Howdy! My 1984 C20 Suburban 6.2 (used to be military vehicle)...low coolant light goes on and off and on and off with cold engine and even warm engine running. Radiator is full with 50/50 antifreeze. It does not have reservoir tank. I just bought it a few months ago. Own many trucks and suburban for 40 years but this one is my FIRST diesel. So what should I go and see if I can have it fixed? Thank you for your help.