The 18-7875 is a Fram oil filter for older Chrysler, Dodge, and Plymouth vehicles

The 18-7875 is a Fram-branded spin-on oil filter that was used on Chrysler Corporation vehicles built roughly between the mid-1980s and early 2000s. It fits Dodge pickups, Chrysler sedans, Plymouth models, and some Jeep vehicles from that era. If you own one of these vehicles and need to replace the filter, you have two paths: use the exact Fram 18-7875 again, or find a cross-reference filter from another manufacturer that has the same thread size, bypass valve pressure, and anti-drainback valve design.

Cross-referencing matters because the 18-7875 may be harder to find at some retailers, and other brands often cost less or are in stock when Fram is not. The filter itself is not expensive — typically $8 to $15 — but knowing what else fits saves you a trip or a special order.

Key Takeaways

  • The 18-7875 is a Fram filter for Chrysler, Dodge, Plymouth, and some Jeep vehicles from the mid-1980s through early 2000s.
  • Common cross-reference filters include the Motorcraft FL-400, Purolator PL14610, and Wix 51056, which have the same thread pitch and bypass valve rating.
  • Cross-reference filters must match the original on thread size (typically 3/4-16 UNF), bypass valve pressure (usually 8 to 10 PSI), and anti-drainback valve presence.
  • Always verify the cross-reference against your vehicle's year, make, and engine size before purchase, because some model years used different filters.
  • If you cannot find a cross-reference locally, the original Fram 18-7875 is still available online and through specialty automotive retailers.

Common cross-reference filters that fit the 18-7875 specifications

Several manufacturers make filters with the same thread size and bypass valve rating as the Fram 18-7875. The Motorcraft FL-400 is one of the most common matches and is often stocked at Ford dealerships and auto parts chains. The Purolator PL14610 is another direct cross-reference and is widely available at national retailers. The Wix 51056 also matches the 18-7875 specifications and is commonly found at NAPA and independent shops.

Other filters that cross-reference to the 18-7875 include the Fram PH3600 (a later Fram variant), the Hastings LF418, and the Luber-finer PH3600. Each of these has the same 3/4-16 UNF thread pitch and an 8 to 10 PSI bypass valve, which means they will screw onto your filter housing and protect your engine the same way the original does.

The reason multiple brands work is that oil filter thread sizes and bypass pressures are standardized within certain ranges. A filter designed for 1980s Chrysler engines uses the same basic specifications as filters made for other vehicles of that era, so manufacturers can make one filter that fits many applications.

How to verify a cross-reference filter before you buy

Before you purchase a cross-reference filter, confirm three things: the thread size, the bypass valve pressure, and the anti-drainback valve design. The thread size for the 18-7875 is 3/4-16 UNF (3/4 inch diameter, 16 threads per inch, Unified National Fine). This is printed on the filter canister or in the product specifications. If a replacement filter lists a different thread size — such as 3/4-20 or M20 — it will not fit.

The bypass valve pressure should be 8 to 10 PSI for the 18-7875. This is the pressure at which the filter allows unfiltered oil to flow directly to the engine if the filter becomes clogged or the oil is too cold to flow through the media. A filter with a much higher or lower bypass pressure can affect oil flow and engine protection. Check the product data sheet or the retailer's specifications before buying.

Finally, confirm that the replacement has an anti-drainback valve. This one-way valve prevents oil from draining out of the filter when the engine is off, which keeps the filter primed and reduces engine wear during cold starts. Most modern filters have this, but it is worth checking the specifications to be sure.

Where to find the 18-7875 or its cross-references

The original Fram 18-7875 is still available through online retailers such as Amazon, RockAuto, and eBay, though it may take several days to arrive. National auto parts chains like AutoZone, O'Reilly, NAPA, and Advance Auto Parts often stock cross-reference filters in-store, which means you can pick one up the same day. Call ahead to confirm stock, because older filter part numbers are sometimes discontinued and replaced with newer equivalents.

If you know your vehicle's year, make, model, and engine size, you can also visit the websites of Motorcraft, Purolator, Wix, or Fram directly and use their filter finder tools. These tools will show you which filters fit your specific vehicle and where to buy them locally. Specialty shops that focus on older Chrysler vehicles — such as Mopar restoration suppliers — often stock the 18-7875 or know the correct cross-reference when ready.

Why cross-referencing matters for older vehicles

Older vehicles like those that used the 18-7875 are no longer in high production, so parts suppliers gradually phase out original part numbers in favor of newer equivalents. This does not mean the filter is gone — it means you may have to search harder or pay a premium for the exact original. A cross-reference filter solves this by letting you buy a newer or more readily available filter that meets the same engineering standards.

Cross-referencing also protects you if you ever need to replace the filter at a shop that does not stock the 18-7875. A technician can look up the cross-reference and install a filter that works just as well without having to special-order the original. This is especially useful if you are traveling or need an oil change on short notice.

What to do if you cannot find a cross-reference match

If you have searched multiple retailers and cannot find the 18-7875 or any of the common cross-references listed above, contact a Mopar specialist shop or a classic car parts supplier. These businesses often have access to older filter part numbers through specialty distributors and can order the 18-7875 directly. The wait is usually one to two weeks, and the cost is still modest.

Another option is to verify your vehicle's year, make, model, and engine size with the owner's manual or a service manual, then contact Fram or Motorcraft customer service directly. They can confirm whether a newer filter part number is the official replacement for the 18-7875 and whether that newer filter is easier to find. Sometimes manufacturers issue superseding part numbers that are direct replacements and more widely stocked.

Frequently Asked Questions

Will a filter with a different thread size fit if I use an adapter?

No. Using an adapter to force a different thread size onto your filter housing can cause leaks, improper seating, or the filter to unscrew during operation. Always use a filter with the correct 3/4-16 UNF thread size for the 18-7875. An adapter is not a safe workaround.

Is the 18-7875 the same as the Fram PH3600?

The Fram PH3600 is a later Fram filter that cross-references to the 18-7875 and has the same thread size and bypass valve pressure. However, they are not identical part numbers. The PH3600 is often easier to find, so it is a good alternative if the 18-7875 is out of stock.

Can I use a filter with a higher bypass valve pressure than the original?

Using a filter with a significantly higher bypass valve pressure (such as 12 or 15 PSI instead of 8 to 10 PSI) can reduce oil flow to the engine, especially during cold starts, and may void your warranty. Stick to filters with the same bypass pressure as the 18-7875 to maintain proper engine protection.

What if my vehicle's manual lists a different filter number?

Check the year and engine size in your manual against the 18-7875 specifications. Some model years or engine variants used different filters. If your manual lists a different number, use that instead, because it was engineered specifically for your engine.

Do I need to change the filter housing if I switch to a cross-reference filter?

No. As long as the cross-reference filter has the same thread size (3/4-16 UNF), it will screw directly onto your existing filter housing without any modifications or additional parts.