1990 isuzu Trooper 127k. I drive the car about 40 miles each day. I top up the rad’ but in about 4 days, the car starts to overheat. It pushes the coolant to the resevoir until the res’ is full but doesn’t suck the coolant back as the the engine cools. Changed the timing belt about 2k ago. Runs very well other than for the coolant problem. Should I have changed the water pump or do I have a head gasket gone? Thanks.

It’s possible you MAY have a head gasket leak but perhaps the rad cap is faulty.

Changed the rad cap already, when the problem started. What I’m wondering is…could the lack circulation, caused by a bad water pump, cause this problem? I believe the answer is a resounding maybe? So, do I go for the water pump change or do I attack the head? Start with the WP. Is there some way to “test” whether or not the WP is in fact working? Thanks.