Slight smell of gasoline in oil

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Hello everyone, I'm a bit of a newb when it comes to oil and I'm here to learn from the best! I've got a 4cyl S10 with 140k miles on it. I've owned it for 3 years and bought it with 100k on the clock. I've been doing 3k mile change intervals with penz hm and a puro classic since I drove it home. I've just switched to maxlife on my last change a couple days ago because there was a bit too much startup noise with the penz and I've had a very slow leak that appears to be coming from the back of the engine block. No oil is burned between changes and the leak isn't even heavy enough to require any oil to be added over 3,000 miles. While I was changing the oil, I figured id pour a small sample into a glass jar and look at the condition and give it a smell instead of letting it all vanish into my dirty old drain pan. The color looked ok, but there was a bit of a gassy smell to it. I have a vacuum gauge installed and the reading at idle remains high(21" or so) and I've done a couple 'tests' using the gauge to get an idea of overall engine health. I think the rings are ok but I'm tempted to do a compression and/or leakdown test just to be sure. Any other ideas as to what may be causing this odor? Just to note, it's my dd and sees highway speeds/10+ mile drives daily so its always brought to operating temp each time it's driven Thanks!
 
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Probably normal, unless the smell is really strong. If you don't do so already, you may want to take the car on a little bit of a longer run, perhaps 40 miles or so, at least once a week. And it wouldn't hurt to send out a sample for a UOA.
 
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In my experience, used oil usually smells like exhaust gases. In any event, you could do a UOA, which would tell you the fuel contamination level and would be easier than running a leak-down test.
 

slowdime

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I don't think it's particularly strong, but I haven't smelled fuel contaminated oil before, so for comparisons sake it just smells like gas to me. It's not overwhelmingly strong like sticking my nose in the gas filler neck but the odor is there. I've got a kit from blackstone, so maybe on my next drain I'll send in a sample since I've never had a uoa done. I like to baby my truck and keep it running and looking nice. I do want to try and track down the source of the leak. All there ever is(or was, hasn't been there since putting in the ml) is just a small drop on the bottom of the bellhousing. I replaced the rear main when I did a clutch job a couple years ago, so unless I buggered it up I can rule that out. I think I'll have a closer look this weekend. There's a little bit of oil & grime around the valve cover, but it seems unlikely that would be the cause of a drop on the bellhousing. Or would it?? My other suspect is the filler neck o-ring. Thanks for putting my mind at ease about the gassy oil odor!
 

slowdime

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One more thing I meant to ask... From everything I've read here, ML sounds like a pretty highly regarded oil. I plan on doing 3k mile oci's with a puro classic. Sounds like an ok combo? I considered the pureone but for a short oci I wasn't overly concerned about using the classic instead. Especially since I'm on a tight budget Would the full synthetic ML be worth it? I'd be willing to pop for the pureone and move to 5k oci's if it works well with motors that have a small leak. I used M1 for a couple oci's in the past but wasn't thrilled with it's ability to sneak past some of the seals. It was also pretty noisy on cold winter mornings
 
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I imagine any oil that has the blessing of API will do fine for at least 3K intervals. The Purolator classic filter will do well also. As for going to a synthetic and drawing the OCI's out, you may want to do a UOA first to make sure your engine isn't producing any significant contaminants in the oil. If the UOA comes back clean then you can draw a conventional oil out to probably up to 4K to 5K with your current driving pattern, and a synthetic to 7.5K to 8K using a premium filter such as the P1 you mentioned. If the UOA shows fuel dilution or coolant then you'll want to stick with fairly short OCI's.
 
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All engine oil smells like gasoline after it's been ran awhile. I'd imagine a CNG powered vehicle doesn't, but I've never smelled the dipstick out of one of those.
 
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Sometimes the air/fuel ratio can get messed up with old sensors. Replace your oxygen sensor and if you have a MAF, clean it. Remove your vacuum line from the fuel pressure regulator and verify no leaks.
 

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Originally Posted By: artificialist
Sometimes the air/fuel ratio can get messed up with old sensors. Replace your oxygen sensor and if you have a MAF, clean it. Remove your vacuum line from the fuel pressure regulator and verify no leaks.
Is replacing the upstream o2 sensor helpful even without a trouble code? As I said I bought the truck with 100k miles on it and have put another 40k on it since then. I saw no indication from the previous owner that it had been changed so it's got a lot of miles and about 12 years on it so I could see why it wouldn't hurt. I should mention the catalytic converter was shot when I bought it, when I was replacing it I turned it on it's end and chunks of the honeycomb fell out, indicating it had melted... Only one way I know of to melt a catalyst and that's too much fuel in the exhaust. I haven't had any indication of too rich a mixture since I bought it, same cat for the last 40k miles and I get about 30mpg on the freeway
 
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Very normal. UNLESS you noticed a big difference from last OC to this one ! Consider sent the sample to BlackStone & have it analyzed just to be sure.
Originally Posted By: slowdime
Hello everyone, I'm a bit of a newb when it comes to oil and I'm here to learn from the best! I've got a 4cyl S10 with 140k miles on it. I've owned it for 3 years and bought it with 100k on the clock. I've been doing 3k mile change intervals with penz hm and a puro classic since I drove it home. I've just switched to maxlife on my last change a couple days ago because there was a bit too much startup noise with the penz and I've had a very slow leak that appears to be coming from the back of the engine block. No oil is burned between changes and the leak isn't even heavy enough to require any oil to be added over 3,000 miles. While I was changing the oil, I figured id pour a small sample into a glass jar and look at the condition and give it a smell instead of letting it all vanish into my dirty old drain pan. The color looked ok, but there was a bit of a gassy smell to it. I have a vacuum gauge installed and the reading at idle remains high(21" or so) and I've done a couple 'tests' using the gauge to get an idea of overall engine health. I think the rings are ok but I'm tempted to do a compression and/or leakdown test just to be sure. Any other ideas as to what may be causing this odor? Just to note, it's my dd and sees highway speeds/10+ mile drives daily so its always brought to operating temp each time it's driven Thanks!
 
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Originally Posted By: slowdime
Originally Posted By: artificialist
Sometimes the air/fuel ratio can get messed up with old sensors. Replace your oxygen sensor and if you have a MAF, clean it. Remove your vacuum line from the fuel pressure regulator and verify no leaks.
Is replacing the upstream o2 sensor helpful even without a trouble code? As I said I bought the truck with 100k miles on it and have put another 40k on it since then. I saw no indication from the previous owner that it had been changed so it's got a lot of miles and about 12 years on it so I could see why it wouldn't hurt. I should mention the catalytic converter was shot when I bought it, when I was replacing it I turned it on it's end and chunks of the honeycomb fell out, indicating it had melted... Only one way I know of to melt a catalyst and that's too much fuel in the exhaust. I haven't had any indication of too rich a mixture since I bought it, same cat for the last 40k miles and I get about 30mpg on the freeway
Sensors gradually lose accuracy over time, and unless the sensor fails dramatically, there is go guarantee that a check engine light and error code will be set. Often the sensor becomes slow, not going from rich to lean and back, creating moments of excessive richness, which can shorten the lift of the car.
 
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