Oil return tubes & silicone grease = problems?

[jlex]

Not used to having any leaks on my '85 Carrera, I was surprised to see the left bank oil return tubes go bad over the winter. I replaced that side (will do the "easy" right bank next oil change) & took about 3 hrs. w/o removing the heat exchanger.
I avoided all the wailing & gnashing of teeth other posters have warned about by liberally applying silicone grease to the O rings & the inside of the female tube prior to installation.... no problems thanks to those who posted the hose clamp info....Thanks.
A couple days after installation, I was thinking about the silicone grease usage & it dawned on me...WON'T USING SILICONE GREASE KILL MY O2 SENSOR??? With all the recommendations to use silicone grease, Dow Corning 111 or 112, and Sylglyde, I hadn't given it a second thought, but afterwards am worried about ANY kind of silicone eventually ruining the O2 sensor. After all, if they warn you against using something seemingly as harmless as silicone gasket material (gasket caulk) or spraying silicone around the throttle intake, won't using a 100% silicone paste directly in the path of the oil return likewise ruin the oxygen sensor? Any problems out there so far? Maybe it's better to use a petroleum based grease for the job....
regards,
jlex.

[TroyGT]

I've never heard of any such. I wouldn't think this would be a problem since there shouldn't be much introduced into the system, if any.

-Troy

[john walker's workshop]

good luck getting the green o-rings to slide on anything but silicone paste.

[jlex]

Troy: I dunno... I slathered up the inside of the female part of the tube (against which the O rings needed to slide) pretty well. Worked great, but I know it's got to be all throughout the oil system now. I can just see it getting into the combustion chambers & eventually passing by the Oxy sensor on its way outside the tailpipe...
Heck, if they're so cautious about silicon gasket stuff, this 100% silicone paste is like main-lining it into the system.
Makes me feel better that John Walker isn't alarmed about it... nevertheless, if my '85 starts acting weird, you can bet I'll be looking long & hard at the oxygen sensor!
regards,
jlex.

[TroyGT]

I'm with you on the John Walker comment... if it was something to be really concerned with, he would have chimed in for sure. Sounds like he's been using the silicone stuff at his shop. I used motor oil on mine and managed to get the rings on fine... so I never had this concern. Hopefully you're okay. Others may chime in on this.

-Troy

[jlex]

Troy:
As the passenger side will be lots easier to do for me (when I change the oil later) I think I'll use lubriplate lubricant to be on the safe side... I believe it's like white grease & is used as a motor assembly lubricant. For that matter, I don't know why plain old white petroleum jelly wouldn't do a good job... it even seems to be a bit more slippery than the sticky silicone paste I used. Happy Motoring!
regards,
jlex.

[MattAlpha]

If you're really concerned about it, you can also use Vasiline (or a generic counterpart) to lube the o-rings. Its completely inert and a re-builder friend of mine told me about it as one of his secrets. It works better than the SlyGlide, that is for sure. It will not harm your O2 sensor unless you remove it and coat it.

On a side note, I've replaced 3 of 4 oil return tubes using SlyGlide and I haven't experienced a single problem.

-Matt

[greglepore]

How do you expect silicone grease to migrate from the oil return tubes to the o2 sensor???????????

[jlex]

Greg:
The oil moves throughout the engine, oil cooler & various lines. The critical spot where it would enter the exhaust system & possibly contaminate the O sensor would be in the combustion chambers (cylinders). The pistons, moving up & down the cylinder walls via the piston rings need oil to be able to slide against those cylinder walls... some amount of oil is displaced & burned up when the spark plug ignites, then the small amount of burned oil & by-product of the air/gas mixture gets exhausted out the exhaust valves & eventually out the tail pipe...
Of course, those with cylinder wall wear would experience a greater amount of oil blow-off than those w/ tight fitting rings. That's how I view the possible silicone contamination, anyway...
regards,
jlex.

