Birty Dastards Jeep Club
Tech Forum => Workshop => Topic started by: PhatDave on June 24, 2016, 11:14:57 PM
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Open to the wider jeep community knowledge Base, I'm confused...
My Jeep Grand (2004 4.7l HO) bubbles air into the expansion tank when stopped after going on a drive.
It does not do this if run up, only after a few miles on the road.
About 2 minutes after switching off the engine there is a bubbling noise coming from the expansion tank accompanied by the expansion tank becoming overfilled but not enough to overflow. Whilst this is happening the top hose is hot to touch and feels empty.
After a while bubbling the expansion tank suddenly reverses and starts going down until it stabilises at the correct level and the top pipe feels like it is full again.
During the drive the temp gauge stays normal (just below 100) but usually creeps up to just above once stopped or if the engine is being worked hard.
It has not overheated or overflowed, the water level always stabilises to the same level (I haven't needed to top it up), the heating inside works fine and there is no evidence of water and oil mixing.
I have just replaced the thermostat (didn't cure it), the coolant is less than a year old as the rad was replaced late last year.
Got a head test done with a sniffer thing at the local garage and came up negative.
Anyone got any suggestions!? I take it this isn't supposed to happen?
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airlock in the system which releases into the coolant bottle - level rises and bubbles the settles back down to a lower level.
this then gives the assumption that air is being sucked into the system somewhere and due to the nature of the leak it only allows air into the system
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As I understand it the cooling system is under quite a bit of pressure when hot, so how would it suck air in under certain conditions .... and where ever the leak is would there not be signs of this as coolant loss ?
Please understand this is not a challenge to your reply but more me wanting to understand better as my TJ has this same issue and has had for a long time.
Cheers .
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I've read that the 4.7's can be tricky to get all the air out, the method I read about and used when i did my water pump was to slowly fill with the bleeder removed till coolant comes out, put the plug in and start the engine and give it a rev up to push the coolant around then turn off, repeat till no more air present at the bleeder then run it thro 2-3 heat cycles
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if you have a pipe with an internal partial split (flap) then when operating normally the pressure is sufficient to hold the system intact and potentially partially weep which creates a misting, this misting then evapourates due to the temperture of the engine etc. this loss then creates a vacuum which then sucks air into the system. this trapped air then migrates to the highest point which is the header tank.
Jubilee clips on coolant system pipes are not advised as these dont expand with heat, and can cause damage to pipework when the system gets upto temperture
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This appears to be sorted now, done a few miles and haven't had the system bubble after stop, and the top pipe now feels quite solid once the engine is warm.
Turns out it was the radiator cap, bought a new one (aftermarket jobby with some kind of manual pressure relief valve in the top of it?) and that seems to have been the problem...
I guess my old cap was allowing no pressure build up causing the system to boil too easily or suck air in?
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