What kind of humidity to you have in Spain? If you're in an area where the humidity is high, you should be careful when forcing cold air onto the hot computer compents. Moisture could accumulate, and damange the mainboard, the support components, etc.
I'd be incredibly impressed to see a water cooled CPU that uses the vehicle's cooling system (antifreeze), pumped through it.
The hard part is the tubing, the pumps, and running it all back to the trunk. I say trunk, because if you can put it in your dashboard, you're probably running an embedded system and not maxing out an overpowered CPU.