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how to fill and burp your cooling system. - burpcoolingsystem

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how to fill and burp your cooling system.

taglines: burpcoolingsystem; suphonfill; burpcoolantsiphon.


compiled from previous posts:



1/ remove vent plug on radiator at top hose.

2/ fill radiator at fill neck / cap SLOWLY. (slowly is key.)


(i have written this a couple of times and it works great, for me. but it is so odd and extreme i really don't expect any one to follow it. sit the jug of coolant on the passenger strut tower and use a long tube, about 1/4 inch diameter, to siphon the coolant in the rad. the process is so slow you will get bored, but slow works in this situation. )


3/ when full install the vent plug and rad cap.

4/ start the engine and run it up to full operating temp. then shut it down and wait for it to cool down.

5/ open the rad and top it off. mine usually only takes a couple 3-4 oz.


(most folks run the engine with the rad cap off to burp it. but i have found that when it burps it looses more coolant than it really needs to so i just heat it up and then let it cool before i open it. all you really want to do is circulate the coolant and eliminate any air bubbles. the siphon is so slow it really does not need much burping or topping off. this is different than most other fill and burp process. )


good luck.




the last 2 times i have filled an empty cooling system on an ej25 engine, i have used a very unusual method and have had NO problems and have not had to burp.


i put the gallon of coolant on top of the engine, either the passenger strut tower or the air box near the firewall. i then use a small diameter tube (~5/16 inch, inside diameter) to siphon the coolant out of the jug and into the rad. (it helps if the tube is clear so you can see the coolant as it gets close to your mouth.) after the jug is empty, i then start over with a half jug (2 qts.).


this is a very slow process because of the size of the hose, but more so due to the very small difference in height. the system fills very slowly and has time to back fill the engine thru the top rad hose. i make sure the rad cap is at least level with or usually higher than the rest of the rad. having the vent cap open helps too.


the first time i did it i tried to burp it but i ended up wit h less coolant in the system than when the siphon had finished. so this last time i just let the siphon do its thing and then put the cap on. no problems.


it works great, but it is really, really, slow. so i do it while i'm finishing up the last little bits of whatever i'm working on.


this is so slow that if you did it and then watched it you would give up and start pouring long before it got done. but it is a great time to open a beer and admire your work.


i doubt this is a good technique for a car that needs to be burped, but it works great for filling empty systems.





for 90s legacys, the small vent cap is the trick to filling correctly. coolant WILL NOT flow into the upper rad hose / engine block unless you have the vent plug removed. and even then you have to fill it SLOWLY.


once you have slowly added as much as it will take with the vent plug open, close that, fill to the top of the rad and start the engine. when the t-stat opens the coolant will burp out of the rad and the level will drop. (in most cases it will drop, but if you filled it slow enough the system MAY be full.) top it off and put on the cap.


(my solution to filling slowly is to siphon the coolant out of the jug and into the rad. i use a 1/4''- 3/8'' clear tube about 10 feet long that i bought years ago and i use it for all of my siphoning needs. it fills the rad so slowly you get bored. but you can rotate tires or change the oil while you wait. once it is full, mine will not burp. it is full.)


on a side note:

if you used a non-subaru t-stat you are going to have trouble. they do not work and it will over heat. i know some of you do not want to believe this but it is true. i was one of them for a long time.


there are several parts on these engines that MUST be subaru. and hopefully you do not damage anything learning that.


SOMETIMES, not very often, a ''high quality'' replacement part will work, but ''cheap'' aftermarket parts are never a good solution for these ''subaru only'' parts. they end up not working correctly and you not only have to redo the work (twice the labor) you have to buy another, usually more expensive, part. buying parts twice is never cost effective, even if your labor is free.

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