Oil Filter

I asked this question on the Subaru forum that I visit and I got a few opinions but nothing backed up by any real evidence or data.

My 2014 Subaru Legacy 2.5 came with a two year free maintenance that is now used up, so I am doing my first oil change on it. I went hunting for an oil filter. At Advanced Auto Parts, the have a Purolator Classic listed for it, but not the higher grade Pure One. Just for the heck of it, I had them check for the 6 cylinder engine. For that engine, there is a Pure One listed as well as a Classic. When I compared the two, I found that both have the same thread six and the same diameter gasket at the base, but the can for the 6 cylinder is a little larger in overall diameter.

I don’t see any reason why I can’t use the one made for the 6 on the 4 cylinder. The filters are remotely mounted above the engine so clearance is not an issue.

I thought maybe the filter used on the 4 cylinder might be unique to that engine or used on very few engines where the one for the 6 might be more commonly used and that demand didn’t justify the production of a Pure One for that engine, but then I looked through a Fram catalog and found that they don’t make (sell) a filter that fits the 6 cylinder at all in any of their lines, but they carry filters for the 4 cyl in all the grades of their filters.

Anyway, back to my question, anyone know why using the filter made for the 6 would be a bad idea on the 4?

Edit: corrected second paragraph to reflect the can is larger, not the base gasket.

You have new car why not just buy the correct filter from the dealer. It’s not likely to be that more expensive and you are only going to do that twice a year. My position is if I do have a warranty claim at least they can’t blame it on the filter.

Personally, and assuming you prefer Purolator, I’d go with the Classic. At least you’ll know that the inside of the filter assembly is correct, even if the filter element itself isn’t the premium one that you’d prefer.

That “slightly larger” overall diameter base gasket just might be just big enough to not seal properly, the flow might not be as-intended, and the overpressure bypass might be a different rating. Putting a “slightly larger” diameter gasket on a part through which fluids flow is always a risk IMHO. It ain’t worth it. Err on the side of safety.

I wouldn’t go for the off-spec filter, either. 99% of the job is getting a new filter, the difference between the 2 Purolators is small, IMO. Use the right one. Or if your really concerned, buy a ‘Subaru’ one from the dealer, or from the internet.

The overall diameter is slightly larger, the base gasket is the same. Its a long drive to the Subaru dealer.

I meant to say the overall diameter of the can is slightly larger.

I only use OEM filters. On the Acura I buy Honda filters and use AC on the Pontiac and Olds. Even at the dealer the filters are only a few dollars more than the discount ones. That amounts to a cup of coffee or two every 5000 miles. I spill more than that.

Apologies for the misunderstanding. I still think the correct filter is a better idea, however.
Besides, I’m inclined to think that if the filter was usable for your engine Purolator would list it for your engine.

Buy two correct filters by credit card over the phone and have them sent to you. The shipping fee is worth peace of mind and might be cheaper than the time and gas to go get them.

I’ve never seen the two filters in question myself. I guess you could do the experiment and give it a try, presuming the type of oil and viscosity is the same for the two engines. Keep an eye on the oil pressure situation and listen for unusual sounds. It might work fine. There are generally multiple reasons and constraints why the parts manufacturers design their products the way they do. Fitment is just one of them. And even fitment can’t be judged by a look-see with a ruler. Fitment parameters need to be carefully measured to insure complete compatibility. And changes of fitment vs temperature need to be considered. Then there’s the inside of the filter, the performance. For example it has to provide the correct range of oil flow resistance for the type and viscosity of oil it is designed for, designed to provide for adequate cold start lubrication, be designed to handle complete filter blockage in conjunction with the engine should that occur, etc.

Me, just to be on the safe side, I’d tend to use a filter spec’d for the engine. And if I had any doubt, I’d just purchase my oil filters from the dealer. A lot of time the dealer filters aren’t any more $$ than the aftermarket versions. Replace the filter a little more often if you want more robust oil filtering performance. I’ve never used Purolator, so I can’t speak to the performance of that particular product, good or bad.

I used to buy the cheapest filter for my cars, usually supertech from Walmart. They stopped having them. But that is not the problem. Most newer cars call for Synthetic oil with longer change intervals. If you are going to go that route, I will get OEM filter from the dealer or online because with the aftermarkets, you don’t know if they are good for 10K miles or no.

If the threads and base gasket are the same I don’t see a problem as long as any filters used are name brand and not some generic Chinese white or yellow box no-name stuff.

I’ll go slightly off-topic . . .

We stock wix filters in our warehouse. And the wix website is also pretty easy to use

I will often install a longer filter, which has the same threads and diameter, but it’s longer. I compare the various specs for both filters on the website, and they’re the same, except for the length

Sure, the longer filter is wrong, in the sense that it’s not listed for the application

that being said, I’ve been doing it for years, and there has not been one single problem.

And since I’m a fleet mechanic, I see these vehicles all the time. If there were a problem, I’d certainly know about it. But everything’s been just fine, and I’m confident it will stay that way

The OP’s alternate filter is bigger in diameter. I’m surprised the base gasket isn’t bigger, too.

Sure, the longer filter is wrong, in the sense that it's not listed for the application

For the 6 years I owned my 84 GMC pickup GM changed the recommended filter 3 times. Each new filter was bigger then the previous. I always bought aftermarket filters (Fram, Wix)…and they followed suit with each change and listed a new filter.

Over at “BobIsTheOilGuy” folks cut open used filters and have found Purolators with torn media.
Lots of heated discussions.
There are alleged advantages to using oversized filters, as long as the thread, gasket diameter and bypass pressure are the same.

There was a similar choice on GM small block V8s. I had an Impala, and it had a small short filter. The same engine in a pickup truck had a much larger one, presumably because trucks operate in a dirtier environment. I always bought he larger one and added some extra oil. There were no clearance problems.


" . . . as long as the thread, gasket diameter and bypass pressure are the same."

That’s why I like the wix website, because they list all that information.

Yes, they are the same.

Thanks for the information so far. The 4 cylinder engine does use a synthetic 0w20 where the 6 cylinder uses 5w30. I don’t know when the 4 cylinder switched to the 0w20 so I don’t know if that corresponds to the change in the filter. I’ll look into that. In the meantime I bought a Fram Ultra Synthetic spec’d for the 4 cylinder engine.

I don’t want this discussion to get into a brand vs brand discussion. The only oil filter I ever got that had an out of box defect was a Mobil 1 filter where the tread cutting insert must have had a burr on it as the threads were rough and the filter was full of shavings from the thread cutting operation. I’m pretty sure that doesn’t happen very often. I’ve never had any brand of oil filter fail in operation and over the last 50 years or so, I have used a lot of oil filters.

I used to use the WalMart SuperTech filters a lot because they were usually the cheapest and they were built pretty good. I went to the Purolator Classic after that and have had no trouble. I guess I just wanted to upgrade because this is a new car. I’ll get over that before too long.

I also wanted to use the new Pennzoil Synthetic but it is getting very hard to find in any weight and impossible to find in 0w20. I wonder what is happening with that? It seems that no one is getting restocked so when their old stock is sold out, its gone.


“I just wanted to upgrade because this is a new car. I’ll get over that before too long.”

you’ll get over it when you get your first scratch or dent :cold_sweat:

Amazon has multi packs of OEM filters at a discount. This is where i get my OEM Toyo filters. http://www.amazon.com/Subaru-Oil-Filters-Washers-Pack/dp/B007NLQO0O/ref=sr_1_1?s=automotive&ie=UTF8&qid=1449262944&sr=1-1&refinements=p_89%3ASubaru