Jujupilote wrote:
Several tables from the oils and engine manufacturers recommend different oils according to OAT,
Lycoming has published a table which Peter posted on a first post of this thread. It’s quite detailed.
Continental however recommends SAE30 below 40F and SAE50 above 40F. That’s all.
SAE 30 used to be W60 or W65? (not available any more in EU I think)
SAE 50 is W100.
I wander why they don’t recommend W80 (SAE40) which is somewhere between and looking at it’s parameters it should be perfectly fine if not too hot.
Several tables from the oils and engine manufacturers recommend different oils according to OAT, but you are right, in flight they reach the same temps.
That’s a mystery 
For reference, Total XPD 80/100 oils “already contain an anti-wear additive similar to TEXTRON Lycoming LW 16702.”
So definitely comparable to W80/100+
I will use W80 in colder periods and W100 in warmer.
I don’t see any basis for that, if the engine has thermostatically controlled oil temperature.
Peter wrote:
Turbocharged engines nearly always don’t make TBO because of cylinder cracks
I want to exceed TBO 
But seriously I think I will use W80 in colder periods and W100 in warmer.
Maybe mixing both when topping up quart or two.
No 15w50 for me any more!
Peter wrote:
There is no evidence I have ever seen that whether an engine makes TBO or not is in any way related to how much the parts are wearing.
Engines don’t tend to make TBO because they have inherent weakneses which the manufactorer doesn’t do anything about.
Camshaft’s failure on O-235’s is well known. Yet nothing is done. Same with the centre main bearing on O-200’s.
In fact I’m surprised Lycoming came out with roller tappets for their larger bore engines.
There is no evidence I have ever seen that whether an engine makes TBO or not is in any way related to how much the parts are wearing.
That’s assuming it was originally built to new limits.
Engines tend to not make TBO because of corrosion, triggering camshaft / tappet surface breakup, and stuff like that, which generates metal in the filter. Turbocharged engines nearly always don’t make TBO because of cylinder cracks.
Raven wrote:
I would be then happy to use a W80 all year (as W100 you should preheat when below plus 16degC), but then my question is:
viscosity of W80 is only 14mm2/s at 100degC – isn’t it too low for summertime flying?
My club is using W80+ exclusively all year round (or equivalent grade from other manufacturers such as TOTAL XPD80). We have had no engine problems at all (at least not that could be traced to the oil) even though we occasionally have OAT of +30°C or more in summer. In winter we use oil sump heaters on all aircraft. (We’re operating in Sweden, at 60°N.)
It would be great to be absolutely sure about it and to have some data from engine manufacturer.
As you say there are also other factors to that.
I have TSIO-360 which is a bit more “stressed” as it is turbocharged, so the pressures on bearings are probably higher than on N/A engines, so maybe my oil should be a bit more viscous to protect.
I am thinking in a long term horizon as I am going to use those engines “on condition”, not to overhaul them immediately after TBO.
isn’t it too low for summertime flying?
I am sure it is absolutely fine. There is plenty of margin there to keep the bearing surfaces apart – so long as your oil pump is working.
Also the above numbers don’t take into account viscosity degradation over the service interval. How bad does it get after say 40hrs? I posted some fairly consistent data here which suggests there are factors in play which are much bigger than 14 v 18.
As I can see the parameters of those oils are the following (speaking about viscosity):
W100:
at 100degC – 18mm2/s
at 40degC – 204mm2/s
W80:
at 100degC – 14,5mm2/s
at 40degC – 139mm2/s
15W50:
at 100degC – 18,2mm2/s
at 40degC – 137mm2/s
It looks like the perfect oil would be 15w50 but it’s not due to reasons described by some experienced maintenance organisations (lower capabilities to absorb lead contents than straight W oils).
I would be then happy to use a W80 all year (as W100 you should preheat when below plus 16degC), but then my question is:
viscosity of W80 is only 14mm2/s at 100degC – isn’t it too low for summertime flying? W100 and 15W50 have 18mm2/s
Are there any official “minimums” of viscosities at working temps? What happens to the engine which is run for 2000hours on about 28% less viscous oil?
I currently use W100 during summer and 15W50 during winter but I am not happy with the multigrade as it leaves a “coffee like” film (water with oil) on the filler cup – engine not warm enough.
On W100 or W80 there was no “coffee” – just clean water droplets from condensation.
What are your opinions?
