Originally Posted By: ron in sc
I've found that what the manuf. says is the oil volume for oil and filter change has always been to high. Am I correct? It seems the amount they give for oil and fiter change is really for a dry fill on a new engine. The manuf specs. also do not seem to take thermal expansion into consideration either.
I notice something similar too, add 4.5qt oil and it's usually too much according to the dip stick. Now I have several explanations:
1) I didn't drain it correctly (not waiting enough, ground is not completely even...)
2) The dipstick is incorrect (notice my dipstick's curvature is different from the new one after years of use)
The last thing I would think is manufacturer get it wrong, this is why:
1) they usually ask owner to add oil to the point that between the low and high on even surface, as long as it's a range, it should be fine, honestly 1 qt up or down should be fine for most engine. Just like mentioned by other post, some manual state dry vs oil change amount.
2) Thermal expansion: good god... don't know where to start, If you look up the thermal expansion of oil and iron/ aluminum, and factor in the volume involved, you would have seen that the difference is small. I did it assuming it's a regular shape, and obviously the engine is not, but we can do an estimation, the math is hard to type here.
Of course we don't know what exactly is the alloy used to build the engine, again we can estimate a range of expansion coefficient base on data published. It's not that they cannot give you advice on how much to put into the engine at different temperature, but this is too much information for regular ppl and difference doesn't change the longevity of the car what so ever.
example: they can tell you the volume of crankcase is expanded by X % every Y%, but since your oil is at room temperature when you pour it in, you have to factor that in also.