I used Constant Contact before for dealer newsletters. It's a great out of the box product. You can be up and running in a short time. Customer service was really good when I was using them. I would even get friendly phone calls from their support team just to see if I had anymore questions...
Overall it's priced right for what you get and it looks as if they have improved even more since I last used them.
Deliverability was very high, templates needed some improving (though I'm sure they have added to the library) and the UI was easy.
Looks like they currently have a 60 day free trial, so you don't have much to loose other than your time loading all your email addresses.
Two things to think about then going with a vendor like Constant Contact for your dealers email marketing.
1. Many of these vendors will allow you to upload your database of emails addresses BUT will send out a verification Opt-in email to each address before adding. To some, this could be alarming because they don't want to risk having that customer NOT opting in and greatly reducing their number of "valid opt-in" customer emails. Others would view this as a "scrubbing" process while getting rid of customer emails addresses that are highly unlikely to respond to your marketing email campaigns anyways.
2. Stream line process for getting your new/potential clients into your email marketing solution. Many times you will need to have a process for exporting your email addresses from your CRM into a spreadsheet to then import into your email marketing (Constant Contact) solution. This again (with many solutions) will trigger another opt-in email to the customer.
There could be a way of having your CRM vendor run a script to automatically export a customers email into your email marketing solution. I'm going to go out on a limb and say this is highly unlikely.
If this is the route your dealer is going to take, I personally would use a solution that allows me to upload my already opt-in customers without sending them another opt-in email address.