Bigger and smaller oil filtersMany are frequently perplexed as to why some modern cars and trucks are equipped with such tiny oil filters. A reader voices his concern and asks if he can use a bigger oil filter.

A reader asks: “My car uses a very small oil filter. Are there any reasons as to why I can’t use a longer filter? Are there are any disadvantages?”

Answer: This is a very common question and one we ask ourselves from time to time. One looks at the tiny “teacup” oil filters on many of today’s V-6 and even V-8 engines and wonders what the engine designers were thinking.

We posed this question to a few of the big-name oil filter makers and the general consensus is that today’s engines run far cleaner than the engines of yesteryear and that capacity is not a concern. Unless there is a malfunction, very little dirt gets into these engines, so the OEM-sized oil filters actually offer a considerable amount of over-capacity.

So if many consumers are concerned about the puny oil filters on their vehicles, why doesn’t the aftermarket provide larger filters (even if it’s just for optics)? There are three reasons as to why the aftermarket is not providing “larger than OEM” oil filters.

1. The first are space concerns. Many oil filters are cramped into tight spots that are difficult to access as it is.

2. The second is clearance. Longer oil filters can be vulnerable to damage from rocks and road debris. If the aftermarket oil filter is about the same size as the factory unit, the filter producer is not opening themselves up to damage claims as they might if they offered longer oil filters that are susceptible to this type of mishap.

3. The third reason why the aftermarket is not providing longer oil filters is that they also don’t consider the filter sizes offered by the car-makers to be too small or short on capacity. They see it as an non-issue.

Reasons Why You Shouldn’t Use a Longer Oil Filter

Many people have used larger oil filters with no problem, but there are some downsides to consider:

1. Relief/by-pass pressure settings

When searching for a larger oil filter, many will consider filter characteristics like thread size, filter diameter and gasket diameter. If all of those match up on a longer filter, they think they can simply use the longer filter and have now got one over on the man. Not so fast…

A major factor in an oil filter’s compatibility is the by-pass pressure valve setting. An oil filter’s by-pass pressure valve is an internal mechanism that opens up if the oil pressure becomes too high. This pressure-relief valve opens either during cold starts when the oil is thick or in the event that the filter is plugged with debris. When this valve is open, unfiltered oil is allowed to by-pass the filter rather than channel it through the filter media. This prevents the oil filter from malfunctioning due to excess oil pressure and also maintains the flow of oil to the engine.

When researching for this post, we searched out a few forum threads to get a feel for types of oil filters that posters were using to replace the recommended units. Often times they were posting specific part numbers, so we could do a search to see if their dimensions and by-pass valve settings were correct. Most were in the ballpark, but one post was not. A Subaru owner was using a filter that was 1.2” longer than the filter recommended for his engine. The rub was that the recommended filter had a bypass valve pressure setting of 23 PSI, while the longer filter had a setting of only 8 to 11 PSI. In other words, while this poster was looking for more oil filter capacity, his longer oil filter (with a low by-pass setting) could potentially be in by-pass mode on a regular basis.

This is an extreme case, but it illustrates how choosing a larger oil filter goes beyond the consideration of only dimensions.

2. Warranty Risks

Virtually every oil filter sold is warranted by the manufacturer. If you have an engine failure caused by an oil filter defect, your repair costs will be covered by the filter company. If you opt to use an oil filter part number that is not recommended for your application, you have given the filter company an out and they will not cover you in the event of a claim. A larger oil filter might give you the “warm and fuzzies”, but more than likely, the extra capacity is completely redundant anyway. Consider if the extra oil filter capacity is worth the risk of operating without warranty coverage (should the unthinkable happen).

When You Should Consider a Larger Capacity Oil Filter

Situations where a larger oil filter should be considered is in engines that have been extensively modified for racing or very high performance. When high volume oil pumps have been installed, a specialized racing oil filter should also be used. These types of oil filters allow for much higher volumes of engine oil circulation. This type of racing oil filter does not apply to normal passenger car/light truck applications.

How to Gain Capacity with Your Regular-Sized Oil Filter

A way to gain oil filter capacity with an OEM-sized oil filter is to use a model equipped with a synthetic media. Synthetic oil filter media materials are able to hold more contaminants, while still allowing for exceptional flow at the end of the oil change interval. Conventional cellulose (paper) oil filters only hold contaminants on top of the media. Think about how coffee grounds are held on the inside of a coffee maker filter. When the cellulose media is covered, the filter’s flow is restricted. These high-tech synthetic filter materials have very tiny openings that actually hold contaminants in the media itself as well as on the outside of the media. This added dimension of viable filtering area means that synthetic oil filters can offer double the contaminant holding capacity over regular oil filters.

How to Gain A Lot More Oil Filter Capacity

If you want to gain more oil capacity, filtering capacity and achieve finer particle removal, consider adding an oil by-pass filter system. Regular full-flow oil filters remove particles in the 15 to 25 micron range. By-pass oil filters are capable of removing contaminants in the 1 to 2 micron range. By-pass filter systems use a much denser filter media and draws the oil through at a very slow rate for exceptionally thorough filtration. These systems work in conjunction with a full-flow oil filter. This type of system is able to extend oil life quite dramatically. The major drawback of this type of oil filter system is that they many modern cars simply do not have space to accommodate these units. For that reason they tend to be more popular on trucks.