[88911coupe]

I dug this thread up since last night I used Dow Corning to ease the installation of the rubber seal between the two halves or sides of the intake manifold on my '88. Just after I finished and was so amazed how much easier it made the process I suddenly remembered something about DC 111 being bad for anything Oxygen Sensor related. Should I take it apart and clean it off, or buy a new rubber seal?

[onboost]

Originally Posted by john walker's workshop

good luck getting the green o-rings to slide on anything but silicone paste.

+1

[KTL]

Originally Posted by 88911coupe

I dug this thread up since last night I used Dow Corning to ease the installation of the rubber seal between the two halves or sides of the intake manifold on my '88. Just after I finished and was so amazed how much easier it made the process I suddenly remembered something about DC 111 being bad for anything Oxygen Sensor related. Should I take it apart and clean it off, or buy a new rubber seal?

Never heard anything like that before. Sounds like internet myth to me. There's no way this stuff is going to get past the rings or valve guides and contaminate the combustion chamber. Still, the DC paste should be used sparingly because it's very resistant to any solvents. Meaning, it doesn't break down very easily and therefore could potentially clog an oil passage if one were to glob the stuff on.

I'll also add that the black o-rings aren't any more agreeable than the green ones. I've had lots of trouble with the blacks too. I finally gave up and decided to fight the battle the next day. I found the next day the rings must have shrunk a bit. The tubes would slide easy after sitting overnight with some DC paste on them?

[jlex]

88911COUPE: you're talking about having used the silicone on the intake manifold, not the oil return tubes, right?? The thread dealt w/ those PIA oil return tubes only, not the intake manifold. I'd have to look at my car to see just what you're talking about, but I would be leery of silicone in the system anywhere & would avoid it if there was a good substitute. Silicone ruining O2 sensors is no myth; I've read lots of manufacturer's warnings & other miscellaneous warnings about possible contamination from silicone.
Regarding the oil return tubes, I used silicone on the left bank and last fall I did the right bank using vaseline. I saw no installation difference between the two (my tubes had the green O rings). If I ever had to do the job again (God forbid) I'd play it safe & just go w/ the petroleum vaseline. Just my .02...

regards,

jlex.

[KTL]

Ooops. Overlooked Buck's reference to the intake manifold union. I'm surprised the grease would be needed to join the manifolds since that coupler is very soft and pliable.

I don't dispute the silicone issue with O2 sensors when it comes to sealants. In that case, we're talking about RTV silicone and not silicone grease, which are two different animals. That's why you'll see on many sealants a "O2 Sensor Safe" notation.

But the grease is likely not going to make it to the O2 sensor because it sticks to the walls of the manifold. RTV can make it to the O2 because when it dries, it can break free, get burned in the combustion chamber and contaminate the O2? I'd not worry about the grease on the manifold coupling.

[Boxer 6]

A little Astrolube does wonders Just kidding, no problems for me using the Dow silicone.

[88911coupe]

Just to clarify, yes, this was the rubber "tube" that connects the two halves of the intake manifold for the 3.2. I wanted to make sure this slipped on easily since I was also trying to mate up the base gaskets. There's not a lot on there but I would assume that as it evaporates the tiny amount that is actually exposed to the interior of the intake manifold will obviously flow through the combustion process and out the exhaust. Should I remove it and start over?

[jlex]

Buck:
I don't know if you'll find an answer to that... depends on your comfort level, I suppose. Is there a difference between grease & sealant? Who knows?? How much of a PITA is it to undo your work? What's the worst that could happen... replace 02 I suppose. Would a new 02 get contaminated? Who knows??
If it was me, and the amount used was minimal, I probably wouldn't worry about it, but then, that's me (slacker). With all due respect, some P owners are really anal retentive about their cars & they'd lie awake nites worrying about it. Weigh the cure vs the possible harm vs whether there is any problem at all then decide. Not that big of a potential problem IMHO.

regards,

jlex.