Oil Consumption/PCV issues
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Oil Consumption/PCV issues
Hey everyone, I could use a hand trying to figure out an oil-consumption issue that I've been having with my Dakota. Truck is a 2002 SXT 4x4 with the 3.9L V6.
I bought the truck five years ago with 92,000 miles on it and sense day one it has used oil. Some research online told me that these magnum-block engines weren't really oil friendly and being over 20 years old I figured it wasn't a big deal, but the truck kept using oil more than I would have liked (Between two and three quarts every several months). A few months later I found out the plenum plate was leaking, so I replaced it with an aftermarket one from Huges Engines. After installing the new plenum plate, I left the oil alone for months without checking it (thinking I had fixed the oil issue). I checked the oil on the truck out of curiosity only to find out the block was nearly empty.
After that scare I spent some serious time under the hood and found out that the oil is coming into the intake through the PCV system, which is where my trouble really starts. After new PCV valves, oil was still coming into the intake, and the internet sources all point to the same thing: cylinder blow-by over pressurizing the crankcase. As bad as this would be, I am not completely convinced this is the issue. I've driven a work truck with bad rings and it was not even comparable to how my truck drives:
1. The truck has never smoked the whole time I've owned it
2. The truck has great power and accelerates with zero issues
3. There is no oil smell from the truck at all
4. There is only 120,000 miles on the truck
5. The truck starts with just a bump of the key
I still need to do a compression test to be 100% certain, but I did a different test today that produced some interesting results. I pulled the PCV valve out of the driver's side valve cover and removed the rubber hose from it (the hose was still attached to the intake, just not the valve). Once it was removed I started up the truck and let it idle. While it was running I plugged the hole in the valve cover with my thumb because I was trying to feel for any air movement or pressure buildup; there wasn't so much as a whisper of air moving past that hole and no pressure built up. When I was done testing that I heard a whistling noise coming from the rubber line I had taken off the PCV valve, I grabbed it and found that there was a VERY strong vacuum being pulled on that line, and it was sucking in a ton of air. Out of curiosity I put my thumb over it to see what cutting off that vacuum would do. I suspected that the engine might see a little bit of change considering I was cutting off a vacuum line, but that is NOT what happened. When I put my thumb over that vacuum line and stopped the flow of air through it, the entire engine stalled and died immediately.
Based on this I think that there is so much air being sucked through the PCV system, that it is actually pulling oil into it and sending it through the intake. But I'm not entirely sure if this is even possible. I'm holding slim hope that someone can tell me it's not the rings, and that they've found a fix it, because outside of putting a catch-can on and driving it until it dies, I really don't have any ideas on this one.
I bought the truck five years ago with 92,000 miles on it and sense day one it has used oil. Some research online told me that these magnum-block engines weren't really oil friendly and being over 20 years old I figured it wasn't a big deal, but the truck kept using oil more than I would have liked (Between two and three quarts every several months). A few months later I found out the plenum plate was leaking, so I replaced it with an aftermarket one from Huges Engines. After installing the new plenum plate, I left the oil alone for months without checking it (thinking I had fixed the oil issue). I checked the oil on the truck out of curiosity only to find out the block was nearly empty.
After that scare I spent some serious time under the hood and found out that the oil is coming into the intake through the PCV system, which is where my trouble really starts. After new PCV valves, oil was still coming into the intake, and the internet sources all point to the same thing: cylinder blow-by over pressurizing the crankcase. As bad as this would be, I am not completely convinced this is the issue. I've driven a work truck with bad rings and it was not even comparable to how my truck drives:
1. The truck has never smoked the whole time I've owned it
2. The truck has great power and accelerates with zero issues
3. There is no oil smell from the truck at all
4. There is only 120,000 miles on the truck
5. The truck starts with just a bump of the key
I still need to do a compression test to be 100% certain, but I did a different test today that produced some interesting results. I pulled the PCV valve out of the driver's side valve cover and removed the rubber hose from it (the hose was still attached to the intake, just not the valve). Once it was removed I started up the truck and let it idle. While it was running I plugged the hole in the valve cover with my thumb because I was trying to feel for any air movement or pressure buildup; there wasn't so much as a whisper of air moving past that hole and no pressure built up. When I was done testing that I heard a whistling noise coming from the rubber line I had taken off the PCV valve, I grabbed it and found that there was a VERY strong vacuum being pulled on that line, and it was sucking in a ton of air. Out of curiosity I put my thumb over it to see what cutting off that vacuum would do. I suspected that the engine might see a little bit of change considering I was cutting off a vacuum line, but that is NOT what happened. When I put my thumb over that vacuum line and stopped the flow of air through it, the entire engine stalled and died immediately.
Based on this I think that there is so much air being sucked through the PCV system, that it is actually pulling oil into it and sending it through the intake. But I'm not entirely sure if this is even possible. I'm holding slim hope that someone can tell me it's not the rings, and that they've found a fix it, because outside of putting a catch-can on and driving it until it dies, I really don't have any ideas on this one.
Administrator
Joined: Apr 2010
Posts: 87,409
Likes: 4,214
From: Clayton MI
Get a genuine mopar PCV valve from the dealer. Should be less than 10 bucks, and it actually has the correct flow rate.
When my 96 full size was burning oil like there was no tomorrow, it only smoked at large throttle openings. Get on the gas hard, and it was like the smoke screen generated by the old PT boats..... Maybe a light puff at startup, but, that was it. Fixing the plenum didn't reduce that by very much either.
Have a look at your valve cover gaskets, mine would leak down onto the exhaust manifolds, and burn off while driving. You couldn't smell it, and drips never reached the ground.....
Compression test is a good idea.
Valve seals are another potential source for oil consumption. Not too bad to change, (at least, on a full size truck....) just tedious. (there's a lot of 'em.)
When my 96 full size was burning oil like there was no tomorrow, it only smoked at large throttle openings. Get on the gas hard, and it was like the smoke screen generated by the old PT boats..... Maybe a light puff at startup, but, that was it. Fixing the plenum didn't reduce that by very much either.
Have a look at your valve cover gaskets, mine would leak down onto the exhaust manifolds, and burn off while driving. You couldn't smell it, and drips never reached the ground.....
Compression test is a good idea.
Valve seals are another potential source for oil consumption. Not too bad to change, (at least, on a full size truck....) just tedious. (there's a lot of 'em.)
Veteran
Joined: Sep 2018
Posts: 330
Likes: 42
Pull the oil fill port and start the engine. Do you feel large amounts of air coming out? Smoke? Set the cap on the hole and if it gets blown off you have two much blowby. If you valve covers are leaking just lightly tighten up the bolts. They don't need much. As for the stalling, that is normal. You gave the engine a massive vacuum leak then suddenly fixed it causing a lean spike.
Champion
Joined: Oct 2013
Posts: 3,771
Likes: 448
From: Atlanta
Never never go months without checking your oil, even if you've never experienced oil loss before.
I second checking the valve covers. Also replacing the valve stem seals. Those two stopped just about all oil loss for me, and I have well over 300K on this 4.7.
https://dodgeforum.com/forum/2nd-gen...tem-seals.html
I second checking the valve covers. Also replacing the valve stem seals. Those two stopped just about all oil loss for me, and I have well over 300K on this 4.7.
https://dodgeforum.com/forum/2nd-gen...tem-seals.html
