Smoking and burning smells are always worrying and you should investigate them at once. They can sometimes mean you've got severe engine issues and the sooner you stop and put things right, the more likely you are to avert a major problem. At other times, smoking and burning smells are not symptomatic of a significant failure, but you should still investigate and take the necessary action.
If you have recently added oil to your engine, you may have inadvertently spilled some onto an engine part that heats up during driving. The smoking and burning smell might be because the spilled oil has heated up and is giving off an odour. Lift the bonnet and look for any oil spills, which may be smoking slightly. Wipe these away with a rag and this should solve the problem. Another likely suspect is oil leaking onto the hot exhaust manifold, according to Popular Mechanics.
Even when your temperature dials tell you your engine is not overheating, it might still be reaching critical temperatures. Like other automotive components, temperature dials sometimes fail. If you are detecting a smoking and burning smell but can't work out why, it might be because your temperature dial is compromised. Consider taking your car to a garage to let them investigate the matter.
Engine component burnout
Most cars have a dial to show water temperature, but motor vehicles do not commonly have dials to show the temperature of other engine components. If an engine component has become worn to the extent that it is generating frictional contact with another component, this may lead to a smoking and burning aroma. Use your eyes and nose to detect anything that seems wrong, is out of place, is split, cracked, frayed, bent or appears to be giving off the odour.
Foreign body infiltration
A likely cause of a smoking and burning smell if the engine is not overheating is the infiltration of a foreign body into the engine housing. An item as delicate as a leaf, should it find its way into the crankcase ventilation system, for example, might interfere with the proper passage of the blow-by gas leading to a smell which could be described as a smoking and burning smell. Check the nooks and crannies of your engine for foreign body infiltration and remove any foreign bodies discovered.
Other possible causes
According to Auto Repair for Dummies, if an engine hose comes loose – perhaps because a hose clip breaks – and lands on a hot part of your engine, the rubber can heat up and begin to perish, causing a burning smell. Alternatively, the odour might indicate that one of your brake shoes or pads has started to stick. More seriously, it could be an early indication that your clutch is overheating.