-What Is "Coking"?-

-What Is "Coking"?-

A question that gets asked quite often...   What exactly is coking??
So what exactly is coking?  Carbon build up on injector nozzles, glow plugs, prechambers, valves, and in the worst cases...  rings.  That doesn't sound like a big deal, and for the most part, isn't..   but it can turn into a real headache.

Coking, or carbon buildup, on the injector tips will alter the spray pattern of the injector.  On an IDI engine, that typically isn't a problem.  With direct injected engines such as the Cummins, Powerstroke, DT, and most modern diesels made after the early 90s, it can cause real problems.  If left unchecked, the spray pattern can be affected to the point of spraying fuel outside of the bowl in the pistons.  This can lead to washing down cylinders and ring coking/loss of compression.

In most cases, a good hard drive on a tank of straight diesel will knock the carbon bits off the injectors..   but not always.  Sometimes, the injectors will have to be removed and cleaned manually with solvent or a brass wire brush.

So what causes coking?  Quite a few things can but the biggest cause is running oil in a cold engine and low load driving/idling on heavy oil blends.  Oil needs HEAT to burn clean.  Sitting at idle for any length of time and you'll typically notice that the exhaust is producing a light haze.  That's how it starts.  From there, it will continue to get worse unless it sees some right foot action.  Other things that can cause it...   oil viscosity too high...   moisture contamination...   oil not clean enough...  etc.

How do we prevent coking?  Properly process your oil for starters.  It needs to be CLEAN!  Obviously I'm a fan of heated direct drive centrifuges...  but if filtration is your method of choice, you need to be filtering down to 1 micron or less AND using some method to remove moisture.  Water separating filters will not remove emulsified water from oil.  You need HEAT and TIME.  Settling goes a long way and bringing the oil up to 170F+ for an extended period greatly helps.

Now we need to adjust the driving habits.  If running on a single tank...   keep the blends to 50% or less (or expect to have issues over time and be prepared to handle them).  Limit or eliminate idle time when running on oil blends.  Start and shutdown on straight diesel fuel (dual tanks FTW!).  All of this can help greatly reduce coking issues.

There are other methods that people have used to combat coking.  One of the big ones is water/methanol injection.  It works.  Is it perfect?  Nope.  Coking can and will still happen.  Water injection will just help prolong the issues from coming up.  Propane and HHO have also been mentioned by quite a few people but I don't have direct experience with them.  I've heard propane works very well for getting a super clean burn on oil blends, but again, I've not tried it.

Eventually, anyone running oil blends will experience some level of coking.  Be prepared for it.  You may have to remove injectors and clean them at some point so keep the needed parts/seals around for the job WHEN (not IF) it comes up.  Know how to do this work yourself!  If you don't...   now is the time to learn.

Even I have issues from time to time...

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