What is a trap oxidizer?

[dannym]

Hello all,
I was reading Msyoder's post about his broken turbo, sorry to hear that, and I had a question but I didn't want to hijack his post.

Someone asked him if he had removed his trap oxidizer and I wanted to know what this is and why would anyone want to remove it?

Thanks

Danny

The trap oxidizer was something that worked sort of like a catalytic converter. It was used from about 85 to 87 or 88 on diesels sold in the US and was put there to meet California emissions.

They were known for disintegrating and when this happened it would destroy the turbocharger and sometimes do even worse damage than that.

MB went through a campaign to remove them at no cost to the owner. In fact the owner got an ENTIRE new exhaust system from engine to rear bumper at zero cost.

Have a great day,

[Dervman]

Trap Oxidisers were the Diesel equivalent of a Catalytic Converter to help emmissions control. They were fitted to 1986 & 1987 603 series engines in the 300D & 300SDL models and maybe later years for the 300D. They were installed between the Exhaust manifold and the Turbo in the exhaust system and look like a big canister mounted horizontally.

Problem was that the material that was used inside the Trap Oxidiser was prone to breaking up over time and causing damage to the Turbochargers. There was a M-B Recall for all models fitted with these Trap Oxidisers where the T-O was removed and replaced with a straight pipe. In some cases if there was any evidence of Turbo damage the Turbo was also replaced.

There are a few cars out there still running around with the T-O installed and it is generally reckoned here that these are just problems waiting to happen.

[keith.o]

I stumbled on these pretty decent before and after pics of trap oxidizer replacement........."www.dhc.net/~pmhack/mercedes/300sdl871.htm"

[diametricalbenz]

My mother was driving our 87' 300SDL on the freeway in 2001 when it experienced a sudden loss of power and so she put the pedal down in an attempt to maintain speed so that the car behind her didn't plow into the car. At that point (according to her) the trap oxidiser IMPLODED and sent a gigantic cloud of carbon out the exhaust pipe. She was able to get the car off the road and called a tow truck and had it sent to the dealer into have the recall work performed. We weren't notified of the recall at that point! I was unaware that the trap oxidizer was capable of exploding like that but fortunately the trap was removed and the turbo was not shredded to my knowledge We did get one of those letters stating lifetime warranty on the exhaust system after the dealer replaced the trap.

[Jimmy Joe]

Anyone got a pic of one of these on a 617 motor?

[J. R. B.]

It's that big ugly elephant turd cleverly hidden under the manifold.

[Dervman]

Originally Posted by diametricalbenz

We did get one of those letters stating lifetime warranty on the exhaust system after the dealer replaced the trap.

My SDL had the recall done by the previous owner back in the nineties, so I have no such letter. Any chance you could scan and e-mail a copy ??
I wasn't aware that M-B was still covering these items under the recall.
Was your mother the original owner?

[diametricalbenz]

Originally Posted by Dervman

My SDL had the recall done by the previous owner back in the nineties, so I have no such letter. Any chance you could scan and e-mail a copy ??
I wasn't aware that M-B was still covering these items under the recall.
Was your mother the original owner?

I can ask my folks....they're vacationing right now. We probably still have the letter from MBUSA....I didn't memorize it . Yes we were the 1st owners until the beginning of last year....234k reliable miles. The 1st 3k was put on by the fleet manager of the Oakland, CA Mercedes dealer in 1987....he was pissed with his job there so he sold it to my folks (who were looking at a W124 300E) for what the gasser would have cost I am told

[Johnhef]

I remember seeing a 124 300D back at the old shop that ran like crap, smoked like a pig and wouldnt go over 20mph. The owner (70 year old lady) had been pulled over by the cops for driving too slow and putting out nothing but thick smoke. After pulling the exhaust off and starting it one more time.... POOF! Bob came out from his bay, actually more like came out from the black cloud that was now occupying his entire stall. It was like a small explosion and black smoke and dust was everywhere! what a sight, it was hilarious!

oh and after it had a new exhaust put on, the car ran fine

[suginami]

There is an article in the March / April 1997 issue of The Star magazine about the infamous Trap Oxidizer.

