What oil filter do you use? short or long?

[Ruby Fan]

On the earlier C4's, like my '85, GM specs a PF25, but I have seen in up to date filter selections, a short type. I think the number is PF454, which is shorter, probably for more ground clearance. I have used both. Just wondering what you folks use. Thanks

[boomdriver]

I have used both as well...the shorter to look at additional ground clearence when I was installing a stack-on plate for an external cooler...

Since 75% of the oil gets bypassed anyway, and all oil gets at least some filter time and we change it more often than most car owners, I don;t believe there is any liability in the short filter and its smaller capacity. If it were a pressurized filter system where ALL oil must go thru before circulation then the small filter would concern me, but this is a "catch me if you can" system that bypasses at the least bit of back pressure so flow is not restricted to the top end...even unfiltered oil in the top end is better than filtered oil of reduced amounts. It all gets filtered eventually..

[Hib Halverson]

If your 85 has KC4 you have to use the PF25. If you don't have KC4, use the PF1218, which is the "long" filter.

It was said in an earlier post in this thread that 75% of the oil is bypassed anyway.

That is not correct.

A new oil filter will either not bypass at all or bypass very little. As the filter begins to trap contaminates, its restriction reaches a level such that a noticeable amount of the oil is bypassed to the engine unfiltered and that amount increases and the filter's restriction level continues to build.

There are two ways to avoid or at least minimize any bypassing.
1) Use a high quality filter
2) Change it at about half your oil change interval.

[boomdriver]

If your 85 has KC4 you have to use the PF25. If you don't have KC4, use the PF1218, which is the "long" filter.

It was said in an earlier post in this thread that 75% of the oil is bypassed anyway.

That is not correct.

A new oil filter will either not bypass at all or bypass very little. As the filter begins to trap contaminates, its restriction reaches a level such that a noticeable amount of the oil is bypassed to the engine unfiltered and that amount increases and the filter's restriction level continues to build.

There are two ways to avoid or at least minimize any bypassing.
1) Use a high quality filter
2) Change it at about half your oil change interval.

Thank you for pointing out my error . ........not being a technical guy I often "cut thru the BS" and make my point as quickly as possible with as few words as possible. Mrs Estes (typing teacher) would be ashamed of my poor typing skills...

What I would have said (or typed) had my fingers not been getting tired was something more like this....

"..... there are times when much of the oil in the pan is bypassed due to high resistence from cold temps or high pump output. This is done so the filter does not explode or have the element blown apart, or worse having the top end (cam bearings, guides etc) starving for oil even briefly. Its more a matter of time than filter size or shape. Because having oil circulate is far more important than having filtered oil, this makes the filter size less important in the scheme of things. Sooner or later it ALL gets filtered regardless of the vol or filter capacity. It just does not take that long to recirculate 5 qts of oil thru such a small closed loop system. Any oil thats bypassed gets recirculated rapidly so there is no harm done. It ALL gets filtered eventually."

It was just easier to say 75% gets bypassed. The statement was to be figurative not literal, but I can see how it could be taken the wrong way.

I'd like to add that IMHO the smaller filter will do the same job as the big one...if anything the smaller can size will have less surface or coverage area so it will get contaminated quicker and become useless a bit sooner requiring a filter change more often. I agree with Mr Halverson in the reccomendation that you change your filter mid way thru a maint cycle. Its not so much the oil thats goes bad, its the filtration thats fails. As the device does what it is supposed to do it becomes useless.

Now that we have superior synthetic oils that do not breakdown nearly as fast as conventional oils, we can take advantage of that by just changing the filter every 2500-3000 miles and let the oil go for 6 to 10,000 miles. Personally I'm tired of spending $7.50 a qt by the old school rules....Oil change at 2000-3000 miles is so wasteful that it should be a crime. We can easily double that today...even triple without worry.



I feel safe in assuming that the revised statement won;t be good enough for some folks, so I leave that to be their problem...I believe that I've clarified my statement.

[WhalePirot]

Remote mounted.. Wix.

[1analguy]

...This is done so the filter does not explode or have the element blown apart...

There's not much chance of the element blowing apart. The direction in which the oil flows through the filter is from the outside of the element to the inside of the element...

[jp1]

The pf25 has been discontinued by ac for years now. It has been replaced by the "overly short" pf454. I only use the pf1218 it does not go under the bottom of my oilpan with a oil cooler so it is good to go.