I have never had that happen with mine. I have the same setup. If you install a thermostat which comes with the hole in it, or drill a small hole in yours, I'll bet your problem goes away. You might have a sketchy thermostat which opens all at once rather than gradually.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission