Hi Folks,

I am new to diesels. I have a 2003 Duramax with six speed Allison in a GMC 2500 HD. Now almost a year old with about 8.5k miles on it (use it mainly for pulling an RV - not used every day.) My question is about a sour diesel exhaust odor in the cab. It's not overpowering, and goes away (as much as possible - gets in seats, etc) after you drive a while. Diesel owners on my RV forum said it was likely Diesel "blowby." I just want to make sure I am likely not poisoning my family (seriously, we've driven 10 hours at a stretch with no problems many times.) Engine runs well - plenty of power. Let me know if it is likely this blowby, and for that matter - what exactly is blowby.
Thanks

Maybe you have an exhaust leak? Do you hear a ticking while driving?

Hi Folks,

Engine runs well - plenty of power. Let me know if it is likely this blowby, and for that matter - what exactly is blowby.
Thanks

The term “blow-by” is same for diesel engines as it is for gassers. Blow-by is the crankcase gasses that are produced by combustion, heat and various chemical reactions within the engine’s crankcase. Blow-by gasses are very toxic. Back in the 60’s the crankcases were closed to outside air circulation and a PCV (Positive Crankcase Ventilation) valve was made mandatory for all motor vehicles. The PCV valve would allow the blow-by gasses to be routed from the crankcase to the intake manifold for combustion. All diesel engines have closed crankcase systems and PCV valves, so if you suspect that you are breathing blow-by, you need to have it checked.

Hi Folks - no, no ticking. I will take the truck in on monday. The odor is not terrible, but there is an odor.

Steve,

Have changed your oil recently? The odor you're describing could be coming from the crankcase vent tube. Whenever I change the oil on my 03 I get a strong hot oil smell for a few hundred miles but it eventually it goes away. Some oils are worse than others.

See the Oil Smell After Changes (http://dieselplace.com/forum/forum_posts.asp?TID=1356&KW=oil+smell) topic for more info.

http://www.dieselplace.com/forum/smileys/Geek.gif Edited by: jbplock

No trying to be a smart aleck...but does this smell occur right after you fill up? Might be your hands or shoes stepped in spilt fuel. Like all troubleshooting start with the obvious and work your way up. http://www.dieselplace.com/forum/smileys/Cool.gif

Hi Tswartos, no - it is not diesel fuel. It's more like old exhaust. You know the smell you get in an old car.... It also is not near an oil change - last one was 5000 miles ago. It may be that I am just too picky - lets fact it, diesel exhaust is not french perfume. Maybe when I just start it gets sucked in through the intake fans of the vents.

...lets fact it, diesel exhaust is not french perfume...

It's not? You think the Duramax is bad, you should smell my Mercedes exhaust. That is only pleasant to the most diehard diesel enthusiast. Of course when I am burning veggie oil it smells much better...

The Allison is a 5 speed unless you are a very lucky fellahttp://www.dieselplace.com/forum/smileys/Approve.gif or you have purchased an 2006 model.http://www.dieselplace.com/forum/smileys/Embarrased.gif


Do you notice the odor when you are not in the truck? If not, then the smell could indeed be youhttp://www.dieselplace.com/forum/smileys/Clown.gif


Once my wife and two kids smelled the diesel odor, they had to have one. My wife is so bad that she will go out to the garage after I have left, and she will stay out there for an hour some times just to smell the diesel fumes.http://www.dieselplace.com/forum/smileys/Big Smile.gif A woman after my own hearthttp://www.dieselplace.com/forum/smileys/Cool.gif I could take or leave the diesel smell. My 5 year old son will smell a truck going down the road and say, "emm that smells sooo gooood, lets start my diesel truck, can we?"http://www.dieselplace.com/forum/smileys/Big Smile.gif

OK, OK, it is a 5 speed, and maybe we do smell like diesel exhaust. You know this post just shows there are some things you can;t quite describe with words - odors is one. Maybe diesel owners should adopt the wine vocabulary - my diesel has a strong nose with hints of citrus overtone.


I'll let you all know what happens after the mechanics look at it. It is still under warrenty, so I'm sure there will be nothing wrong (on the other hand if it was a day out of warrently I would need a new exhaust manifold, and new engine to go along with it.)Edited by: stevenschwartz

Steve,

Have changed your oil recently? The odor you're describing could be coming from the crankcase vent tube. Whenever I change the oil on my 03 I get a strong hot oil smell for a few hundred miles but it eventually it goes away. Some oils are worse than others.

See the Oil Smell After Changes (http://dieselplace.com/forum/forum_posts.asp?TID=1356&KW=oil+smell) topic for more info.

http://www.dieselplace.com/forum/smileys/Geek.gif


Bill


Please correct me if I'm wrong, but isn't the crankcase under negative pressure so the gasses are not allowed to vent to the atmosphere? I'm not familiar with the crankcase vent tube that you are referring to. I know there is a vent on the passenger side valve cover, but I was under the impression that the vent was a crankcase air inlet during engine operation.


