Losing Coolant

[Kisner]

After I drive my 68 Mustang and turn the engine off, coolant runs out of the overflow tube for a few minutes. It's not a lot, maybe a half a cup or so. I'm puzzled as to what might be causing this. It has a mildly sooped up 302 in it with a mild cam and a 600 cfm Edelbrock carb and a 20-inch 3 row radiator. Am using a 13 lb. radiator cap and a 160 degree thermostat. I've been told to just add one of those aftermarket overflow containers but wanted to keep it as original as possible. Was also told to use a 16 lb. radiator cap but the folks at AutoZone told me it should have the 13 lb. cap and that running a 16 lb. cap would just make it run hotter. It's not overheating according to my temperature gauge, just curious what might be causing this and is it something I need to worry about.

[rbohm]

you do need an overflow tank, but it sounds like to me that it is just that you have a bit too much coolant in the system. try not filling it after it does this and see what happens after the next drive. the cooling system will seek it own proper level and will puke out excess coolant. it has to have the expansion room. that said, if it does it again with you not refilling the rad, the you might have the begining of a head gasket problem or other cooloing system problem.

[66StangGuy]

you might be having the same problem as I did.
is the coolant really foamy?

what is the coolant mix 50 50 or 30 70?

whats the condition of the water pump. Is the pump rusted internally?

check all your hose clamps. i had a problem where one of my clamps were not seated right so the cooling system sucked in air and made bubles in the coolant making the foam. i removed them all and reset them down. doing that and flushing the cooling system with water and then putting in a 30 antifreeze and 70 water mix. all my problems went away.

also if this does not work or you may want to do this first. check compression in all cylinders and see if one or more vary from the rest. you may have a blown head gasket. also check the oil and make sure there is no water in it. you will be able to tell by the dipstick after running the motor. it will be nice and creamy white or brown.

[Kisner]

The motor is newly rebuilt (less than 100 miles on it), however, it sat up (cranked every weekend though) for about 8 years during the restoration process. There's no foam in the coolant, no water in the oil, and no other leaks anywhere else. Water pump appears (on the outside) to be working perfectly and engine runs great. All hoses and clamps are new and seated perfectly. One thing I may have screwed up though is that I believe I'm running 70% anti-freeze and 30% water. I also had it filled to the top of the radiator - didn't think to allow room for expansion. If I have too much anti-freeze will that make it expand out the overflow tube?

[mustangII460]

Its going to spurt out water about everytime it gets hot then is shut off. Normal.

Go to the junk yard and get a recovery tank/washer fluid bottle and mount it on the fender well. I like the mid 80's type, any Ford.

After your motor cools off, it will suck back the freeze it pushes out, filling it back up.

[gofastmercury]

I've heard that there is two types of caps out there, one for a closed system and one for an open(like you have). I would check into this, becauce this sounds just like that kind of problem.

[Kisner]

Thanks for all the info. Wasn't aware there were 2 different type of caps - will check into it. I did siphon out all the coolant that could be from the cap (less messy than draining radiator and starting over) and added straight water since I got the impression I might have too much coolant. Based on my measurements I dropped the ration from 70 - 30 to about 63 % coolant and 37% water. Is this still too much coolant? Stupid me wasn't aware that the anti-freeze expanded when heated.