I use LiquiMoly in my fiat Uno. Lasts for 5000kms without any problems. Has gone through a hot summer and full ac w/o problems too, and same is the case in winters.
Engine seems to run smoother and quiter on the engine, and mileage is gradually increasing too.
Good oil if you want my opinion. I just slick50'd my engine too since I have amazing results with this additive, despite many claims of it being ineffective or useless!
Cheers