My friend has a '91 RS with the 305 TBI. During our cold spell he was letting his car warm up for 10 t 15 min. before driving to work.

When he would get in the car it was toasty warm, but after 5 t 10 min. of driving the heat would turn to cold air and the temp. gauge would drop drastically (below 80 Celcius).

His fan is not running on, the thermostat is new, system has been checked for flow and press., mixture is good, sending unit has been replaced aswell as the divertor valve(?).

His mechanic has put calls in to other GM mechanics to no avail.

Any thoughts?

tj

 

Couple of things, one if there is trapped air in the system the temp will fluctuate drastically. Second, what temp thermostat does he have? Did anything else occur when he developed this problem, was it after it was serviced? What does the level in the coolant recovery bottle measure. Does it read properly between full cold and full hot? The only time I have seen this is with either low coolant level or if the system was not properly bled of air when it was opened up. More info might help.