My SUV (it's actually an ML 350, but this should also be applicable to the 2016+ W166 GLE 350s with the M276 engine) is now 10 years old and is approaching 100,000 miles on the odometer. I have already addressed the very few weak points of this otherwise reliable (for us, at least) vehicle. The only common source of trouble in older and higher mileage W166 vehicles that we have not yet addressed is the cooling system, and I'd also like to perform a coolant replacement soon (has never been done yet...yes, I realize that Mercedes specifies 15-year intervals for this). Based on my understanding, the most common problem areas are: leaks from the plastic thermostat housing or the associated seals, leaks from the plastic water pump inlet flange or its seal, leaks from the radiator hoses at the connector ends (i.e., from corrosion at the metal end: ...and I also don't trust the plastic connector ends at the radiator), leaks from the plastic coolant expansion tank line or its connector ends, and leaks from the plastic fitting and the hose connector at the firewall going to the heater core/exchanger. I've also read of leaks developing at the upper corners of the radiators, but I'll just wait out that potential issue and keep an eye on it. There's also a plastic fitting going from the thermostat between the cylinder heads, but this is extremely uncommon on the naturally-aspirated M276 engines, I believe (I had the service coordinator at my shop, which has performed that particular repair and authored online videos about it, scan through their customer records, and they only encountered the problem on the turbo-charged variants, at the time...), so I am going to skip that (removing it is a tricky job if that plastic pipe/fitting hasn't already begun to crack apart, and it's an involved job nonetheless...). I'm also not too sure about replacing the water pump either, since I haven't heard from too many out there who have experienced failing/leaking water pumps on these yet. What sort of lifespan are owners getting out of these water pumps on the M276 (I realize that the pulley and housing cover inside on the engine side are plastic...and that pulley is a weak spot)? Has anyone had to replace his/her car's M276 engine's water pump already (I know that the plastic pulley is notorious for "walking out" from the M278 & M157 V8 engines' water pumps at 10+ years/100,000+ miles)?

So, 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 2015 ML 350. I'm leaning towards replacing the water pump too. I was wondering whether to also replace the coolant expansion tank/reservoir while I was at it, since I have been reading on the W166 & X166 forums of owners experiencing plugged radiators and heater cores resulting from burst additive packs in recent years. On my old S211 E 500 (M113 engine), there was an additive pack in the expansion tank, which I replaced together with the radiator, old hoses, lines, water pump, thermostat, and coolant temperature sensor (all were the originals, and the transmission cooler lines were severely corroded...and the car was due for a coolant flush anyway, since the previous owner last had one performed over 13 years ago when he had his Mercedes repair shop replace the changeover/heater control valve). Is the additive pack found in the coolant expansion tank/reservoir (i.e., Mercedes-Benz part#: A 166-500-00-49)? What's interesting is that I noticed the W166/X166 coolant expansion tank/reservoir is pulled/NLA from the dealerships' and MB U.S.A. parts catalogs...which is unusual. Is a new revision/supersession of this part expected?

 

Good idea to post it in this sub-forum, best of luck in getting this fixed OP.

 

Good list of projects.

Good news, and strange because it is unlike other German brands, that MB cooling systems seem generally robust and do not have too many immediate catastrophic failures like Porsche and BMW do.

Upper radiator mounts are known to crack and coolant residue is the symptom. I would let that one happen and not proactively replace it.

Water pump, t/stat, top and bottom hoses, expansion tank, and dedicated cooler hoses and fittings (engine oil, transmission oil) are good to proactively replace.

 

That is surprisingly positive.

