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Temperature fluctuating because your thermostat opens up. How low it drops depends on your driving habits, but I can easily guess that you heavy on foot. Temperature drops to 80 by forced cooling during moderate heavy loads. There's a heater pin to keep thermostat open for that.
Check for air bubbles in heater system.
Repeat the same test with engine warm and increase engine rpms as high as the ECU allows. See if HVAC performance is related to engine rpm.
Did not get to this test yet...
As far as I can tell, I only have a single coolant expansion tank.
Jumped in the car tonite and no fan blowing at all! On any setting. Dash says correct fan speeds, but, nothing.
Now this thing is completely undrivable here in the winter in Chicago.
I can 't really find any threads relative to this issue, except a YouTube video of a loose wire under the passenger floor mat. Before I start theorizing what it might be...
We are dealing with the same issue. Our heat stopped working. Cause is a burst Dessicant bag (Silica beads) in the coolant system. These beads go through the entire coolant system and clog everything. We were told we could try to flush the system - but that did not work. We are now being told we have to replace the entire cooling system - quote is $10,000. This is a $20 part that they place in the coolant to “preserve” the liquid to avoid replacing the fluid. I am trying to figure out if there is a way to make Mercedes accountable for the horrible design and make them help pay for the damages. My car, that is in otherwise perfect condition, is now trash due to these unnecessary silica beads. The dealer has been no help - and we’ve always only serviced the car through Mercedes’ and did all recommended services through the dealer.
We are dealing with the same issue. Our heat stopped working. Cause is a burst Dessicant bag (Silica beads) in the coolant system. These beads go through the entire coolant system and clog everything. We were told we could try to flush the system - but that did not work. We are now being told we have to replace the entire cooling system - quote is $10,000. This is a $20 part that they place in the coolant to “preserve” the liquid to avoid replacing the fluid. I am trying to figure out if there is a way to make Mercedes accountable for the horrible design and make them help pay for the damages. My car, that is in otherwise perfect condition, is now trash due to these unnecessary silica beads. The dealer has been no help - and we’ve always only serviced the car through Mercedes’ and did all recommended services through the dealer.
Yep, spent all the $ at the dealer.
Find a reliable indy shop. Dealer did my coolant flush and like my original post, problem came back.
I did find a good indy shop and did a 2nd coolant flush(real flush, not just a drain and refill), WAY better results. I will do another(3rd flush) and perhaps a 4th as time passes.
The indy mechanic sent me pictures of all the crap the dealer missed. Unimaginable. But, considering the shortage of vehicles, turning and burning cars in and out of the service dept these days, seems routine.
We are dealing with the same issue. Our heat stopped working. Cause is a burst Dessicant bag (Silica beads) in the coolant system. These beads go through the entire coolant system and clog everything. We were told we could try to flush the system - but that did not work. We are now being told we have to replace the entire cooling system - quote is $10,000. This is a $20 part that they place in the coolant to “preserve” the liquid to avoid replacing the fluid. I am trying to figure out if there is a way to make Mercedes accountable for the horrible design and make them help pay for the damages. My car, that is in otherwise perfect condition, is now trash due to these unnecessary silica beads. The dealer has been no help - and we’ve always only serviced the car through Mercedes’ and did all recommended services through the dealer.
I had the same issue in my 2012 ML63. Low or no heat, intermittent fan force on defrost. It was indeed the desiccant and it fully blocked my heater core. I also had two directional control motors (there are eight under the top dash) that were jammed up. I had the whole system flushed, replaced the heater core and the two directional motors and now it is working perfect. Total cost was about $3000 because to replace the parts the entire dash has to come out (11 hours of work). The work included bleeding out any air in the system and a second flush. I still have to decide if I want to replace the desiccant bag. I am with others. Might be better just to replace the fluid from time to time. BTW, I cut open the old heater core and it was definitely crystals of desiccant inside. Now, it is back to fine motoring.
Hi! I have a 2018 GLE63 S Coupe. My heat suddenly stopped working, and I brought it to Mercedes-Benz after indy shop told me to. After inspection, they found the desiccant bag inside the engine had ruptured, releasing silica gel throughout my entire coolant system.
This silica contamination damaged the radiator, heat exchanger, oil cooler, heater valve, electric water pumps, expansion reservoir, and air quality sensor. They told me the only fix is to replace all of these components and do multiple coolant flushes. Total cost: $12,000.
The service team acknowledged this is a design flaw, not caused by misuse or wear-and-tear. Mercedes-Benz corporate offered me only $2,500 in goodwill — barely enough to cover a single flush.
