Several manufacturers jumped on the diesel bandwagon back in the 80’s, but in a half-assed kind of way. Some of them were making purpose-built diesel engines, while others who were new to the game took gas engines and “converted” them to use diesel fuel. The high compression of burning diesel fuel cracked engine blocks and caused a lot of problems for these converted engines that weren’t made for diesel. I know that Mercedes and VW made purpose-built diesel engines, but beyond that I’d recommend doing some research, especially if you’re looking at older pickup trucks.
Some of the older diesel vehicles have a harder time starting in cold weather, such as when it gets down below 20*F. I believe diesel fuel begins to congeal around 20*F, which can make the vehicle more hesitant to start on a really cold day. I don’t want to get too much into the technology of diesels here, but (if I understand correctly) the thing that is starting the diesel vehicles is glow plugs, which rapidly heat the fuel in the engine to get things going. If the engine and fuel are only 10*F, those glow plugs have to work hard to get that engine to turn over. VW claims their TDI’s have glow plug technology that will start the car at temps below 0*F. Outside of VW’s I don’t know how well other vehicles start in the cold, so I’d suggest doing some homework on that before you buy. Of course, there are aids in helping fight the cold temperatures, such as anti-gel additive (I use this in the winter) and engine block heaters or radiator fluid heaters that plug in at night.
My grandmother had a diesel VW Rabbit in the 80’s and you could hear that thing coming a mile away! Sounded like the car had marbles under the hood. Most diesels I’ve heard are at least a little louder than the average gas car, so when shopping for a vehicle you may want to keep engine noise in mind.
You may see a diesel vehicle in the classifieds occasionally that has already been converted. Great, you say, that saves me the cost and time of having to get it done. Finding a vehicle that has already been converted CAN be a great help, but I would exercise caution here.
There are several conversion kit manufacturers and they all have their strengths and weaknesses. This is a good topic to dive into further in another dedicated post. The major kit companies in the U.S. are Greasecar, Frybrid, Greasel, and Plantdrive. I’d recommend finding out which kit was installed in the vehicle and find out more about the differences of each company.
DIY conversion kits – I’ve met people who saw the kit components and decided to save money and go cobble the parts together from hardware stores. If you’re looking at a vehicle converted in such a way, I’d say it’s up to your comfort level in buying a vehicle with a self-made kit; I personally would not be comfortable with that.
DIY Installations – Find out who installed the conversion kit, if possible. The kits are sold for DIY installation with instructions, but it is an involved process, especially for a non-mechanic. Most of the problems I’ve heard about with using veggie oil have been from improper installation. If the kit was put in by an experienced installer, I’d feel more confident in that. Also, some people install a kit and vary from the instructions, thinking that they’ve found a better way to do it. The mechanic who installed my kit said that Greasecar has tried over several years many, many different configurations of their kits. He said that the DIY’ers should just call Greasecar with a supposed improvement and they’d likely say “oh yes, we tried that three years ago and here are the reasons that it doesn’t work as well.” Again, I’d recommend using a lot of caution when looking to buy an already converted vehicle, and do your homework.
Diesels, especially older ones, can be more sluggish than their gas equivalents. I’m sure it has to do with the difference in combustion and other technical concepts I know little about, so I won’t try to explain it. Turbo diesels make up for that difference in large part. When I bought my Beetle, the turbo was clogged and not working, and I was a little dismayed by the fact that it didn’t have much get up and go. My installer was actually the one to point out when doing the Greasecar installation that the turbo wasn’t working and that it should be a lot more responsive. I had that repaired and wow, what a difference.