I'm finding that I have a strange "oil-like" smell from time to time and I've been unable to locate the source. BTW I run Delo 15w-40. The smell could possibly be exhaust since I leave the climate control on all the time, so there is always inbound air. Edited by: Dura_Mike

I get a smell in mine. Ventilation on or off. I notice it sitting at a stop light. Someone suggested to me that the vents in the back of the cab (behind back seats) are letting in some fumes. The vents are used for letting out air pressure when closing doors. They have like a flap to them. Possibly?

I also have 2003 always had oil smell in cab just like yours i was running kendell 15w40 for oil i switched to delvac smell went away for good. that was 7000 miles ago

You know, Oil might describe the smeall. As I said, it is not really diesel exhaust - more sour and almost petroleum. What is Delvac? I'm using a regular 15W 40 oil. Also, I'm must admit to being a bit confused as to the source of oil smell. This is supposed to all be sealed - you certainly don't smell oil in gasoline engines unless there is a major problem.





SteveEdited by: stevenschwartz

Delvac is Mobil Delvac 1 synthetic 5w-40 oil. It is also being repackaged as Mobil 1 Truck and SUV 5w-40 synthetic oil that you can find at Wal-Mart or at most auto supply stores. The Delvac 1 can be hard to find.

Bill


Please correct me if I'm wrong, but isn't the crankcase under negative pressure so the gasses are not allowed to vent to the atmosphere? I'm not familiar with the crankcase vent tube that you are referring to. I know there is a vent on the passenger side valve cover, but I was under the impression that the vent was a crankcase air inlet during engine operation.


I'm finding that I have a strange "oil-like" smell from time to time and I've been unable to locate the source. BTW I run Delo 15w-40. The smell could possibly be exhaust since I leave the climate control on all the time, so there is always inbound air.





Mike,

You bring up a good point about crankcase ventilation … I’m not an expert but it is also my understanding that pressure in the crank case is regulated to remove blow-by gases (from the crankcase) and to help prevent oil leaks. My 6.5TD had a crankcase depression regulator (CDR). The 6.5 CDR was a tuna can sized thingy with a diaphragm valve located on top of the passenger side valve cover. IIRC one side of the CDR was connected to the valve cover and the other side was connected to the air filter outlet (turbo inlet). It would control pressure in the crankcase by drawing gasses from the valve cover to the intake. It was also normal for the inside of the intake tube to have some oily residue.

Your question got me thinking about how the DMAX crankcase ventilation system works (??http://www.dieselplace.com/forum/smileys/Confused.gif). On my 03 (non EGR) there is a vent tube that exits under the engine on the passenger side. There is always a small amount of oil around the end of this tube. I first read about the oil smell coming from this tube in some TDP posts but I never really thought about how the DMAX crankcase ventilation system works. I believe this tube will also spew oil/fuel when a failed injector causes the crankcase to fill up with fuel.

Your question aroused my curiosity and got me thinking http://www.dieselplace.com/forum/smileys/Geek.gif… So first I looked in the Helms manual and the only thing I could find was a “Crankcase Ventilation Inspection Diagnosis” table On page 7-36 in the 03 manual. The top of the table has the following statement:

“Definition: During normal operation the crankcase gasses can be seen exiting from the hose at the oil separator. The maximum crankcase pressure is 4kPa or 16in of water at 3100 rpm

My experience says they all expell an oily mist when the engine is running. My Cummins does it too. Hang under your truck at night and shine a flashlight... that's when you can really see the smoke coming out.

Here is the smoking gun on the Dmax (01)...

http://www.dieselplace.com/forum/uploads/CFA_ventclose-smaller.jpgEdited by: hoot

Thanks guys - I'm still goingtobring it in - need an oil change, but at least now i don't worry.

I'm positive the crankcase vent allows crankcase fumes to exit - last winter while loading snowmobiles I let my truck idle/warm-up for 10-15 minutes and I noticed a huge soot spot on the ground roughly 1 foot in diameter that looked just like an exhaust leak. Dealer said "no problem found". Later I realized this is exactly where the crankcase vent dumps. It was a very still morning/no breeze and is the only time I have actually seen it do this. But I also get the "oil smell" after every oil change, Rotella, Valvoline Blue, etc., they all seem to do it to some degree.

HeySteve, also you might want to check your in cabin A/C filter, if there is one. Seems I recall the '03's did not come with one, but could be installed. If your filter is saturated with the smell, your A/C vent system will keep circulating the smell. If no filter, you might as well put a pair in.


txguppy

Hi Guys, I had a smell problem with my 2004 also. And i believe finney is right ,I used delo for my first oil change,and i got a oily smell kinda like a gear lube smell.delvac 1300 and delvac 1 ,mobil1 truck/suv should make a differnce,delvac 1 and mobil1 is fully synth. oil and is a exxon product. any exxon gas station should guide to a vendor that can help you. thx,Alex

I get a smell in mine. Ventilation on or off. I notice it sitting at a stop light. Someone suggested to me that the vents in the back of the cab (behind back seats) are letting in some fumes. The vents are used for letting out air pressure when closing doors. They have like a flap to them. Possibly?


This comment strikes a familiar chord ~ seems that there was an issue w/those vents being installed wrong and allowing intake instead of flow thru ventilation. Can't recall the details but was on the page iirc