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420A "To burp, or not to burp?"


Proven Member
Jan 21, 2006
San Diego, California

Straight to the point: Are we required to "burp" our cooling systems?

I read multiple posts that swear by burping, and only a few that say it isn't required.

But it seems to make sense that the system will naturally expel air through the radiator cap/overflow reservoir upon cooldown. (Provided that you keep the fluid level in check so air isn't sucked back in)

But then I read all the issues that can happen with air trapped in the system...

History: I recently repaired a coolant leak. It appears that I've only lost less than a liter of coolant (the rubber heater hose clamps next to the t-stat housing were bad on my 420a). I elevated the car, turned on the heater full blast, waited for the thermostat to open, squeezed hoses, and added coolant as necessary.

Seems like I spill more coolant that the amount I try to top off.

I know about that special burping funnel, but for $20-$25? :/


10+ Year Contributor
Mar 2, 2010
treefall, Washington
A properly purged system is an efficient system. Some people think that the water pump will force liquid through the system and remove all air but the reality is that cavitation from the blades can keep churning it into a froth. 20-25 dollars to prevent overheating is a cheap price to pay. Just like the choice between paying $20 for a cheap socket set vs buying a mechanic grade set of tools, in the long run you'll spend more later trying to save a dollar or two now. You don't put the cheapest tires you can find on your car do you?


Proven Member
Feb 2, 2006
baltimore, Vermont
Had the radiator out of my car twice in the last month, never burped anything. does not over heat. Just fill the thing, check it after a few heat cycles, and be done with it.

As far as cavitation goes, it only occurs when the motor is running, then the air goes to the highest part of the system..... the filler neck.


Proven Member
Apr 1, 2009
Cary, North_Carolina
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Haven't airlocked an engine a single time that I've used it


Proven Member
Apr 6, 2008
Nampa, Idaho
I just drill a .050 hole in the flange of the T-stat.

Definitely cures any airlock in the cooling system - and this is with any vehicle that uses a T-stat that doesn't have a wiggle valve located in the flange..

..and those 420A blocks where the T-stat is mounted vertically, I'd fully recommend a hole drilled in the flange..


Banned Member
Dec 27, 2007
West Lawn, Pennsylvania
i voted "Suggested to get at least most the air out, but not a big deal if you don't."

it's not rocket science. you just fill it up, turn the car on, keep filling whenever it gets empty. for me it gets frothy but that clears up. i never have problems with low coolant. on these dsm's where you add the water is the highest point in the cooling system, so it's easy.

with cars like mr2's they have pipes that run under the car from front to back. people make those out to be a pain in the ass to get air out, but in my experience they aren't bad, and you don't even have to be on level ground.
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