What engine oil?

[thunderace]

Nope, car stuff has nasty additives in it that can wreck a bike engine.

To educate myself here...what are these additives and what will they do?
I ask because all my previous bikes have used Castrol GTX with no apparent ill effects even at high mileages although granted this is my first Honda...

Mainly friction modifiers following the removal of all that nice lubey stuff from our fuel.

Wiki

[Bike_Nut]

Bike engines mostly have wet multiplate clutches (run in the oil), and share engine and gearbox oil. The friction modifiers in car oils such as moly can contaminate the clutch plates and lead to clutch slipping.

[harvey_s]

Interesting stuff - some reading since has revealed a CBR900RR with 200,000 miles on it using GTX - however, that was back in 1996 and there is certainly plenty of data to say that oils have changed somewhat since then...
So I've learnt something today thanks

[Neosophist]

Nope, car stuff has nasty additives in it that can wreck a bike engine.

To educate myself here...what are these additives and what will they do?
I ask because all my previous bikes have used Castrol GTX with no apparent ill effects even at high mileages although granted this is my first Honda...

There are multiple reasons to use bike specific oil, many old timers will say this makes no difference.

However, modern bikes are in a much higher state of tune than old 50's / 60's bikes...

Much the same reason you wouldn't put SAE 50W in a new Porche 911.

Here is the reasons I know of.

Friction Modifiers

These are a car oil thing. Firstly... not ALL oil will have friction modifiers in, it's more common in Fully Synthetic but even some brands of semi-synth do, and the amount varaies between mfgs.

Friction modifiers are commonly Molybdenum Sulfide, aka moly grease (the black gooey stuff in drive-shafts and that you lube camshafts with)

The idea is that this will make less friction in the engine and improve mpg.

However, bikes have wet clutches that run in oil.. if you have an oil with a high quantity of friction modifiers in then you risk having clutch slippage, which can be a pain to drop the oil and clean the clutch plates. (i've seen this happen on bikes..) a worn clutch is more likely to be affected too.

The more worrying part is that bike oil runs through a gearbox too.. modern motorcycle oil chains dont' break down as easy inside a gearbox as car oil does (it has a higher sheer strength)

What this means in English is that most car oil, espeically cheaper stuff will degrade a lot quicker than bike oil and offer less engine protection, so in extreme conditions, like cold / very hot the oil will be giving less protection, so can lead to engine damage.

It all depends on the oil but for peace of mind and to maximise engine life then either a 'safe' car oil changed more frequently or a proper motorcycle oil changed at the correct interval (I use Honda S9 or G1 I think (fully synth / semi-synth) depending on what is on offer at the time.

I ran the NC24 for 2 years when I had a drum of mineral 10/40 dino oil very very cheap... changed it every 1000 miles and never had a problem (this is wouldnt' have friction modifiers in it)

Hope that helps.