This is not the most relaxing of jobs for a man who was thinking about early retirement in 1990, after 30 years with Ford. Since then he has been Aston Martin Lagonda's engineering director and spent 18 months with Ford in America, running the Special Vehicle Engineering team responsible for producing sporty versions of mainstream cars. His qualification for that role was having run SVE's very successful European counterpart from 1980 until 1990, when such models as the Escort XR3i and Sierra Cosworth worked wonders for Ford's image.
After retiring at the end of 1993, five months before his 60th birthday, he and his wife returned to Britain and started chugging along the canals aboard their narrowboat, Toad Hall.
"We had a vague plan to explore the whole of the inland waterways system over the next few years," he grins. "Several people had said, 'Give us a ring when you're fed up with being retired', but the only moves I made involved rejecting a few tentative offers.
"One day last summer I was invited to visit Lotus and talk about becoming a consultant. The main hope was that I would be able to attract Ford business to Lotus Engineering."
The proposal became difficult to reject when he was given a sneak preview of the Lotus Elise sports car, shortly before its debut at the Frankfurt Motor Show this September. Typical of the gospel preached by the company's founder, Colin Chapman, the Elise is a compact, mid-engined two-seater whose lightness and strength is based on an innovative structure that combines extruded aluminium with space-age glues. Mansfield's heart beat faster when he saw it for the first time.
"Here was a company that was about to go into production with the technology that had fascinated me for years," he recalls. "What the Elise represents is a wonderfully elegant, cost-effective way to build niche vehicles. This was what I had been trying to get Ford and Aston Martin to do.
"We had reached the stage of talking about how many days a week I would work, and so forth, when all of a sudden I was invited to come here and run the show! Just like that. Right out of the blue. Deciding to say 'Yes' took me all of three milli-seconds."
The circumstances surrounding his arrival are a reminder that Lotus has a turbulent history. The roots run back to the late 1940s, when Colin Chapman built himself a "special" based on a pre-war Austin Seven. A mercurial character, and an exceptionally talented engineer with a genius for lateral thinking, he went on to create technically brilliant road cars while establishing Team Lotus as one of the biggest names in Grand Prix racing. Five world champions - Jim Clark, Graham Hill, Jochen Rindt, Emerson Fittipaldi and Mario Andretti - won their titles driving for Lotus between 1963 and 1978.
Like his great Italian rival, Enzo Ferrari, Chapman regarded road cars as little more than a source of finance for the Grand Prix programme. As a result, the likes of the original Elite and Elan were praised for their technology and performance, but did not become synonymous with reliability. There were cynical jokes made about customers being treated as development engineers.
Things became really bad when Lotus became involved with John de Lorean's notorious attempt to build a sports car in Belfast. Chapman's associate, Fred Bushell, was eventually fined pounds 2.5m and jailed for three years for his part in what the judge described as "a bare-faced, outrageous and massive fraud" in which pounds 9.49m was plundered from the government-funded project. Chapman would have been in the dock with Bushell had he not died of a heart attack in 1982.
Lotus soldiered on and was owned by General Motors from 1986 until 1993, by which time it was obvious that the new, frontwheel-drive Elan was a commercial failure. Its latest problems are detailed below. The company would have folded years ago were it not for Lotus engineering, which undertakes projects for clients in Europe, America and Asia.
Group Lotus employs 900 people at its base on a former airfield near Norwich. Mansfield's priorities include bolstering morale following his predecessor's sudden departure and preaching the gospel of confidence while the parent company sorts itself out.
The big question, of course, is can a "boutique" manufacturer as small as Lotus get by on sales of only around 800 cars a year? Sales of fast Fords averaged 50 per cent more than that per week during the 1980s, when Rod Mansfield was Mr Special Vehicle Engineering.
"There is no way Lotus can survive by making cars," he asserts. "While people tend to think that's all we do, Lotus Engineering accounts for about two-thirds of our business, which is expanding and profitable. But our consultancy work is generally undertaken on a strictly confidential basis, so there's not much to tell the world about. That being the case, it's a huge advantage to be making cars, because they showcase our technology. The new Elise, which we've said will cost less than pounds 20,000 when it goes on sale in April or May, is a good example of a flag-waving exercise."
He also has high hopes for the turbocharged, 3.5-litre V8 engine that is being launched next year. Designed to power the long-serving Esprit, it will also be available to Lotus Engineering's customers. Blue eyes sparkle with anticipation when he talks about the new engine giving the competition version of the Esprit the power to become an outright winner. Being involved with the Esprit team is a far cry from his own racing debut, 36 years ago, when he tackled Silverstone in nothing more mettlesome than an Austin A35 van.
"It was modified, of course," he laughs. "I spent the equivalent of pounds 4.50 on a laminated windscreen, put tape on the headlights and removed the hubcaps."