Originally Posted by jacob.a.gasparp
I just got this aluminum expansion tank for my 89 gt 5.0 and was wondering if the tiny hole in the top that looks like factory drill hole is supposed to be there. There isn't a hole in the stock coolant tank and was wondering if any of you know about this. I bought it from Mustang Parts & Performance - American Muscle
It is probably just a vent hole to keep it from building too much pressure in the tank. The stock one may not have it because the lid probably does not seal up as well as the aftermarket aluminum tank's lid does.