Ford Mustang/Capri 1979-1988 Repair Guide

Heat Riser


Some models are equipped with exhaust control (heat riser) valves located near the head pipe connection in the exhaust manifold. These valves aid initial warm-up in cold weather by restricting exhaust gas flow slightly. The heat generated by this restriction is transferred to the intake manifold, resulting in improved fuel vaporization.


The operation of the exhaust control valve should be checked every 6 months or 6,000 miles. Make sure that the thermostatic spring is hooked on the stop pin and that the tension holds the valve shut. Rotate the counterweight by hand and make sure that it moves freely through about 90° of rotation. A valve which is operating properly will open when light finger pressure is applied (cold engine). Lubricate the shaft bushings with a mixture of penetrating oil and graphite. Operate the valve manually a few times to work in the lubricant.