Mixing Different Oils

[FrankieG]

I have heard a rumor that it is not advisable to add for example 20W-50 oil to a car with 10W-30 already in it. Anybody ever hear this? I am also a new Porsche 911 (1982 SC Targa) owner, and was wondering what oil most of you use. I've been told either 10W-30 or 20W-50 is the best.

[Rot 911]

20W50

[FrankieG]

Thanks Kurt..so there is no problem adding it to a car that already has 10W-30 in it?

[Rot 911]

Doesn't hurt anything, but the viscosity will not be 20W50. It will be a lighter weight.

[FrankieG]

Thanks Kurt...appreciate it

[91C2wrencher]

FrankieG, Kurts probably right. Some considerations should go into the proper oil selection. Some rules of thumb, multi-viscousity oils should have the weight and viscousity numbers with in 25 or 30, ie: 10w-40, or 20w-50, or for cooler weather and light driving 10w-30 (only 20 apart even better). Oils like these tend to maintain their lube qualities for longer periods. With that said I use 15w-50 Mobil1 why? I like it and keeps the inards of my motor clean. to each there own. Oh, and there's nothing wrong with adding different make/grade oils when topping off.

[FrankieG]

Appreciate the help. As is the case with Porsche's, there are a million rumors and facts flying around out there and new owners like myself have a hard time making head or tails of them. I actually heard not to mix regular with synthetic, but I see that is false now. A number of friends have told me NOT to use 10W-40, and they all have a valid reason...not sure if they're right. I have always topped off my other cars with whatever I had nearby, but I am very careful with this baby. It's great to know that there are so many people out there that can help. Thanks!

[Rot 911]

Frankie if the car is new to you the first thing I would do (unless it was done at the time of purchase) is change the oil, oil filter, air filter and spark plugs so you at least have a baseline to go from.

[FrankieG]

Did all of that...had the car completely checked over, new brake pads, lines, rotors and calipers rebuilt (see my post about painting them), all fluids replaced, new tires...cost 3 G's but it was worth it..I love the car.

[steve911]

I actually heard not to mix regular with synthetic, but I see that is false now.

I don't think you want to mix dino oil and synthetic, unless its an emergency.

[Bill Douglas]

When you do an oil change you can't help mixing oils, as a quarter of the old oil is in the oil lines and the cooler, and doesn't get changed.

[Superman]

Mixing oils would create a HUGE problem. If you add a quart of 20w50 to a tank that already has 10w40, then your engine will seize up, the brake calipers will explode and the earth will break away from its orbit and spin out of the solar system. Gives me chills just thinking about it.

Seriously, if my tank needs a quart, and there is a quart nearby, I'll use it. Only one exception: The filter is between the scavenge pump and the tank, which means that tank oil is not filtered before it enters the engine, which means I use...yes, you guessed it, CLEAN oil.

[Noel]

I actually checked with Mobil about this. My A4 recommends 15w40 witch is hard to find here. They confirmed for me that if I mix 2 quarts of 10/30 and 2 quarts of 15/50, I would get 4 quarts of 12.5w40.

Noel