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 baybuscamperkid
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| posted on August 13th, 2006 at 07:23 PM |
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bleeding air from water system with under car rads?
hooray hoorah, got my bus running today for the first time this year! after some battery issues she fired up and ran incredible smoothly, most of my
wiring seemed to be right, etc, only one small problem - airlocked water system. i have 2 small radiators hooked up together under the car, so the
highest point of the water system is the thermostat housing at the top of the engine. to counter this (and act as a top-up filler) i have installed a
tank in the van which has a rad cap and 2 connectors on its base which run to the overflow inlets on the radiators. this setup worked successfully to
fill the engine and is mounted high enough that when the system appears to reach equilibrium the tank is 1/2 to 3/4 full. i have also installed a
thermostat housing off a saab, seeing as they came stock with the rad lower then the engine, they had a threaded valve at the top of the thermostat
housing that could be twisted to release air (which it did successfully when i was filling)
so when i ran the engine today i opened up the valve on the thermostat housing and left the cap off the filler tank in the hope that it would visibly
drop in level when the engine warmed up and the thermostat opened. after a little while i checked on the valve on the thermostat housing and found
that it was slowly dripping water so my father decided it would be best if it was closed. he then noticed that water was overflowing from the filler
tank. i shut off the engine when it reached 110deg as i found both rads to still be cold. about a minute after i shut off one of my joiners on the
lower rad hose popped, sprayign steam and water.
my assumption is that there was an air bubble at the top of the engine whichwas stopping cold water from entering the top, and this is why pressure
built up and the bottom line blew. does this sound like it would be the reason?
if so what is the best way to clear the air block? my current thought is to remove the thermostat, run the engine cold to get it flowing, then once
all the air seems to have cleared, remove the thermostat housing and replace the thermostat, then open the valve on the housing and fill the filler
tank to force the air bubble created by removing and re-fitting the thermostat housing out of the valve. does this sound like the right way to deal
with it?
sorry about the long post, any feedback/comments/ideas greatly appreciated. cheers
Ryan
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tassupervee
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| posted on August 13th, 2006 at 09:18 PM |
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K the header tank you have (which is pressurised) needs to work as a de-aerator from the highest points in the system.
Having the tank feed the top of the radiators is fine enough so long as the radiators themselves dont have pressurised caps.
If you have pressurised rad caps then that syatem will only really work as an overflow bottle.
If the header tank feeds directly into the rad tops via the rad tops sans pressure valves (plain caps) then thats fine.
Bootom line is tho that you dont have any way of de-aerating your system and the very business and important end.
You need a bleed point from preferrably immediately below (but if the thermostat is drilled then above in the thermostst housing will work) the
thermostat feeding into the header tank and the return from the header tank feeding back into the waterpump inlet.
Any air in the system will make its way to the top of the system, out via the bleed into the de-aeration tank, and the tank feeds the pump inlet
ensuring there is some pressure differential and water actually flows all the time when the pump is running.
If you like to be real scientific, you can bleed the high points in the radiators into the de-aeration tank as well to remove pesky air that has
gotten past the bleed hole at the thermostat and will tend to sit in the top of the radiators.
At the very least, a bleed nipple at the very top of the thermostat housing feeding the header tank and the header tank drain plumbed back low in the
system will suffice and will provide a path for air to go up and away from the thermosts housing.
Also ensure your thermostat has a small bleed hole in it.
Some thermostata have a small ball valve thingy in there.
The thermosts should be kinda offset and the thermostat guts itself should be placed at the lowest point in the system (if its not straight up and
down) and the bleed hole to the top.
If the thermosts does not have the hole, just drill one (3mm will do) in it in the widest part of the flange and make sure the hole is uppermost.
This will allow any air trapped under the thermostat to bleed out.
The amount of water bypassing thru the hole is insignificant and not to be considered.
I hope all that makes sense M8
L8tr
E
Im not a complete idiot, quite a few parts are missing....
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GeorgeL
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| posted on August 14th, 2006 at 08:16 AM |
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Consider the burp tank to be a air collection chamber. It has to be higher than the high point of the cooling system and have some manner of getting
air into the tank and trapping it there.
The simplest way is just to put a burp tank on the coolent outlet of the engine and then plumb the botton of the burp tank to the radiators. Pretty
hard for bubbles to bypass the tank when all the coolant passes through!
Others put a tee on the high point of the outlet hose pointed upward and then connect this to a burp tank with a single line. This works, but it's a
lot harder to get the system full with this setup.
Any system where the burp tank is connected anywhere below the high point of the system is unlikely to work. There's just too many places for air to
hide out.
George
[ Edited on Aug 13, 2006 by GeorgeL ]
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baybuscamperkid
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| posted on August 14th, 2006 at 10:38 AM |
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cool, as mentioned i do have a bleed nipple at the upper most of the thermostat housing which is adjustable - on/off via loosening/tightening it. i
will have to check if the thermostat has a hole, i did think about it but i have a feeling there mightent be one there. i was intending to leave the
bleeder nipple free as it was on the saab that the thermostat housing came from, and just open it to release the air when necessary, do you think it
would be better for it to be premanently open and hooked to the top of the header tank (there is a spare opening there) or should it be sufficient to
open it when filling and during the first run to release air?
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pete wood
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| posted on August 14th, 2006 at 02:34 PM |
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bbck, a pic says a thousand words. can you put one up so we have a better idea of what the system looks like? a pic of the top of the motor where the
thermostat housing is and a pic of your pipe work would be great. It'll really help us to understand how it works better.
BTW, good stuff on getting the rad off the back of the car and putting it underneath. 
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tassupervee
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| posted on August 14th, 2006 at 05:29 PM |
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| Quote: | Originally
posted by baybuscamperkid
..... do you think it would be better for it to be premanently open and hooked to the top of the header tank (there is a spare opening there)
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Hook it up permanently. Always have a live point at the top of a system where the radiator is below the top of the cooling system. Air can gather in
the system again from a variety of conditions which may not appear obvious at first.
A not so good water pump impeller design can cavitate at high revs and aerate the water (a-la-2Ltr OHC Ford) and the list of gremlins can go on.
L8tr
E
Im not a complete idiot, quite a few parts are missing....
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baybuscamperkid
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| posted on August 14th, 2006 at 06:44 PM |
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hmm, will have to find soemwhere safe in the engine bay to fit the tank then, at the moment it is mounted inside a cupboard above the rads, so a hose
running from the thermostat housing to the tank would have to go up and down and therefore would create another potential airlock
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baybuscamperkid
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| posted on August 14th, 2006 at 06:54 PM |
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heres a rough sketch, hope it explains it a little better
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boof2332
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| posted on August 15th, 2006 at 07:13 AM |
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Park it on a hill with a 2 litre water bottle full, sitting in the fill point. It will not piss out, like a spring water holder in a doctors surgery.
It will increase the high point and slowly bubble away purging the air and replacing it with water.
The other way, like I have, is from the high point on the rads, have a little ball bearinig valve that you can open to expel air on the end of some
fuel line.
Matt
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baybuscamperkid
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| posted on August 15th, 2006 at 10:05 AM |
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interesting idea matt, i happen to have a steep driveway 
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