What to use on rubber O-rings?, Oil? Grease? Nothing? Options

[highways]

Ok, I'm putting parts of my engine back together and I'm using some old rubber parts that are in good shape- but I'd like to lubricate and protect them.

For example- I have the rubber O-ring right under the oil filler neck. Don't have time to run to Pep-Boys again today so I gotta use something I've got. The choices are:

*Engine oil
*CV joint grease
*WD 40
*White Lithium Grease from spray can
*3in1 Houshold Oil

Or I probably have lots of other stuff that would apply. I just don't know what dries out rubber (alcohol? acetone?) that I should avoid, and what I should use, if anything. Also, I have wiring boots on the outside- what to use on them?

[highways]

Ok but the only thing that gave me doubts about the White Lithium Grease in a spray can is that it says it's for metal to metal, and the ingredients are mineral oil, hexane, propane, isobutane... which I thought would be similar to acetone and dry rubber out.

[Johny Blackstain]

Ok but the only thing that gave me doubts about the White Lithium Grease in a spray can is that it says it's for metal to metal, and the ingredients are mineral oil, hexane, propane, isobutane... which I thought would be similar to acetone and dry rubber out.

OK, perhaps 3&1? Engine oil, WD40 & CV grease are all petrolium based, which breaks up rubber over time. I don't know what's in 3&1. I like the sound of the marine sealant... sounds like a type of plumbers grease, which is also OK for rubber. (IMG:style_emoticons/default/cool_shades.gif)

[DBCooper]

OK, perhaps 3&1? Engine oil, WD40 & CV grease are all petrolium based, which breaks up rubber over time. I don't know what's in 3&1. I like the sound of the marine sealant... sounds like a type of plumbers grease, which is also OK for rubber. (IMG:style_emoticons/default/cool_shades.gif)

Careful there. No o-rings for automotive applications are made of natural rubber, they're all of materials intended to be used around oil. Gaskets are used where there's no movement between two pieces, and o-rings are used when there's movement. That's why it's so important to make sure the pushrod tube receivers in the head are smooth, for example, so those o-rings can move in and out without being scored by a rough surface. And since they're designed to move they NEED lubrication to work and seal. If you install an o-ring dry or with any kind of sealant you're turning it into a gasket and preventing it from working the way it was designed. Sometimes that's fine, like that oil filler neck where that "o-ring" is really functioning like a gasket, but the general rule is to lube them on installation with whatever liquid they're going to be around, and that's generally oil.