Motorists are being advised to only purchase fuel from trusted sources to minimise the risk posed by petrol stretching.
Contaminated fuel has damaged hundreds of cars around the country in recent weeks.
The Society of the Irish Motor Industry has said the majority of problems arise in Co Mayo, but problems have been reported in Westmeath, Roscommon, Galway, Cavan, Meath and elsewhere.
It is advising motorists that price alone does not guarantee value for money and it is urging people to purchase petrol from trusted retailers.
Estimates suggest up to 400 cars have developed engine problems in Co Mayo, with one garage repairing around 80 vehicles in recent weeks.
It is understood similar numbers of repairs are being carried out at other workshops around the county.
While it is suspected that kerosene has been mixed with petrol, Revenue said an analysis of 50 samples from filling stations around the country has only revealed two incidents of fuel being interfered with.
Further testing is being carried out by the State laboratory.
Stretched petrol causes a carbon build-up on the piston mechanism, causing it to seize up in time.
Mechanics say the scale of damage varies from car to car, depending on age and usage patterns. In many cases, engines have to be replaced, at costs in the region of €5,000.
Motorists with third-party insurance policies are not covered for repairs and the damage caused to engines would not normally be covered by a manufacturer's warranty.
Public meetings in Co Mayo in recent weeks have attracted hundreds of people, concerned about the impact the compromised fuel has on their cars and their potential resale value.
Petrol stretching is described as the illegal addition of a low-tax commodity to defraud the State.
A Revenue spokesman said fuel samples would be analysed extensively to ensure that any additional mix was identified.
The supply of petrol to a number of stations in recent months is also being investigated.
Motorists affected have reported a lack or loss of engine power, failure to accelerate or a knocking sound coming from the engine.