Oil in fuel tank

[Throttlehogg]

So I changed the fuel filter on my 99 Cobra today and when I drained the old filter I noticed the fuel was an odd color - not rusty looking, but dark. I then grabbed a paper towel and finished draining and noticed that it looked to be very oily. Besides a blown head gasket, what else might be happening to create this condition?

 

[3B99SVT]

Are you still talking about the fuel filter? The only thing that goes through a fuel filter is fuel -- a blown head gasket won't put oil in the fuel filter. I'm guessing it is old fuel since fuel filters on IRS equipped cars typically don't get changed often enough due to the limited access. You should be good to go w/the new fuel filter installed.

Edit: Member for over 4 years and that was your first post? Hopefully the first of many. Welcome to the board.

 

[Throttlehogg]

I know, I know, I've been a bad girl. No more lurking. Thanks for the welcome. I'm not even going to tell you how long it's been since that filter was changed - it's embarrassing. Nevertheless, I have a couple of more details to add now that I'm done for the day. While poking around back there I discovered that the fuel filler neck seal is leaking, it looked to be dry rotted so I've bought a new one and will change that soon. Normally, I would blame any discoloration on rust and/or crud in the tank, but this one is different. I poured the majority of the fuel in the filter into a clean bucket and after all the fuel evaporated, what was left behind in the bottom of the bucket was a thick oily sludge. Like the crud stuck on the bottom of your motor after you've ignored an oil leak for awhile. Definitely not rust.

Since I already had the car in the air, I thought I'd go ahead and do an oil change, and wouldn't you know it, the old oil smelled like gas! Weird. There has got to be a way that the two are coming into contact with each other. What about a bad piston ring? Could they be intermingling in the cylinder? What happens to unburned fuel? Doesn't it go back to the tank? Usually I'd first reference the shop manual when confronted with this kind of dilemma; however, I can't use my damn shop manual anymore because it runs only on XP and the Virtual XP I previously used to run it in a Win 7 environment doesn't work with Win 8. Chilton's and Haynes are virtually worthless anymore...ARRGH!

 

[ashleyroachclip]

If you only drive short trips , where the engine doesn't actually get to full operating temperatures for any period of time , there is a chance you will be getting some fuel in the oil.
I see you are in Northern Californian, probably similar temps as Southern Oregon, which is where I am at.

Just a thought.
I think you are confusing a return fuel system , which these cars are not .
It is not the unburned fuel, but the unused fuel that returns to the tank.

Another possible reason for your oil to smell of gas , is a poor tune , or sticking injectors.

 

[DSG2003Mach1]

^^ a failed FRPS (fuel rail pressure sensor) can dump fuel as well but there are usually other issues.

as mentioned the fuel system on these cars is returnless so fuel does NOT return to the tank from the engine.

If youre replacing the filler neck gasket, personally I would drop the tank down enough to look inside and see whats going on in there if anything. It may just be the old old fuel filter, depending on just how old the filter is and how much crud was already it in when you started running fuel with ethanol in it that can make some nasty messes of stuff from what Ive heard

 

[01yellercobra]

How long have you owned the car? There's a chance a previous owner poured something into the tank as an additive.

 

[3B99SVT]

In addition to the other comments above, I'll as the question about how quickly your car starts The time that the starter motor is turning your engine over but it hasn't started running can be wash your cylinders down and put a small amount of fuel in the oil.

It doesn't take much fuel in the oil to give it a gas smell. Since you just changed your oil, I would periodically smell the oil on your dipstick and see how quickly the gas smell returns.

To check your FRPS as DSG2003Mach1 suggested, just pull the vacuum hose off it. It's at the front of the driver's side fuel rail. If there is a fuel smell in the vacuum hose, you have a hole in the diaphragm of the FRPS and it needs to be replaced. What kind of fuel mileage are you getting?

 

[Throttlehogg]

How long have you owned the car? There's a chance a previous owner poured something into the tank as an additive.

I'm the original owner and I did put SeaFoam into the tank about 3 years ago. Other than that, nothing but premium has gone into the tank.

 

[Throttlehogg]

In addition to the other comments above, I'll as the question about how quickly your car starts The time that the starter motor is turning your engine over but it hasn't started running can be wash your cylinders down and put a small amount of fuel in the oil.

It doesn't take much fuel in the oil to give it a gas smell. Since you just changed your oil, I would periodically smell the oil on your dipstick and see how quickly the gas smell returns.

To check your FRPS as DSG2003Mach1 suggested, just pull the vacuum hose off it. It's at the front of the driver's side fuel rail. If there is a fuel smell in the vacuum hose, you have a hole in the diaphragm of the FRPS and it needs to be replaced. What kind of fuel mileage are you getting?

