oil dilution with diesel

[wrench buster]

Hello all, Can anyone provide some information on the relationship with too frequent re-generations (code 3375) and rising engine oil level (fuel dilution). I have cleaned the EGR SYS. and replaced all of the Injectors with OEM ones. I have also had the DPF and DOC cleaned. I am stumped on this one. From my understanding the ECM injects fuel in the cylinders on the EX. stroke instead of having a 7th injector. My hair is turning grey on this and it's keeping me up at night. Thank you for your input. This is in a Freightliner M2 with Cummins ISL 9 (2014 Year)

[Rawze]

most common cause of fuel dilution is a cracked cylinder head.

[tree98]

Have you done an EGR tuneup?

Will it pass a fuel rail leakdown test?

Does it have exhaust leaks?

You have 2 separate issues here with frequent regens and also fuel dilution.

[wrench buster]

Hi Tree, I have done the EGR tune up, cleaned the intake sensor, The rail leak down test passed. I also pressure checked the CAC, I saw no EX. leakage. From what I've read the frequent regens could be causing the oil dilution since fuel is injected in the cylinders to accomplish re-gens. Let me know what you have found out to make this happen in your cases. Thanks for your quick response.

[Rawze]

(10-31-2025 )wrench buster Wrote:  Hi Tree, I have done the EGR tune up, cleaned the intake sensor, The rail leak down test passed. I also pressure checked the CAC, I saw no EX. leakage. From what I've read the frequent regens could be causing the oil dilution since fuel is injected in the cylinders to accomplish re-gens. Let me know what you have found out to make this happen in your cases. Thanks for your quick response.

Frequent failed regens can cause fuel dillusion to show up, in a lab report for an oil sample, yes .. but it is NOT likely going to be so bad that it measurably raises the oil levels at the dipstick.

What does the regen history look like in Insite?.

How old are the DPF/DOC uints?.

Have you actually REPALCED the IMAP and other sensors with new OEM?.. because simply cleaning them is NOT good enough!.. especially for the IMAP sensor. Have you actually takem the intake and EGR systems all apart and cleaned all the soot buildup out?.

Have you replaced the crank case filter with a new one?... or removed it all together?.

Overhead valve adjustment?.

checked/cleaned the circuit passage for, and replaced, the exhaust back-pressure sensor?. .. replaced the IMAP sensor, and Delta-p sensor + cleaned out the mounting block for it?.

etc.etc.etc.

Did anyone use any liquids for cleaning the DOC/DPF?.. if so, they are ruined and will not regen properly!.

Has anyone checked the DECOMP TUBE and SCR injeector for leakage and exhaust pipe blocking?.
info: https://rawze.com/forums/showthread.php?...07#pid1807

and yes .. DPF/SCR issues are most likely a separate thing from the oil illusion issues if it is so bad that it cause the oil dip-stick levels to raise.

Also, has anyone taken the DPF/DOC, etc. off of it and taken photos of theior faces?.. and determined what is deposited onto them?. Posting pics of the faces of the units onto the forum here can often reveal what is wrong.


- How fast does the oil levels raise after a fresh oil change?.
- Are you sure oil level rise is fuel in the oil?... or can it be from coolant intrusion?. - Has anyone sent an oil sample to a lab? or drained the first bit from the oil pan into a freezer-baggie and let it sit to see if there is water getting in?.

[marek4792]

Just a guess, but I would make sure the gear fuel pump seal behind the pump itself hasn't failed.

[wrench buster]

(10-31-2025 )marek4792 Wrote:  Just a guess, but I would make sure the gear fuel pump seal behind the pump itself hasn't failed.

Thanks for your response, and I have replaced the gear pump below the HP pump. The seals were not broken or brittle, however the shaft where the seals contact were really worn down. I don't know if the shaft was machined in that manner or was it worn. I would think it should have the same dia. all the way down. I did replace the pump on account of that, and we will see what's going to happen. If the oil is thinned enough it may be getting past the rings causing frequent regens.

[wrench buster]

(10-31-2025 )Rawze Wrote:  

(10-31-2025 )wrench buster Wrote:  Hi Tree, I have done the EGR tune up, cleaned the intake sensor, The rail leak down test passed. I also pressure checked the CAC, I saw no EX. leakage. From what I've read the frequent regens could be causing the oil dilution since fuel is injected in the cylinders to accomplish re-gens. Let me know what you have found out to make this happen in your cases. Thanks for your quick response.

Frequent failed regens can cause fuel dillusion to show up, in a lab report for an oil sample, yes .. but it is NOT likely going to be so bad that it measurably raises the oil levels at the dipstick.

What does the regen history look like in Insite?.

How old are the DPF/DOC uints?.

Have you actually REPALCED the IMAP and other sensors with new OEM?.. because simply cleaning them is NOT good enough!.. especially for the IMAP sensor. Have you actually takem the intake and EGR systems all apart and cleaned all the soot buildup out?.

Have you replaced the crank case filter with a new one?... or removed it all together?.

Overhead valve adjustment?.

checked/cleaned the circuit passage for, and replaced, the exhaust back-pressure sensor?. .. replaced the IMAP sensor, and Delta-p sensor + cleaned out the mounting block for it?.

etc.etc.etc.

Did anyone use any liquids for cleaning the DOC/DPF?.. if so, they are ruined and will not regen properly!.

Has anyone checked the DECOMP TUBE and SCR injeector for leakage and exhaust pipe blocking?.
info: https://rawze.com/forums/showthread.php?...07#pid1807

and yes .. DPF/SCR issues are most likely a separate thing from the oil illusion issues if it is so bad that it cause the oil dip-stick levels to raise.

Also, has anyone taken the DPF/DOC, etc. off of it and taken photos of theior faces?.. and determined what is deposited onto them?. Posting pics of the faces of the units onto the forum here can often reveal what is wrong.


- How fast does the oil levels raise after a fresh oil change?.
- Are you sure oil level rise is fuel in the oil?... or can it be from coolant intrusion?. - Has anyone sent an oil sample to a lab? or drained the first bit from the oil pan into a freezer-baggie and let it sit to see if there is water getting in?.

Thanks for your reply Tree, I have removed the air intake and cleaned out carbon, and cleaned EGR diff ports and replaced the sensor with new OEM, the back press sensor was changed when I did the DOC and DPF service, however I just cleaned the IMAP sensor and did not replace it.
I will pursue that and also the decomposition tube inspection. I estimate I had 1/2 gallon of diesel in my oil pan when I changed the oil and filter. The oil pan holds 5 gallons. I replaced the transfer pump below the HP Inj pump and When I dis-assembled the old pump the shaft looked really worn where the seals ride. Maybe that is where the diesel is coming in. This truck is doing a regen about every 6 hrs according to my INSITE.
Thanks for your input

[Rawze]

(Yesterday )wrench buster Wrote:  ...This truck is doing a regen about every 6 hrs according to my INSITE.

4 - 6 hours is about normal for the frequency of the regen process while driving it. More often iof it gets cancelled, such as excessive out of gear (coasting out of gear a lot) while driving, frequent stops-n-go driving where it gets cancelled, etc.


Maybe post a screen shot of the regen history, sowing the numbers.