DIESEL SMELL IN CAB

First off, I have checked the engine bay for residue and wet spots, none found....yet.

Second, no drips found under vehicle whether parked over-night or shortly after driven.

Third, neither primary nor secondary filters are wet, nor the connections as far as I've been able to see.

Have a fairly strong diesel smell inside the cab with windows up and A/C on/off while driving.

EDIT: truck starts and seems to run fine, no CEL displayed as of yet. Noticed the smell a few weeks ago when trailering a camper to/from play grounds.

Any suggestions?

THX

If you don't see any leaks or drips anywhere, return lines are good, and the truck has no starting/air intrusion issue, are you sure it's fuel? Could it be exhaust fumes you are smelling? That seems more likely based off what you say.

Never-Have-I-Ether

NeverHave-I-Ether said:

If you don't see any leaks or drips anywhere, return lines are good, and the truck has no starting/air intrusion issue, are you sure it's fuel? Could it be exhaust fumes you are smelling? That seems more likely based off what you say.

Never-Have-I-Ether

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I'm pretty sure it isn't exhaust related. The smell comes into cab whether windows are up or down, and it is a straight diesel smell, no apparent exhaust smell. Raw diesel.

I appreciate your reply, but like you suggested about lines, I'll need to look more frequently for leaks to see if a wet spot shows itself. The wet may be drying up before I go to look, which is typically enough time for it to evaporate as I'm always on the run somewhere and getting home late, being too lazy to pop that hood right away.

Thanks again!

I've had the same issue with 2003 6.0 for five months now, it started all at once. I get the smell mostly though with a window open or the fan running. Its particularly strong in front of the truck too.
My mileage also dropped suddenly around the same time. I was getting 20-21mpg, now I'm seeing 10mpg at best.
I've been through five tanks of fuel and I've seen no sign of any leaks, no codes, and no fuel in the oil or coolant.
The smell is strong, definitely not exhaust.
A buddy who works on these at the dealer said to check the fuel filter and regulator orings, so I replaced all the orings to be safe. A few were starting to harden up a bit but none were broken. I also did a blue spring kit at the same time.
Mine starts and runs perfect, no smoke, no leaks, nothing. I just smell fuel. Its bad enough that it smells like its on my hands or something.
With mine, the smell is gone completely the instant the engine is turned off. It doesn't linger at all.
If I stand in front of the truck while its idling, the smell is very noticeable. I also can smell it by the drivers door. Its worse outside the truck than inside but I get the fuel smell at stop lights.
I park my truck in a garage with a tile floor, so if there were any leaks, I'd see them right away. The bottom of the truck is bone dry.

So far the fuel filter up top has been resealed, the fuel unit on the frame has been replaced, and the tank was removed and checked for leaks but they found nothing wrong.
With the loss in mpg, I really figured by now I'd have seen something obvious but in 400 or so miles, nothing has shown up. If it were dumping fuel that bad, it would be pouring out black smoke, if it was leaking, I'd see diesel fuel all over the bottom of the truck or on the garage floor, if it were leaking internally, the oil or coolant levels would be rising, and they are not.
Worse yet the truck has only 21,000 miles on it.

reelfishin said:

I've had the same issue with 2003 6.0 for five months now, it started all at once. I get the smell mostly though with a window open or the fan running. Its particularly strong in front of the truck too.
My mileage also dropped suddenly around the same time. I was getting 20-21mpg, now I'm seeing 10mpg at best.
I've been through five tanks of fuel and I've seen no sign of any leaks, no codes, and no fuel in the oil or coolant.
The smell is strong, definitely not exhaust.
A buddy who works on these at the dealer said to check the fuel filter and regulator orings, so I replaced all the orings to be safe. A few were starting to harden up a bit but none were broken. I also did a blue spring kit at the same time.
Mine starts and runs perfect, no smoke, no leaks, nothing. I just smell fuel. Its bad enough that it smells like its on my hands or something.
With mine, the smell is gone completely the instant the engine is turned off. It doesn't linger at all.
If I stand in front of the truck while its idling, the smell is very noticeable. I also can smell it by the drivers door. Its worse outside the truck than inside but I get the fuel smell at stop lights.
I park my truck in a garage with a tile floor, so if there were any leaks, I'd see them right away. The bottom of the truck is bone dry.

So far the fuel filter up top has been resealed, the fuel unit on the frame has been replaced, and the tank was removed and checked for leaks but they found nothing wrong.
With the loss in mpg, I really figured by now I'd have seen something obvious but in 400 or so miles, nothing has shown up. If it were dumping fuel that bad, it would be pouring out black smoke, if it was leaking, I'd see diesel fuel all over the bottom of the truck or on the garage floor, if it were leaking internally, the oil or coolant levels would be rising, and they are not.
Worse yet the truck has only 21,000 miles on it.

