Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

Oil Cooler Bypass Valve



See Figure 1

  1. Raise the car and safely support it on jackstands.
  3. Remove the under cover from beneath the engine.

Click image to see an enlarged view

Fig. Fig. 1: The oil cooler bypass valve is retained by a cap nut

  1. Drain the engine oil.
  3. Remove the cap nut and pull out the bypass valve. If necessary, test the valve as described later in this section.

To install:
  1. Position the bypass valve in its chamber, then install the cap nut.
  3. Install the under cover beneath the engine, then lower the car.
  5. Fill the crankcase with engine oil. Start the engine and check the bypass valve cap nut for leaks.


Remove the valve from the oil cooler and place it in a pan of cool oil, then gradually heat the oil until it reaches 149-158°F (65-70°C). Use a thermometer to verify the temperature. When the above temperature is reached, measure the protrusion of the valve end. The end of the valve should protrude through the valve housing at least 0.2 in. (5mm). If not, replace the valve.

Oil Pressure Control Valve

See Figure 2

The oil pressure control valve is located at the bottom of the front engine cover and is accessible by removing the oil pan. The valve prevents engine oil pressure from becoming too great. The valve should be trouble-free. However, if you suspect a malfunction, remove the valve, then check the plunger and spring for signs of corrosion or damage. Measure the free length of the spring. It should be 2.87 in. (73mm). If not, replace the spring.

Click image to see an enlarged view

Fig. Fig. 2: Oil pressure control valve assembly