This is outrageous for a performance vehicle that cost six figures new and clearly has a known defect. I’ve now been without my car for over two months, and the only solution Mercedes offers is to pay the rest out-of-pocket or accept a short-term patch.
If anyone else is going through this — you’re not alone. This needs more visibility. I am currently not sure if I should use the $2500 towards a flush ($2300 at the dealer) or towards replacing the parts ($12k at the dealer). The credit can only be used at MB dealers.
Can the Indy shop do it and how much? I lost all faith in the dealership as they want to replace anything and everything they can. On a different matter, I was quoted $7,800 for a repair, had it done elsewhere for $1,400. Nothing they claimed that needed replacement actually needed replacement.
2004 E 500 4MATIC Wagon; 2015 ML 350 4MATIC; †2003 C 240 4MATIC Wagon (2003-2022)
Originally Posted by arifk
Where is the desiccant bag located on the GL450?
I'd also like to know. I'm preparing to perform replacement of the thermostat and seals, plastic water pump inlet flange and seal, upper and lower radiator hoses and seals, plastic coolant lines, plastic fitting and hose at the firewall to the heater core/exchanger, and the coolant on my W166, a 2015 ML 350. I was wondering whether to replace the coolant expansion tank/reservoir while I was at it. On my old S211 E 500 (M113 engine), there was a pack in the expansion tank, which I replaced with the radiator, old hoses, lines, water pump, thermostat, and coolant temperature sensor (all original).
Is the pack in the W166/X166 coolant expansion tank/reservoir? I noticed that Mercedes-Benz seems to have pulled the W166/X166 coolant expansion tank/reservoir from their dealerships' inventory...which is unusual.
Same. I am furious. Have warranty from Continental. That was basically lighting $3500 on fire they never cover anything. You would think Mercedes would cover this as it is poor design. Pissed.
Also, upon further research on AllData, the AC drier that contains the desiccant cartridge is pretty cheap ($100-170 for genuine part from dealer). AllData shows 1.7 hours of labor time (minus AC evac and recharge).
I could not see any TSBs related to the issue discussed in this thread, but I didn’t dig too far.
I am curious if it is possible to remove the desiccant bag from the AC drier. Regardless, maybe this should be a preventative maintenance item?
What a bad design….
Last edited by mercbusky; Jan 29, 2026 at 09:05 PM.
Had the same issue with my 2012 r350.
Heat stopped working.
Fixed the auxillary water pump, no difference.
Flushed the heater core, worked great for 1 month, then back to no heat.
Finally, got the heater core replaced, and this fully remedied the problem. Once the silica beads rupture, they love to jam in the heater core.
Originally Posted by ChicagoPete
Hi,
New member here.
GL went into the dealer in early Dec... all 4(?) cooling lines to the turbos needed replacement.
That got fixed and picked up the car and had no heat. Said the desiccant bladder ruptured:
Replaced coolant bottle
Replaced heater pump
Replaced thermostat
Flushed entire system
Worked great for 3 weeks. Same issue returned. Minimal, luke warm heat.
And, I can literally see/watch the temp gauge fluctuate from 80-97, up and down while driving. Temp sensor bad?
Can the replacement coolant bottle with new desiccant bag rupture again?? How would I visually check if the bag is ruptured?
I’m sorry for you all that are experiencing this failure. Very frustrating. See image below from WIS regarding location of the desiccant cartridge:
After further review, it looks like there is also a silica bag in the coolant reservoir, which is probably what pertains to this issue (rather than the desiccant bag in the AC dryer).
Mercedes’s recommended replacement of parts for a ruptured silica bag is pretty extensive: radiator, oil cooler, heater valve, heat exchanger, and “electric water pump for the residual heating utilization system” (if applicable). Yuck. I’m guessing replacing the expansion tank preventatively every 100K would be a good idea?
First off the "desiccant filter" in the AC system has nothing to do with heater core problems. Its purpose is to remove moisture from the AC system. It never mixes with anything coolant related which is what circulates thru your heater core to provide heat via a blower to the cabin.
Theres a "silica cartridge" in the coolant resivoir that was designed to release silicates over time to protect aluminum components from corrosion as aluminum easily oxidizes. While they were meant to be a "lifetime" device, clearly they didnt test it long enough when they designed it and they're prone to failure. Just take the old ones out and replace with a new one. Or leave it out and flush your coolant at regular intervals with quality coolant and distilled water.
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