Wednesday, March 14, 2007


Piston Rings Probably Just Not Doing Their Job

This is an email I received from Craig Reece that he passed along to a mechanic.
The mechanic responses are in blue.

CRAIG: The most probably reason for your car's using oil - with such low miles on the engine (well under 100K I assume) is that the incompletely combusted fuel (as indicated by the "white mist" problem you had prior to getting the MAF contacts working, and perhaps due to the faulty MAF, and/or perhaps due to the fact that the PD engine is not a good candidate for WVO) ran down the cylinder walls and caused coking and/or gumming of the ring lands - the grooves in which the piston rings fit.

MECHANIC: Which means they won't rock in the lands and scrape down/compress up

CRAIG: If the ring lands are gummed up or coked up, then the rings can't expand and contract as they're designed to, and they don't seal properly. The function of the top rings is to maintain good compression, and since diesels, lacking spark plugs, ignite the fuel due to the high temperatures created when you compress the air in the cylinder and the combustion chamber, good compression is vital for complete combustion. So, it's obviously a vicious circle.

MECHANIC: Top rings do the scraping by rocking to a different position on the down vs. up

CRAIG: The bottom ring or rings are the oil control rings, and their job is to scrape the oil from the oil pan, which by design is splashed up onto the cylinder walls, and prevents that oil from getting into the area above the top of the piston.

MECHANIC: Oil control ring holds oil to lube cylinder walls.

CRAIG: So, it's unlikely that your piston rings are badly worn, and much more likely that the rings are not doing their job in preventing the oil in the crankcase from making it's way into the combustion chamber and being burned. Burning oil shows up as bluish smoke in the exhaust, and of course low compression will show up via a compression test, which is why I've suggested you get one. The other possible cause of using so much oil could be that it's leaking, but you'd see that on your driveway. A final reason could be worn valve guides, and the traditional way to isolate this from rings as a cause is to first take a compression test, then, if it's low, squirt some oil into the cylinder, and if the compression numbers increase, it's a sign of worn rings, not bad valve guides, since the oil has sealed the rings and improved the compression.

MECHANIC: Worn guides usually show a lot of blue smoke on start and then go away or greatly reduce after start because the cylinders fill up at night. Unlikely he has bad valves guides or seals. Squirting oil in the cylinders is not recommended for diesel engines because of the fact that if you put fuel (oil) in the combustion chamber it might fire. Compression test should be done on hot dry cylinders.

CRAIG: DieselPurge *can* free up stuck rings or rings that aren't expanding and contracting as they should be burning away the carbon and/or gumming. And there are probably other strong solvents that could be used. Tom and Ray, the Car Guys, recommend Rizlone for this, and you might try that too.

MECHANIC: Just pull the glow plugs and dump that purge stuff in. Just pull the oil plug while you do it and then do and oil change after. Marvel Mystery, WD-40 sometimes also work for this.

CRAIG: And if you do in fact have stuck rings, and your oil consumption is due to your car's burning crankcase oil, you should remember that soy is not what you want to be running, since it has a polymerizing effect on the motor oil, and it's even possible that the fact that you used it as your main fuel source, and had (probably) incomplete combustion for a long time, did in fact thicken the oil and thus reduced it's lubrication of the cylinders, and even that some polymerized motor oil got into the ring lands of the oil control rings - and once again we have a vicious circle/downward spiral. Did oil analysis indicate thicker oil?

MECHANIC: Just change the oil more.

CRAIG: And it's because of the polymerizing effect of soy, and the fact that we can assume that some is still getting into the crankcase, that I wouldn't use it, and I'd also change your engine oil a twice the recommended intervals. And I'd use Delvac I or Mobil 1 "Turbo Diesel Truck Oil" (which is just rebadged Delvac 1 and which replaces "Truck and SUV Oil." (And I've gone half-blind reading many of the many threads at the Tdi Club Forum on which oil to use in the PD engine, and my vote is still with Delvac/Mobil 1.)

So, once again, here's what I would do, in approx. order of importance (and cost) - that is, most important and (more or less) least costly first:

1. Buy the DieselGiant VW Tdi DieselPurge kit with DVD and watch the DVD with your mechanic, then pay him to use DieselPurge. Buy enough to do it twice or more. I'd get 4 of the 500ML cans.

2. Try some Rizlone (most auto parts stores should have it.

3. Drive it hard 1x a week - WOT (wide open throttle up a long grade.) Aka an Italian Tuneup.

4. Change your oil if you haven't in the last 3000 miles, and do so every 3000 miles. Send a sample, every time, for analysis, and tell them you're most interested in viscosity. (Who do you use?) Use Delvac or Mobil I - and I know it's a drag to dump a quart of $5.99 oil into your car every 1000 miles, but that's only .006 cents a mile, and you're still getting over 30 mpg even if you're running diesel.6. Run diesel or pure Canola, not soy WVO or soy biodiesel (sorry.)

5. Get a compression test done. Have him squirt some of cheap non- snyth. oil down each cylinder, per the above.Let us know what happens.

And, once again, if it turns out (and the jury is still out) that the PD engine is not a good candidate forWVO: I'm sorry! (And even if it is a good candidate, I'm sorry you're going through this!)


Craig needs to butt heads with the engineers at Bosch over the injection system as well as volkswagen engine engineers.

Your rings are sticking due to clogged injectors due to the glycerine in the WVO you are burning, causing poor atomization of the fuel, which aggravates the glycerine sticking in the rings, carboning and coking them up until they fail to control oil and seal.

Let Craig buy you a new motor when the one you have currently fails altogether, and it will. Yo are doing irreversible damage to your motor running it on WVO, get ready to pay through the nose.

Your car is to be run on VW approved 505.01 oil only, not any Mobil -1 synthetic. Go to Mobil's website and ask about suitable oils for your TDI passat motor. Even Mobil recommends nothing as being suitable for your car and it's moto r as a motor oil.
The dichotomy between Craig's responses and that of a trained mechanic only underlines the whole "seat of the pants" experience that many of the VO scene are going by.

Traditionally gearheads and environmentalists have been polar opposites. Now that a few greenies have gotten into turning wrenches, their lack of fundmanentals sometimes screws up the process.

Diesel fuel is a very closely spec'd product. VO is not. I'd say that shipping engines which burn bunker fuel (aka crude) are more suited to using WVO than a diesel.

Your fuel should be free of sodium. Not much chance of that with WVO. It should also be heated much to much higher temps than 160. Even at 212 it's 4x thicker than diesel. This assumes the fuel pump and injector can handle such high temps without fail. Often they require the fuel to cool them down, not vice-versa.
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