The figure is even worse for cars imported from the UK, where nearly one in five has an unreliable or questionable mileage reading.
The study was carried out by Cartell.ie in association with AA Ireland.
Over 120,000 vehicles were checked on the Cartell.ie database and the results show that “clocking” is widespread in the market locally and is worse for potential buyers of UK vehicles.
Cartell.ie and AA Ireland examined a random sample of 60,047 vehicle history checks on Irish vehicles carried out recently by potential buyers. Of those checks, 11.04% returned mileage discrepancies.
A supplementary study of 64,742 vehicles, which displayed at least two mileage readings on the National Mileage Register, found 11.15% had a mileage discrepancy. These results represent a rise in the overall numbers of both domestic and imported vehicles recording a mileage discrepancy since the practice was criminalised in 2014.
John Byrne, legal and public relations manager, Cartell.ie, said: “We wanted to get a clear picture of the extent of “clocking” in Ireland both with respect to domestic vehicles and imports. Based on an overall study of more than 120,000 vehicles, these results are very concerning.
“On the Irish side we are painting a picture worse than the Government did when it conducted its own research in 2013 when it returned a rate of 9.8%.
“More worrying still is the situation with respect to imports — at 18.43% this rate is alarming.”
Commenting on the findings, Conor Faughnan, director of consumer affairs at AA Ireland, said clocking was a serious issue that anyone looking at purchasing a secondhand car, whether in Ireland or from the UK, needed to watch out for.
“Our AA Rescue team regularly encounter car breakdowns which can be directly connected back to mileage discrepancies in the car,” he said.