I have a four winns 2000' with a volvo penta4.3L GL model with vdo gauge cluster. While running at what seems to be a normal operating temp the water temp indicator always reads cold. The temp sensor resistance is good drops when engine warms up. I check also resistance at the gauge cluster connector, same thing reads higher when cold and lowers when warmed up. I am assuming it is the temp gauge. The four winns 2000 has a vdo gauge cluster is there any way to check the gauge before changing?