3406E/C15 Fuel In Coolant Engine Miss Explained


CAT 3406E Engine | Highway & Heavy PartsCAT C15 Engine | Highway & Heavy Parts


If you're running a C15 or 3406E diesel engine, you may have experienced your engine missing. So, why does that happen? 

Well, in some cases, it can be caused by coolant entering your engine. This normally happens because of a failure in your engine, often related to your injectors and o-rings.

We're taking you through how that coolant can get into your engine and what you can do about it. 

Need parts for your 3406E or C15? Call our ASE Certified Technicians to make sure you get the right parts the first time!

Give Us A Call!



How Can Coolant Enter Your C15 or 3406E?

Caterpillar 3406E, C15, & C15 ACERT engines all use the same style cylinder head, injectors, and injector cups (see images 1 & 2 below). The injector on these engines seats directly against the cylinder head casting, not on the injector cup.

The seat is located below the injector cup and should completely seal the cup from combustion pressure and heat. (see images 3 & 4 below). The injector doesn't actually even touch the injector cup.

One issue with this design is that it is possible for the injector to not seat completely against the cylinder head. This may be due to imperfections in either the head casting, the injector, or both.

If the injector to head seat is not sealing, it will let engine cylinder pressure go past the seat and pass in-between the cup and injector. When this happens, the cylinder pressure and heat can now reach both the injector o-ring and the upper injector cup o-ring. These o-rings will then fail as they were not designed to withstand the high cylinder temperatures and pressure.

These engines might be similar, but there are a few key differences. Learn more about how the C15, C15 ACERT, and the 3406E differ in our blog post!


Symptoms of Failure

Some of the signs that an injector seat is not sealing correctly are:

  1. Burnt injector o-rings
  2. Carbon buildup or tracking on the inside of the injector cup or on the injector body above the sealing line (see images 6 & 7 below).
  3. Traces of coolant or leaking coolant around the injector cup.

The failure of these o-rings can lead to problems such as:

  1. Fuel in the coolant
  2. Engine miss from combustion pressure aerating the fuel
  3. Overheat of the injector tip causing a miss

The cause of this type of failure can be contributed to a few possibilities such as:

  1. The injector body is worn, warped, or damaged.
  2. The cylinder head casting is worn, pitted, or otherwise damaged.
  3. The injector hold down bolts were improperly tightened or stretched.
C15 Injector | Highway & Heavy Parts
Image 1. Complete injector for 3406E / C15
C15 Injector Cup | Highway & Heavy Parts
Image 2. 3406E / C15 Injector Cup
C15 Injector Seat  Highway & Heavy Parts
Image 3. Seating surface of injector tip to cylinder head
C15 Injector and Cup 2 | Highway & Heavy Parts
Image 4. Seating surface of injector to head is below the injector cup
C15 Injector and Cup | Highway & Heavy Parts
Image 5. C15 Injector shown installed in the injector cup
C15 Injector Cup Carbon | Highway & Heavy Parts
Image 6. Start of carbon buildup due to leak at injector seat
C15 Injector Cup Carbon 2 | Highway & Heavy Parts
Image 7. Carbon buildup due to leak at injector seat
If you notice this failure in your CAT C15 or 3406E, it's important that you get it taken care of right away, before it can cause even more problems in your diesel engine. Highway & Heavy Parts can help you get the diesel engine replacement parts you need to keep your engine running for miles to come.
Think you might be having a problem with your cylinder head components? Read our post to learn the symptoms that you need to replace your C15 cylinder head components.




Not sure what diesel engine parts you need for your repair? Our ASE Certified Technicians can help! Call us at 844-304-7688, or request a quote online!


Originally Posted November 13, 2014; Edited February 7, 2020


Comment Post Comment