Indirect Injection vs. Direct Injection

From my research of modern Diesel engines I have discovered there are two basic forms of fuel injection. Indirect Injection (IDI) is the first form and is found on most Diesel vehicles until around the mid 1990s. The fuel is mechanically injected through a high pressure pump to the injectors, a pre-chamber, then the combustion chamber. This is good for WVO users because the fuel is already starting to combust before the main chamber, providing more success for complete combustion. This allows more "forgiveness" to those of us who may have not had our fuel up to temperature before we switched to grease. These engines will combust colder vegetable oil easier than directly injected engines. The down side to the IDI is that you're not going to have the kind of performance you would get on a newer, directly injected engine. I currently am driving a 1980 Mercedes IDI and I don't have to worry or lose sleep at night that I'm going to ruin it, as the car is barely a step above a "parts car". However, I do try to always make sure my engine is at operating temperature before I switch to grease and I try to filter down to 1 micron when possible and do a hot pan test.

Direct Injection (DI) is the second basic form of fuel injection in a Diesel. In this type of injection system fuel is drawn with the pump, then when it reaches the injectors a set amount of fuel is sprayed at very high pressure directly into the combustion chamber. There is no pre-chamber to heat the fuel up further before combustion. Therefore, adequate heating of WVO is imperative to have success with this kind of vehicle.

With both DI and IDI engines it is a safe assumption to say that the engine should be warmed while burning Diesel fuel and only be switched over to WVO at operating temperature. The veg oil should be heated properly for success with complete combustion. Injecting grease into a cold engine (no matter what temperature the grease) can cause incomplete expansion of piston rings leading to what is called "blow by". The glycerin in WVO can get by the pistons and into the crankcase, causing lube oil contamination. Even with good practices, WVO users should change their lube oil at shorter intervals than those just running Diesel fuel alone. Diesel fuel should always be burned at shutdown, and the WVO purged almost completely from the lines. This is more important in colder climates, as the grease will congeal.