Excessive white exhaust smoke

Tiny
GARYNB1
  • MEMBER
  • 2007 MERCEDES BENZ ML350
  • 3.5L
  • V6
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
I have the car listed above 4MATIC, mileage 152,000. Recently I've noticed light gray smoke coming from the exhaust when at idle. If I rev the engine, the smoke becomes thicker and more "white", and when driving it becomes much thicker. I've checked the coolant, including the overflow cap (looks normal, not milky). I checked the oil, looked and felt fine, no coolant smell. Also I removed the overflow cap started the engine and let it idle to normal operating temperature. There were no bubbles or anything else that would indicate a bad head gasket. The vehicle does not leak coolant anywhere that I can see nor does it burn or leak any oil. The car runs fine, the engine is smooth and responsive. I did not do a compression test, however I did remove the plugs and they looked fine (no indication of a coolant leak). At first I thought perhaps it was simply condensation in the exhaust system that was causing the excessive smoke. However, it doesn't go away after driving a few miles. One more thing, the Check Engine Light has not come on. Any ideas on this? Thanks for your help.
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Wednesday, January 16th, 2019 AT 9:48 PM

12 Replies

Tiny
SCWICKEDSTANG
  • EXPERT
Hi Garynb1, my name is Alex and I will be helping you today. If you have no coolant loss than I would definitely rule out coolant leaking into a combustion chamber. This could possibly be just normal wear on your catalytic converter. Water is a byproduct of the catalytic process and it could just be being released as steam. In any event, when a catalytic converter degrades down to the point it needs to replaced, your MIL, or Check engine light will illuminate and the PCM/ECU will set DTC/Code P0420. Hope this helps.
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Thursday, January 17th, 2019 AT 3:19 AM
Tiny
GARYNB1
  • MEMBER
Thanks so much for your help, Alex. Due to the CEL not being on is there something I can do to tell for sure if it is the catalytic converters causing the white smoke, without taking it to a repair shop? Thank you.
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Thursday, January 17th, 2019 AT 5:50 AM
Tiny
SCWICKEDSTANG
  • EXPERT
GaryNB1, I wouldn't worry to much about this. It sounds like your vehicle is running just fine Is it cold where you live? If so, this would cause your warm exhaust to cool and produce noticeably white thick exhaust plume. Again, no coolant loss, no illuminated MIL, no misfires. It sounds like your vehicle is running exactly as it should. Thank you for getting back with your concerns.
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Thursday, January 17th, 2019 AT 1:37 PM
Tiny
GARYNB1
  • MEMBER
Hi again, Alex. Regarding the excessive white exhaust smoke: Could my problem also be fuel related? Like a stuck or bad fuel injector? From what I understand a fuel injector problem would normally blow black smoke but it also could emit white smoke is that correct? I also checked my driveway for oily coolant, gas spots etc, where my car was sitting. If water was coming out with the white smoke there would be water puddles obviously (but that would evaporate within an hour or so, but if say gas or oil was mixed in with water there would be stains on the asphalt. Correct? There are several stains possibly gas? In addition, the white smoke only appears after the engine has reached normal operating temperature and then it is a lot of smoke. When I drive the car, it becomes a huge, thick amount of white smoke. And I do mean a lot, so much so when I turn the engine off it still continues to come out of the exhaust for a minute or so. What do you recommend? Perhaps do the chemical (can't recall exactly what its called) test to check for a blown gasket and check the injectors?
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Thursday, January 17th, 2019 AT 1:37 PM
Tiny
GARYNB1
  • MEMBER
I live in the Pacific Northwest, lots of rain in the winter months. About 45 degrees in the winter 30's at night. The amount of smoke isn't normal at all, it is excessive believe me. I don't ever see cars driving around the streets and freeways with this amount of smoke. Perhaps you misunderstood my post.
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Thursday, January 17th, 2019 AT 1:43 PM
Tiny
SCWICKEDSTANG
  • EXPERT
GaryNB1, where about in Pacific Northwest do you live? I am in Pacific Northwest also. I live in a little town called McKinleyville in Northern California, right on the coast. Same weather. The only fluid that I am aware of that I am aware of that would cause white smoke would be coolant getting into the combustion chamber. If you are not having to add coolant than its not leaking into the combustion chamber via the head gasket, intake manifold, or cracked block or head. Where do you purchase your fuel? Is there a possibility that you are getting bad fuel mixed with water, or rain is getting into your gas tank?
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Thursday, January 17th, 2019 AT 5:02 PM
Tiny
GARYNB1
  • MEMBER
I'm located in Seattle - definitely not a nice place to be in the winter due to the ridiculous amounts of rain which is mostly drizzle. I got gas at Chevron the last time. Anything is possible regarding "bad gas" I suppose. As far as "getting water into your gas tank" - I honestly have no idea. Would that cause the white smoke? If water did get into gas tank, wouldn't the car show other symptons too? I've read somewhere that a bad booster seal could be sucking brake fluid into the combustion chamber which would cause white exhaust smoke, but I don't know if that applies to a MBenz ML350.
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Thursday, January 17th, 2019 AT 7:20 PM
Tiny
SCWICKEDSTANG
  • EXPERT
Are you having to add any brake fluid, or having any brake related issues?
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Thursday, January 17th, 2019 AT 10:13 PM
Tiny
GARYNB1
  • MEMBER
No, not at all, but I'm going to check the fluid today.
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Friday, January 18th, 2019 AT 5:20 AM
Tiny
SCWICKEDSTANG
  • EXPERT
Garynb1, hi, sorry for not getting back to you sooner. This one is a stumper. If it still smokes after you shut it off I would tend to think it would have to be something in your exhaust system. When your engine is shut down, your exhaust valves should be closed, save a cylinder or two and shouldn't be able to produce any exhaust. Is it possible an animal or something crawled in the exhaust?
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Friday, January 18th, 2019 AT 10:22 PM
Tiny
GARYNB1
  • MEMBER
It is just that the smoke. It takes a few seconds to clear from the exhaust so no animals or anything like that.
More than likely I'll take it to the dealer and see what they have to say. I'm sure they'll have the answer for a price of course, but sometimes that's what it takes to find out what's going on. Thanks for all your help. You've been great!
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Friday, January 18th, 2019 AT 10:33 PM
Tiny
SCWICKEDSTANG
  • EXPERT
Okay. Let me know what you find out. Thank you.
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Saturday, January 19th, 2019 AT 4:06 AM

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