GL450 constant air pockets on coolant
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gl450
GL450 constant air pockets on coolant
Hello all, Im new to the site. I have a 2009 GL450 and I have a strange at least to me a coolant overflow issue. I used a burping funnel to try to get all the air out of the system but like clockwork every 2.5 minutes the cooling system pushes out 1-2 gallons of water with a bunch of air/gas then sucks it all back into the cooling system to then repeat again. I gave already done a gas block test and it was negative the test fluid did not change color at all. No other leaks at all just the same sequence of the "high and low tide" of the coolant with air being expelled. Ive observed this for hours, not sure where all the air is coming from. HELP PLEASE!!!!!!
Super Member
Joined: Apr 2004
Posts: 625
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From: Germantown, MD
'07 GL450
A simple coolant flush and fill should solve your problem (video linked). Or you can try bleeding the system (video ref: 5:10). If this does not solve your issue, then you have a blockage somewhere which is indicative of a more serious problem.
If you go the flushing route, run some water through the system for a few minutes (AFTER you drain all the coolant) to push out any debris.
If you go the flushing route, run some water through the system for a few minutes (AFTER you drain all the coolant) to push out any debris.
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gl450
Hey there. So I've. Already ran a flush and drained the cleaning solution was actually pretty clean just a tiny bit of sediment came out. I would think a blockage would not cause the overflow pressure with so much air/gas every 2 minutes like clockwork? Also it seemed like a combustion leak but the block gas test was negative???
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Joined: Jun 2010
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From: Emmett, ID, USA
2007 GL450
Hey there. So I've. Already ran a flush and drained the cleaning solution was actually pretty clean just a tiny bit of sediment came out. I would think a blockage would not cause the overflow pressure with so much air/gas every 2 minutes like clockwork? Also it seemed like a combustion leak but the block gas test was negative???
I found getting the air out of the cooling system to be quite difficult. If air is trapped anywhere, coolant will boil within in the air bubble and push coolant out the expansion tank. You have to run the engine quite a while at idle, with the heater on (? it won't hurt; not sure if there is a valve on the heater line or it's just changing the routing of the air), and keeping only a modest level of coolant in the reservoir.
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gl450
Hi. I flushed the coolant system after the overheating issue. I used a burping funnel for over 2 hours just to see the same cycle of coolant pushing out 2 gallons, a bunch of air/gas, then engine sucks it all back in again. The large amounts of air/gas that constantly comes out would suggest a head gasket failure, but if there is even a tiny pin hole somewhere the cooling system once pressurized car will stay pressurized for hours. How would a high pressure system stay pressurized for so long with a potential air leak somewhere?
Super Member
Joined: Nov 2019
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From: Yeast Coast, Canada
GL550 X164
Do you see a correlation with the radiator fans kicking in and the fluid motion/bubbles? Run the heater when you're trying to remove air. It will open the thermostat and the fluid will circulate though the large heater loop.
I was chasing a biolover on a bike recently and after flushing the rad, I noticed an intermittent inoperable radiator fan, which is likely related to a fan sensor. I was told by my uncle who rides it, that sometimes he would see the fluid just get sucked out of the fill reservoir when that happened, and restore itself once the bike cooled off.
You might be dealing with similar conditions.
I would also drain and refill, with the thermostat open, then bleed, if you have not done it this way. It probably is not what WIS says to do, but you don't have much to lose. You can always drain and refill/bleed with WIS procedure afterwards if that does not work out the air out of the system.
I was chasing a biolover on a bike recently and after flushing the rad, I noticed an intermittent inoperable radiator fan, which is likely related to a fan sensor. I was told by my uncle who rides it, that sometimes he would see the fluid just get sucked out of the fill reservoir when that happened, and restore itself once the bike cooled off.
You might be dealing with similar conditions.
I would also drain and refill, with the thermostat open, then bleed, if you have not done it this way. It probably is not what WIS says to do, but you don't have much to lose. You can always drain and refill/bleed with WIS procedure afterwards if that does not work out the air out of the system.
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MBWorld Fanatic!
Joined: Jun 2010
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From: Emmett, ID, USA
2007 GL450
Hi. I flushed the coolant system after the overheating issue. I used a burping funnel for over 2 hours just to see the same cycle of coolant pushing out 2 gallons, a bunch of air/gas, then engine sucks it all back in again. The large amounts of air/gas that constantly comes out would suggest a head gasket failure, but if there is even a tiny pin hole somewhere the cooling system once pressurized car will stay pressurized for hours. How would a high pressure system stay pressurized for so long with a potential air leak somewhere?
If you had no incident, e.g. overheating, that would have caused head gasket failure, it's unlikely it happened quietly.
Hate to be so not useful, but: Did you run the motor at idle with the heater on?
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Joined: May 2015
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From: Allentown, PA
'08 GL 320 CDI
Maybe I'm missing something, but I don't understand... if 2g is pushed out the system through the reservoir (which is darn near the capacity of the entire system), how does it get "sucked back in"? Once it's out of the reservoir, it's out and on the ground.
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NGL450 w/EORP, S550
It’s doesn’t get sucked in, it gets compressed out.
There’s a gas bubble in the system somewhere, and since that is compressible, that’s where the reservoir fluid goes.
Until that gas bubble pressure overcomes the pressure in the reservoir and the fluid returns.
There’s a gas bubble in the system somewhere, and since that is compressible, that’s where the reservoir fluid goes.
Until that gas bubble pressure overcomes the pressure in the reservoir and the fluid returns.
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From: Emmett, ID, USA
2007 GL450
kinda like a toilet flushing and refilling, rite?
MBWorld Fanatic!
Joined: Jun 2010
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From: Emmett, ID, USA
2007 GL450
