I've seen postings here about different sounds that are produced by a Diesel engine, and have experienced them all, I'm sure. One thing I would like to see here is a solid set of definitions for these sounds. For instance- what I've noticed from my car-

-Normal warm idle- smooth sewing machine sound- probably no special name for this one, except maybe "all's well"
-Cold Idle on straight Diesel fuel- winter or summer- idle is much more noisey- what causes this in a Diesel but not a gas engine?
-Cold idle with 30% WVO- deep knocking sound- almost like rod bearing failure, but it goes away after 5 mintutes of warm-up. Is this called "nailing" or just "knock"?
-Warm idle with 30% WVO- engine becomes so quiet, you might believe it's not a Diesel. Why does WVO make the engine so much quieter?
-Cruising with straight Diesel, especially winterized fuel- frequent bursts of what sounds exactly like spark knock or pinging in a gas engine, except it happens opposite to gas engine- on trailing throttle, as opposed to accelerating. Should this be called nailing, knock or pinging, and again what causes it?
-Cruising with 30% WVO- absolutely no pinging sounds, smooth drone, seemingly more power. Seems like such a good thing, but again, I can't understand why WVO would cause this.

Dave

1976 300D

Because Diesel designed his engine to run on plant oils!

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Possibly just different flame rate spread causes the diferences primarily. On normal diesel the activity of buirn in the cylinder is over a long time before the piston is very far down the bore. I suspect with non petrolem products the period is much longer and translates into much smoother and less noisy power strokes. A softer primary ignition of the fuel is also going to go a long way to reduce knock,The start of the initial burn is much less dramatic but endures longer in my opinion. With gas engines the period of burn lasts a great deal longer than diesel in fact not unusual to get flames out the exhaust headers. WVO should in theory be a lot less punishing to the block. During certain operating loads and rpms there are probably some other complications that are harder for a simple guy like me to understand when wvo is either the fuel or a portion of it. I am probably wrong in what i think but I did not notice a lot of people jump on this thread so thought I would mention one of my thoughts. Still burning petro products myself. Wife hides her canola oil everytime I mention alternative fuels.

Unless you have a 603 then it goes; tick, tick, tick, tick.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Diesel noise is something I've spent a long time analyzing. A diesel engine makes loud noise when the combustion is sudden but it can be quiet if the combustion is gradual or weak/non-existant, i.e. a quiet diesel doesn't necessarily indicate all is well.

Increased noise at cold idle is caused by delayed combustion which is caused by insufficient combustion chamber temperature. Cold WVO probably delays the combustion even further because of its viscosity, but when heated up it has a higher cetane number than straight diesel, thus it burns quicker and more gradually -> less knock.

A diesel should not have any pinging noises while cruising, otherwise you probably have a bad injector. My 82 developed this problem and I found out #5 injector was just pissing. Replaced the injector and pinging went away, but idle got louder because previously the #5 cylinder wasn't combusting.

My 96 has a very nice sewing machine idle, but when cold there's some pinging while cruising around 3000 rpm. I suspect a bad injector and will try some diesel purge.

My 83 is strange however. It has a quiet idle when cold and semi warmed up, but when fully warmed up it's noticably louder with a slightly varying combustion knock. The only explanation that I can come up with is that when it's cold the combustion temp isn't high enough for complete combustion, thus the lower noise, but there's barely any smoke even when cold. Does anyone have another explanation?

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

"quicker and more gradually"- that sounds like a self-contradicting statement, but not at all at odds with the mysteries of Diesel combustion. For instance, I've read posts here that say WVO has higher Cetane, hence ignites much quicker. Yet, one would think that a faster explosion would create a louder knock. But I only get a much louder knock when the WVO is stone cold. Once things warm up a bit, the engine gets very quiet on WVO blend.

Note that I don't have a heated tank- the fuel mix gets heated from the rubber return lines from each injector.

Dave