Series L
Apply a layer of engine oil to the valve and check that it moves smoothly down in the oil filter bracket under its own weight. If this condition is not met, replace the bypass valve. If necessary, replace the oil filter bracket.
KZ series
Press down on the valve with a wooden rod to check for sticking. If sticking is found, replace the valve.
2. Checking the oil cooler. Check the oil cooler for damage or blockage. If necessary, replace the oil cooler.