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Motor oil as lubricant - corrosion?

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Neville Quick23/08/2010 14:31:03
2 forum posts
I use car engine oil as lubricant on my steam locomotive's motion and have done so for some time.  Someone told me that this oil contains sulpher and will attack bronze.  I was surprised and wondered if it would attack brass and gunmetal too.  Why would engine oil contain something that actually causes corrosion!?
Alexander1323/08/2010 21:12:15
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8 forum posts
Car engines have phosphor bronze bearing and valve guides, so I would be surprised if engine oil would attack bronze. 
Gray6223/08/2010 21:57:18
1058 forum posts
16 photos
Old engine oil contains many by-products of the combustion process, these being carbon monoxide, nitrogen dioxide, sulpher dioxide and other particulates. Much of these are ejected through the engine exhaust system however as engine wear increases, some of these elements will inevitably be absorbed into the engine oil due to blow by of the piston rings etc - this among other factors determines the reason and frequency for oil changes.
 
So, to sum up, old engine oil is a dirty contaminated substance which should not be used as a substitute for good quality lubricants, after all, the purpose of a lubricant is to prolong bearing surface life and not to introduce unwanted contaminents.
 
\if you are using new fresh oil, then there should be no problem, but do not be tempted to use the oild you just drained ou of your sump !
 
regards
 
coalburner
Clive Foster23/08/2010 23:01:42
3630 forum posts
128 photos
I think the bronze attack reputation refers to gear oils rather than engine oils.  Some of the older EP additives are said to be very badly behaved in this respect.  Allegedly one reason for aluminium bronzes being developed although I can find no reliable source for this so it may be pure myth.  Its worth remembering that EP additives in general behave in a chemically complex manner, especially at the localised high temperatures associated with heavy shearing loads.  Oils of this type really do need to be used as the maker advises.
 
Motor oils aren't a very good choice for outside motion work as the modern breed are loaded with fairly inappropriate (for this application anyway) additives.  Probably better to use some of the bearing or slide-way oil you keep for the lathe.  Any sensible choice here will be formulated to work well at normal temperatures and exposed to the atmosphere.  As they are easily available from RS Components I use Castrol Hyspin AWS32 as machine bearing oil and Magna BD68 for slide ways, feed screw etc. duties and find them excellent as thin and thick "oil can" oils too.  BD68 being excellent on squeaky hinges, more effort to work in than thinner stuff (or WD40) but it lasts for ages.
 
Clive 
Howard Jones05/10/2010 10:32:53
70 forum posts
112 photos
the castrol gtx oil I used for a while on my lathe certainly leached out zinc. my brass oilers all went slowly a red shade of copper.
I now use shell tellus 46 which leaches silver but since there isnt any on the lathe causes no problems.
 
wd40 *causes* corrosion!!!
it seems that after a period the chemical makeup deteriorates and becomes hydroscopic.
I have fought a corrosion problem for years in my workshop and it became proven that the wd40 I was using was the actual cause. I now oil with the tellus and have had no further problems.

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