Mixed oil weights?

[skidoo]

What is the most serious consequences of adding a quart of SAE 50W to 7 quarts of existing 15-50W? Sump is 9 quarts max.

 

[Trapper John]

I wouldn't worry about it at all. But, what do I know...this guy does, though:

ALL AVIATION OILS ARE COMPATIBLE
For Walt Silveira, Phillips 66 Aviation Oil Product Technical Manager, the answer is simple, “Stick with a brand you when you can, but use any approved aviation piston engine oil brand for emergency top-offs. Topping off your oil level is much better than flying low on oil, even if it is not your brand or the right viscosity.”

Silveira says the proof is printed on the container’s label. All aviation OEMs (Original Equipment Manufacturers) — including Lycoming, Continental, and Pratt & Whitney — use the same SAE (Society of Automotive Engineers) tests and specifications to assure that approved oils meet the stringent standards to protect their aviation engines.

“All aviation piston engine oils are compatible,” Silveira said. “Whether mineral-based, synthetic blend, straight grade or multigrade, all aviation oils are compatible and can be mixed without harm to the engine.”

“I’m not recommending that owner/operators make their own oil by mixing a quart of one type of oil with a quart of another type oil during oil changes, but rather when a situation arises where you are down on oil, the decision to add a different brand or grade is a good one since this will not cause any engine problems.” Silveira said.

http://www.swaviator.com/html/issueJA03/Hangar7803.html

 

[poadeleted20]

What is the most serious consequences of adding a quart of SAE 50W to 7 quarts of existing 15-50W?

The most serious consequence is not knowing just what effective weight the oil has now. But unless it's pretty cold out, adding SAE50 to 15-50 multigrade shouldn't cause any problems.

 

[dmccormack]

The most serious consequence is not knowing just what effective weight the oil has now. But unless it's pretty cold out, adding SAE50 to 15-50 multigrade shouldn't cause any problems.

If sump is 9 quarts max, likely 1/2 qt is overfill.

So 7 qts plus 1.5 quarts.

I'm thinking it's SAE 50.

 

[skidoo]

Thanks.

With my recent aircraft purchase, there were two quarts of sae 50 and one quart of 15-50 in the back. The level got down to 7 quarts, so I decided to add a quart. I thought that perhaps it already had 50W since it came from a warmer climate. It was getting warmer here, and I figured to get it changed soon anyway. So, that is what I added. Later, I looked at the logs and found that it last was changed with the 15-50.

Sounds like it will be fine until the next oil change. Thanks again!

 

[skidoo]

If sump is 9 quarts max, likely 1/2 qt is overfill.

So 7 qts plus 1.5 quarts.

I'm thinking it's SAE 50.

Actually, the POH says to fill it to 8 quarts for normal flights up to 3 hours and to 9 quarts for extended flights beyond that.

 

[dmccormack]

Actually, the POH says to fill it to 8 quarts for normal flights up to 3 hours and to 9 quarts for extended flights beyond that.

Unless you have an air-oil separator, that quart over 8 is going out the vent.

 

[skidoo]

Unless you have an air-oil separator, that quart over 8 is going out the vent.

Well, it does say "to reduce oil consumption" fill it to only 8 quarts for normal flights up to 3 hours... Good point.

 

[dmccormack]

Well, it does say "to reduce oil consumption" fill it to only 8 quarts for normal flights up to 3 hours... Good point.

Honestly, I never fill to max on any airplane anymore. It requires cleanup and rarely does much oil get burned or lost below 7 or 8 (depending on the engine).

Even in the Chief I keep it at 3.5 quarts. Any more and it simply coats the belly.

 

[Tom-D]

Honestly, I never fill to max on any airplane anymore. It requires cleanup and rarely does much oil get burned or lost below 7 or 8 (depending on the engine).

Even in the Chief I keep it at 3.5 quarts. Any more and it simply coats the belly.

Funny my aircraft will run 35 hours at the full mark, and never throw a drop over the side.

my dip stick is marked 1/4 - 1/2 - 3/4 - full, its a 3 gallon tank.

it doesn't have any oil air separator or recovery system and I get about 3-4 drops of oil on the floor under the vent tube, over night after a 3 hour hop.

 

[Tom-D]

The most serious consequence is not knowing just what effective weight the oil has now. .

as long as the oil pressure gauge is in the green, why would any one care?

 

[dmccormack]

Funny my aircraft will run 35 hours at the full mark, and never throw a drop over the side.

my dip stick is marked 1/4 - 1/2 - 3/4 - full, its a 3 gallon tank.

it doesn't have any oil air separator or recovery system and I get about 3-4 drops of oil on the floor under the vent tube, over night after a 3 hour hop.

My engine (1940 O-145-B2) is supposed to consume some oil -- no use indicates a problem.

 

[timwinters]

no use indicates a problem.

There are a lot of people who believe this to be true of almost all piston airplane engines but I've known quite a few that have gone to TBO (and beyond) and not used a drop until very late in their life, if at all.

 

[dmccormack]

There are a lot of people who believe this to be true of almost all piston airplane engines but I've known quite a few that have gone to TBO (and beyond) and not used a drop until very late in their life, if at all.

Well, the Lycoming manual gives an expected oil consumption rate.