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Old 04-24-2021, 03:07 AM   #1
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Cummins ISM showing white smoke? coming out of dipstick.

So I recently started having an issue on my Cummins ISM engine on a bus that I bought from someone. The owner told me that its normal on cummins engines, but I just want to be sure.

My Cummins ISM engine is putting out some sort of white smoke or fog from the engine oil dip stick, and if the bus is being driven for more then 10 hours at a time, the oil level will start to drop (not a lot) but I refill the oil anyway just to be safe. There is no loss of power, I succesfully drove it for 15 hours straight with no issue (except I had to refill a few quarts of oil in the end). The dipstick is also not properly secured so that could also be why. Here is a picture of the issue:

Could the oil just be evaporating and that's why I'm losing oil level?


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Old 04-24-2021, 10:29 AM   #2
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This condition is called blowby, the fog is combustion gases leaking by the piston rings. It is a sign of a worn engine. The oil consumption supports that the rings are worn and oil is being burnt because the piston rings are not scraping the oil off the cylinder walls on the way down. The only fix for this is a engine rebuild, though this does not necessarily mean the engine is on the brink of failure. The engine may continue to run and produce decent power for a long time, but it will only get worse.

The previous owner made a false statement, this is not a normal healthy condition and it's far from exclusive to Cummins engines. Any engine, gas or diesel can produce blowby. The presence of blowby is often regarded as a red flag to a potential purchaser.
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Old 04-24-2021, 10:34 AM   #3
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Originally Posted by Truthseeker4449 View Post
This condition is called blowby, the fog is combustion gases leaking by the piston rings. It is a sign of a worn engine. The oil consumption supports that the rings are worn and oil is being burnt because the piston rings are not scraping the oil off the cylinder walls on the way down. The only fix for this is a engine rebuild, though this does not necessarily mean the engine is on the brink of failure. The engine may continue to run and produce decent power for a long time, but it will only get worse.

The previous owner made a false statement, this is not a normal healthy condition and it's far from exclusive to Cummins engines. Any engine, gas or diesel can produce blowby. The presence of blowby is often regarded as a red flag to a potential purchaser.
I see. I also asked several shops, they told me it could be the coolant mixing in with the oil and thats what's causing the blowby, or it could be the piston rings. If it is indeed the piston rings, does that necessarily warrant a full rebuild?
The only reason why I ask is because I'm making a 1.5k mile journey with it and need it to just function long enough.
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Old 04-24-2021, 10:52 AM   #4
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I see. I also asked several shops, they told me it could be the coolant mixing in with the oil and thats what's causing the blowby, or it could be the piston rings. If it is indeed the piston rings, does that necessarily warrant a full rebuild?
Hmm, coolant mixing with oil could be a possibility, but fairly easy to rule out. If the smoke starts immediately while cold then it is definitely blowby. This is because the engine wouldn't be warm enough to start vaporizing any coolant or water out of the engine. Also because the engine is not yet warm, all parts in the engine are at their loosest, blowby generally improves as the engine warms up. Reving the engine may also make the smoke appear worse.

You can also take an oil sample and send it off for analysis, the report will outright tell you if you have coolant contamination, which I would regard as a much more serious issue than blowby. This can range from a bad oil cooler, to a leaking head gasket, to a cracked or leaking cylinder liner, cracked block, or a cracked or warped cylinder head.

I'm still hedging my bets on blowby, I suppose from a technical standpoint you could just put new cylinder rings in it, however you're already spending the effort of tearing the engine down and removing the pistons. It's not that much more effort to do a full overhaul and more worthwhile for longevity

That all said, buying another bus may likely be much cheaper than an engine rebuild. Tho it sounds like you bought a coach if you have an ISM?
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Old 04-24-2021, 01:11 PM   #5
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Hmm, coolant mixing with oil could be a possibility, but fairly easy to rule out. If the smoke starts immediately while cold then it is definitely blowby. This is because the engine wouldn't be warm enough to start vaporizing any coolant or water out of the engine. Also because the engine is not yet warm, all parts in the engine are at their loosest, blowby generally improves as the engine warms up. Reving the engine may also make the smoke appear worse.

You can also take an oil sample and send it off for analysis, the report will outright tell you if you have coolant contamination, which I would regard as a much more serious issue than blowby. This can range from a bad oil cooler, to a leaking head gasket, to a cracked or leaking cylinder liner, cracked block, or a cracked or warped cylinder head.

