Naamsa has compiled a damning report about the effect of MMT, a heavy metal additive in unleaded fuel, on cars’ catalytic converters – a fact CAR magazine alluded to in an editorial as early as March 2001.

Naamsa has compiled a damning report about the effect of MMT, a heavy metal additive in unleaded fuel, on cars’ catalytic converters.

The quotes the report as saying that the manganese-based additive used in the fuel clogs catalytic converters, which are designed to reduce air pollution by removing pollutants from vehicle tailpipes, and can cost up to R10 000 to replace in new cars.


In the column of CAR’s August 2001 edition, we reported “there are highly qualified technical experts in this country who have serious doubts about the use of MMT. Health concerns aside, catalyst exhaust units are extremely expensive to replace – all such systems require oxygen (lambda) sensors, which might also be at risk from MMT.


“Given sufficient transparency on the part of motor companies, we should begin to find out whether catalyst exhaust systems in Gauteng fail sooner than they do in other markets, where MMT is not added to fuel,” the column said. Now, according to the new Naamsa report, BMW, Nissan, Saab, VW/Audi and Delta Motor Corporation have all contributed results indicating that manganese from fuel is the cause of clogging in catalytic converters.

Last week, BP was the first vehicle manufacturer to introduce heavy metal-free fuel in the country, at a cost of R20 million in changes to its Durban refinery and an extra cost of R10 million to cover the cost of separate holding and transport to avoid contamination of the fuel.

In response, BMW spokesman Richard Carter said that all BMWs had catalytic converters, and that the company had conducted independent tests after customers complained about poor performance and jerking, forcing them to replace catalytic converters at great cost.

Stuart Rayner, Naamsa chairman, says the organisation has called for all metals, including MMT, to be taken out of unleaded fuel so that catalytic converters can function properly.

"We have proposed to government that unleaded petrol should be entirely metal-free. The research that our automobile manufacturer members have done certainly indicates that metal additives like MMT in unleaded petrol have negative effects on catalytic converters. The research has been rejected by the oil industry and the MMT manufacturers, who put the problems down to other reasons," Rayner said.

In November 2002, CARtoday.com reported on the World Wide Fuel Charter’s (WWFC) caution against the use of MMT in fuel after it found it damaging to the environment and catalytic converters.

The WWFC stated that studies had shown that the majority of MMT-derived manganese consumed in fuel remained within the engine and its exhaust system. One of the effects of this was to “coat internal engine devices such as spark plugs, causing a misfire condition that can lead to increased emissions and poor engine performance”.

John Aitken of Ethyl Corporation, manufacturers of MMT, said he was "disappointed" that Naamsa had not shown him the report. He said about 70 per cent of the oil industry in South Africa used MMT.

"There is not a single instance where MMT has been found to be detrimental to the catalytic converter system," Aitken said.

He added that a report compiled by Ethyl Corporation in July this year had shown that MMT would not do any harm to vehicles or emission control equipment.

The report, which drew on industry sources, concluded that there was no evidence that vehicles were adversely influenced "to any significant degree" by the use of MMT.