Engine Oil

[mistergixer]

I've been given a load of (unused) engine oil by a mate who's giving up bikes.
My bike never really uses any except at service time.
My car on the other hand has a Yamaha engine and drinks loads of oil.
What (if any) are the differences between bike engine oil and car engine oil of a similar rating i.e 5w40
I've often heard it said that you shouldn't put car oil in a bike engine - why is this? If the ratings are the same, surely the oil is the same?
If there is any reason for the above, does it work both ways round - i.e i shouldn't put bike engine oil into my car?
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[Rookie]

People say not to put car engine oil in a bike engine because there's some car oils which have additives which bike engines don't like. Like that Magnatech stuff, the stuff that clings to the engine and stops wear before the car heats up? Apparently that really doesn't agree with bike engines.

[iooi]

[Kickstart]

Hi

I have often used car oil in the bikes. Not had any problems. There do seem to be some oils that can sometimes cause problems. Magnatec for example. Ste had problems with Texaco oil (I think).

The spec for bikes oils is generally lower than for cars (look at the API rating on the side of the bottle).

While I would generally not worry about mixing oils (it can very occasionally cause problems), I think lobbing in half a dozen varieties of bike oil into a sump already containing half a dozen varieties of car oil might be asking for trouble.

The only thing that you must not do is mix mineral based oils with castor based oils (eg Castrol R). Mixing sythetic and non synthetic is unlikely to cause an issue.

All the best

Keith
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[Gazdaman]

I always use Halfords cheap shit 10W40 in my bandit. Did in my XJ600 as well.

Granted not top of the line sports bikes but it sure did the job.

Gaz