Plantoil/diesel conversion basics
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danalinscott

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Reply with quote  #1 

It is especially important to not purchase a diesel near the end of its useful life for conversion ...unless you plan to overhaul it and run it in on diesel before converting it.

HERES WHY:
Worn out engines tend to have lots of "Blow-by". Blow by refers to some of the hot gases above the piston leaking past the rings as the pressure above the piston builds during the compression and power stroke. The partially combusted VO in these gases tend to cause accelerated coking on piston/lands/grooves and crankcase (lubricating) oil polymerization. Crankcase oil polymerization in turn tends to lead to cylinder and bearing damage.  So engines with large amounts of blow by/poor compression are not good candidates for VO conversion.

The best way to tell how worn out an engine is it to perform..or have someone else perform a compression test on it. This  is basically a test to determine the amount of leakage past the piston rings and valves in an engine cylinder.  This is usually not practical when you are at the prospective sellers home however, so you can do a "quick and dirty" visual blowby test that will allow you to eliminate obviously worn out engines from your list.

Open the hood and remove the oil filler cap. Excessive blowby will cause exhaust fumes to pulse out of the opening. Lots of exhaust means that the engine is not a good candidate for conversion to VO. Here is a video of a mercedes engine with too much blowby.
Don't dicker on the the price if the blowby is this bad...just walk away.  The engine might runfine on petrodiesel for 40,000 miles...but on VO or biodiesel the lube oil will probably turn to "poly pudding" when you least expect it and the engine will be junk shortly afterward.

If however there is no exhaust showing at the oil filler hole like this videao shows it is a good engine. Start dickering. You have a good candidate for a VO conversion right in front of you!

Most likely any older diesel will have SOME blowby slowly wafting out of the oil filler hole when the engine is cold. But if it is blowing out with any force at all when the engine is up to operating temp it needs rings...at the very least. And engine work on any diesel is expensive. You've been warned!

You may still want to perform compression tests on the engine every other oil change...to get a decent warning of when the rings begin to coke up.

Heres how to do that:
(From "The Driveway Mechanic" and Gregs Engine and Machine)
 To perform a compression test on a diesel engine, you need to have a diesel compression gauge and a glow plug or injector adapter. Remove all the glow plugs to check any cylinder. Crank the engine at least five revolutions and the same number of revolutions for each cylinder. It would probably be a good idea to have a battery charger hooked up during the test. You will need to check  a shop manual to determine the minimum compression values that are acceptable...but if any cylinder is 10% lower than the others it is a good indication that this engine is probably due for some major work soon.

Doing a leak down test, particularly in conjunction with a  compression test will give you a great deal of additional information and allows problems to be pinpointed. The condition of the engine is determined by measuring the degree to which a cylinder with valves closed leaks air. In simplified terms, if air is pumped into the cylinder at 100 PSI and the gauge reads 97 PSI, then the leak down percentage is 3%. Doing a leak down test is a fairly simple matter.

A cylinder leakage test is done with the engine at normal temperature, not running, and the piston at Top Dead Center on the compression stroke. During this test, compressed shop air is pumped into the cylinder, and a cylinder leakage gauge gives a reading of air leaking out of the cylinder in percent. Listen for escaping air at the oil fill cap, the exhaust pipe, the intake manifold, and the cooling system (for safety reasons, let the system cool first). This helps pinpoint the problem area. Total cylinder leakage should be no more than 25 percent; leakage from the cylinder head and valves should not exceed 10 percent; leakage from pistons and piston rings should not exceed 20 percent.


 


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phillybruce

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Reply with quote  #2 
What about other quick tests? Oil condition? Can you detect blow by in gas escaping from the oil fill port? 

Any tips for other trouble spots under the hood?

Bruce

danalinscott

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Reply with quote  #3 
Quote:
What about other quick tests? Oil condition? Can you detect blow by in gas escaping from the oil fill port?  
 


Yes...but the devices for doing this are not commonly available.  There is a team developing a how to file for a simple but accurate blow by meter now. It should be available in a few weeks and I will post a link here when it is.

