Interesting Thermostat To Purge Air From System

[NoNeck]

OK, I know we have argued over whether to drill an 1/8" hole in the thermostat to allow trapped air to escape from the cooling system. Some say "NO" and some say "I Always Do". Well, I put this 68 year old brain to work remembering what an old Auto Parts guy told me around 1971. My 1966 SS 396 Chevelle started overheating after I changed the thermostat.

He explained to me that even though the parts books (no computers back then) called for this particular Stant thermostat, it was not the BEST CHOICE. He went on to explain that most of the earlier thermostats utilized a "Air Bleed" design to help eliminate pockets of air in the cooling system. Later designs were going away from the Air Bleeds for one reason... closed systems. Basically, the newer cars featured coolant recovery tanks which helped bleed off trapped air more efficiently.

I guess what I am saying is that maybe if your truck has coolant recovery tanks you really don't need the bleed hole? But if you have the old fashioned system with just the overflow tube maybe you do need a bleed hole?

Just food for thought. Just so happened that I bought 6 of those thermostats from him back in 1971. After cleaning out my garage yesterday, I found the last one stashed away inside an old box of junk. The original Stant box is long gone and I forget the part number, but here is a picture of what the thermostat looks like. You will notice the bleed valve (red arrow) as seen from the top and bottom.

POP

[Steve Cole]

Great post with useful information! Also, good to see a 68 year old that is computer savvy!!

[mike16]

function of coolant recovery tank has little or no relationship to the need for a bleed hole in the thermostadt other than that they are both part of the cooling system. Also I would caution you to consider the lack of corilation between a thermostadt bleed hole and air pockets in and around the cooling system.

GMC six's up through the late 50's had those notorious air pockets that would actually result in overheating bad enough to crack the head. no bleed hole of any size would prevent those air pockets from going away.It required a special hand pump of some sort that fit over the radiator fill opening to fill with water pressurize the system and displace the air with water. it was a process that had to be done several times to remove all the air. If I recall the mid engined Fiero needed the same device to displace the air and allow the addition of coolant. failure to do so would result in overheating and cracks in those unique fiero 4 cylinder heads...

Stant makes a very good thermostadt But the one....with the bleed hole.... that most nascar boys use are made by stewart.