Auto-bleeders ....Yes or No?

I tried two separate types of auto bleeders. The first didn't seem to actually let the air out; the second had the bleeder unit on the thermostat separate and leak coolant about a year after I installed it. Luckily, I was close to home city driving when I smelled coolant and could see coolant vapour/smoke billowing off the hot engine.

While appealing, I decided that these units designed for home radiator use aren't built adequately for the high vibration environment of an automotive engine cooling system and that the risk of failure is too high for the added convenience that they bring. Possibly just my opinion (as a mechanical engineer), but I sleep better at night knowing that I don't have to worry about and watch for another coolant auto bleeder failure.

On the other hand, there are quite a few members who have installed these successfully and have not experienced any failures.

 

I installed one because I THOUGHT I was having a problem with air in the system. Turns out it was caused by using the incorrect type of radiator cap - one in which the little disc on the underside hangs down instead of being spring-loaded shut.

IOW, if there is air in the system after being properly bled or air enters the system, there is a problem that needs to be corrected. The auto bleeder may do the job expelling air but it is just disguising something that needs to be fixed.

As far as function, I had no trouble at all with the auto bleeder for the year I had it on the car. But admittedly, that's not much of a "long-term" test.

 

I bought a set from an fchatter a number of years ago. They've served me well.

 

I bought one too but have not installed it yet as my car has been running normally well, temperature wise.

 

Same here.

My car collects a pocket of air in the top of the radiator but it stays a stable volume so I don't worry about it and just leave it there.

 

My case was an actual "air in the system" problem caused by a blown head gasket. In the process of troubleshooting this issue I tried the auto bleeders and in my experience they don't work, at least not past the point after you first install them. The way they function is a hydroscopic material (that may not technically be the proper term) they bleed dry air until liquid contacts the substance and it closes. The problem however is that even if a new air pocket forms at the top of the radiator the active substance in the bleeder never dries out so it does not reopen and bleed the air. At least mine didn't, maybe it's the glycol I don't know. I replaced them with the drilled bleeders, I also fixed my head gasket, which was the real issue.

If all is right there should be no need for anything like this.