How do I know if I have a burnt exhaust valve?

Written by andrea stein
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How do I know if I have a burnt exhaust valve?
An operator can use several methods to check for a burnt exhaust valve. (sand car engine image by Clarence Alford from

Exhaust valves allow burnt exhaust gases from a vehicle engine's cylinder to escape into the exhaust manifold. Exhaust valves can grow too hot and burn for numerous reasons, which can negatively impact engine function.

Deposit Buildup

Approximately 75 per cent of combustion heat passes from the valve through the valve seat. Deposit build-up, which can appear as a dark sludge on the valve seat, can prevent this heat from being conducted away, resulting in exhaust valve overheating and, in turn, erratic engine function. You can check for deposit accumulation on the valve seat, clean it with parts cleaner and replace the burnt valve as necessary.

Intermittent Tailpipe Suction

A burnt exhaust valve can prevent proper tailpipe suction. An operator can check for a burnt exhaust valve by allowing the engine to cool overnight, then starting it and placing the palm of one hand over the tailpipe while it is still cool. If suction remains intermittent, a burnt exhaust valve is likely the cause.

Valve Recession

Valve seats can wear down over time, causing the exhaust valves to recede or sink into the head. This results in poor contact with the seat, leading to valve overheating and burning. The operator can inspect for such recession by checking for an exhaust valve that appears sunken, which is more prevalent in older-built engines lacking hard seat valves.

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