What does a gas smell in the oil mean? | Ford Explorer Forums - Serious Explorations

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What does a gas smell in the oil mean?


Well-Known Member
September 20, 1999
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I have a rough idle and it used to stall when i first turned it on and put it in reverse. It is a 4.0L 93 OHV. I recently replaced my head gaskets and all the other gaskets that had to be replaced to get to the head gaskets because the engine was using coolant. I also noticed a whole lot of carbon build up in the #5 cylinder. Anyway ever since there the oil smelled funny and today I realized that it smells like gas. What is going on? Any help would be greatly apreciated!!


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Shade tree guess

Don't take this as gospel, just an idea. You don't give a whole lot of useful info like miles on the engine, previous events/maintenance and other etc so it makes this kinda tough.

I'd say there's at least a chance that the engine has overheated at least once, maybe warped the head slightly to cause the need to fix your coolant leakage/gasket problems. Maybe it was a simple head gasket leak, but your other info makes me think maybe not.

To directly answer your topic question, "What does a gas smell in the oil mean?", gas in your oil means it is getting there. Simple as that. Carbon in #5 cylinder tells you that's where the gas isn't completely combusting so that's where that liquid fuel could still survive. Your head gasket could have had the leak at #5, causing this, but that would not get fuel into your oil. That's why I think there's more to this, and why an overheating may have occured.

I'd say your rings in cyl #5 are shot, and gas is leaking past them to drain into the oilpan. While you were taking the trouble to bandage your top end it looks like you shoulda gone ahead and done the whole overhaul; put new rings in, rehone the cylinders, etc.

Hopefully a more knowledgeable modern-techno-engine nerd can give you better news, but that's how I would have diagnosed my old 289, and I would have been right back then. Maybe there are different possibilities now.

Good luck, hope it's a relatively cheap fix.

[Edited by GJarrett on 06-29-2000 at 06:41 PM]

I had the same problem with mine. Execpt the head gasket and the whole nine yards. Anyway. The gas smell in the fuel. I changed the pcv valve and changed the oil and the problem was solved. This might not solve the problem but I hope this might help.


Thank You for the advice. GJarrett you got it right when u said that the heads might have been warped. When I was replacing the Head Gaskets I took the heads into get remachined and one was warped. Anyway the engine has 70k on it and the gaskets were replaced at 64k. I started using this truck at 45k and it hasnt overheated while i have been using it. Although the temperature will easily go past the word "normal" on the coolant temperature gauge if I am idling in 90+ degree heat with the a/c on. That has only happened twice and I shutdown the engine before it could overheat. I figured this was normal because this seems to me like an extreme condition. When I replaced the gaskets I also went through and changed the plugs, cleaned the MAF, cleaned the Idle air control valve, changed the oil and filter, the air filter, the pcv valve, fuel filter, and flushed and filled the coolant system with 50/50 water and prestone anti freeze. Before the gasket replacements I regularly changed the oil and filter every 3k and had the coolant system flushed once. Before I recieved the truck i have no idea what she had been through. I was thinking that maybe the lower intake manifold gasket failed or the bolts loosened and allowed the injectors to spray a little bit of gas into the crankcase and that is why it smells like gas? Also since I replaced the head gaskets at 64k I have changed the oil twice because of the gas smell. One last thing both the lower and upper intake manifolds are covered in a layer of what seems to be oil residue inside them. Is this normal? Thank you for your help GJarrett and Big E. You've already given me much more help then any of the local mechanics that only said "that isnt right".

If you have oil residue in the intake the most common way it get there is the tube hooked to the side of the intake hose. You know the big black one in front of the engine compartment. If you look there will be a hose running from your oil fill tube to the intake hose. I am guessing but I am pretty sure you have some worn out rings and some blow by is occuring. And the blow by will actually blow oil "cloud" into the intake. The cloud is a very fine mist I guess. Something else that will cause it is a plugged or bad pcv valve. Make sure if you get one only use Ford parts. I had one from Auto Zone. It rattled but was no good. Put a Ford one on and hand no problem. I hope this sheds some light of stuff for you.


I'm gonna go out and get a compression tester and see whats going on. This should indicate a bad seal or ring right? Thanks again...this site is great!


Ok i did the compression test and it goes like this. 195psi for #1, 190psi for #2 and #3, and 200psi for #4-#6.


Chav,can't read that post on #4-#6; are you saying #5 is at 200psi?

If that's true it ain't your rings.... we need another gearhead to help you since my theory is junk now. Back to basics. You changed the PCV valve, and on etc. Rings are good or you wouldn't be reading those high pressures. Where else can fuel get into oil?

Sorry I couldn't help you, but it was a valid theory at least....


Could be a vacuum leak , the computer reads the engine running lean and injects more fuel into the cylinders than needed- and the unburned fuel mixes with the oil.