 

The only reason I am delaying is that I'm not sure what is going on with the coolant expansion tank. Every W166 & X166 (both MB and AMG variants) forum seems to have a growing number of owners reporting burst additive packs resulting in plugged radiators and/or heater cores in recent years. Unless I am mistaken, the culprit pack is located in the expansion tank (much like the one for the W211 M112/M113 cooling system), but it (i.e., Mercedes-Benz part#: A 166-500-00-49) seems to be unavailable from Mercedes-Benz USA and the dealership parts departments now... This is a big red flag to me. Although there are some NOS expansion tanks available at a few of the online Euro part suppliers' warehouses (being marked up/gouged...), I think that I will wait until a new revision/superseded expansion tank becomes available, in case there is an issue known at Mercedes-Benz internally that is being addressed. Reports from owners who have experienced this issue indicate that they are getting reported back to MB USA via the dealerships' service centers and even receiving some amount of goodwill assistance from Mercedes (honestly, not very much compared to how much the total repair costs are at the dealerships...). Anyone know the story? I realize that there are a few aftermarket options for the coolant expansion tank, but I don't know anyone who has experience with those...

Last question (if you don't mind): Are you still on your original water pump? I am curious as to their longevity for the naturally-aspirated M276 engines. The shops I deal with in the area have already replaced a number of the original water pumps for the V8s (M278 & M157), which is a different part than for V6 engines. I'm not seeing reports of failures of the water pumps for the M276 NA V6 MLs/GLEs reported online, but I might just be missing them... Other sources of problems and leaks are a different story. I'd rather just leave the water pump itself alone, if they aren't an issue on vehicles with the M276s.

 

120 k miles here… no water pump issues.
The V-6 engine…

 

I ran the W166 M276 3.5NA for approx 105k miles and it had no cooling problems or failures and had factory components when I sold it.

BMW puts the desiccant bag in the expansion tank. If there is a high mileage problem with ruptured desiccant bags on W166 I would put expansion tank replacement higher on the priority list.

I would not wait for MB to make a design change on an out of production car/part. W166 has been out of production for 6 years and car companies put nearly zero effort into supporting such products.

 

The radiators that come on the 164's and 166's are crap. Just proactively replace that along with the coolant breather hose at the top of the engine at 100k.

 

Yes, I'm planning to replace that plastic line. There's a another plastic line running on top on the left side (driver's side in North America) behind the coolant expansion tank/reservoir towards the back of the engine, but I cannot figure out the part number. Does anyone know what it is?

As for the radiator, would you happen to have a recommended make? Are the Nissens any good? I'm a bit reluctant about the Chinese-manufactured Mahle-Behrs. The only other aftermarket ones from a reputable manufacturer I know of are the Densos, and they are much cheaper (around $150 still). I've mentioned them elsewhere on the W166 forums but haven't gotten any feedback. Incidentally, I don't even know who the manufacturer is for the OE Genuine Mercedes-Benz W166 radiators in Mexico. If I were planning to hold onto the vehicle for more than a couple of years and put on significantly more miles (I'm not...it's sitting at a little over 95,000 miles, and I don't have long commutes with it anymore), I would have already purchased a radiator for it. The prices of radiators are shooting up now. I had loaded up on the more expensive parts I wanted to replace for my vehicles starting last fall (got a ton of deals for items that have since gone NLA for my older vehicles or have more than doubled in price since then)...and I'm glad that I did. I can still get deals on a few items (thermostats, plastic parts, coolant hoses, pneumatic lift struts, brake parts, etc.), so I am stocking up on those now, while I can...

 

It's a priority, but I'm just not sure what part to get. Do I trust the remaining NOS/remainder stock Genuine Mercedes expansion tanks when some owners with 2018 MY GLEs/GLSes are already experiencing failures (admittedly, I don't have full data on the scale of the issue...only anecdotes/reports from owners on the MB & AMG GLE/GLS forums)?

In addition, I haven't heard any feedback from those who have installed aftermarket ones. I've listed a number of them below*...but there are also a bunch of off-brand Chinese ones in addition to those.

The latest from Mercedes-Benz's Parts Specialists is that there are zero of the Genuine Mercedes expansion tanks in stock at the dealerships, MB USA, or in Germany... According to them, they have not been discontinued entirely. Rather, they are actually on backorder and trying to re-stock them with new units (but perhaps with a new, superseded part #?), but there is no ETA yet. Latest prices for these were most recently $144 at MB USA and $160+ at my local dealership. It seems that Mercedes-Benz is being silent as to whether there are known issues being addressed in the forthcoming parts.

