Hey, Gate cutoff as per 2017 for qualifying in thermal engineering is 32.87 for Gen, 29 for OBC, 21 for SC/ST/PH. There maybe a small difference in cutoffs of 2018 as it differs from year to year. But if your looking for cutoffs for joining an institute there are different cutoffs released by individual institutes. Like if you're looking for IIT's and NIT's the cutoffs are from 600-750 depending on the location of the institute as per 2017. These institutes will be releasing the cutoffs of 2018 once the admissions are announced which will most probably be after the results and cutoffs of Gate are declared which is assumed to be at march17,2018 as of now. To get more details and analysis about the cutoffs you can go through the link I have provided below. I hope this info is of help. Best of luck for your results.
https://engineering.careers360.com/articles/gate-cutoff