There have been a couple of threads lately concerning the use of a single oil filter over TWO oil change intervals.
Wix question
Swedish novice
Maybe the interest is because of Gary Allan's testing showing low pressure drops in well-used filters.
Theoretically, a filter's efficiency will increase as it becomes more clogged, so using it twice is a benefit (as long as it doesn't bypass or fail- which doesn't seem likely given Gary's testing). In addition, some cars have filters mounted in "difficult" locations, so only having to get to that location every other time would also be a benefit.
Many people in the above threads (Pablo had good arguments, for example) seem shocked that anybody would even consider using a filter twice, though. The reason is that there is some old oil still lurking in the old filter that would not be changed.
So, I'm looking at some hypothetical math here of keeping an old filter installed. What do you think? Is there really much difference...
1/2 quart of used oil left in filter on an engine that normally takes 4 quarts for a drain and fill,
plus... 1 quart of dirty oil hidden in engine regardless,
yields 70% fresh oil in engine. (Compared to 80% with a filter change).
If your OCI is normally 4000 miles, the 10% extra dirty oil will be like starting out 400 miles into your 4000 mile interval. So if you drop your second interval to 3600 miles, you will have the same level of dirtiness at the next oil change.
If oil is $2/qt, then you normally spend $16 for two 4-qt changes in 8000 miles. Because of the one reduced interval, it is now $16 for 7600 miles or $16.85 converted to 8000 mile equivalent. But, you just saved $3 for a filter.
Economically, then, I see a tiny benefit. Hassle-wise (on cars with difficult filter locations) I see a BIG benefit.
Reducing the OCI seems to make up for the 10% extra dirty oil.
And the filtration was slightly better during the second run.
But, you run a higher risk of filter failure.
What else??? To me, changing the filter only every other time looks like a very reasonable idea.
Wix question
Swedish novice
Maybe the interest is because of Gary Allan's testing showing low pressure drops in well-used filters.
Theoretically, a filter's efficiency will increase as it becomes more clogged, so using it twice is a benefit (as long as it doesn't bypass or fail- which doesn't seem likely given Gary's testing). In addition, some cars have filters mounted in "difficult" locations, so only having to get to that location every other time would also be a benefit.
Many people in the above threads (Pablo had good arguments, for example) seem shocked that anybody would even consider using a filter twice, though. The reason is that there is some old oil still lurking in the old filter that would not be changed.
So, I'm looking at some hypothetical math here of keeping an old filter installed. What do you think? Is there really much difference...
1/2 quart of used oil left in filter on an engine that normally takes 4 quarts for a drain and fill,
plus... 1 quart of dirty oil hidden in engine regardless,
yields 70% fresh oil in engine. (Compared to 80% with a filter change).
If your OCI is normally 4000 miles, the 10% extra dirty oil will be like starting out 400 miles into your 4000 mile interval. So if you drop your second interval to 3600 miles, you will have the same level of dirtiness at the next oil change.
If oil is $2/qt, then you normally spend $16 for two 4-qt changes in 8000 miles. Because of the one reduced interval, it is now $16 for 7600 miles or $16.85 converted to 8000 mile equivalent. But, you just saved $3 for a filter.
Economically, then, I see a tiny benefit. Hassle-wise (on cars with difficult filter locations) I see a BIG benefit.
Reducing the OCI seems to make up for the 10% extra dirty oil.
And the filtration was slightly better during the second run.
But, you run a higher risk of filter failure.
What else??? To me, changing the filter only every other time looks like a very reasonable idea.
