Troubleshooting a Butterfly Exhaust Valve

closeup of a car's Exhaust Valves

When your engine's butterfly exhaust valve is working properly, the engine runs more quietly at low rpm, and starts quickly and smoothly. The heat from the exhaust manifold warms the fuel-air mixture for a cleaner start. Several situations can cause this valve to malfunction. Learn below about how to troubleshoot the butterfly valve and ensure it works correctly.

Butterfly Exhaust Valve Stuck Closed

If the butterfly valve sticks closed, superheated exhaust gases may become trapped in the exhaust manifold. This can affect the car's performance, because the trapped gases will not allow enough fuel to enter the engine to allow it to start effectively. The hot gases can cause warping or cracking of the exhaust manifold and may warp the valve itself.

Releasing a Butterfly Valve that is Stuck Closed

At about 50,000 miles, the butterfly valve may develop problems with sticking closed. This can be fixed during an oil change, by rotating the counterweight that controls the motion of the valve. If the valve shaft is jammed so that the butterfly valve will not rotate, tap the ends of the shaft with a hammer to free them. If this process is not effective, replace the entire valve. In a 6-cylinder engine, you will need to remove the exhaust manifold to get at the butterfly exhaust valve to remove it.

Butterfly Exhaust Valve Stuck Open

When the butterfly exhaust valve is stuck open, your engine will not get a warm start because the exhaust will be channeled straight out the tail pipes, instead of around the base of the carburetor to warm up the engine. You will find your engine is slow to start and will not stay warm. The gas-air mixture will be too rich, because the automatic choke will not activate at the proper time to allow in air for a balanced fuel mixture. Unburned gasoline will slosh around the inside of the cylinders, causing your spark plugs to foul. Lubricant will also be washed off the engine parts, causing increased friction and poor performance.

Enable the Butterfly Valve to Close Again

Using a small brush, apply a solution of alcohol mixed with powdered graphite to serve as a lubricant for the butterfly valve shaft. If this does not loosen the shaft, spray it with a spray solvent that removes rust. The spray can penetrate where the liquid graphite solution will not reach. This removes built-up particles and allows the valve to rotate properly again around the shaft with just the vacuum pressure provided by the engine.

Butterfly Valve Chatter

The chattering sound you hear when the engine is first starting may be due to a loose or broken butterfly valve spring. Remove the spring with a screwdriver and replace it. If the valve spring breaks in an 8-cylinder engine, you will need to replace the entire exhaust heat thermostat containing the butterfly valve. The valve is usually welded to the thermostat shaft after it is assembled.

Mistakes to Avoid

Do not lubricate the butterfly exhaust valve with any kind of oil. Even the thinnest oil will make the valve seize and seal it tighter than before in either the open or closed position.