On the face of it I would say bad UNLESS you can get a mortgage rate (lower than a car loan) but still pay it off over 3/4/5 years. Paying for a car over 20/30 years is madness. You would still be paying for the car years after it's been sent for scrap.
Also, bear in mind that if you do remortgage, you'll have to use a solicitor, reapply for mortgage protection insurance & get a valuation of your property.
That's only one opinion - it's just quite expensive to have to go through all the legal red tape for a car loan, as opposed to say, remortgaging for a considerable amount of money for an extension or whatever. But some banks will pick up legal fees for you if you want to remortgage - still have a look at your options, but if you do go ahead, just don't have the car loan at 20/30 year term. It's more expensive in the long run.
I've just done this to the tune of €20k and it works for me as I intend repaying the sum in approx 2.25 years (Some people may be expecting SSIA money around then). Including €70 p.a mortgage protection and €225 legal charge its still better than the regular 7-10% APR and I was even allowed a 1 year fixed rate of 2.75% before it reverts to 3.3% variable. ReMortgage Repayments are approx €120 p.m over 17 year term.