A logbook loan involves putting your vehicle up as collateral. This means that if you cannot pay back the loan, the vehicle will be sold to get the money that is owed. This means that the loan will not be worth more than the vehicle because the company will need to make sure that they can get the full value owed on the loan back, if necessary.
Most logbook loan companies will not lend you the full value of the vehicle. They will have to take in to consideration that if they do have to sell it, there will be costs that they will have to pay and so they will need to recoup those as well. This means that they will want the vehicle to be worth quite a bit more than they will be prepared to lend to you.
If you already owe money on the vehicle, perhaps having had a loan when you bought it, that is not yet repaid, you may not get a logbook loan at all. However, they may be prepared to lend you some if the vehicle is worth more than what is owed, but again, it will not be the full value.
So the amount that you can borrow, will be determined by how much value there is in the vehicle minus any money owed and a bit more. You could still borrow a significant amount, if you have a valuable vehicle. The company does not tend to have a limit, they will decide how much you can borrow depending on your vehicle. The amount you can get may vary between logbook loan companies and so you may want to compare them. They will want to take a look at the vehicle though, just to make sure that it exists and it is worth enough. If they feel that it is not in a good state of repair then they can refuse to lend the money as they want to be sure that they can get back what they lent if they need to sell it.
It is important though, to consider how much you need to borrow. You may not need to have the full amount available and so consider borrowing less. It is best to just take what you need rather than what you can have. This is because the more you borrow, the dearer the loan and so by only having the minimum amount, you could save yourself a lot of money. It will also make it easier to repay the loan. It is important to consider this because if you do not pay it back, your vehicle will be repossessed.