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New Mercedes Sprinter Owners: Beware Catastrophic Engine Failure from Piston Rod Through Cylinder Head — Caused by Intercooler Overflow

re: ethics in medicine


Real science is never settled, and anyone who has certainty on such things is not qualified to discuss it.

Sprinters have serious issues you must understand even before you even drive it off the lot. If you know what the issues are and do the right things, the odds are high for a long and enjoyable lifespan of your Sprinter. If not... good luck.

Don’t even think of buying a Mercedes Sprinter without the 7-year extended warranty, but negotiate for a discount, which most dealers will agree to.

The core issues revolve around a terrible design for the turbo cooling, brain-dead intercooler design (more on that below), and especially the emissions systems which together with exceptionally poor OEM oil for a diesel engine causes early failure of many different components.

Some of the design issues can be mitigated, e.g., better oil and much more frequent change interval, and adding an oil catch-tank to prevent ingress of vaporized oil into all sorts of places it should not go. But the core design failures of a modern Sprinter with all its emissions control components mean that the long life one expects of a diesel are highly unlikely unless one is very proactive.

There are other issues too, such as the now-recalled toy-grade steering fluid hoses.

Beware of the latest Sprinter 4-cylinder engine—it is a rehash of the old, with all the same problems and emissions-systems headaches.

Catastrophic Engine Failure

Few dealers either understand what follows here, or won’t tell you. So you can ask, but don’t expect confirmation or honesty. Mercedes corporate has not and likely will not acknowledge this issue, which they are very much aware-of.

This issue is only one of many costly problems that can occur, many of which the dealer will try to blame on you. Dealers are told to NOT discuss many serious issues and their cause with customers as Mercedes does not want to pay for it. Dieselgate is only the tip of the dishonesty iceberg, and that’s not speculation as many Mercedes XENTRY documents prove, most of which are hidden from customers except in Germany where laws require its release (yes, Mercedes actually firewalls this stuff off for USA customers, so they won’t be aware of it, nor are most dealers).

I had heard of this a few months ago from a highly reliable source. And just yesterday I met a Sprinter owner in Bishop CA whose nearly-new Sprinter (10K miles) just had a new engine installed for this very reason.

I have it on expert authority that as many as 1 in 100 Sprinters are throwing piston rods through the cylinder head as early as 5000 miles, requiring engine replacement. Let’s discount that to 1 in 200 or 300—whatever—it’s a major manufacturing defect that stems from very poor design.

Beware of dealers trying to blame you for the problem.

The cause is the intercooler steadily filling with oil residue*, then overflowing into cylinder #6**. The overflow warps the piston rod, so the engine start running very roughly, though it might appear to come and go for a while. This will be your first symptom. Death of the engine is now imminent (within a few weeks/months).

Before long... “BAM!” the piston rod goes through the block or cylinder head. In either case, then engine is then dead within minutes.

Mercedes claimed a fix for the intercooler problem, but all it was is a slightly higher outlet valve, which only defers the issues a little longer.

* Exacerbated from the garbage-grade OEM-spec oil which is wholly inappropriate for a diesel engine, combined with the lack of an oil catch tan.

** Just one case of many poor design choices, it should vent into one cylinder in each bank, not just #6

Why some engines and not others?

As with any manufacturing process, there is a normal curve (Gaussian distribution) of how well the pistons seat within the cylinders. Some engines have a very tight excellent fit of the pistons to the cylinders. A tight fit means little leakage of the byproducts of combustion. A loose fit means a lot of leakage.

But those engines that by chance have poor tolerances leak a lot of crud. This fills up the intercooler which then overflows into cylinder #6, causing the problem.

There are ways to avoid this issue, or largely preclude it, and the solution not only largely eliminates the risk, but will greatly extend the longevity of the entire engine and emissions systems—an oil catch tank and proper diesel break-in oil. But Mercedes has made no effort to build sprinters with an oil catch tank, or offer this fix, even after replacing the engine!

TIP: do NOT break-in your Sprinter engine with the stock oil; use a high-grade diesel break-in oil. Using the stock 5W30 oil will guarantee poor engine break-in and increased leakage for the lifetime of the engine.

Dieselgate is not over

Already in 2021, Mercedes paid 2018 and later Sprinter owners a cash payment of $3000 along with repairs to address the tip of the corporate shenanigan iceberg. More is coming.

Dieselgate is front-page news over in Europe, though the press is ignoring it here. The truth is corporate malfeasance is far worse than just a little emissions cheating, but I cannot go into that here.

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