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RVing in Mexico - Take Your New Diesel Truck to Mexico

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Written by Ted White   
Sunday, 07 February 2010 00:00

 

While RVing in Mexico, many owners are concerned about taking their new diesel trucks to Mexico. In 2007, new EPA (Environmental Protection Agency) rules came into effect in the USA, requiring all diesel engines to use ultra low sulphur diesel fuel (ulsd) containing less than 15 parts per million (ppm) of sulphur. Canada also adopted the new fuel standards, but Mexico, as of the time of writing, has still not converted from it’s standard 300-500 ppm low sulphur diesel (lsd). As a result, owners of 2007 and later diesel pickups are often worried that damage could occur to the engines in their trucks while RVing in Mexico. Notes in the owners’ manuals often warn of loss of warranty coverage if damage occurs due to the use of Mexican diesel fuel.  In order to understand why high sulfur diesel fuel might theoretically pose a problem for the post 2006 trucks, it is important to first have a basic understanding of how the emissions system works on those trucks.  
RVing in Mexico - Take Your New Diesel Truck to MexicoIn the interests of keeping things simple, this discussion will deal only with the main components of the emissions system - the DPF (Diesel Particulate Filter), and the DOC (Diesel Oxygen Catalyst), both of which are installed in the exhaust line. The job of the DPF is to capture soot from combustion, usually in a ceramic honeycomb, while the DOC has a special function to perform once the amount of soot captured in the DPF reaches a preset level. Once that level is reached, additional fuel is injected into the exhaust, raising the exhaust gas temperatures. The DOC, which is installed ahead of the DPF, then creates oxides of nitrogen, which react at high temperature in the DPF with the soot, converting most of it to carbon dioxide in a process known as regeneration. If the truck operates mainly under load or at highway speeds, the exhaust gas temperature is often high enough to facilitate continuous regeneration. Due to the high temperatures achieved during regeneration GM trucks have a venturi tip on the exhaust to mix cooler air intoRVing in Mexico - Take Your New Diesel Truck to Mexico the exhaust gas stream for safety reasons. 
The reason the EPA mandated the use of ulsd in 2007 and later diesel engines is because sulfur compounds in the exhaust stream, like sulphuric acid (H2SO4), are considered to be particulates, and burning fuel sulfur levels above 15 ppm creates excessive amounts of these particulates. At 300 ppm the amount of sulfur particulate matter begins to exceed the savings in carbon (soot) emissions achieved by the DPF. In addition, some of these sulphur compounds get captured by the DOC, along with the soot, posing the risk of a problem known as “sulphur poisoning”.  If the sulphur compounds captured in the DPF are allowed  to accumulate, they will reduce the effectiveness of the DPF, and eventually poison it, preventing it from operating. 
So what is the real risk faced by owners who use diesel fuels with higher than 15 ppm of sulphur while RVing in Mexico? Well, before you read any further, it is important to note that in writing this article I am not counselling or advising anyone to ignore warranty warnings from GM, Ford, or Dodge, regarding the taking of a 2007 or later model year  truck into Mexico. I am simply sharing some well documented scientific and observational information in the interests of ensuring that owners have access to the facts about the occasional use of higher sulfur fuels. If you choose to take your post-2006 pickup into Mexico, as hundreds of RVers and Snowbirds are now doing, the responsibility for that decision is entirely your own.
That having been said, extensive testing of the DOC/DPF emissions systems, using various fuel sulphur concentrations, was carried out by vehicle manufacturers, and agents for the EPA, a number of years prior to their utilization on assembly lines in 2007. In those tests, the results of which can be found in their entirety on the net, it was found that the accumulation of sulphur compounds in the DPF did not cause significant degradation of performance unless higher sulphur fuels were used continuously for more than 40,000 miles. In other words, occasional use of lsd, or even a few thousand miles running on lsd, as would be the case over a winter in Mexico, did not result in any lasting damage. As soon as the engine was put back on to ulsd the sulphur compounds were burned out of the DPF during normal regeneration cycles. This would appear to be why, some 3 years on, hundreds of RVers and Snowbirds have taken their post 2006 diesel trucks into Mexico without reporting any problems. At an RV park near Puerto Vallarta, in the last few days, I counted 8 Silverados newer than 2007, 1 Sierra newer than 2007, 6 Dodge RAMs newer than 2007, and 6 Fords newer than 2007. While RVing in Mexico, the only “symptom” of lsd use which has been observed, and only by owners of GM trucks with the Duramax engine, is copious emissions of bluish smoke during regenerations as the sulphur compounds are burned out of the DPF. This occurs for just a couple of minutes and then ceases. These smoke emissions during regenerations disappear as soon as the tank is filled with ulsd again on returning to the USA.
However, one issue which is VERY important for owners of 2007 and later diesels, if those trucks are taken into Mexico, is that CJ4 (or better) low ash oil is not available in Mexico. As the use of older specification diesel oil will result in excess ash being deposited in the DPF , shortening it’s effective life, sufficient supplies of a CJ4 or better oil, like Shell Rotella T, should be taken into Mexico to cope with any expected oil changes.
Further reading on this subject can be found via the following links, including the results of tests on the DOC and DPF using high sulphur fuels:
www.aseanenvironment.info/Abstract/41014571.pdf
for the effect of sulfur on DOCs (Diesel Oxygen Catalysts).

www.nrel.gov/docs/fy02osti/31600.pdf
for Diesel Emissions Control Sulfur Effects Project

http://www.nrel.gov/vehiclesandfuels...pdfs/40015.pdf
for the Effect of Biodiesel Blends on DPF performance

http://www.osti.gov/bridge/servlets/...ive/828945.pdf
for Fuel Formulation Effects on Emission Control

www.sae.org/technical/papers/2002-01-2788
for Fuel Sulfur Effect on Membrane-Coated Diesel Particulate Filter

http://www.nrel.gov/vehiclesandfuels...erim3final.pdf
for Diesel Fuel Sulfur Effects on Particulate Emissions


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