Hi,
I've decided to change me engine oil in the Megane (1999, 16V, 1.4L). I bought the new oil and have now emptied the old oil. Opened the new oil and it looked different.
Oops. Have bought two bottles of Castrol GTX Magnatec 10W-40 where the Haynes Manual says use 15W-40. I get the impression from my Googling that it will be ok to use. Especially since winter is approaching. So what do you guys think? Should I fill her up with the lighter grade or is that a bad idea?
Cheers,
Rob
Don't worry about it, 10-40 will be fine. The 10-40 is the slightly lighter oil by the way. The higher number means thicker oil. You will find that you can normally operate across a range of viscosities anyway, anything from a 5w-30 to a 15w-40 will do OK.
If you're at all uneasy about using the thinner oil and you bought it locally from a reputable supplier I'd expect there'd be no difficulty in getting the unopened bottle exchanged for 15W-40, particularly if you were to buy a further bottle of 15W-40 at the same time. You might then use the 10W-40 for topping-up over a protacted period of time.
The only difference between a 10W-40 and a 15W-40 is when the engine is cold, the oils will have the same viscosity at operating temperature. A lower xxW number is better for cold starting. That said, the lower xxW oil will have more additives to achieve the multigrade effect.
In some warm countries or when the engine is running all day, this may seem unnecessary, and the oil with less additives might possibly last longer.
Thanks to everyone for knowledgeable answers. You backed up what I thought initially: that the 10W-40 would be fine. I have therefore decided to go ahead use this oil.
Cheers, Rob
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