Auto Repair Help
Carl’s Corner – Auto Repair Help


By Carl O’Reilly

There is a burning odor emanating from under the hood. The symptom may be more noticeable after the engine is hot or operated for an extended period of time.

This symptom can be created by numerous causes. A burning odor is usually caused by a fluid leak, such as engine oil, coolant, power steering fluid or transmission fluid contacting hot engine parts. These types of fluids do not evaporate but instead burn slowly causing a noticeable burning odor that may also be accompanied by smoke. The possibility of an electrical malfunction that causes the vehicles wiring to get hot enough to melt may also be the cause. A piece of debris picked up from the road could also cause this if it is contacting hot exhaust parts. Often overheated brakes will emit an odor that may easily be confused as an odor that seems to be coming from under the hood. If the symptom only occurs after driving and heavy braking, you should also inspect the brakes for proper operation.

A careful underhood inspection can usually reveal the cause of the ordor. Look for leaking coolant hoses. Inspect the power steering hoses for leakage. Check the fluid level of the automatic transmission. If the fluid level is low, inspect the transmission cooler hoses that connect to the radiator or check the transmission cooler for leaks. Check for engine oil leaking from the top of the engine onto the exhaust manifold(s). You should also inspect the drive belts. If one of the drive accessories is locked-up, such as the alternator, air pump, water pump, or A/C compressor, the belt will spin on the frozen pulley. This will cause the belt to melt creating a burning rubber odor. This usually will be accompanied by a loud squeeling noise.

The cause of the odor will determine what corrective action will be necessary. If the odor is caused by an oil leak from a gasket or seal, replacement of the gasket or seal will be necessary. Tightening the mating surfaces of the gasket will only provide temporary relief at best and may cause the leak to worsen if the gasket is heavily saturated with oil.

You should use extreme caution when working around hot or rotating engine parts. Refer to the general precautions article on this website for more information.

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2 years 6 months ago

I just had my transmission filter and fluid change a month ago and I then I started hearing a rattling noise under the truck and a strange odor I had the transmission fluid changed again and the fluid was burnt. I don’t know what else.