Weaker Yen Is Mixed Bag for Japan Auto Makers

That is because they should be among the biggest beneficiaries: A weaker yen makes Japanese-made cars and trucks less expensive around the world and helps increase overseas earnings when they are repatriated into yen.

But a closer look at two auto makers, Mazda Motor Corp. and Nissan Motor Co., shows that the benefits of a weaker yen to Japan Inc. are anything but clear.

Hiroshima-based Mazda is the car company most likely to pop the Champagne when the dollar hits ¥100. That is because Japan’s fifth-largest auto maker produces about 71% of its cars at home and exports roughly 80% of them, meaning a move in the currency can deliver a heavy blow or sudden windfall.

One reason for the high percentage of exports is Mazda’s small size: Last year it produced only 1.18 million vehicles, versus Nissan’s 4.88 million. Despite the currency risk, Mazda decided it would be more efficient to concentrate its factories in Japan, rather than spreading them throughout the world.

Even as the yen strengthened in 2012, Mazda brought production of its Mazda6 sports sedan back home, after falling vehicle sales in the U.S. spurred them to pull out of a Michigan assembly plant run jointly with Ford Motor Co.

For the fiscal year ended March 31, the move means the amount Mazda lost for every one-yen appreciation versus the dollar climbed to ¥3.5 billion—about 6.4% of the company’s ¥53.9 billion operating profit—¥1 billion more than it would have been two years ago. A strong yen—the dollar hit a post-World War II low of ¥75.31 in October 2011—has been a big factor behind Mazda’s four consecutive years in the red, totaling ¥245.7 billion in net losses.

Now the yen’s rapid slide means Mazda’s fortunes are changing.

Assuming ¥100 is worth a dollar, “we estimate additional profit of ¥60-¥70 billion versus” Mazda’s guidance of ¥120 billion in operating profit for this fiscal year through March 2014, J.P. Morgan analyst Kohei Takahashi said in a research note after the company announced earnings on April 26. Mazda projects its operating profit could increase ¥56 billion based on currency gains in the current fiscal year, ¥17 billion of which can be attributed to dollar-yen gains alone assuming a conservative rate of ¥90 to the dollar.