would a bad head gasket/bearing cause a car to be undrivable? (i.e. the car may have air bubbling through radiator, and there is coolant on the cylinders (bad head gasket is my guess)
thanks
It can cause an engine to run badly and destroy the engine entirely if allowed to continue for very long.
If the engine oil is diluted by coolant there may already be problems in the lower end of the engine; not just up top.
can it do this though with an engine that has 90k on it?
Yes it can. As ok4450 said, left to long will cause major damage.
A customer bought a brand new VW from a dealer I worked for one time and absolutely burnt the engine to the ground from overheating it. This near new car had less than 500 miles on it so they can become toast anytime.
Did the engine overheat on this one and did you continue to operate the car?