Any suggestions as to what oil is best for my '86 240? With winter coming, should I use 10w30, or 5W30? Synthetic or conventional?

Also, I am about to flush my auto trans. Should the trans be hot when this is done, or does it not matter?

Any thoughts?

THANKS!!!

Transmission fluid change? It’s very easy. Go buy about four feet of ½ inch inside-diameter clear plastic hose and a hose clamp the right size for it. This will go over the fitting on the radiator. Also, buy a funnel for filling automatic transmissions, and a case of the correct ATF.

This method has worked for me. I'm sure there are other ways of doing it too. With the engine off, loosen and remove the top fitting on the passenger side of the radiator. Use a wrench to keep the fitting from turning in the radiator. Use a rag to catch any fluid that might come out. It won’t be much. Put the clear plastic hose on the fitting and snug it down with the clamp. Run the hose over the fender into a container with measured marks on it. Start the car and run it in park until two quarts are in the container. (The fluid comes out at a comfortable rate. No rushing around.) Shut off the engine and pour two new quarts into the tranny through the dipstick. You’ll need the special funnel for this. Run the engine again and pump out two more quarts, add two more, etc., until the fluid runs out clean. I think it takes about 10 quarts for the job, if I remember correctly, maybe even 11 or 12. When you’re convinced the fluid is coming out really clean, remove the clear plastic hose and put the original fitting back on the radiator and snug it down, holding the male piece so it won’t spin in the radiator. There is no o-ring. Run the car and check the connection for leaks. Remember, if in doubt, add a little less fluid rather than too much. It’s a lot easier to add a little bit later than to drain fluid from an overfilled transmission. Check the fluid level before you start the job. If it’s right, and you cycle the exact same amount, you should be OK. From my experience, though, it’s better to add a half quart less, then check with the dipstick, and top it off to get it just right.

You’ll find the job is easy and clean if you are careful. You’ll be satisfied that the job was done correctly. It’ll be cheaper than Jiffy Lube and much less dangerous for your car.

Good luck.
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Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 133k

As with many things the answer is: "It depends". If the car will be operated in sub-zero temps at times and the highest temp expected will be no more than about 60F, I'd suggest 5W30...and I'd stick to Castrol or Pennzoil - just my personal preference. Then there are the synthetics.

I did a little homebrewed experiment a few years ago by putting small containers of Castrol 5W30, 10W30, and Mobil-1 synthetic 10W30 in the deepfreezer (5 degreesF) overnight, then watching as I poured them out. From that unscientific test I observed that the Mobil-1 flowed best, the Castrol 5W30 was notably thicker and the 10W30 more so. This is a well known property of the synthetics, so no surprise. They are much better in cold starting conditions.

Synthetic is 4-to-5 times the cost of petroleum-base oils so you need to be convinced of a definite advantage to justify them. We have a number of vehicles in the family, and I don't want to spend a lot of weekends under them and hauling used oil to the recycle depot. I use Mobil-1 10W30 and stretch the change interval to about 10,000mi. (The cars see mostly highway use in mild-to-hot weather in California.) Now that Mobil-1 is available here in the "Euro" SAE 0W40 rating, I'm changing all cars (and motorcycle) to it as their oil changes come up.

In my opinion, it's bad practice to mix types or even brands of motor oils. They each have an additive package which is designed to work with their own base stock to deliver good lubricating performance. You are trying to outguess the refining engineers when you mix them. Probably no harm done, but it's not optimal.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD)

My preference is to use regular Mobil 10W-40 oil in my '86 245 (285k miles) and change it around 4000 miles.

I like to run the engine hard and hot and then immediately dump the oil. And I let it drain for about an hour before installing the plug and refilling with fresh oil.

One thought on the tranny flush..... Add about 6-10 ounces of lacquer thinner to the existing ATF and drive it a few hundred miles. Then dump the fluid.

The lacquer thinner dissolves the varnish that tends to gum up the valve body. The lacquer thinner and dissolved varnish will go out with the old fluid.
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Don Foster (near Cape Cod, MA)

I think 10w-30 is best. Also I like to use 1 qt mobil 1 synthetic to 3 quarts castrol. Hot or cold on tranny shouldn't matter much as you won't be able to drain completely. Usually drain from plug(around 3or4 quarts)then reinstall plug and refill. Then disconnect tranny cooling line from radiator start car and run until new fluid appears. Reinstall line and refill. This way you can replace twice as much fluid with new fluid.