I think i'll stick to what is listed in the owners manual

 

UF, the first number is it's cold start viscosity, so probably best ignored for operating viscosity.

 

Probably best, for anyone who is unsure about oil grades.

 

The times i've switched to 0 40 in previous cars, they've all used more of it. Only car that needed it was the Leon Tdi due to the PD system - it destroys itself unless you use the correct VW 501 stuff.

 

Probably because it's relatave viscosity at cold means it will easily pass the rings, and get burned... ie it's the wrong grade for the ambient.

 

Cheers!

Off to Asda tomorrow then...£30 for 4 ltrs of Castrol Edge TD 5w40 atm!

 

I downloaded the Honda manual and it says 10w40, my car also ran quiet from when it was last serviced by Honda until I put the 5w40 in :s

 

You will need about 5 litres for a *full* change!

 

10Ws are usually thicker at operating temperatures than 5Ws so it makes sense.

Bas oil viscosity (BOV) is whats key here and whilst the xW indicates the cold flow it also gives an idea of the BOV. The amount of polymer determines the Kv100 of the oil and hence its higher grade, however this is measured by seeing how long the oil takes to flow down a tube under gravity, nothing like the conditions in an engine. Often the VM is temporarily sheared down too (depends upon the type of VM used).

Base oil doesnt shear down and you can have oils varying from a 4.5 to a 6 cSt BOV that all 'look' the same. So you can see there is more to it than just reading the xW number.

In something like a TCT i think BOV is more important than either the xW number or the Kv100 and is why I wouldn't use a 0W in an S2000 engine.

 

Not a well advertised number though eh, Si