Quote:
Any tips for other trouble spots under the hood? 


Yes...Look for oil and fuel leaks of course. If liquid oil is visible in the tailpipe it is a very bad sign.

And though diesels normally DO have louder ping and knock sounds than gasoline engines if a sound is alarmingly pronounced have it checked out by a mechanic.


It is always best to insist that the engine be "cold" when you arrive to inspect it. Feel it to see if it has been warmed up before you arrive. A cold diesel engine will not start or run as smoothly as a warm one..and if it smokes and stumbles a LOT as it warms up it is a sign that some additional pre-purchase investigation into the condition of the engine is warranted.

Although as a rule diesel engines are more expensive to repair/overhaul than gasoline engines it MAY be worth buying an engine that needs some minor repair such as replacement of the injectors and timing adjustments. It may even be worth having an engine re-ringed or completely overhauled considering how much can be saved on fuel costs in some cases.

Check out the forums devoted to specific makes/marques/models for more specific tips on what to look for to determine if the car/truck you are thinking of buying is in good condition or not. And remember..the cost of having a competent mechanic may seem like a lot...but avoiding a lemon is priceless.  And often having the mechanics estimate of what it will cost to bring an allegedly "cherry" engine up to "reliable"  will lower the asking price substantially....saving you MORE than the cost of the mechanics evaluation.

If you do check the Automotive forums for tips on this subject please remember to come back to this discussion and add the links you found most informative. Those who come looking for this information will thank you.

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gjain89

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Reply with quote  #4 
Hi,

I just graduated from high school and wanted to take up a diesel to WVO conversion project during my summer break.

My Dad is considering buying a used car (up to 5 years old) for this project and I needed some guidelines on what to look for.

I had been browsing a couple of websites and found out that WVO doesn't work well with certain types of diesel engines.  From Wikipedia, I can see there are two main types, direct injection and indirect injection.  Direct injection has distributor and inline pump direct injection, unit direct injection and common rail direct injection.  Out of all of these, is there a specific one I should look for?  Are there certain disadvantages or advantages associated with any of them?

Oh and also, the car will most likely be a very small one, like a Suzuki Swift with a 1.2 L engine.  I'm guessing there shouldn't be any disadvantages to having a small engine, right?

Thanks..
Gautam


danalinscott

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Reply with quote  #5 
Small engines are not inherently less viable candidates for conversion.
But...it takes a LOT longer to have the fuel savings allow one to break even on the cost of conversion and wvo collection and processing equipment.

Generally speaking indirect injection engines are likely to last the longest when wvo is substituted as fuel and fail to completely purge often, use the vehicle for shorter trips, or don't have a well engineered conversion.

If you plan to use this converted vehicle for short trips (where the engine does not come to full operating temp for at least 15 minutes) I advise you to consider that this may significantly shorten the engine life no matter what you do.

Dana

Quote:
Originally Posted by gjain89
Hi,

I just graduated from high school and wanted to take up a diesel to WVO conversion project during my summer break.

My Dad is considering buying a used car (up to 5 years old) for this project and I needed some guidelines on what to look for.

I had been browsing a couple of websites and found out that WVO doesn't work well with certain types of diesel engines.  From Wikipedia, I can see there are two main types, direct injection and indirect injection.  Direct injection has distributor and inline pump direct injection, unit direct injection and common rail direct injection.  Out of all of these, is there a specific one I should look for?  Are there certain disadvantages or advantages associated with any of them?

Oh and also, the car will most likely be a very small one, like a Suzuki Swift with a 1.2 L engine.  I'm guessing there shouldn't be any disadvantages to having a small engine, right?

Thanks..
Gautam




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Dana danalinscott@yahoo.com
ReynoldDoveton

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Reply with quote  #6 
A blow-by also called a back-compression happens in a worn out engine. The gases leak out of the piston rings and escape out of the tappet covers (also via valves).

It is very necessary to take precautionary steps on a high mileage used engine to prevent more engine damage. There are some DIYs here http://www.automotix.net/autorepair.html which could help in preventive maintenance to avoid long bills in the future.
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