Familiar "burning engine" smell returns

Jibbaman150 · Post by **Jibbaman150** » 26 Feb 2020, 12:03

Hi everybody. So I have put about 3500 miles on my 05 xc70 since I rebuilt the head for a burnt valve (cylinder #4) For the first 2000 miles there was ZERO oil consumption. Recently I have been adding some(not more than a quart) Going up hill I get a burnt rubber/oil smell. The same smell that has preceded burnt valves in 2 different xc70’s I’ve owned...Yes the PCV system FAILS the glove test. However it was replaced 8,000miles ago and of course cleaned/inspected when I replaced the head 3,500miles ago..So am I looking at dropping the oil pan to replace the lower part of the PCV? Should I just plan on having to replace or clean my PCV every other oil change? 104,000miles on car. Thanks for reading.

Post by **abscate** » 26 Feb 2020, 13:55

I could be the oil port wasnt cleaned on the PCV job, or bad parts were used.

Post by **vtl** » 26 Feb 2020, 16:11

I vote for a hole/crack in exhaust. Did you replace exhaust manifold gaskets? Also the nuts can slacken there, may need another torque to spec.

ignatz · Post by **ignatz** » 26 Feb 2020, 16:28

Or maybe engine compression is leaking back into the crankcase. Check compression and look for an oily or darker plug. I'd make sure the top end is good before you go forward with other repairs.
Did it ever pass the glove test?

Jibbaman150 · Post by **Jibbaman150** » 26 Feb 2020, 22:23

Ok thanks this has got me thinking. The PCV system was from Volvo and wasn’t that dirty when I took it apart and cleaned it. The port on the side of the block was cleaned. I am unfamiliar with the lower part of the system(the part that goes into the oil pan) Compression test after I completed the head rebuild was 145 in cylinders 1-4 cylinder 5 read 130..I had a tuff time using my cheap harbor freight tester. Could my rings be worn? I don’t think it’s the exhaust mani, yes I used new gaskets/seals all Volvo brand blue box stuff. It failed the glove test right after I got it back together. However it didn’t smell like it was burning oil or a valve or whatever that smell is until a few thousand miles later. Thanks for the thoughts guys.

Post by **vtl** » 27 Feb 2020, 07:23

My 05 has engine w/ 223k miles, PCV develops a good vacuum at idle. Under boost it has some positive pressure, that started in less than 2 years. I.e. no crankcase problems for 13 years and 200k miles.

Engine is pretty much cooked if a good, newly installed PCV can't get a negative pressure in crankcase at idle.

Post by **chrism** » 27 Feb 2020, 19:33

Did you replace the hose that runs from the breather box up to the top of the engine? They like to split open just above the breather box and exhale an oily smell.
Also, when you serviced the PCV system, did you replace the little nipple fitting that attaches up under the intake manifold?

Post by **vtl** » 27 Feb 2020, 21:14

Every single bit was replaced. Twice in 120k miles, in fact.

Banjo bolt (the nipple) I replaced one more time just a week ago or so, because I could not figure out what revision it was when PCV was replaced last time. Turned out, the latest, and it was not clogged: the check valve was pressuring PCV from manifold when it had boost.

Because positive pressure happens under boost, I installed an oil catch can using 14 mm ID silicone hose, plus drilled PTC nipple as much as possible. Idle vacuum is worse now (it sucks more air from intake before the turbo), but should be better under the boost. I hope.

Jibbaman150 · Post by **Jibbaman150** » 02 Mar 2020, 14:02

All of my hoses were in good condition. The cylinder head was off so I of course cleaned everything including the ptc nipple. I guess I’m going to order the PCV kit and have it on hand while I get in there to inspect everything. Anyways here’s some pictures from the last time I had her apart

Post by **vtl** » 02 Mar 2020, 14:06

What a clean head! I'm planning to boil mine in dimethyl sulfoxide to dissolve carbon that seems to be everywhere in donor engine.