BlownV8

330 hp is the most I've seen with just a tune and that's with removing all the emissions components. What have you seen out there?

geniushanbiao

Same here. But the 330hp diesel is putting out 750Nm torque which is more than the V8 in the 550. You can't compare diesel and gas engine simply by looking at the hp. Diesels are born with smaller hp and larger torque. More tune is available but you need to upgrade hardware like turbo and HPFP. The stock turbo is really crappy. Also some people talked about increasing the pressure in the fuel rails.

Be frank the biggest factor that limits the tuning is the crappy diesel sold in US. With only 40 cetane the OM642 was initially detuned to make it work with the diesel here. In europe the standard diesel sold are 51 cetane. The motor is stock tuned to 261hp/620Nm in Europe even with the DPF and EGR installed. And you have to take into consideration that the OM642 has only 3L displacement while the M278 has 4.7L. Diesel engines easily outcompete gas engines at similar displacement due to the higher overall efficiency of Diesel cycle compared to Otto cycle.

BlownV8

The M278 with just the tune will make over 780 NM of torque. Where the diesel falls flat, the gas engine is still going. There is no magic here. HP= (Torque X RPM)/5252. Since the diesel does not rev it won't typically make big Hp. Remember, again, HP is just the measurement of torque at an RPM. No replacement for displacement but the diesel does a good job with what it has.

The diesel does have an advantage with power generation and efficiency since diesel fuel contains more BTU's than gas. Yes, the diesel cycle is also more efficient than the Otto cycle. I'm a huge diesel fan just not a fan of the OM642 based on the extremely high maintenance costs as well as the high failure rate of components that lead to high engine failure rates.

RostamDastan

If your goal is acceleration, then a gas engine with high HP is the way to go. If your goal is to tow a heavy load, then a Diesel engine will easily outperform a gas engine. You don't need that much HP with a Diesel engine. Our first gen. GL 350 only produces 210 HP (400 ft-lb of torque). I can pull a 6000# camper up a 10% grade at 60 MPH and the RPM hits 3000 only near the peak of the 4 mile grade. A gas engine with 400+ HP can do the same, yet the engine would be screaming, as there is more likelihood of engine overheating. On level ground, the trailer is noticeable only when doing hard acceleration/braking. Granted GL350 is not fast, yet you do not see much de-gradation when towing a heavy load. You would also get something no gas engine can give you: range. With much better MPG towing (or not) you can drive all day without need to refuel. There are 2 main issues I have seen on most OM642 engines: oil cooler leak and DEF tank failure. Both were fixed under warranty for our GL350 (I think MB should fix these after warranty too, as clearly something is wrong with these parts). MB gas engines have issues too. One member (who shall not be named!) had the engine in his GL450 blow up beyond repair (I think his username was inspired by that incident!). I still think gas engine should be more reliable as they have fewer moving parts (specially the NA engines in first gen GL 450/550). If I could go back in time, I would still buy our GL350, but I recommend to most people to buy a gas engine GL (unless they are a diesel head).

BlownV8

Not sure why you feel that a gas engine with even more torque as low or lower than the OM642 would be screaming? The MB bi-turbo engines, especially the V8's and V12's, create massive torque at low rpm's due to the small turbos and instantaneous boost at very low RPM's. My old SL600 was making 800+ lb-ft at 2,000 RPM and the M157 GL63 has 800 NM of torque between 2,000 and 4,500 RPM stock. Do you really think it would have to scream to tow a 6,000 lb trailer? Heck, the stock/base M276 has 369 lb-ft of torque at 1,600 RPM while the 350 has 455 lb-ft at 1,600 RPM so it does have an advantage stock. With a tune, the M276 bi-turbo has 454 lb-ft so it would be right there with the diesel but, with the tune, it has an additonal 150+ HP and carries the average torque higher in the RPM so it would also accelerate much more quickly than the 350.

Back to OM642 reliability issues. In addition to the above mentioned items that will cause a OM642 engine to fail, there is also the serious issue of the timing chain tensioners that are known to fail at intervals of less than 100k miles. It is very well documented with many examples on this forum. Most owners ditch their diesels around 80k miles when the serious issues start rearing their ugly head. Very few issues with any of the gas engines in relation to how many they produced. The early OM642's were OK but after the addition of all the emissions control equipment they were no longer reliable or even close to being reliable.

BlownV8

Good story on the 450's towing abilities.

https://www.roadandtrack.com/new-car...e-tow-vehicle/

RostamDastan

As I said, those high HP gas engines are great for acceleration, but if you put a heavy load behind them, you will realize why people use diesels. I have heard of multiple GL550's with 400+ HP and 516 ft-lb of torque overheat while pulling a trailer up a grade in the summer. I have heard of zero GL 350's overheating while towing (with 210 HP and 400 ft-lb of torque). Without a load, those gas engines are much faster and more powerful. With a heavy load, they cannot perform as you might expect from their specs. They are not designed to be under heavy load for long period of times. Think sprinters vs weight lifters. I think NA gas engine are actually better for towing. And not just Mercedes. I've heard of many F150's with EcoBoost engine overheat as well. Not any overeating with NA 5.0 V8. Even though EcoBoost engine has much better HP /Torque numbers.

geniushanbiao

I think generally MB should make both their gas and diesel engines more reliable. Toyota can do this on Lexus so there's no reason MB cannot do it, but I can see there are generally 2 theories explaining why MB is building their stuffs not so reliable. The first theory says that MB intentionally did this to make people replace the car after the warranty expires. They make the car ride so good to attract buyers, while making them replace the car frequently. The second theory put this into a culture difference that reflects on the parts supply system. Usually Japanese makers have dedicated parts supplier (like Denso to Toyota/Lexus) that they can have better control on the parts quality, while European/American makers shop around a few parts makers for a better deal, thus make the parts quality out of control. It's an interesting topic though. On those German cars, additionally there's a problem with overengineering that the design is good but some parts cannot reach the design requirement so it causes failure. For example the oil cooler seal thing.

geniushanbiao

It's not fair to compare your M157 to the OM642 first of all. Think about the price difference. With twice the price what do you want to get? Not to mention the M157 has almost twice the displacement of OM642. And I'd say when towing a trailer the AMG will likely not perform too much better than the diesel. Again you cannot simply focus on those data on the paper. Real world experience on heavy trailers all proved the excel performance of diesel when it comes to heavy load, even if the paper spec doesn't say so. People have compared the towing performance between the 350 and 450 nobody says the 450 can even compete with the 350.

