They said the air filters on models purchased to comply with impending tougher emissions controls rapidly become clogged up with harmful pollutants such as particulates.
The solution is to leave the engine on for up to 40 minutes twice a day to clear the filter – or costly and time-consuming oil changes which drivers said were setting them back £300 a time.
The problem affects the more popular of the two black cabs with the latest Euro 6 engines, the Tourneo-based Ford ProCab.
Only taxis with Euro 6 engines will be permitted in Edinburgh city centre from 2022 and Glasgow city centre a year later.
Edinburgh taxi driver Danny Tebb said his ProCab has had to have four oil changes since last December.
Colleague Richard Dourley has had nine in 18 months.
Tebb said: “I’m livid. The Euro 6s are clearly unfit for taxi driving. Ford has produced a prototype software update that allows a driver to manually initiate the filter clean (as an alternative to oil changes).
“We have worked out each driver would need to do this twice per day. That’s 40 minutes twice a day sat stationary with the engine running to clean the filter.”
David Facenna, sales director of Glasgow-based Cab Direct, which produces the ProCab, admitted the Euro 6 standards had “stretched” manufacturers.
He said: “There appears to be knock-on effects for vehicle maintenance, including more frequent oil changes.”
Ford said it was “willing to hear” from drivers with “major issues”. It said: “Short stop-start drive cycles generate more particulates, which is well within the filter’s ability to handle and avoid clogging via a regeneration cycle when the engine’s up to temperature, running for 20 minutes and under load.”