Plantoil/diesel conversion basics
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Posts: 934
Reply with quote  #1 

This is a major concern of my fleet conversion clients and has been a primary concern of mine for many years. I think what I have learned as I was driven by that concern may be helpful to others..especially if I can condense it and discussion that remains on topic results. So here goes.

Since VO fuel research began in earnest the same basic problem has been noted with substituting VO for petrodiesel in diesel engines. It tends to leave carbon deposits which either directly or indirectly damage the engine and eventually lead to rapidly accelerated wear and/or catastrophic engine failure.

These deposits generally occur in three places...the injector tips, the manifold side of intake valves, and the piston (ring) lands/grooves. The process is generally referred to as "coking". Piston land Groove Coking is described at: and if individuals are interested I will create a separate discussion on the other two. It is sufficient to say here that injector coking generally tends to accelerate ring/land/groove coking and that ring/land/groove coking leads to the early demise of diesel engines run on VO.

In early testing of VO fuel engine longevity was very short. So short that VO was deemed to NOT be a viable alternative fuel. This was because VO tended to only partially combust due to its high viscosity at room temperature. The partially combusted VO tend to collect on piston sides and quickly damage the cylinder walls as well as do secondary damage to other parts of the engine. Reducing the viscosity of VO prior to injection by heating it dramatically improved the completeness of combustion but did not completely solve the problem.

But there are many things that individuals can do to delay ring/land/groove coking and the subsequent shortened engine life it causes.
The most basic are:

1. Do not convert engines in the last stages of their life or in need of major maintenance unless you consider them disposable. If you DO at least test your crankcase oil for polymerization so it can be changed often enough to prevent gelling and the secondary damage this causes.

To test for crankcase oil polymerization:
1.Retain about a cup of the used lube oil in a small jar.

2.Seal it up and refrigerate overnight.

3.Tilt the jar to see if the oil flows at all. Since refrigerators typically are set at between 37-45*F it may flow like molasses or tar...but it should still flow.

If it appears at all jello-like it indicates polymerization is occurring in your lube oil and that you should increase the frequency of your oil changes. If it remains jello-like after warming to room temp you may have advanced ring coking and should immediately determine if this is severe using compression tests before major engine damage occur rs.

2. Do not allow your injectors to become leaky. Leaky injectors speed up the ring/land/groove coking process since their effectiveness tends to quickly degrade. Use very "dry" VO fuel. Even very small amounts of suspended water (add link to suspended water discussion) tend to erode injector tips and allow leaking.

3. Do not add "performance" chips or other "power" mods to your engine. These are designed with diesel fuel use in mind and are not well suited to VO fuel use. They tend to add more fuel to the combustion chamber and so hasten ring/land/groove coking.

4. Do not switch to VO fuel until your engine is at normal operating temperature. The cooler the combustion chamber (piston,head,walls) are the faster ring/land/groove coking progresses.

5. Make certain that VO fuel is as hot as possible (200°F to 275°F) at the injector inlet.

6. Make certain that your purge cycles are long enough to completely purge VO from your injection lines and injectors. Starting a cold engine on cold VO will hasten ring/land/groove coking even in an engine with no other issues.

7. Do not ignore the manufacturers regular diesel engine maintenance schedule or any symptoms (hard starting, increase in crankcase oil consumption, excessive smoking upon start-up,etc) which might indicate that the engine is not running optimally.

8. Have a compression test performed..or do it yourself..before you convert to VO. This will provide a good indication of how worn the engine is and possibly of problems that need attention before conversion. It will also provide a "benchmark" that can be used to compare later yearly compression tests to.

9. Make certain that your purge (diesel) tank cannot become too heavily contaminated with VO due to VO being "returned" to the diesel tank during purge cycles. Starting on a high percentage VO "blend" probably contributes to accelerated ring coking much as cold starting on VO does.


Posts: 16
Reply with quote  #2 
Good afternoon Dana:

In one link you mention that you use mild steel tanks because the cost is so much less, and in the polimerization link you mention the biggest culprits for polymerization are large amounts of copper and steel.  Can you please help me with my confusion here.

Posts: 934
Reply with quote  #3 

Originally Posted by oldmanc
Good afternoon Dana:

In one link you mention that you use mild steel tanks because the cost is so much less, and in the polimerization link you mention the biggest culprits for polymerization are large amounts of copper and steel.  Can you please help me with my confusion here.

VO reacts very slowly at room temp with oxygen and forms long chain molecules via polymerization. These can clog filters. Nearly all metals speed up this very slow reaction slightly. Mild steel can. Copper can. Aluminum can.

It might be best to advise using only plastic tanks if metals had a significant effect on how fast polymerization takes place under normal real life.  But except in extreme cases this is not really a major concern IMO.


Posts: 4
Reply with quote  #4 
two questions, probably covered already, but couldn't find.
1. is 100r7 hose suitable for wvo?
2. for second(wvo)tank, any problem from using salvage
gasoline tank?  1980vw requires pump anyway, no pressure.
Either the manuals I bought don't cover or I failed to notice.


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