RE: How hot is too hot for oil?

["Allen Mitchell" <allenom@domain.elided>]

I have a few related questions:

I have read some posts which discuss boiling the gear oil in their
transaxle. How hot does the fluid have to get for this to happen?  Has
anyone here ever fit their transaxle with a temperature sensor?  What is
an acceptable temperature range for gear oil?

Thanks,

Al "Callaway Tea Tray" Mitchell

>From: "John Fielding" >Reply-To: "John Fielding" >To: "Alfa-Digest"
>Subject: RE: How hot is too hot for oil? >Date: Wed, 19 Jun 2002
17:49:50 +0200 > >In AD V8 #835 Robert Watson queried the safe oil
temperature of his GTV. Well funny >thing is that only the other day I
came across an old technical publication I purchased >when I was in the
UK. It deals with the development of the Jaguar V12 motor designed for
>Le Mans and later detuned for the UK car market. The XJ13 mid engined
prototype is a >beautiful car, shown on the front cover. > >One of the
very interesting parts deals with the oil temperature and the design of
the oil >pump and oil cooler. The first couple of motors used a large oil
cooler incorporated into >the water radiator and the oil temperature ran
around 90C. Later this was changed to >increase the oil temperature! The
explanation is that at the higher oil temperature the >oil system
actually works better! > >The graphs published show oil flow and pressure
at the two different temperatures, at the >higher temperature the oil
flow and pressure increased by as much as 25%. And before >anyone says
they were using an exotic oil, nope the test were done with SAE 20W50
grade. > >In my reply to Robert I pointed out that too low an oil
temperature is wrong, the oil >needs to exceed 100C to boil off the water
content which gets absorbed from various >sources. It is also a well
known fact that too many modern motors are overcooled. For >efficient
running the motor needs to run at above 100C, hence the use of
pressurised >cooling systems and anti-freeze solution to raise the
operating temperature. Somewhere >amongst my thousands of technical
articles I have a paper on the optimum engine >temperatures for various
fuels, perhaps Eric Storhok has an up to date version he can give
>details from? Also modern oils can tolerate much higher temps than older
oils, a figure of >200C seems to be about the safe maximum today from the
manufacturers literature. > >Another interesting fact in the paper is the
discussion on cylinder head shape. As the >development of the racing
motor was cancelled late in its development the Jaguar company >decided
to convert the motor for road use. To quote from the paper- >
>"Investigations indicated little advantage with any particular
combustion chambers shape >except that simple shapes devoid of traps for
unburned hydrocarbons appeared best and NOx >production proved
considerably less with the flat type chamber than one of hemispherical
>type. Tests on variations in bore/stroke ratio also appeared to
influence the results far >less than was originally expected, except that
the long stroke/small bore favoured low NOx >emission." > >Thought you
would all like to know! > >John >Durban >South Africa >Alfetta 1.8L turbo
- which runs 140C oil temp at full load on the track, with a cooler. >--
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