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Recently, someone suggested that I apply some vaseline to an O-ring connection to see if I can find a leak.
I've read that oil-based lubricants, especially vaseline, can desolve rubber. It seems like a bad idea to do this. Does vaseline (or any other oil-based lubricant) inherently degrade/desolve rubber?
I think that neoprene o-rings are used in special places (like an A/C line) where oil is going to be present, just for this purpose.
tl dr - Have no fear of Vaseline and o-rings
O-rings are made out of many different materials. I would suggest that those o-rings which are made to work in the automotive realm are made to be resistant to things such as oil, gasoline, and other petroleum products. This would include Vaseline. While Vaseline and other petroleum products may degrade real rubber (actually made from the rubber tree), current o-rings technology does not use natural rubber. The Parker O-ring Handbook states:
A polymer is the “result of a chemical linking of molecules into a long chain-like structure.” Both plastics and elastomers are classifi ed as polymers. In this handbook, polymer generally refers to a basic class of elastomer, members of which have similar chemical and physical properties. O-rings are made from many polymers, but a few polymers account for the majority of O-rings produced, namely Nitrile, EPDM and Neoprene.
Emphasis mine.
Looking further into the handbook will give you this matrix of how well different types of materials fair against different things:
Looking throughout the matrix you can see that natural rubber does very poorly against oil, while Neoprene does fair to good and Nitrile does excellent. (Note: Even though EPDM is said to be used as one of the big three substances, I'm not finding it on the list.)
With this in mind, you should have no worries about whether to utilize Vaseline on any of the o-rings. Vaseline is a very mild petroleum product. If it wasn't, we wouldn't use it in so many products which involve skin care. If o-rings were actually made of rubber, then there would be concern.
As far as I can tell, there is no reason that Vaseline might gradually degrade the rubber O-ring on which it has been applied.
O-rings that are manufactured for automotive purposes do tend to be made in a rather durable fashion so as to be able to withstand whatever sort of fluids that might accidentally get spilt during car maintenance.
If you are worried however, there are also silicone based lubricating compounds such as Sil-Glyde for example. These tend to be more expensive alternatives due to the fact that they do not benefit from economy of scale (decreased cost per unit for anything produced in mass quantities) nearly as much as something like Vaseline would.
Also as you mentioned, neoprene is another alternative but as there is nothing wrong with using Vaseline for most automotive purposes, you might as well go ahead and use that as it is probably going to be the cheapest option.
Yes it might, if it's made from Ethylene Propylene Diene Monomer (EPDM) like what is used on some MAF sensors. It might make your o- ring swell larger so it won't fit correctly anymore.
Not all oils rot rubber, for example transmission oil or brake fluid does not rot rubber. However engine oil will. That's why if one uses engine oil for brake fluid or in their power steering pump, it won't be too long before you will need a new steering pump or an entire brake system overhaul. Engine oil will cause the rubber to swell up and fall apart.
P.S. One can use transition oil for their power steering pump. Though I wouldn't recommend that for brake fluid as it's the wrong viscosity and does not have the same heat resistance as proper brake fluid has.
I rebuilt a cars suspension two years ago and to avoid using grease (which I knew to be bad to rubber bushes) I used vaseline. One year on and the car has hardly done 1000 miles, the bushes have started to break up.. They are either poor quality bushes or the vaseline has degraded the rubber very fast..
Bad news as I now have to do the whole job again 😣