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Yes, very frustrating. I too have replaced filters and o-rings, have the blue spring. I even replaced the engine fuel filter cap with a BulletProof aluminum one. Did the latter mostly because the plastic one was rounding out, had to use a pipe wrench to get it off.

My symptoms are pretty much exactly like yours.

When I bought my 06 I had a similar situation. My up pipes were cracked and also loose on the driver side manifold. Mine did not smell like exhaust but more like diesel fuel.

Good luck!

3Kp said:

When I bought my 06 I had a similar situation. My up pipes were cracked and also loose on the driver side manifold. Mine did not smell like exhaust but more like diesel fuel.

Good luck!

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Thanks for the heads up. I will inspect them. Something I hadn't thought about, especially like your experience, I have no exhaust smell either.

Again, appreciate the reply!

I've been there and checked that on mine, but mine also has only 21k on it. Its been sort of a garage queen since day one.
More so lately with the cost of fuel these days.

With mine, I would have figured that any fuel leak would have either led to it sucking air or leaving a puddle on the ground by now but I find nothing, the only hint other than the smell that something is wrong is the sudden drop in mpg. It went from really, really good to horrible. I noticed it the first time when I got it out last fall. I left the house, realized I forgot my phone and turned around to get it. I left the truck running in the driveway while I ran in to grab my phone, when I walked past the front of the truck I got a strong whiff of diesel.
I didn't think much of it right away but I noticed it again waiting at a traffic light later on my way home, when I got home I looked it over real good expecting to find fuel dripping somewhere but it was bone dry. I parked it in the shop garage overnight, came out the next morning to unload the truck and gave it another look but all was dry. I then started the thing up and noticed I was down to 1/2 tank of fuel, and it was full when I left with only 11 miles on a full tank. (It was locked in the building so no one siphoned off any fuel and I hadn't noticed the gauge reading that low the day before but it often takes a few key cycles for the gas gauge to adjust for some reason. (A problem I had complained about many times when it was new but it never got resolved, after buying two more of these trucks at work, I realized they all acted that same way).

I've since put about 500 miles on it and the smell hasn't gotten any worse, and I can't find any leaks. Its burning double the fuel it used to though but with no codes and no tail pipe smoke. It also doesn't run any different. If it were dumping that much fuel from an injector or leak it most certainly would have affected performance or driveability.
I've crawled all over this thing looking for a leak and found nothing, I've had it on a buddies drive on lift with the truck running looking for any sign of a leak but its all bone dry. I've had the top fuel filter off and resealed it, I replaced the lower filter unit after the dealer said there's a bulletin about removing the fuel heater. I chose to just buy a complete new unit rather than just disabling the heater. It changed nothing. The truck went through four ICP sensors back when it was new, and again a couple of years ago. I bought a Japanese one that was supposed not have the issues with leaking oil through the top and that's been fine ever since, about 2,200 miles or so.
The truck doesn't 'make' or use oil, the coolant is clean and looks new, there's no sign of fuel in either the crankcase or the coolant.
For 17 years and 20,000 miles it was pretty much fine engine wise other than a few ICP sensors. I've been parking it on clean cardboard to be sure to spot any drips but there's been none at all.

The odor is extreme, its not just a hint of fuel, its as if there's fuel spilled on my clothes.
When its running, I can smell it strongest in the driver's seat with the window open, or out in front of the truck about 6 foot in front of the truck. I've not been able to find or smell it when under the hood, running or not, and its stronger in the driver's seat or at the drivers window than anywhere else. Passengers can smell it but also said its outside, not in the cab.
Running with any of the other windows open doesn't do it, only with the drivers window down, with or without the heater fan on.
When I first smelled it I fully expected to open the hood to find fuel slinging all over the place but there's nothing.

Could you have a small leak at one of the plugs in the back of a head?

Wouldn't that produce a leak?

On mine, I've driven it enough miles and gone through enough extra fuel that any leak, whether or fuel or exhaust should have become obvious. Not mention it would most certainly caused a drive-ability issue.

On mine, I tried something the other day, with the engine running, with the hood open with the smell super strong if i stand four feet out in front of the truck or next to the drivers door, I smell no sign of any fuel odor while hovering over the running engine, or crawling around under the truck. The smell is only noticeable when standing next to the driver's door, standing out in front of the grill, and when sitting in the driver's seat with the drivers window open. Its far less noticeable in the passenger seat for some reason and if I open two windows or the rear slider the smell doesn't seem to make it into the cab.