The timing chain issue is actually present on a lot of MB engines including gas ones. Do some research you will find that M156 and early M157 also have the timing chain issue, as well as the M276 and M278. I had a 2013 C300 that was totalled by insurance company a couple months ago with the M276 engine. It started to have the rattling noise upon start since we bought it as CPO with less than 10k miles. Dealer was never able to solve it although it doesn't affect driving at all. I did some research and it seems to be not uncommon on these gas engines.https://diag.net/msg/m7gexhtjw6zhdfyqbk520fguau

BlownV8

Yes, I'm aware of the timing chain issues across the other models too. Just seems to hit a higher percentage of OM642's than anything else. At one time, the 320/350 had better resale in the X164 but, after the market was exposed to the unreliable engine, the resale is less than the gas counterparts.

Again, not a diesel hater. I've been in the logistics business for the last 20+ years and all we have are big diesel trucks so I'm familiar with what a diesel engine can do an how long they can last. We have impeccable maintenance schedules and, given they are a machine, we still have some that have failures too soon much like a gas engine. A gas engine would never survive or have the abilities to do what these diesel engines do but comparing these engines to the OM642 would be like comparing a large excavator to a shovel. For occasional towing and passenger car uses, I would still choose the larger V8 counterparts than the small displacement OM642 due to reliability and driving pleasure. To each their own but the diesel is no longer sold in the US by MB and probably never will be sold again in the US. If you live in the US and want to drive a diesel, you will need to choose a different brand or keep throwing money into your OM642 equipped MB.

geniushanbiao

You are absolutely right but what I'm seeing, at least in my area, is that the diesel W166/X166 sells much better and higher than the gas counterparts. Both my 2012 W166 and 2015 X166 are bought used and when I searched for vehicles at that time, it was extremely difficult to even find a diesel X166 within 100 miles around me. Every time a diesel X166 comes out, the price is set to be higher than 20k, while I can easily find a GL450 same year with lower mileage within 20k. The lowest GL350 I've seen is a white one with damage on rear bumper that needs a rear bumper replacement and it was set to 19k. Not to mention those at the dealership with some warrenty just go same day turnover most of time.

MB stopped diesel sales in US but Chevy introduced Duramax to the Suburban/Tahoe. I'll try to keey my two diesels as long as possible and then I might just switch to a diesel Suburban.

I personally feel that the unwelcoming environment of small diesel vehicles in US is a strategy of those oil vendors, that there are a lot of diesel trucks on the road so they want to balance the gasoline and diesel sales. The "emission scandal" is simply a joke to me. It's basically an effort from the govt to eliminate the sales of those small diesel vehicle.

BlownV8

If that was the case there would be no electric vehicles. MBUSA released they are not persuing any new diesel technology and instead switching to gas/electric vehicles going forward.

When I researched KBB, the diesel was worth less on the retail side but it was always, until the last few years, worth more. Knew the reliability would tank the car value when I noticed the dependability issues more than 10 years ago. Now, if they are selling for more, it's simply a supply/demand issue but the diesel crowd, especially for most who owned a OM642 equipped vehicle, is diminishing rapidly.

BlownV8

Just checked KBB. Data is 2015 GL350 vs 2015 GL450, 80k miles, standard options, good condition, and black color.
GL350
Trade in
$16,946 - $20,097
Private party
$20,951 - $23,750

GL450
Trade in
$17,004 - $20,165
Private party
$20,267 - $24,006

Looks like the gasser still has a higher average resale value according to Kelly Blue Book.

geniushanbiao

At least in my area, KBB is not very accurate. I just looked around local dealer websites and apparently the prices you showed for the GL450 is only good for one with less than 60k miles for a 2015. And for 2013-2014 with about 80k miles or so even those private dealers won't sell it for more than 20k. Check those deals.
https://cnj.craigslist.org/ctd/d/lak...107571364.html
http://dream-car-gallery.hammerwebsi...rce=craigslist
http://dream-car-gallery.hammerwebsi...rce=craigslist

The price you showed for the private party are even close to a CPO 2015 GL450 from a MB dealer. Check this.
https://www.mbusa.com/en/cpo/invento...1737?zip=19041

There are not comparable diesel ones to compare with for CPO, but I got my 2015 from a private dealer for 25k with 72k miles and it's not a CPO just a couple months ago. It's a "standard" package with most common features except for the panorama sunroof, distronic and rear entertainment. When I did the search there were a couple more GL350s 2013-2015 and they are very much close with similar price and features. One had rear entertainment and lights package and was priced at 24k with about 85k miles but I was not satisfied with the engine condition. I couldn't find one with distronic though. I did an extensive search when I was seeking for my family SUV and the outcome was that an equivalent GL450 is about $2000-4000 cheaper than a GL350 at least for the price range I was looking for (20-30k). I even debated with my wife if the additional $2000-4000 was worth it to go for a diesel, as we don't have frequent towing needs and the problems we are expecting to face with the OM642, but I voted for it since there are lots of parts exchangable with my 2012 ML350BT so it might make some work easier for me.