileage log for each of my vehicles, and I'd use them to do maintenance properly. Now I rely on my memory and how each car is doing. One way is best, the others end up costing more money or having some old parts missed, and end up with preventable symptoms. Do what you want to.

 

[Odrapnew]

Lots of truth in above post.

I am curious at what point a modern auto would see an impact on fuel economy ( i.e. AFR). I personally saw no change in fuel economy with my fuel injected motorcycle.

Under closed loop engine control, fuel target is stoich. Under open loop, that's where you'll see the most variability.

I believe many people change/clean filter more often than they should. It's also a repair shop's tactic to say a dirty filter needs to be changed ($$$ for them). In truth, the filter should be changed based on restriction set by the engine manufacturer, unfortunately most (all?) auto manufacturers don't publish that restriction or a means to measure so they just specify a general change interval.

Since I drive on paved roads, I'll stick to the ~40k filter change intervals knowing that my engine is getting more protection with a partially dirty filter vs a clean one.

 

[peterk9]

Please note that the thread topic is Oil Change Interval. There is another thread on engine air filters. Thanks.

Peter