With diesel being just under $6/gal right now there's not much chance of me using that truck right now. Especially since its been blowing through fuel so much faster than it did before this started.

What gets me is that the odor goes away 100% the instant the engine is turned off, there is no residual odor. The instant the engine starts, the fuel odor is there.
What I don't understand is why the fuel smell is so strong so far out in front of the truck but not up close in front of the grill, regardless of the wind direction. (I've also put a hose on the tailpipe running it far out back away from the truck to be sure I wasn't smelling exhaust). The odor is the same as smelling an open can of diesel fuel up close.

When mine first started this, it had sat for a few months unused. I had parked it last March with no issues. It sat all summer with a near full tank of fuel, in the garage. I moved it a few times here and there to work on something in the garage a few times in June of last year, then it sat till late Sept. It started right up as usual, but I noticed the odor soon after.

I'm not blind to working on diesel engines, I worked as a heavy truck mechanic many years ago. Although my main experience though was with Cummins and the older Navistar engines.
I know the difference between exhaust and fuel smell, and have a better than average understanding about how these newer engines work, which is why I'm even more puzzled as to where the smell is coming from.

The simple fact that it appears to be using more fuel than it could possibly burn and yet has no signs of a leak is what bother's me the most. With as much fuel as its been using I should have a a trail behind the the truck. If I had a fuel leak in the system before the main pump, it would suck air and have issues starting, if it started at all, that's not the case. If I had a bad injector, external or internal leak, it most certainly would have shown up in some way by now. If it was pumping fuel into the coolant, I'd have seen the coolant system overflowing, if it were leaking into the crankcase, I'd have seen it bubbling out of the dip stick tube, or even hydro locked the engine by now. If it were running out externally, certainly would have fuel on the floor of the garage or the underside of the truck would be wet with fuel. Its not, its bone dry, as is the engine under the hood. Also, if it were leaking externally the smell wouldn't be completely gone when I turn off the engine.
If it were burning that much fuel, enough to put raw fuel out the tailpipe, I'd see either white or black smoke, or even fuel running out the tailpipe. I have none of that, the truck runs the same as it did day one. A diesel engine that's running rich also sound different, they get louder with harder detonation knock. More so, I can stand at the tail pipe at all I smell is diesel exhaust. To prove to myself its not burning any excess fuel, I had a buddy check it at the pipe with an opacity meter, the highest reading he could get was 6% and that was at 2500 rpm and on a cold engine.
Other exhaust specs were good as well with a 14.7% O2 reading, which he said was about average for one of these. Both of us were satisfied that its not burning any extra fuel.

Keep in mind that were dealing with a garage queen type truck here too, its only got 21k on the clock and has spent its life in a heated garage 95% of the time.
I'd be less surprised if it were an old beat up work truck with a few hundred thousand miles on it. The longest time this truck had ever spent outside was when I had thought it may have had a fuel leak. I parked it out side for a few months till I was convinced it wasn't going to dump any fuel on my garage floor.

Almost the exact same symptoms, although I've done none of the testing you have.

I also have over 260k miles on the odo.

I think I would have to have the oil analyzed for diesel content just for peace of mind. I would probably also remove the coolant from the degas bottle to get a better look/smell of it. The thing about a leak at one of the back head plugs is that it isn't easily seen and could drip on an exhaust manifold and evaporate before it ever had a chance to hit the ground.

Also, it might be helpful to post the actual (hand calculated) fuel economy you are getting now, and what it used to get (if you have that information).

For me, mileage whent from over 30 to under 3mpg almost overnight.
I never let it go below 1/2 tank after being warmed by the dealer early on about lift pump failure. I left the house with a full tank, about 3 miles from a fill up where I super topped the tank. Drove 10 miles to work, parked the truck and it sat there for 8 hours. It never left my sight all day, as I was theonly one on site that day and the truck was parked in full view of where I was working 50ft away. I noticed the tank was half empty when I got back in the truck. Thinking it was a recurrance of a fuel guage issue the truck had when new I went to a fuel station next door to the site when I left and refilled the tank, it took 9.5 gallons.
I then drove the 10 miles home. About a mile from the house I noticed the gauge was down to almost half tank again. When I pulled in, a neighbor walked up to the drivers door to ask if I could help him unload something from his truck, he said he smelled diesel. I got out, left it running and looked high and low for a leak but found nothing. The smell though was STRONG as if it were spraying fuel into the air. There was no smell of fuel back at the tail pipe, only at the drivers door and out ahead of the truck about 8ft or so. I couldn't detect it up close or under the hood. I refilled the tank right then, it took 11 gallons.

