The weird thing is that it renders as 2 cores, which should mean there are 4GBs added up, but the system sees it as 2gb, soo… (https://www.dropbox.com/s/dx28kpyelpoe9qj/Screen%20Shot%202017-08-12%20at%2002.25.14.png?dl=0)
Second weird thing is that I use MacOs (Hackintosh), so it may be harder to fix
Third thing is that whenever I reboot it can render without problems(without changing anything)
Forth, it only uses 1Gb? 
. (https://www.dropbox.com/s/v2e6us2tbbzm5vu/Screen%20Shot%202017-08-12%20at%2002.27.24.png?dl=0)
On Windows it has an even more annoying eror which makes it stop in the middle of the render
Thanks in advance for you answers
The GTX 690 has 4 GB, but that’s 2 GB per GPU. Those do not add up, since the scene has to fit into every card’s individual VRAM. So, you effectively only have 2 GB VRAM available, which is very much the bare minimum by today’s standards.
If you’re that sparse on VRAM, make sure you don’t have any other software running in the background that might cut away on graphics memory (web browsers!!).
Blender’s internal calculation of memory consumption is notoriously unreliable. The memory usage may very well have spiked just after that last displayed value, thus leading to the crash. Use an external GPU monitoring tool.
Hi, may you can use a third cheap GPU for display or the integrated iGPU from you CPU.
The system alone use 3-400 MB, with separate GPU for display you have the full 2 GB for render.
You can try smaller tiles to reduce memory footprint.
Cheers, mib