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Oil temps & oil viscosity

 
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TxAgfisher
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Joined: 23 Sep 2015
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Location: Colorado

PostPosted: Mon Jul 09, 2018 2:57 pm    Post subject: Oil temps & oil viscosity Reply with quote

I can't remember which way is which...

Does the multi-vis run cooler or the straight 100?

Coming into Denver with XC 20w50 oil temps were high. Seem to recall switching to w100 in my last Maule for the hot months.

Am I right or do I have it backwards?
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TJ Van Matre
1965 M4-210
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Joined: 12 Feb 2014
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Location: Wisconsin

PostPosted: Tue Jul 10, 2018 6:48 am    Post subject: Reply with quote

By straight 100 I assume you are referring to Aeroshell W100 or Phillips 66 100AD These are both SAE 50 weight oil. At higher operating temperatures this is no different from your multi-viscosity 20-50. The 20-50 will flow easier at lower temps and thus provide better lubrication at the lower temps and engine start up in a cooler environment.

So it depends on overall conditions in the environment in which you operate in the summer.

Personally as I live north and even in the summer early AM temps could be in the 50's but may rise to 100 I use multiviscosity.
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andy
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Location: Lake James, NC, USA

PostPosted: Wed Jul 11, 2018 2:02 am    Post subject: Reply with quote

My experience using Aeroshell W100+ and 15W-50 is that the multi-grade oil is thinner so it will flow easier at low temps. Aeroshell says that they both provide the same amount of lubrication once warm and I have no reason to doubt them. I found that oil temp ran higher on my O-360-C1F with the 15W-50. It's usually between 180F and 210F with W100+ in the summer but it would get to 225F with the 15W-50. In the winter the 15W-50 is a better choice since it provides easier cold starts and warmer oil temps in flight. Aeroshell says that all of their oils mix without a problem so when the temperature gets below 50F, I add W80+ rather than W100+ to thin the oil out a bit for cold starts. This arrangement has worked well for me for about 15 years. The reason that I stopped using 15W-50 was because my mechanics said that in their opinion the thinner multi-grade oil is more prone to leak through engine seals as they get older.
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Andy
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LCDRLES



Joined: 13 Mar 2016
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PostPosted: Wed Jul 11, 2018 2:12 am    Post subject: Reply with quote

Absolutely agree with Andy. In my experience in hot West Texas temps, the single weight oils seem to run cooler in our high temps. AeroShell W100 Plus runs the coolest for me in my O-360
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Mark - AK



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PostPosted: Wed Jul 11, 2018 4:24 am    Post subject: Reply with quote

It seems to me that if the oil temp is higher it means that it is more efficiently removing more wasted heat from the engine, and that is what you want as long as the oil is not thinning so much that lubrication is compromised.
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andy
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PostPosted: Wed Jul 11, 2018 6:03 am    Post subject: Reply with quote

When it gets really hot here in the lower 48 the CHTs can easily get up to red line, especially when climbing with reduced airflow over the cylinders due to Maule's close cowling. High oil temp isn't necessarily a good indication of the oil removing heat efficiently from the engine. It could mean that one or more cylinders are running too hot. Here's an article that I found online that provides some insight: https://generalaviationnews.com/2004/12/10/the-heat-is-on-our-experts-agree-on-the-best-oil-temperature/
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Andy
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Mark - AK



Joined: 24 Dec 2007
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Location: Alaska

PostPosted: Wed Jul 11, 2018 6:40 am    Post subject: Reply with quote

That's a good article but I don't see how it relates to my question. If I were to ask the question a different way it would be, "What is the relationship between viscosity and heat removal from an engine? Is there an optimum viscosity for an air cooled aircraft engine"? Flying here in Alaska my problem is usually getting the oil hot enough and the article you linked for me certainly does apply to my flying in the cold country... Thanks for the link.
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TxAgfisher
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PostPosted: Fri Jul 13, 2018 9:00 am    Post subject: Reply with quote

Thanks, that is what I seemed to remember. I haven't seen much oil burn up until now, but my trip to Denver I burned a couple quarts. My thoughts are the 100 degree and high alt ops let temps get up and the higher temps thinned the oil to the point where it could potentially get some blow by.

Going to switch to w100.
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TJ Van Matre
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TomD
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PostPosted: Fri Jul 13, 2018 10:40 am    Post subject: Reply with quote

TJ said: [/quote]What is the relationship between viscosity and heat removal from an engine?
Quote:


Short answer I don't see why there would be any relationship.

Since your concern seems to be the removal of heat from the engine, all oils once the engine is at operating temperature are pretty "thin" and flow through the engine about the same. Multi-grade 20/50 might flow a bit faster than straight 100 at operating temp but I would be surprised if the difference was significant when talking about heat "removal"

Cylinders are air cooled and provide heat removal through convection (movement of air) . I believe the oil is primarily cooled in the oil cooler.

Back to basic physics the higher the difference between the OAT and the temp of the hot object ( cylinder or oil) the faster the heat will transfer to the lower temperature. Surface area is also part of the formula. More surface area exposed to OAT the more heat is transferred to the lower temp. object or area.

Given the flow rate of the oil through the oil cooler is pretty constant at a given RPM, I would expect the heat removal to be dependent on surface area, delta between OAT, and flow rate. Since flow rates of a multi-grade vs a straight 100W at operating temp is probably very close to equal, the cooling should be the same.

Bottom line, a larger more efficient oil cooler will keep engine cooler than a different weight oil. Which is why our Alaska guys then to restrict air flow through the cooler in the winter.

Far more than I meant to write.

TD
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