My mileage is crap... about 150 miles on a full tank, which is approximately 50% less than before. As far as starting goes, most of the time it starts right up; but, every now and then I have to crank it longer than I like or it may even take more than one attempt. Just last week it wouldn't start at all - but that was right after my BF moved it from the driveway to the street. It started OK for him, but he's got this nasty little habit of mashing the pedal right before and during start.

I'll definitely check the FRPS right away - does it matter if it's warm or cold? Like, could I check now that it's been in the driveway for 3 hours?

 

[Throttlehogg]

If you only drive short trips , where the engine doesn't actually get to full operating temperatures for any period of time , there is a chance you will be getting some fuel in the oil.
I see you are in Northern Californian, probably similar temps as Southern Oregon, which is where I am at.

Just a thought.
I think you are confusing a return fuel system , which these cars are not .
It is not the unburned fuel, but the unused fuel that returns to the tank.

Another possible reason for your oil to smell of gas , is a poor tune , or sticking injectors.

May be a stupid question:??:, but, what is the difference between unburned and unused fuel?

Just within the last couple of years I've started driving shorter distances/quick trips. I'd estimate that the last 5 - 10 thousand miles were accrued in increments of no more than 10 miles.

 

[71catruck]

Unburned fuel would be if your running to rich or if you aren't getting adiquite spark and there is fuel in the cylinders that isn't getting burned. This will exit out the exhaust. Unused fuel would be with a return style system where the fuel actually has a line to go back to the tank. The only line that runs from the engine to the tank is the evap stuff. But that is under a vacume so I dont see this being possibl .

 

[Throttlehogg]

Unburned fuel would be if your running to rich or if you aren't getting adiquite spark and there is fuel in the cylinders that isn't getting burned. This will exit out the exhaust. Unused fuel would be with a return style system where the fuel actually has a line to go back to the tank. The only line that runs from the engine to the tank is the evap stuff. But that is under a vacume so I dont see this being possibl .

Thanks for clarifying that. Unburned just seemed like unused to me, but as I now understand it, the distinction is made simply for the type of fuel system, i.e. return or returnless. Do I have that correct?

 

[3B99SVT]

My mileage is crap... about 150 miles on a full tank, which is approximately 50% less than before. As far as starting goes, most of the time it starts right up; but, every now and then I have to crank it longer than I like or it may even take more than one attempt. Just last week it wouldn't start at all - but that was right after my BF moved it from the driveway to the street. It started OK for him, but he's got this nasty little habit of mashing the pedal right before and during start.

I'll definitely check the FRPS right away - does it matter if it's warm or cold? Like, could I check now that it's been in the driveway for 3 hours?

It doesn't matter if the engine is warm or cold when you pull the vacuum line off the FRPS. I wouldn't do it hot though just for comfort's sake. A drop in fuel mileage unfortunately could be a lot of things but includes a vacuum leak so your engine is dumping fuel to make up for it. Is your SES (service engine soon) light on? If so, do you know what the codes are?

 

[Throttlehogg]

It doesn't matter if the engine is warm or cold when you pull the vacuum line off the FRPS. I wouldn't do it hot though just for comfort's sake. A drop in fuel mileage unfortunately could be a lot of things but includes a vacuum leak so your engine is dumping fuel to make up for it. Is your SES (service engine soon) light on? If so, do you know what the codes are?

I did recently have a check engine light and it was for a misfire in the #8 cylinder. I reset it (approximately 3 weeks ago) and it has not returned as of yet; nevertheless, I sometimes feel like she's not running on all eight. Just yesterday, as I was leaving for work, I noticed a HUGE cloud of white smoke (like a rock concert) behind me. Then, sitting at a red light about 2 miles from home, I'm still seeing some smoke, though not as much as earlier. It has an acrid smell with a faint hint of fuel. The rest of my 10 mile drive to work is smoke free as is the drive home later. I have not been overheating or needing to add water and the oil I drained last weekend was not milky at all.

 

[01yellercobra]

10 miles isn't much of a trip for these engines. They're barely warmed up by then. That'll kill mileage. When was the last time the plugs were changed?

Thanks for clarifying that. Unburned just seemed like unused to me, but as I now understand it, the distinction is made simply for the type of fuel system, i.e. return or returnless. Do I have that correct?

A returnless and return system can have unburned fuel. As was pointed out it's caused by an overly rich condition or failing ignition system. Unused fuel is only for a return system. In a stock configuration our cars won't have unused fuel.

 

[DSG2003Mach1]

a check engine light for a misfire requires a certain number misfires in a certain number of revolutions to trip the light I believe. You are more than likely still having a misfire condition it just hasnt happened frequently/severely enough to trip the light again just yet. Id check the FRPS and fix the misfire and go from there