I'm still hedging my bets on blowby, I suppose from a technical standpoint you could just put new cylinder rings in it, however you're already spending the effort of tearing the engine down and removing the pistons. It's not that much more effort to do a full overhaul and more worthwhile for longevity

That all said, buying another bus may likely be much cheaper than an engine rebuild. Tho it sounds like you bought a coach if you have an ISM?
Sadly this bus holds a place closest to my heart so I can't buy another bus. I could just swap out the engine with a functional one and save me a few thousand bucks, but that's not the point.

I have to still get this bus across another 1.5k miles to my shop, in your expert opinion, do you think if I keep my eye on the oil level and refill as necessary I'll be able to make it? It ran for almost 650 miles so far with no issue.
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Old 04-24-2021, 01:27 PM   #6
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It won't be coolant making it smoke out of the dipstick tube, unless you see a lot of coolant in the oil. If it smokes out the tailpipe, then maybe.


It sounds like it is blowby to me. The missing oil is the taddle-tail. Keep your eye on the oil level when driving, and you should be OK.


Keep in mind your motor is making it harder for us all to breathe; please do address the problem sooner than later.


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Old 04-24-2021, 01:46 PM   #7
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Sadly this bus holds a place closest to my heart so I can't buy another bus. I could just swap out the engine with a functional one and save me a few thousand bucks, but that's not the point.

I have to still get this bus across another 1.5k miles to my shop, in your expert opinion, do you think if I keep my eye on the oil level and refill as necessary I'll be able to make it? It ran for almost 650 miles so far with no issue.
Yes. Blowby in and of itself is not a serious concern so long as no other significant symptoms are present, for example a misfire from lack of compression. You most likely have plenty of time to consider how you wish to address the engine.

My pickup with the 7.3l also has blowby and it's not something I worry about stranding me. Most of the fuel injection system on that truck has done a good enough job of that...
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Old 04-24-2021, 02:46 PM   #8
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How old is the oil? Can be some water in the oil that is evapoRating of. Take the oil filler cap of the engine while it is idling and see how much smoke is coming out.
Pure blowby is more blue brown..
Is the engine wet from leaking oil somewhere?
Can you see your exhaust in the mirror? How much smoke when you are driving?
Some white smoke out of the exhaust during cold startup is normal.
White exhaust smoke can also mean poor combustion because of poor timing.
You do not say if it started suddenly or how many miles are on the engine.
If it runs ok with enough power and no bad noises then keep driving.

Good luck, johan
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Old 04-24-2021, 03:40 PM   #9
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I've had two cars 'blow up' from bad rings.
They drove just fine, until suddently one day they didn't. The volvo was a complete smoke screen blowout, the Prius just lost a cylinder, and a dozen miles later, could barely stay running.

So you can take your chances, maybe make sure you have some towing insurance as towing a school bus takes a big rig and can be quite expensive.
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Old 04-24-2021, 10:11 PM   #10
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It definitely sounds like blow by. Check your crank case vent tube and see how much smoke is coming out of it. If nothing is coming out of the vent tube then it may be plugged forcing the blow by out the dip stick. For more information on blow by search "adept ape blow by" on youb tube. He is a CAT mechanic and has great diesel repair videos.

Another question is how many miles are on your oil change. Engine oil with high milage will begin to break down and oil consumption will increase. I have C-15 in a dump truck that will use no oil until it hits around 200 hours on the oil change and then it will start needing make up oil. It will usually take a few quarts until I change it at 250 hours.

Ted
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Old 04-25-2021, 07:03 AM   #11
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if the coolant level isnt dropping or getting milky looking or oily then likely not a mixing issue..



ive run engines with lots of blowby for a long time.. tended to run them at just a little under full on the dipstick.. I have founf in worn engines that having lots of blowby will tend to blow more oil out of the tube and onto the ground.. running an engine that holds 5 gallons just below the full level wont hurt it.. over-filling the engine (I do it frequently by accident) will cause lots of oil to be blown out the draft tube and therefore looks like its burning lots of oil..



if theres no coolant mixing and its running fine i say change the oil, pour a bottle of Lucas in it and drive it the 1500 miles.. dont get it hot and take it easy in the mountains...
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