Mixing Oils

[BEXIL160]

Question from a friend:

Are there any reasons why (aeroshell) 15W50 Semi synthetic oil should NOT be used to top up an engine (Continenal C90) running on "straight" mineral 100 oil?

Mate says this is okay because teh aeroshell is "semi" synthetic. I'm not convinced.

Don't know the answer myself as I've always stuck to W80/100.

Over to you, clever people.

Rgds BEX

[Davidt]

My engineer told me not to mix straight oil with multi grade, but it was pefectly ok to mix different weights of straight.

He didnt say why.

If I mix w80 with w100 do I end up with w90 or multigrade 80/100 ;)

[shortstripper]

The short answer is he's right, but the long answer is DON'T!

Theoretically you can top up mineral oil with synthetic, but there are problems associated with doing so. It's far better to stick to one oil type. If you decide to change, do it at an oil change and stick to the new oil from then on. Basically, mineral oils will soak into old gaskets and also sludge deposits may build up here and there. When you add a new sythetic oil it may act like a detergent and dislodge all the crap that's built up, and that's not a good thing! ... well at least it isn't when you don't want it too.

I'm not a great fan of straight 80 or 100 (for reasons you will know ;) ) and prefer multigrades. I've not had much experience with synthetic oils, as I've always found mineral oils to do the job very well! :) However, I expect they do the job just as well if not better ... but I certainly would not mix them.

SS

[helicopter-redeye]

Different oils for different phases of the engines life. Straight 100 when its new and running in. Moving to AD80 at 100+ hours and the parts are bedded in. Other types for other phases and engine types.

You can mix the oils but its a kinda emergency thing (do it more in the bush than anywhere else) but then change the oil when back in civilization.

h-r:)

[ShyTorque]

"In the bush?"

Near Sheffield? Is that the Manor estate, H-R? :p

[helicopter-redeye]

I wuz referring to my flying adventures in Australia, you cad!

(anyway on the 'Man Orr' they'd steal your skids before you had time to get the chip fat in the sump)

h-r:(

[ShyTorque]

Yes, when delivering goods by road up there you need two folks - one to take them to the house and one to guard the van! :p

[411A]

Ram Aircraft in Waco Texas, which builds mighty fine engines has particular thoughts on aircraft oil, and its use...

http://www.ramaircraft.com/Maintenance-Tips/Oil-Recommendations.htm

[BEXIL160]

Thanks to all who replied...

I will copy this off to the gent concerned

VBest rgds BEX