The Chetzemoka — the new 64-car ferry serving Vashon’s south-end route — went out of service for much of Tuesday last week after the crew saw white smoke billowing from one of its exhaust stacks, according to the state ferry system.

It turns out the crossing from Tahlequah to Point Defiance, which the boat began serving last month, is too short for the Chetzemoka to burn off all the oil that builds up in its exhaust system, David Moseley, who heads the state ferry system, said in an email bulletin. On Tuesday, the engine finally got hot enough to burn off the built-up oil, resulting in the clouds of white smoke, he said.

The Chetzemoka underwent sea trials after the incident, and the U.S. Coast Guard approved its return to service by late Tuesday afternoon.

Marta Coursey, a spokesperson for Washington State Ferries (WSF), said engineers were concerned about the buildup “because they weren’t expecting it.” But WSF officials believe they’ll be able to find a permanent fix, Coursey said. Meanwhile, she added, they still believe the boat — built in 2010 and assigned for its first year to the Port Townsend-Coupeville route — can handle the much shorter crossing from Vashon to Tacoma.

“The vessel has proven extremely reliable and safe, and it was doing remarkably well up in Admiralty Inlet, which is our most difficult route,” Coursey said.

The goal with the new 64-car ferries — WSF now has two of them in service and a third one about to enter service — is for them to be versatile enough to handle several kinds of runs and to provide back-up service when needed, Coursey said.

“We’re just grateful to have these new boats,” she added.