*Aftermarket W166/X166 Coolant Expansion Tanks (not listing all of the Chinese ones on eBay, Amazon, etc. such as Hamburg-Technic, SKP, etc.):
AKS DASIS 123025N
FEBI BILSTEIN 101013
MAHLE BEHR CRT231000S
METZGER 2140156
NISSENS 996207
NRF 454091
OSSCA 24453
REIN EPT0126
SWAG 10101013
THERMOTEC DBM014TT
TRUCKTEC AUTOMOTIVE 0240319
ÜRO URO011471, URO018236
VAICO V308405

 

Thank you for sharing. My preference would be 5 years all fluids out, except brake for every 2 years and oil twice a year. Over 10 years old, all fluids every 3 years -- either German or Japan.

I don't know much about 2018 GLE 43 AMG/M276. In the last 4 years of ownership, I did not have any issues yet. Just added 2018 GLE400 into the family, search around for common issues in the forums, and will replace all fluids soon. I hope to run GLE over 250K miles like Lexus.

Past experience, I ran Lexus ES330 over 250K miles with original hose, water pump and power steering. Just start leaking now -- power steering pump and front/rear head gaskets. The engine and transmission is still going strong.

 

There is no guarantee that the M276 can reach 250K miles with the original stuff but I guess not impossible, the M276 is still a very reliable engine but maybe not as reliable as the Lexus.

 

As far as what type of radiator, I purchased a Chinese radiator off Ebay and they have all been better than OE. I had one that was slightly warped so it was a bear to get on a car that is terrible to do a radiator install on, GL63, but works beautifully. The OE versions of the GL/GLE/GLS radiators are terrible and have been so for a long time. Every one of mine has leaked around the plastic coolant expansion line or the upper main hose area. The plastic cracks, leaks, and it's done. I've had 5 of the 164/166 GL/GLE/GLS's and everyone that had over 100k miles had to be replaced. In full transparency, I live in a very hot climate so they may last longer in a cooler climate.

 

I previous owned a M113 (W209) /M113k (W211). The issue with the coolant was the Valeo radiator. Where it cause the coolant to mix with the transmission fluid.

 

Well, it looks like I am also adding a radiator to the list. Just ordered a Nissens radiator while it's still reasonable (165 USD). Like I mentioned last year, the radiator "might be a matter of when and not if it will fail."





Close-up image shows that coolant is starting to seep out of a seam in the upper left-hand corner of the radiator just below the mount bracket...

 

Yep, they are crap!

 

From the small number of reviews I've read, the cheaper Slovakian-made Nissens aftermarket radiator is decent and supposedly fits perfectly. I saw only one comment online (on Reddit) regarding an installation of a Chinese-made Denso radiator (some online parts dealers are now listing it as discontinued...) in an AMG GLE 43 that also "went well," but there wasn't any follow-up regarding subsequent reliability. I'll follow up once I get the job done.

 

I have used Behr on my CLK Never had any issue. Something to look into

 

2017 AMG GLE 43 under 70k

Had Expansion tank cap fail and replaced in 21. Starting to smell antifreeze evaporation, had a small puddle once after sitting a long time in late winter under passenger side radiator Have had to add cooling fluid (warning light) in the last week or so, so into the shop it goes. Suspect radiator / hose issue as described above, will report back once repaired.

 

Source for leak was the lower radiator hose combo "T valve" (shown in OP's YT video) was seeping, replaced and system flushed.

 

Thanks for the follow-up on your coolant leak. That's why I have included the radiator hoses on my list and already purchased them for my cooling system overhaul/maintenance service.

 

I just drain the radiator and reservoir tank, then refill, usually G05.

It's really just a matter of recharging the additives. HD diesel trucks use a concentrated additive for this purpose. MB usually has a packet of silicate in the reservoir tank for this very purpose.

Changing half to fresh fluid is good enough for a passenger car. Do it again in a few years if you're picky.

Really the only technical reason to change is if a part in the coolant system is changed, in order to recoat the metals.

G05, G40, G48, G12++, G13 all the same. The only difference is color and mfg part numbers