NFU Scotland (NFUS) said they had been on farms this week taking more independent samples of fuel for testing following complaints from hundreds of members in recent weeks.
According to MSP Liz Smith, who represents Mid Scotland and Fife, the problem is particularly bad in Perthshire. She said she had spoken to a farmer who had to fork out £1,000 last week because two vehicles had broken down, and another who had to devote his whole week to changing filters because they last only 24 hours rather than the normal 500 hours.
Despite tests showing biodiesel used by the industry is meeting EU standards, it is believed that levels of animal fat have been increased in red diesel and with the sudden cold weather, these fats solidify and clog filters.