hi

i´m tempted to put oil 5w40 in my ELX once that my car takes long to warm up in the winter. anyone here tried before??

no don't do that, use the recommended oil, semi-synthetic 10w40.

ELX models have a temp gauge correct??
If your car takes too long to warm investigate that properly.. Check thermostat is operating properly first, the most likely cause of the car taking longer than normal to warm up.

hi

actually i changed the thermostat this last winter. but i´m more worry if i´m going to hear what i call "sing from the valves" once that is more thin oil

No advantage just stick to 10w-40w semi-synthetic changed every 10000miles; have always used this and my mk1 has now done over 200,000 miles; slow warm up is either stuck thermostat or dud gauge;
Start engine from cold and let tick over and see how long radiator takes to get warm; if it gets warm straightaway then the thermostat is stuck open; if not wait until cooling fan kicks in and check gauge when it should read at or slightly above ....

is it an 8v or 16v?