Originally Posted by
Longdistancetrucker
I'm pretty sure that pinhole is supposed to be there it could be one of 2 things
1) The "jiggle valve": allows air to escape and not become trapped in the cooling system and create a vacuum. In other words it is there to help the head fill after coolant has been drained.
2) The hole in the casting to allow vapor (steam) to vent. If you have a lot of fluid coming out of it, it may be a sign to check your water pump.
Regarding your special coolant question: Yes, there are different grades of coolant required, just MAKE SURE it is aluminum safe
I'm absolutely certain you are dead wrong. Unless of course these engines are designed to leak coolant into the valley and drain the cooling system completely overnight. Get real dude. Pin hole is supposed to be there. Seriously?
It is definitely as a result of either corrosion or damage from a botched repair. Either way, I am fixing it and probably selling it.