Frank King, the long time technical editor of the Star Magazine, wrote a long two page article on this Trap Oxidizer.

He basically says that it was introduced in 1985 on California versions of models with 617.592 and 617.591 diesel engines, and was also done in 1986 to California cars with 603.961 engines. In 1987, use of trap oxidizers was extended to cars with diesel engines 603.960 and 603.961 in all 50 states.

"The component was a filter known as a trap oxidizer, designed to meet California emission standards. Located between the exhaust manifold and the turbocharger, the trap oxidizer is a monolithic labyrinth of ceramic rods housed in a steel cylinder.

Due to the extreme range of temperatures to which the trap oxidizer was subjected and the vibration inherent in the application, the ceramic monolith did not have the expected service life. Sometimes pieces of the ceramic, ranging in size from dust to chunks, broke off and were blown into the turbocharger. The abrasive ceramic particles could damage the turbo blades. As a result, Mercedes-Benz instituted an extended exchange or warranty policy. Owners of affected cars were protected from repair expense due to trap oxidizer failures.

Mercedes Benz developed a new device called an oxidation catalyst with sufficient durability to replace the trap oxidizer.

Owners who have had the job done report a noticeable performance improvement after installation of the oxidation catalyst, probably due to the decrease in exhaust back pressure."

Recently in school I have been given good info on the Diesel Particulate Filter (a.k.a TrapOx.) HERE is some more good info about it.

The ceramic Cylindrical filter has many small square channels running in the axial direction seperated by thin porus walls. These channels are plugged in one end but open on the other. This way the soot laden exhaust gases are forced through the walls. Particulates are too big to escape and are trapped in the filter walls. (Called Wall-flow monolith) (See attachment.)

A Catalyst is also coated to these walls giving the soot a lower combustion temp allowing the filter to regenerate (This is why it never gets completely clogged.) Periods of exhaust temps of 615-750*f cause the soot to burn, regenerating the filter. This makes our systems "passive" as there are no active mechanisms to clean them.

The filters efficiency raises with soot accumulation, but even at low soot levels, it is 90%+ effective at catching soot.

Typical exhaust pressure drops are 20-40" of H2O (Not HG.)

Uncontrolled Regeneration
Runaway regeneration or thermal runaway.
This refers to the uncontrolled burning of a Large quantity of soot accumulated in the filter media.

It is caused by a series of events starting with overloading the TrapOx with soot at exhaust temps not high enough to cause regeneration (Lots of stop-go traffic on a cool morning with exhaust below 600*f) followed be a period of high exhaust temps that ignite the soot, and followed finally by low power or idle operation which raises the Oxygen level of the exhaust (Race on the highway at 85mph with a warm/hot engine then stop for rush-hour traffic.)

Thermal runaway can easily cause filter temps that will MELT the filter media or cause thermal stress that can crack the filter (This is what caused so much turbo damage on MB's). If water gets in/on the filter it is possible for the unit to EXPLODE! (This HAS happened, but you will never hear it from Mercedes-Benz)

If you have not had the FREE recall performed on your MB, this should be more than enough reason to swap it for the OxCat (Or replace the entire setup with a "federal" intake/exhaust system ).

[mgt83300D]

As I read these posts, I see multiple references to the FREE MB recall. Is this recall still in effect for older (1985) cars?

[vwbuge]

You have to call a dealer with your VIN to see if your car was retrofitted. The Trap Ox and the Catalyst look exactly the same.

As stated incorrectly and then later corrected, the trap ox was NOT replaced with a straight pipe but a catalyst.

Here are some pics.

emissions swap...part one

[mgt83300D]

Are there any identifying marks or numbers that would identify the part as a catalyst vs a trap oxidizer? And BTW... it is a big ugly thing.