so i can fill my resevoir up to max and about two weeks later its at the minimum line. how can i check to see what the problem is? would the nismo radiator cap make a difference?

 

Is there a puddle under tha car ? Is there smoke coming out of the exhaust ? Did you check your oil ? If so....is it a milking grey ?

 

Did this just happen once or is it happening all the time?

 

Coolant system pressure tester is a mandatory tool in any Master Tech's box.

 

That tank will eventually re-circulate that coolant back into the system... If you had an air bubble in there it will bring it back in...

The best way to fill up with coolant will be to take off the radiator cap, put a funnel in there... add coolant to the funnel and leave the car running for a while... it will SLOWLY bring in coolant... if it gets really low, then add a little more if needed, but after about a half hour, if you are left with a full funnel, then your filled up...

If you are afraid of actualy burning up some coolant, take your car to a dealer / shop and get a pressure test done...

 

FWIW the last time I had my oil changed my coolant was low. I had just made a 1k mile trip so I suspect that had something to do with it but I dunno. So far it's been fine.