Few points to clarify:
1) pre-approved check carries issue date and has a note which says "Valid for 90 days from date of issue", so the check is valid for 90 days since the date issue mentioned in your check
2) Just below the box where you will usually fill your amount in check it says "Amount not to exceed $<whatever the amount is>" so you cannot go beyond that amount.
3) This is the disclaimer from the website loan page "Rate current as of April 2011 unless otherwise noted and are subject to change.", I have provided the website loan page link below for quick reference.
https://www.penfed.org/productsAndRa...wAutoLoans.asp
I am not trying to upset you guys, but that is what I see as of now. Also when I talked to the banker when I opened by account he mentioned "even though your check is valid for 3 months, it does not mean the 2.49% rate will be valid until then, your loan interest rate really depends on when you actually cash the check.", this is true because when I am pre-approved for my car loan I could not see the interest percentage against my loan account in penfed login, but only when I cash my check the interest rate appeared. It doesn't mean that you will not get 2.49% beyond april, you might, I am thinking PenFed will see the increased demand and might extend the 2.49% beyond April, but only way to check this is to keep checking the website for the disclaimers.
Good Luck to you All.