Hello folks,

Can any one give me recommendation on the proper oil viscosity and reasons why. I own a "93" 940 Turbo w/ 103k and live in the northeast where it gets quite cold 2-3 months out of the year. Currently use castrol 10w-30 during winter and 10-40 during summer. I know, everyone says use synthetic but I tried mobil 1 last winter and it leaked out the seals like crazy. My volvo mechanic says you have to replace main seal ect. I then drained the mobil one and added the usual Castrol 10-30 (no more leaks) to date. I change oil & filter every 3000K

Any responses well recieved!

I understand that Volvo doesn't recommend 10-40 multi-viscosity oil is because this oil requires excessive amounts of viscosity improvers to move the base 10W oil up to a 40W rating. If you change oil every 3000 miles, why not use a single weight oil (30W) during the summer? I've also used 20-50 weight as a summer oil in my 240 turbo.

I am now using Mobil 1, 10-30 grade based on several recommendations that came from here. I would like to add that I was leaking oil, a little more than a third of a quart in my first seven hundred miles, on my 91 turbo 940 wagon. The oil leak was not new, a careful inspection showed I (and the previous owner) had been leaking for some time. I checked all the breather hoses, flame trap, and the breather box. The hoses were shot, the flame trap plugged. I cleaned everything out, replacing hoses and flame trap. My leak has now disappeared. You might want to consider that the only type of oil used in jet engines is synthetic. Your turbo does get hot.

Volvo recomendss 5-30. 10-30 is also acceptable. They do not recomend 10-40.

I live in New Jersey and have both an 88 740 Turbo Wagon and 91 Bertone Coupe (turbo). The previous owners of both cars recommended 10W-30 year round.

The main concern is to make sure your dyno-oil says "TURBO APPROVED". Non turbo approved oils can't take the heat within the turbo.

I switched to Mobil-1 for the Coupe, since the mileage is only 65,000.

Be sure to let the car idle for a short time before turning off the engine

(cool off time). Also, when you 1st start the car - allow a 20 second idle period before taking off. This will allow oil from the pan to get up to the turbo.

Ed