Menu Sign In Contact FAQ
Banner
Welcome to our forums

Is there any point in multigrade oil IF the engine starts ok?

Peter wrote:

The reason for my original post was to ask whether there is anything wrong with using W80 provided the engine starts up ok.

Not sure I understand the original question then. What does OK mean? With a good battery Ive started engines in the -5c range. But that was before the club mechanic grabbed my instructor and chewed him out. I learned to preheat since then. Never start an engine when the overnight temps were below 0c.

KHTO, LHTL

So is there any point in using 15W50 at all? It will be very runny at cruise engine temperature.

Eh? It should have the same viscosity as W100 (SAE 50) at 100 Celsius.
Aero D100
Aero DM 15W-50

On the other hand, this chart suggests that the low-temperature “advantage” of 15W-40 over SAE 40 is about 6 or 7 Celsius.

Of course, oil viscosity is but one of many factors affecting engine wear.

If we use an airplane for short journeys instead of a car and take off more or less straight from the hangar, a multigrade oil means less time and fuel wasted on the ground. If we mostly fly for 30 minutes or more and have to taxi and wait to enter a runway, the case for multigrade seems less compelling.

Last Edited by Jacko at 14 Jan 23:02
Glenswinton, SW Scotland, United Kingdom

do I interpret this right? Looking at typical winter temperature range of 0-5C, there is however a quite clear advantage in using something like a Phillips X/C 20W50 instead of AS W80.

Switzerland

I’ve merged in some older posts on the same topic. This one is pretty interesting. Also reading this long one the reason for avoiding AS 15W50 is that there seems to be good evidence that it is responsible for sticking valves. Hence my Q about whether a single grade oil is ok to use, and the aforementioned linked posts clearly suggests the answer is Yes.

Looking at the graph posted above by Jacko, W80 would be off the scale, never mind W100, so maybe all the oils end up really really runny at the engine operating temperature.

Administrator
Shoreham EGKA, United Kingdom

C210_Flyer wrote:

Never start an engine when the overnight temps were below 0c.

FWIW: From my POH (Teledine Continental TSIO-550-C)

COLD TEMPERATURE
The use of preheater is required when the engine has been cold soaked at temperatures of -7C or below for more than two hours. After starting the engine set the idle to 1000RPM or less until an increase in oil temperature is noted. As much 30 seconds may elapse before oil pressure is indicated.

CAUTION
IF PRESSURE IS NOT INDICATED WITHIN 1 MINUTE SHUTDOWN ENGINE. IF NECESSARY, REDUCE POWER BELOW 1000 RPM TO MAINTAIN OIL PRESSURE BELOW 100 PSI

Charlie_Alpha
EHBD, Netherlands

@Peter,

Remember that “W80” for aircraft is actually SAE 40 grade/viscosity and “W100” is SAE 50.

Not sure why single grade aeroplane oils use that confusing nomenclature; perhaps there’s an interesting bit of history there…

Lastly, just to confuse further, single grade oils of the same grade do not all have the same viscosity index. So a cheap SAE 40 and expensive (highly refined) SAE 40 have the same viscosity at 100 Celsius but the viscosity of the expensive one may vary less with temperature.

Glenswinton, SW Scotland, United Kingdom

I plan to gradually move over to W80 and Camguard, for the whole year.

That sticky valve I got a few months ago was a huge hassle.

Administrator
Shoreham EGKA, United Kingdom

But how do you know that was due to the 15W-50.

I know people who are thinking of going the other wat due to sticking valves?

Peter, W80 is OK in the UK most of the time but as soon as you go south in the summer it is likely to fall outside its operating range and W100 would be required.

I very much doubt that the sticky valve you had was as a result of the oil, all the Lycoming engines I look after are running Shell multi grade without any evidence of valve problems.

As for those who are worried about the cold starting with straight oil putting extra load on the starter this is most likely down to a weak spark from the slow turning magnetos the result being an engine that is slow to start. Rather than change the oil type fitting a slickstart to boost the power of the magneto spark during start is most likely to be more beneficial .

Electronic ignition, discussed in other threads, if available for a given reg / airframe / engine, should also help with spark quality / power.

tmo
EPKP - Kraków, Poland
Sign in to add your message

Back to Top