combustion chamber coking when running motor oil

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
got some pics from a while back that some of you might be interested in
engine hung a valve because a lifter that'd been tacking along for the last 50k miles finally got eaten, nothing to do with the coke buildup
the coke extends out from the injector nozzle holes in a cone shape, real interesting

it is easy to notice when it is building up because you'll have bad white smoke at idle, when you beat on the engine very severely it does knock loose most of the time on its own but sometimes you've gotta pull the injectors and crank it with them out in order to break it loose and eject it
I'd imagine it gets this bad about every thousand miles or less from that white smoke metric alone.

Fairly soon I'm gonna try some thermal barrier ceramic coating on the piston and head to see if it'd be enough to keep the combustion chamber temperatures high enough to keep it from sticking.
Got the engine apart again and it is about the same, 40k miles later (broke a piston ring, probably from using ether to start it because the high-viscosity fuel burns so poorly) no pics yet, just gotta get around to transferring them from the camera to the computer one of these days/months/years... Anyways, this time the exhaust valve heads got this white ash buildup on them that's pretty thick. I'm betting that is from the metallic antiwear additives or some such. It scrapes off real easy but I did notice some gentle imprints in the coke on the piston tops from the valve heads so that is certainly a concern worthy of... concern. Nothing like timing belt marks, just outlines in the buildup.

anyways, pictures:




 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
HI,

What percent of RUG are you using w/ the WMO ?

Are you using any additives (like Power Service etc) ....

I'm thinking of using WMO in my IDI 7.3 since it uses so much fuel relative to the TDI.

Thanks

Andrew
 

GlowBugTDI

Veteran Member
Joined
Jul 20, 2018
Location
Cambridge, MN
TDI
2001 Beetle GLS TDI (BIODSL). Glow Bug TDI (sold)
When the coke is breaking loose how is it not damaging a valve? Is it just really soft or are you rotating it by hand to get it out?also thanks for posting pictures.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
When the coke is breaking loose how is it not damaging a valve? Is it just really soft or are you rotating it by hand to get it out?also thanks for posting pictures.
I dunno, it might hang up between the valve and seat, but it isn't like it's strong enough to provide much of an impediment to the piston closing the valve with mild force

piston/head is the one I'm more worried about, but it doesn't seem to have caused failures for me yet, so we'll worry about it when it comes time to worry about it
Kinda like how the exhaust valve guides on every single used tdi head I see have a good 1/16" or more of slop in them, yet it doesn't seem to hurt anything so why worry?

ETA: turbine wheel also probably doesn't enjoy having solids introduced into it at 120k rpm, but inconel is some tough stuff... lol
What percent of RUG are you using w/ the WMO ?

Are you using any additives (like Power Service etc) ....

I'm thinking of using WMO in my IDI 7.3 since it uses so much fuel relative to the TDI.
additives... I'd like to do some learning to figure out what sorta cetane-boosting additive is actually worthwhile instead of overpriced snake oil, but "true believers" make that basically impossible, so I run nothing.

gasoline kinda sucks as a diluent, it causes vapor lock, and I've been told it adds to the coking issues but I don't know
antiknock additives are kinda the opposite of what you want in diesel after all
I'll throw in whatever "bad gas" is around, and during the winter it'll get 10-20% of gasoline
By a quirk of minnesota's tax laws, "fuel additives" are non-taxed and they don't specify an upper limit for percentage on the "additive", so I always make sure there's some taxed fuel in the tank. I just have 10 gallons of lubricity additive in the tank along with it.

look up the 4kw freightliner application 5.9 cummins starter for your IDI if you're gonna be feeding it oil
they are not the happiest motors at the best of times
 

GlowBugTDI

Veteran Member
Joined
Jul 20, 2018
Location
Cambridge, MN
TDI
2001 Beetle GLS TDI (BIODSL). Glow Bug TDI (sold)
I imagine that adding gas would make it burn hotter and clean it up a bit, but with that i also think you would have to use a decent amount to get it to do so. Which would not be good for the IP. Would lowering the amount injected also clear up the coking? I know its not ashless oil, but having less injected would allow for a more clean burn? more of a gasoline engine line of thinking i know but maybe similar....
 

GlowBugTDI

Veteran Member
Joined
Jul 20, 2018
Location
Cambridge, MN
TDI
2001 Beetle GLS TDI (BIODSL). Glow Bug TDI (sold)
I think (don't know for sure) that using seafoam sprayed right in the intake would clean it up quite nicely. It may take more of the can to clean it up because the amount of coke build up.

I know lucas also has a version that is pretty good.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
I imagine that adding gas would make it burn hotter and clean it up a bit, but with that i also think you would have to use a decent amount to get it to do so. Which would not be good for the IP. Would lowering the amount injected also clear up the coking? I know its not ashless oil, but having less injected would allow for a more clean burn? more of a gasoline engine line of thinking i know but maybe similar....
nah, I was talking to some oilfield guy and he says they have a lotta issues with coking on their diesels when they feed them napthenic crude as fuel
naptha is polish for gasoline, so I assume they were taking about a kind of crude that has a lot of natural gasoline fraction in it

Probably something to do with the hydrocarbon chains happening to be rather "sticky" and combining to make longer chains as they're leaving the injection nozzle rather than just burning like the slightly longer chained and more stable diesel type chain length fractions would do?
Dunno. There's a lot of magic going on in there.

