Fel-Pro 18-23 Ford F-150/15-21 Mustang Engine Coolant Thermostat Gasket

Engine coolant thermostat gasket for the 2011-2025 Ford F-150 and 2011-2025 Ford Mustang. It does one job: seal the thermostat so coolant stays where it belongs. Fel-Pro part 35991.

Why Upgrade to a Fel-Pro Thermostat Gasket

Per Fel-Pro, here is what this gasket is built to do:

• Designed for the repair environment. That means a used engine in your driveway or a shop bay, not a clean room.
• Made to seal against imperfect surfaces. If the mating face is not perfectly flat or clean, this gasket is designed to seal it anyway.
• Meant to hold a reliable seal on the troublesome applications, the ones that are hard to keep dry.
• Made with proprietary materials. Exactly what those are is [VERIFY: gasket material].

Fitment Notes

Fits the 2011-2025 Ford F-150 in Base trim, plus the Raptor (2017 only) and Tremor (2023-2025). Fits the 2011-2025 Ford Mustang GT, the V6 (2011-2017), Boss 302 (2012-2013), GT350 (2016-2020), Bullitt (2019-2020), GT500 (2020 only), Mach 1 (2021-2023) and Dark Horse (2024-2025). Does not fit the F-150 Lightning or Raptor R. Does not fit the Mustang EcoBoost or GTD. [VERIFY: the title says 18-23 F-150 and 15-21 Mustang while our fitment data lists 2011-2025 for both, confirm the year range before you buy.]

More Gaskets that fit your truck or Mustang

Install and Honest Talk

This is a fix, not an upgrade. Nothing changes from the driver's seat once it is in. The win is a thermostat that stops weeping coolant. Fel-Pro designs it to cope with an imperfect sealing surface, but check the included instructions for surface prep before you count on that. What else you need: check the included instructions for whether fresh coolant, sealant or a new thermostat is called for. [VERIFY: contents of the box, tools, torque spec, what comes off the vehicle to reach the thermostat.]

Specs

• Brand: Fel-Pro
• Part number: 35991
• Part type: Gasket Kits
• Quantity: [VERIFY: quantity in the pack]

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Free US shipping over $99

Orders over $99 ship free by ground to the lower 48 states. Alaska, Hawaii and Canada are not included; shipping to those addresses is calculated at checkout. Some oversize or heavy parts (long-tube exhausts, bumpers, full lift kits) go freight instead of parcel: free to a commercial address with a loading dock, and residential freight delivery carries an additional charge.

When it ships

Parts ship direct from the distributor warehouse that stocks them, so dispatch timing depends on the part, not on a single cutoff. You get a confirmation with tracking as soon as it leaves, and tracking shows the delivery estimate for your address. If a part is backordered we email you an expected availability date.

Missing or damaged items

Report a short shipment or shipping damage within 5 business days of delivery. For a packing error, send us the date or package code printed on the label along with the part number so we can trace it with the warehouse.

We have a 30-day return policy, which means you have 30 days after receiving your item to request a return.

To be eligible for a return, your item must be in the same condition that you received it, unworn or unused, with tags, and in its original packaging. You’ll also need the receipt or proof of purchase.

To start a return, you can contact us at help@anythingcoyote.com or fill our our contact form. If your return is accepted, we’ll send you a return shipping label, as well as instructions on how and where to send your package. Items sent back to us without first requesting a return will not be accepted. 

You can always contact us for any return question at help@anythingcoyote.com.

Damages and issues
Please inspect your order upon reception and contact us immediately if the item is defective, damaged or if you receive the wrong item, so that we can evaluate the issue and make it right.

Exceptions / non-returnable items
Certain types of items cannot be returned, like perishable goods (such as food, flowers, or plants), custom products (such as special orders or personalized items), and personal care goods (such as beauty products). We also do not accept returns for hazardous materials, flammable liquids, or gases. Please get in touch if you have questions or concerns about your specific item.

Unfortunately, we cannot accept returns on sale items or gift cards.

Exchanges
The fastest way to ensure you get what you want is to return the item you have, and once the return is accepted, make a separate purchase for the new item.

Refunds
We will notify you once we’ve received and inspected your return, and let you know if the refund was approved or not. If approved, you’ll be automatically refunded on your original payment method. Please remember it can take some time for your bank or credit card company to process and post the refund too.