I have just bought a car recently (Nissan) and dealt with "QNB al islami".

The interest rate is 3.99% if loan is 1-3 years.
The rate is 4.1% for 4-7 years.
For non-Qatari citizens, I think maximum loan period is 6 years.

BUT I DID BUY DURING A PROMOTION PERIOD, SO I CAN'T JUDGE IF THIS IS GENERAL.

The good thing about islamic loans is you get a up to six payments permit without having extra interests imposed, as long as these are not within the beginning payments.