Trade groups representing major automakers and suppliers have asked the state to reconsider a recent decision to allow Tesoro Corp. to sell gasoline that does not meet standards aimed at preventing vehicles from stalling or having difficulty starting.

San Antonio-based Tesoro asked state officials in January to relax industry volatility standards for its ethanol-blended gasoline. The state Department of Agriculture granted Tesoro an exemption in March.

State officials acknowledged the move increases the risk that people could have problems with their vehicles; however, they said the risk was minimal and did not warrant notifying consumers.

Kaneohe resident Mike Rethman disagreed. Rethman said he ended up replacing a $150 lawn mower because of problems he attributed to Tesoro gasoline.

"The state granted this and didn't tell anybody," Rethman said. "I'm really annoyed that nobody told the public."

Tesoro competitor Chevron Corp. did not seek a waiver, and now the Alliance of Automobile Manufacturers and the Association of International Automobile Manufacturers are questioning the state's decision.

The trade groups are concerned that the Tesoro gasoline could create driveability problems that will be blamed on cars. The trade groups also said the risk to drivers is greater than the state has acknowledged. In addition, state officials should not have given Tesoro an exemption without going through a public process or without gathering supporting research, according to a June 14 letter sent by the trade groups to the state. The Advertiser obtained a copy of the letter yesterday.

"The changes adopted in Hawai'i for ethanol-blended gasoline could result in significant consumer issues with hot-start driveability," the letter stated.

"These kinds of issues are very, very difficult to diagnose," said Ellen Shapiro, who signed the letter on behalf of the Alliance.

Department of Agriculture spokeswoman Janelle Saneishi said the department administrator that granted the waiver was on the Mainland and unavailable for comment yesterday.

Tesoro sought relaxed standards because of manufacturing complications with the ethanol blending, said spokesman Nathan Hokama. He said the company plans to continue making gasoline under the state exemption.

"If the state for some reason felt the need to rescind that, then we would have to take a look" at changing the gasoline manufacturing processes, Hokama said. "But we haven't received any indication that we need to take a look at that."

The issue with Tesoro gasoline arose as a result of a state mandate that gasoline include 10 percent ethanol starting in April.

Fuel volatility, or its evaporization quality, is affected by ethanol. Unless gasoline is changed to compensate for the effects of ethanol, the blended fuel can cause vehicles to lose power, idle roughly, stall and have difficulty starting at high temperatures. Any problems resulting from the waiver granted to Tesoro would likely show up at temperatures above 90 degrees Fahrenheit, according to the state.

State officials said such risks were not large enough to warrant notifying consumers of the Tesoro exemption.

If Tesoro's gasoline creates such problems, "people are going to blame the car," Kailua auto dealer Mike McKenna said. "It's hard to tell if it's the fuel" that's the problem. People need to know that this could be a problem."

In general, blending ethanol into gasoline should not be causing problems for Hawai'i drivers, said Maria Tome, an alternative-energy engineer with the state Department of Business, Economic Development and Tourism. DBEDT, which runs a consumer ethanol hot line, said that there's been no indication that Tesoro gasoline is creating problems for consumers.

"That hasn't happened," she said. "But then again, it isn't that hot yet, so we'll see."

Reach Sean Hao at shao@honoluluadvertiser.com.