Brought 2017 Hyundai Elantra Limited with 53 miles on it on 12/29, warm winter day. Drove it that day and didn't use it till 1/05 when it was "0" degrees outside. Couldn't get any heat out of the heater and dash thermostat stayed on C. Took it to dealer 1/06 with 123 miles on it. They called me to pickup cat on 01/09 saying they replaced the thermostat, test drove it & it was OK. Drove it home, gauge didn't go above C, no heat and took it back to dealer. They gave me a 2017 Elantra Limited to use as aloner. Drove it home and drove it back to the dealer. Gauge didn't go above C and no heat from the heater again. Dealer gave me a 2016 Sonata Limited to use. Dealer called me 1/13 said changed thermostat (I believe 3rd time since August, 2016) & a Hyundai Technician/Engineer looked at it with no solution. 1/16 dealer called & said they had no solution. Dealer stated I should call Hyundai & file a complaint which I did. 1/20 dealer called said they changed water pump. test drove car & no solution. I checked car mileage showed 178 so dealer was test driving it. Dealer, Hyundai technical bulletin stated thermostat was software/computer controlled and was a know problem on some Elantra's since August, 2016. Ss of 1/20 had no solution to fix problem.