Oil must be a magical 178.924 Degrees before entering injection system…

There is a commonly accepted myth out there that when you are using veggie oil as a fuel, that the oil in the tank, filter and fuel lines, up to the injection system have to be at some magical, exact temperature to work properly, and that if the oil isn’t to that arbitrary temp, the system is somehow deficient and there will be engine damage.

Now, to dispel the myth.

How hot does the veggie oil have to be, to burn trouble free, in a diesel engine?  The first thing we have to establish is, why is it a concern? When a diesel fuel system injects fuel into the combustion chamber it forces it through tiny holes in the end of an injector, causing it to atomize, or in other words, spray in a very fine mist to mix with the air so it will burn completely.  The viscosity of diesel fuel is low, or you could say it is thin. Vegetable oil, at room temp. is thick, or the viscosity is high, if you tried to spray it through an injector at room temp, it wouldn’t spray well at all, it would just drip.  The problem with that is that the fuel would not combust properly because it would not have mixed with the air. You would eventually get coking or the build up of carbon (incompletely burned fuel) on the end of your injectors and in the combustion chamber.

What to do?

There are two ways that you can run this higher viscosity fuel in your diesel, both ways have to do with reducing the viscosity of the veggie oil. One way to do it would be to make Biodiesel, a chemical process called transesterfication, where you mix methanol and lye with veggie oil to separate out the glycerin. This thins out the oil to a viscosity similar to diesel.

The other way to do it, and the one that makes most sense to Golden Fuel Systems, is to thin out the oil with heat.  Every one has put a pot of oil on the stove to cook something, and what happens when the oil is heated? It gets runny, thin, or in other words the viscosity is lowered.  This is the approach that we use: If the oil is above 160 deg.F, the viscosity of the oil is getting close to the viscosity of diesel, and will spray just like diesel.

It is generally accepted that if the oil is over 160 Deg. F. it is safe to inject into and engine, in other words, it will atomize properly.

OK, we have established veggie oil is thicker than diesel, the veggie oil must be thinned in order to spray the oil properly. No arguments up to this point.  But here is where people start to get off track when it comes to designing an SVO system. The myth has been perpetuated by individuals and other upstart, Johnny come lately conversion companies, that the oil has to reach some magic arbitrary temp. in the conversion system before it gets to the engine, or the whole world will come to an end and your diesel will turn up its toes and die instantly. They design systems with solutions to problems that do not exist. No matter how hard you tried it would be impossible to inject cold oil into an engine that is up to Normal operating temperature.

The part they are missing, is that every component in the fuel injection system IS A HEAT EXCHANGER. Every engine has an ambient core temperature of between about 160 and 200 degrees. This is determined by several factors, the thermostat being one of them. And although the ambient temp. is between 160 and 200 degrees, there are components and parts of the engine that get hotter. The function of the coolant is to take the heat away from the engine and disperse it into the atmosphere through the radiator, and although the coolant is circulating around the head of the engine where combustion is taking place the metal in the head, where the injectors are embedded is hotter than the coolant. Think of a cast iron skillet boiling water, the water will be 212 deg.F but the metal on the underside of the skillet will be much hotter.  Lets go over a couple of scenarios:

Scenario 1

Lets say we have a diesel engine with a VE style distributor pump, married to the side of the engine, that is up to normal operating temp. of 190 deg. F.  We then introduce veggie oil that has been heated to 95 deg.F, much cooler than the desired injection temp. The first thing it will do is enter a hot pump, that if you shot it with a infrared temp gun will be in the neighborhood of 150 or more. The first thing it will do is pick up the heat from the interior components of the pump that will be hotter than the exterior. It will then start its journey to the injector by being pressurized to thousands of pounds per sq. inch. What happens when you pressurize something? The molecules get close together and start bumping into each other, friction = heat. Think of squeezing a snow ball, water comes out because the temp was raised because of pressure. Also think of a pressure cooker, it is a fraction of the pressure that an injection pump created, but it still has significant results.

To drive this point home I want to share an experience I had when doing the research on the VP44 injection pump used on certain Cummins engines. I went down to Little Rock, Arkansas to a fuel injection shop that worked on the VP44. While we were there we went into the test room where they had a pump on the test stand calibrating it. The room was air-conditioned to about 65 deg, and the fuel was cooled to 80 deg.F for calibration purposes. The injector lines going to the injectors and the injectors themselves were in the open, cool air, not in a hot engine compartment. They started spinning the pump to simulate normal operating speed, and within a matter of a few minutes the injector lines were too hot to touch, and the injection pump itself was over 150. This is in an air-conditioned room with nothing but the temp rise from pressurizing the fuel. See my point?

Ok, so we have gone into the hot pump and picked up some heat, then went from no pressure to a highly pressurized state, more heat, then the final stage is the injector. The injector, no matter what the style will hold a small volume of fuel, this injector is embedded in the hot block, and the end of it is exposed into the combustion chamber that is thousands of degrees. The new fuel comes into the top of the injector and has a bit of time before it gets spit out into the hot combustion chamber. This final heat exchanger is allot hotter than the engine coolant could ever think of getting.

Scenario 2

Lets say we go through some heroic efforts, and have some oil that we were able to get to 275 Deg. F. If that oil was to then enter the injection pump, the pump which is also affected by the core engine temp, would start to absorb the heat and the oil would acclimate and inject at about the same temp as the cooler oil in scenario 1. was injected.


The massive heat sink, that is your engine, is far more effective a heat exchanger than any coolant or 12 volt heat exchanger you could use.  All you have to do is get a infrared temp gun, a hot diesel engine, and you will see that this is sound Logic. Just shoot the pump, and the injectors as they go into the head and you will se what I mean. And that is external temps, the internal will be hotter.

I used the VE style pump as the worst case scenario as far as temps is concerned, because it is separated from the engine by a few millimeters. If you have an engine with unit injectors where the fuel rail is embedded in the head, the cards are stacked even more in your favor. Also shoot the rail on a common-rail diesel that is up to temp, and tell me if you think you could actually inject cold oil into your engine.

So if the engines core temps dictate the injection temp, what is a well designed SVO conversion systems goal?


Oil that is too cold and thick, wont flow, so by heating the tank, the hoses and the filter, you can reduce the viscosity of the oil and ensure that it will flow, unrestricted up to the injection system, and then, let the engine, your final heat exchanger do its thing.

Trying to get the oil up to some magic temp. in the tank, or putting in a temp sensor so you won’t inject cold oil is missing the point and unnecessary. A vacuum gauge to measure restriction is much more useful than a temp sensor.

Now, I expect from this essay there will be a fair amount of screaming from the other side that this is blasphemy, everyone knows that the oil has to be 178.924 deg before it goes into the injection system or you will inject cold oil and coke your engine  Don’t let them, or me for that matter, make up your mind for you. If you have questions or doubts, do the temperature tests. Simple as that.

It is impossible to inject cold oil into an engine that is up to operating temp. The inherent design of a diesel engine will not allow it, and neither with the laws of thermodynamics.


Posted in: Myths Misconceptions Misinformation

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