I am in England and it gets pretty cold out here. Would it be ok to use 10W-40? I dont wanna use synthetic because I heard it's bad for our cars. The type of oil is Castrol for higher mileage cars. The car has 100k on it. Any help and advice would be greatly appreciated. Thanks in advance.
I use 10W-30, but then again, I drive my car once a month and never worry about the cold because my car is kept in a heated garage. 10w-40 sounds good. Some people are going to argue that synthetic is the only way to go. I don't buy it. Unless your revving the motor to the moon, or working the motor in tough conditions (like towing), I wouldn't buy it. It's not that it is bad, it is just completely unnecessary in most cases. Some synthetics are really sick, and can get by the rings on an higher mileage motor much easier than a regular oil could. When it comes down to it, oil is oil. The grade and type of oil you've selected sounds good.
Also another problem with switching to synthetics on a higher milage car is the synthetics can get by your old seals/gaskets and start a leak.
And I agree that 10-30 would be good just don't get anything higher than 10 for the first number usually the colder it gets the lower first number you want. It just help get the oil to the top of the engine faster.
The W stands for Winter, so the first number is what you go by for cold temp weight. A 10 should do fine, unless you plan on subzero conditions. Another thing to think about is the range of your oil; greater range means more additives, which can lead to breakdown and/or engine failure. You want the shortest range necessary for your climate. As for synthetics, what has been said is true, however, most of the time there is much to benefit from synthetics compared to the perceived risk in leaking past a seal or ring. I'll bet if your engine is in good condition, you would gain hp switching to synthetic. I've seen dyno sheets to prove it. Try Mobil 1 or Royal Purple.