I backed the truck into the garage and put cardboard underneath figuring I'd look closer in the morning. The next day the cardboard was dry, and I could smell no fuel with the truck not running. The bottom of the truck was spotless and dry.

Its way too much fuel gone to be burning it, and like I said, I don't smell it at the tailpipe and there's nothing wet. Its been like this now for about 6 months. Two dealers have looked, neither put any time into it other than a short road test, computer scan and a look at it on a lift. They said there's nothing wrong.

The fuel gauge has always had a delay action thing going on, if it was low on fuel I'd top it off and the gauge wouldn't show the tank as full for 50 to 100 miles or so. they changed the tank, the sender, the dash and put a harnet in the cab when it was new. Nothing fixed it.
Then we got two trucks at work and they did the same exact thing. I later figured out that where ever the gauge reads when the engine starts, is where it stays for the first 1/2hr or so, then it re-calibrates and registers. If I refill the tank, cycle the key a couple of times each time letting the gauge creep up to full, it works fine.
I've known 7 trucks, all 2003 models that did the same thing.

f this were some high mileage old work truck I'd be less surprised, or if it were running poorly or smoking I'd say it was burning it but its blown through 5 tanks of fuel in 100 miles now with no trace of where it went. It gets parked in an alarmed, video camera monitored garage when at home, and its only seen work twice. Its never unattended to to where someone could have stolen that much gas, and then there's the obvious odor of fuel when it runs. What I've not been able to figure out is how the odor is only noticeable way out in front of the running truck, the fan is drawing air toward the truck not away, so the fan isn't pushing the smell forward, and its absolutely not detectable behind the truck.

I really thought I was going to find dried up or cracked orings at the fuel filter or regulator but they were fine. I even taped a piece of newspaper to a stick and pocked around down in the valley of the motor to look for leaks but its dry.

I have a coolant filter on the truck, someone said it was need on these 6.0L trucks. I change the filter every 1000 miles or so. I've gut it open a few times and never found any metal in it and I smell no diesel in the coolant.
Besides, if it had pushed that much fuel into the coolant I'd have it bubbling out the cap long ago. Keep in mind this truck has under 25k on it and I've owned it since new. The only vehicle I have with fewer mildes is my '88 LTD Wagon with 12k since new.

I'm actually looking at another 2003 diesel almost identical to mine, there's an old guy who bought ne nearly identical to mine around the same time around the corner, he's in his 90's and never much drove his either. I think it read 3,600 miles on it sitting in his attached garage. Its still got the factory floor mats and new smell. (I was there helping him change the batteries in it last month, he said someone keeps stopping and offering to buy it, he said they offered him $3,500, he was livid that they would take him for a fool like that because he was old. He told me if he sells it, it'll be to me since I've kept it running for him all these years. Its an XLT 4x4 super cab like mine but with less miles.
(He's got a 67 F250 too with 18k on it but his son has dibs on that. The 'kid' (67), hates the smell of diesel and is pushing his dad to sell the '03.
I have no clue what its worth thought but I do know that the dealer here had a 230K model on the lot for $22k and it sold in a week or less. Even with fuel at $7/gal. My buddy sold his crew cab last Friday because of the cost of fuel with 300k or more on it for $19k.
I won't price the neighbors truck, I told him and his son to come up with a price and we'll talk. I'd likely only use it till mine is sorted but I also have two other daily use trucks here to use. "Need" is never the reason I buy another truck. If it were, I'd have not bought any of my newer trucks. I do regret letting my 1986 go, my current '03 took its parking place in the garage and it wasn't doing me anygood parked outback in the unheated garage for months on end. I was just replacing tires and changing oil for no reason, it got 100 miles a year and I was throwing away tires that rotted with less than 500 miles on them.

Are you sure you meant to say you would get over 30 mpg?

If so, then what engine are you talking about?

Yeah, I've never had better than 18mpg. I'm currently getting 16.7mpg because I'm cruise controlling at 60mph to save on fuel. My VW TDI got wrecked by an UBER driver, so fuel is killing me right now.

BTW- mileage checked by filling tank to the neck, and trip meter reset every fill up. The trucks MPG reads 15.6 currently, and it's because I didn't reset it after towing camper on last trip. I did get 14.5MPG towing though. And yes, I keep my foot off the WFO throttle even when I'm not fuel price stressed.