No, nothing you dump in the intake will do much of anything.
Was trying water injection (know how a leaking head gasket will sometimes make for a sparkly nice steam-cleaned cylinder?) for a while but it didn't seem to help.

Severe abuse knocks it loose. Big injectors and a reasonably sized airflow-maker. Imagine it gets the piston tops hot enough that the coke falls off, because it smokes REAL bad once, then burns clean on all subsequent pulls.
 

DivineChaos

Top Post Dawg
Joined
Jul 27, 2019
Location
Minnesota
TDI
mk6 jetta sportwagen tdi
nah, I was talking to some oilfield guy and he says they have a lotta issues with coking on their diesels when they feed them napthenic crude as fuel
naptha is polish for gasoline, so I assume they were taking about a kind of crude that has a lot of natural gasoline fraction in it

Probably something to do with the hydrocarbon chains happening to be rather "sticky" and combining to make longer chains as they're leaving the injection nozzle rather than just burning like the slightly longer chained and more stable diesel type chain length fractions would do?
Dunno. There's a lot of magic going on in there.

No, nothing you dump in the intake will do much of anything.
Was trying water injection (know how a leaking head gasket will sometimes make for a sparkly nice steam-cleaned cylinder?) for a while but it didn't seem to help.

Severe abuse knocks it loose. Big injectors and a reasonably sized airflow-maker. Imagine it gets the piston tops hot enough that the coke falls off, because it smokes REAL bad once, then burns clean on all subsequent pulls.
I agree. Mine seemed to run wayy better after a 130+mph pull. Got those egts up there. Still white smoke for 20 sec on startup.
 

GlowBugTDI

Veteran Member
Joined
Jul 20, 2018
Location
Cambridge, MN
TDI
2001 Beetle GLS TDI (BIODSL). Glow Bug TDI (sold)
Windshield washer reservoir with plain water into the intake with a nice mist nozzle lol.

I haven't used seafoam on a diesel engine i just know from my experience on gassera it works well. That being said there is nothing better then just taking the time to clean the part weather that be carb, throttle body, IAC, ect. Its always better done that way. But i have used it amd seen results. Same with lucas.

I get why people don't belive in many additives for sure as there is so much garbage out there.
I never really believed in "stop leak" fluids (cause most are crap) until I used the lucas stop leak steering fluid. When its 5° out and the steering rack seals gave out on a vehicle I have your kinda forced to do something. Like literally drained the steering reservoir in ~8mi. Stopped at a gas station and they had some bought 3 bottles and kept driving. Went about 15 miles more, didn't have to add after that and has yet to leak since. Have put on maybe 8k more and its good so far. Who knows when it'll go now but i don't care at this point.

Also, could add a little dawn it will break those hydrocarbons down a smidge smaller😁
 

rocky raccoon

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Joined
Jun 11, 2020
Location
Greater metropolitan Beaverdam
TDI
2014 Jetta Sportwagen
I can't believe someone has not already said this in this thread so I guess I have to.

Our engines are Diesel engines and are designed to run on Diesel fuel. Running anything else is an interesting experiment but will definitely result in problems, sooner rather than later. The old OM617 engine in my Benz was more tolerant to low quality Diesel but even it wanted the right fuel. The modern oil burners in our VWs are not happy on exotic fuel mixtures.
 

Andyinchville1

Veteran Member
Joined
Apr 7, 2016
Location
Virginia
TDI
2003 Jetta TDI wagon, 5 sp, 226K miles
HI,

I believe what "works" from the reading I've done so far is :

1) cleaning the oil real well (some say down to 2 microns)

2) cutting with gasoline (or something else) until the viscosity is similar to diesel

3) using a fuel supplement like Power Service gray bottle

Optional but may help:

4) 2 tank fuel system .... start on Diesel / end on diesel

5) Water misting syatem to "stem clean" combustion system

6) IDI rather than DI diesels

7) Supposedly Turbo diesels driven "hard" will stay clean

Personally, after I get my centrifuge, I'll do 1,2,3, 4 (my ford truck has 2 tanks from the factory) , 6 (my truck is 1993) so IDI already , 7

I think if you do steps 1 , 2, 3 it should be better or OK

Andrew
 

ToxicDoc

Veteran Member
Joined
Mar 1, 2018
Location
Virginia, US
TDI
2001 Jetta, S7, .216
I can't believe someone has not already said this in this thread so I guess I have to.

Our engines are Diesel engines and are designed to run on Diesel fuel. Running anything else is an interesting experiment but will definitely result in problems, sooner rather than later. The old OM617 engine in my Benz was more tolerant to low quality Diesel but even it wanted the right fuel. The modern oil burners in our VWs are not happy on exotic fuel mixtures.
You're in the alternative diesel fuels section. I think they know it's not what was called for.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
Windshield washer reservoir with plain water into the intake with a nice mist nozzle lol.
I was spitting water in through my ether line
just take a swig and blow it in there after having it pinned to the floor for a while to get everything nice and hot, didn't really do much of anything and I put a full two liters of water through there
 
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