How long do these vehicles last before stuff starts falling apart?
Is buying a used 2020-2023 with 140-150k miles a dumb idea?
Is the 450 V6 known to last, say, 200k miles? Thanks!

Respectfully, yes, I'd vote that buying a 140-150K miles GLS X167 is a dumb idea. Can you even find a GLS X167 with 150K miles now?

As for the lifetime, I don't think there's a large, statistically valid sample of owners to weigh in on the 450 inline-6 lasting up to 200K miles. It's an inline-6, by the way, not a V6. I do think it'd be my go-to engine if you are planning to drive the car up to that mark.

It ALL depends entirely on the maintenance history of the car. Buying a Toyota Corolla with 150k miles with spotty maintenance history is a dumb idea.

The only questionable aspect of the 3.0t 48v hybrid engine that MB has in the 450...is the 48v battery itself, in my opinion. The engine itself is proving to be a very worthy setup in terms of reliability thus far. I'm at 90k on ours, and have had 0% issues mechanically with the car. Still on the same brake pads in fact, which is pretty remarkable considering how heavy it is. But, I maintain my fluids, at a minimum, to the manual's requirements. I change oil every 5k instead of 10k. At 50k intervals, all fluids / filters / plugs get flushed/replaced (except the fuel filter). We let it warm up before driving off. We don't floor it very often, if at all. We take care of it. I have little doubt it'll see 200k if it continues to operate the way it has been for the last 5 years.

When I went to pick it up off the delivery truck in September 2020, there was a guy parked in front of me in a white X166 GL450, trading it in for a new one. I asked him how he liked it - said he loved it and the new one was to be his 3rd new one in a row. I asked him how many miles he got out of the one he was trading in......430,000..... No BS, I looked at it myself to verify. Said the trick was all in the fluids. His interior looked ok, but clearly a family hauler, needed some attention but nothing that couldn't be fixed up.

Mercedes could not afford to screw up this new 3.0t engine set up. They've got it spread across multiple vehicles with different variations. If it were a bad setup, MB would be in deep trouble as a company.

I don’t disagree. But I also wouldn’t let that reasoning be my guiding light. There are way too many examples of engines that have problems that only show up after years of use — oil check valves, failing head bolts, faulty radiators, etc. I’m waiting to see what the long-term effects of ECO Start/Stop, cylinder deactivation, and 2-stage oil pumps, all in an effort to improve gas mileage, have on engine longevity.

I'll echo what nc211 said. With those miles, type of driving, environment, maintenance, etc are more important than anything else. I presume it has a significant amount of highway miles to be that high for the age. It could be a realtor or salesperson in which case it could be a lot of city driving. Were they doing 10k oil changes? I would want closer to 5k oil changes. Have the batteries (including the 48v battery been replaced? How long ago? You cannot determine how the person drove it unless you personally know them.

Lastly, I would have a good independent Euro shop inspect it closely before buying. AND the price is very important. At a certain price point, you can spend a little more and buy one with half the miles which should give you more miles before repairs.

Great advice. I think expectations have to be realistic, as well. If the price is $10,000 or $15,000, and your budget is $30,000, it might be a bargain if you are willing to put money into it. But with that many miles, I’d want detailed maintenance records and a good inspection. Otherwise, walk away.

I think most of the things you listed were for other engines, so doesn't apply to a GLS450.
The Start-Stop is innocuous on a 450 with its ISG, with few moving parts.

High mileage cars have the advantage of fewer city miles with the associated stop and go driving. It has probably been fully warmed up at each driving episode. Plus plus.
In many cases, the better choice is the higher mileage car. The only thing that wears out are the tires, and maybe the driver's seat.

I would be more suspicious of a five-year-old car with 15,000 miles than one with 100,000 miles.

I agree. But my response was to his comment that Mercedes could not afford to screw up this new 3.0t engine…it would be bad for business. I wasn’t saying that the problems I listed were for any specific engine since they were problems from multiple engines.

Just not the one he's considering.

The inline six has been trouble free, except for spark plug wire insulation deterioration, which can be handled during an A or B service, under warranty. It doesn't affect drivability.

I don't think we've seen any recurring failures on the forum.

When you trade your car in, it is worth more if it has less than 75000 miles on it. With less than 75000, it can be sold as a certified pre owned by the dealer.

Reb

Any engine will last hundreds of thousands of miles if you take care of it correctly and don't treat it like a rented mule. That's the key to any vehicle longevity, and an important reason to document your maintenance history if you plan on trading it in within 10 years. After that, who cares. There are many VW 2.0t's roaming out there with 200k+ miles because the owners were willing to spend the $1k to walnut blast the valves at around 75k miles, and replace the PCV for $300 about every 50k miles, while also doing the normal routine maintenance stuff.

What we don't know about this 3.0t I-6 yet, is how well they're holding up at 150k miles and what special tricks are needed for them. Don't think we've ever seen a carbon issue pop up, or any real oil leaks from blown seals (suggesting clogged PCV's). I'm probably one of the higher mileage GLS's on here at 90k, and it's been smooth sailing the whole time. Still purrs like a kitten and smooth as glass. First 50k were 80% highway mileage. Last 40k have been maybe 20% highway mileage - short runs to the store / schools.

Only item that is of focus to me is the transmission fluid. But that's not just on the GLS, but most MB's as the process to replace the fluid per the schedule tends to leave the torque converter ignored. It's a drain/fill of the pan, not a flush of the torque converter too. So, you're basically replacing roughly 50% of the total fluid with new. Yet, if the intervals (as way of example, I don't know them specifically at the moment) are say 75k miles for transmission fluid service, well that's 75k miles from 100% brand new fluid from the factory. The next 75k miles interval after the fluid change, is for roughly 50% of total fluid being brand new. Math doesn't add up in my brain.

When I had my W212, I did the trans fluid at 40k the MB way. At 65k I did it the flush way through the cooler lines to get the torque converter too and switched it over to Amsoil transmission fluid. The difference was night/day in smoothness across the board. The car would move nearly effortlessly. I'm going to do this with the GLS in a few weeks too (but sticking with MB transmission fluid).

@nc211 you bring up a point that I've been wondering about - the tranny fluid change.
Do MB shops normally drain both the torque converter at the required 60k (or other interval) service? Or do they just default to the pan only?
As I understand it, the torque converter has a handy drain and fill port that's accessed when the pan is off, or maybe even if the pan is left on.

Do I have to ask for the drain of the TC, (I will) or is it SOP?

I know on my 2014 W212, the TC was left untouched with no way to refill it. At my indi shop, owner has an older G550 as his personal baby and noted that most MB they work on (their bread & butter, a former MB master tech) don't get the TC addressed either. I'm not 100% sure on the GLS, I never asked when we did it at the 50k mark. I do know the entire pan has to be replaced as the filter is actually part of the pan (dumb), which is lovely. I'm pretty sure it's a drain & fill at the pan location only, but don't quote me on that. You can ask for it, but if the MB procedure doesn't call for the TC to be drained/filled, I wouldn't trust that a dealership will do it for you (liability). They won't have anything to fall back on if they screw it up, since MB didn't call for it as part of the service.

My indi, always flushes his fluid on his personal vehicles, never does just the drain & fill. They have a machine, goes in through the cooling lines I believe. Just have to bring him enough of the fluid you want to use. I had bought two 5 gallon jugs of the Amsoil for the W212, which ended up being far too much. Only needed one, but the difference it made was worth the wasted $50 (or so) for the left over.