Hi Alan
Unless the car loan is sitting in your bank a/c then it will not be classed as capital, it is a debt with scheduled payments, this will not affect your wife's UC, however savings over £6k will affect your wife's UC.
Any capital/ savings you have under £6,000 is ignored.
Any capital/ savings you have between £6,000 and £16,000 is treated as if it gives you a monthly income of £4.35 for each £250, or part of £250, regardless of whether it does or not.
So if you have £6,300 in a savings account, £6,000 of it will be ignored and the other £300 will be treated as giving you a monthly income of £8.70.
If you have capital/ savings over £16,000 as a single claimant or as a couple you will not be entitled to Universal Credit.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