Engine running ok otherwise- what about temp. If the engine is not getting up to operating temp then it may be in an enriched mode (putting more gas in the cylinders).

Although with the cylinder pressures not sure if this is the answer, I would think the rings would have lost some of their seal if the fuel was washing the oil away. Also could be the cause for the oil in the intake - blow by oil mist getting by the rings as mentioned above, except that the cylinder pressure seems ok once again.

I would check for vacuum leaks again.

Do ypou have a code scanner? Run it, or check the temp senders on the intake, the plenum, the air intake see that they work- all on the idea that the engine is enriching itself.

I would get the oil tested for the presence of fuel, make sure what your nose is telling you is true.

Good luck.

Yeah GJarrett #5 was at 200psi...sorry about that and ur input was very useful thankyou again. Without ur input I would still be wondering what is going on. Yeah a lot of people told me that it might be a vacuum leak too because of the rough idle. I am going to check each vacuum line and could i plug up the vacuum octopus and see if the idle smooths out? And i have an idea. When I pulled the heads I'm pretty sure that dirt entered the fuel rail and the injectors and now they are making a very audible ticking noise at idle. In order to check the injectors could i pull the intake manifold and disable the ignition and crank the engine and watch the spray? I will put the code scanner on there and check again and I'll get the oil tested. You guys have no idea how much i apreciate the input!! Thank you


I am not sure about the fuel system setup on this engine, I haven't seen it, but if there are individual injectors foreach cylinder, then the problem is simple, # 5 injector is leaking. When the engine is off, fuel leaks into the oil from the bad injector by running past the rings. There is a gap in the rings that will let this happen. The other clue that make me think this is the carbon buildup on the plug. If there was a richness problem due to a bad sensor, you would have trouble codes and at least 3 plugs would be fouled. Do a leakdown test of your fuel system to determine this.

what's a leakdown test and how would i go about doing this test? Thanks Kilroy and yeah there is an injector for each cylinder.


You say it stalls out sometimes or is hard to start? My grandpa has a 96 Lincoln and has had it not start on him 2 times. The Lincoln people told him when it turnes over a l,ot but doesn't start gas could leak down into the oil and you should replace the oil immediatly. He only has 30,000 miles so i don't think he has much wear, but they told him the oil HAD to be changed immediatly whenever it cranked but didn't start.

Ok thats it I've begun tearing her down again. :( You guys know that Power Foam stuff that removes carbon build up? WOW Man that stuff works good!! Remember I said that I had an oil residue all over the intake...well its gone! Only a couple runs of residue, but I didnt let the Power Foam work for long. I'll let it sit over night next time. Oh yeah and umm....dont try the idea of pulling just the fuel rail and injectors. The injectors like to fly out of the fuel rail under 38 psi. See I thought this would happen, but I read on the ranger power sports page that "The injectors can be tested for the proper spray pattern by removing them from the intake manifold (leaving the electrical and fuel connections intact) and running the engine briefly, making sure the spray pattern is an even cone shape." I think the only way to do this and still be safe is to pull the entire intake manifold so that the injectors are still sandwitched between the fuel rail and intake manifold. Anyway I thought I'd let everyone know how its going. It looks like I'm going to be with out a car for a little bit. I think I'm going to be replacing all the injectors, the fuel pres. reg, the upper intake manifold and fuel rail gaskets, the oil and oil filter, the oxygen sensors, and the thermostat I think 198 degree? Oh well I'll find out what temp it should be. I better be getting to bed since its 2 in the morning. Nite.


This is just a suggestion. You might want to have you injectors tested before you just replace them. I think they are over 75 bucks a pop. It could get really expensive to fix a cheap problem. Just a though.


I'm going to get those performance injectors from Vanir Technologies.

Matched Injector Set (24 lb/hr)

I hope they have them instock cause if they dont I gotta go buy rebuilt ones from napa for $240. Big-E thanx for the suggestion, but short of pulling the intake manifold I dont know how to get them checked and I am fairly certain that at least one is bad.


No problem. I was not sure if you knew the price of them. Does anyone know what the rating of the stock injectors are? I am just curious.


I think I remember reading that the stock injectors are 19 lb/hr.
I also remember reading that the stock injectors were good for 200 -225hp maybe more. (in this cas if the negatives are not too bad the price for the 24lb from Vanir is much better than Ive seen for stock replacements)

Anyone know of the downside to running larger injectors if you dont need them?

What HP level does the 5.0l crowd switch to higher flow injectors. Reason- the cylinder volumes are similar so at 3/4 the HP level would be a rough guestimate for the 6 cyl.

Just curious 2

I've heard that the bigger injectors decrease your gas mileage. When I talk to Vanir tomorrow I'll find out and post what they say. I plan on making future modifications and I know I'd be kicking my self if i didnt get the high performance ones now. I also like the price. :)


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