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Ford F-150/F-250: What is that Burning Smell?

Burning smells from under the hood of your F-150 or F-250 can mean many different things. Here are a few helpful tips to get you in the right direction.

By Makeda - October 22, 2014

Different mechanical failures result in different types of "burning smells." Some, like burning oil followed by heat and smoke, are an immediate hazard. Others, like the smell of plastic burning through your A/C, are less disastrous.

Brake Caliper Sticking

Your wheels might smell like burning if your brakes are dragging. Sticking brake pads smell faintly of burning rubber or burnt carpet. This happens when the rails that the brake caliper slides along are dirty, unlubricated, or otherwise damaged. Occasionally this happens after installing new brake pads without lubricating the pins the caliper slides on.

A dragging brake will heat up the caliper and brake disc much more than a functioning brake will. You can use this fact to check your wheels. After driving, go to the wheel that you think is producing the burning smell. Put your hand near the wheel. All of your brakes and wheels will be warm, but the one with the dragging caliper will be much hotter.

When cool, replace brake pads with new ones while being sure to grease the caliper slider bolts.

Figure 1. These bolts are located in the bust boots of your brake caliper carrier. Make sure the slides are greased before reinstalling.

Pro-Tips

After your tires receive a rotation, remove the brake belt and squeeze the side pin. If it gets stuck, pull the coin out and lubricate using dielectric grease. We recommend PSD or Bendix pads which will provide better breaking power with less fading of your brake. Phenolic pistons are better quality than aluminum because it does not generate heat to the brake fluid which causes it to boil.

Burning Oil

Anyone who's spilt a bit of oil on a hot engine will be able to recognize this scent immediately. Most often, you'll get this from a leak somewhere in the engine bay. Oil will have a strong, acrid scent. Even a small amount of oil leakage will be pungent if the oil hits something hot, like the exhuast headers of your F-150. Check your truck's dipstick to make sure your engine isn't low on oil.

Do your best to avoid filling the oil too high past the operating range if it is.Your engine might be burning oil too. Leaky valve seals will drop oil into the cylinder, resulting in white, acrid exhuast smoke. The valve cover gasket can fail in the same way and leak oil onto the exhaust headers. Several components in your truck's engine bay could possibly leak, so be sure to pay attention if the smell of oil burning comes through your heating and air conditioning vents.

Figure 2. You're looking at the "V" of an F-150 V8 with a bad oil leak. The inside

A/C "Plastic Burning" Smell

First, be sure you haven't run over a plastic bag recently. We're serious; frequently plastic bags get stuck under cars and trucks. They'll melt if they get hung up on the exhaust which can cause that burning plastic smell.

If your AC hasn't been working well recently and smells like plastic or burning, there's a good chance you're out of refrigerant or lubricant. The AC compressor can overheat if it runs without the proper fluids to cool it. As it heats up, the plastics in the unit outgas and fill your cabin with stink.

Also, it's worth having a mechanic check out your truck's heater core. These can crack and cause your F-150 or F-250's engine compartment to smell "plasticky." That's the smell of warm coolant being blown into your ventilation system. Coolant leaks in general will smell sweet and sharp, more than they smell like burning.

Figure 3. The heater core is outlined above. A cracked one will leak coolant. The coolant will dry quickly, but it will also smell.

Clogged Catalytic Converter

Catalytic converters use chemical reactions to convert some of the harmful products of exhuast into less harmful ones. The reaction does create some sulfur when the engine is running well, but it creates a lot more when it's running rich. Exhuast gas with a pungent, rotten egg odor is a tell tale sign of a dying catalytic converter.

Pro Tip

Sulfur smell in the cabin points to another possible issue. Battery leaks are corrosive and often smell like rotting eggs too. Look under your hood around you battery for evidence of corrossive leaks.

Figure 4. An engine that's running rich will clog a catalytic converter with sulfur. As a result, your exhaust will smell like burning and rotten eggs.

Worn Out Serpentine/Drive Belt

Typically the first sign you'll get of a bad serpentine/drive belt is horrible screeching and squealing whenever you start the truck. That's the sound of them slipping on their rollers as the pulleys and belts get warmed up. Excessive slipping will cause the belts to heat up and smell like burning rubber. This is even more of a sign that you should change your drive belts for a new set.

Open your hood and check the belts for missing ribs and fraying. Some cracking is okay, but long, lengthwise cracks are a bad sign. Fraying and obvious physical damage (like on the belt below) are also signs that you should install new serpentine belts.

Figure 5. This serpentine belt is glazed and frayed. Click on it for a better look.

Featured Video: What is that Burning Smell in My Ford Truck?

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