Faisal wrote
i mean coasting as in putting ur foot down on the clutch and holding it down (keeping the revs at 0)
Revs at 0 means you have switched the engine off. This isn't particularly bad: some eco-cars have been designed to do this, (switch off when not needed) but they have bigger batteries and starters designed for frequent use - the intention is that when stopped in traffic the engine shuts down, restarting (first time, every time, of course...) when you put your foot back on the accelerator pedal to move away.
iv heard this puts strain/pressure or something on the clutch...
The
problem with this practice is the temptation to restart the engine by letting the clutch out. The clutch is not designed to spin up a stopped engine, the speed mismatch is way too high, and it will wear out your clutch lining prematurely. If for some reason you are switching the engine off when the car is in motion, restart it with the starter motor, not the clutch.
Costing with the engine off and clutch in is bad, as it pumps unburned mixture into a cooling catalyst. This will kill the catalyst stone dead in short order.
I don't think either of these is what
andycupra meant, though. By coasting in gear he meant foot off throttle - nothing more. The ECU will detect this and cut fuel injection to zero in most cases, which aids cooling down. This is better than coasting with the engine on but the clutch pressed down, because the ECU has to supply fuel to keep the engine ticking over
