Thought I'd replace the tensioner and idlers today along with a new serpentine belt.

I have a 36mm spanner placed on the fan nut and whacked it with a hammer, all it keeps doing is turning the whole lot.

How do I stop the pulley from turning as well, Is there another tool I need as most forums say a hammer should be enough to loosen the nut.

Managed to replace the serpentine belt although the old one still looked like new.

You can buy a tool that holds the water pump pulley to stop it from turning. If it has been on there long enough without being removed like my first one was, it just wasn't coming off with the spanner alone.

I didn't have one of these tools... so took the rather dodgy approach of putting a trolley jack under the car, and then putting a metal pole between it and one of the bolts on the pump pulley, jacking it up just a tiny bit so it all stayed in place... then tapped the fan spanner lightly. Didn't take much once the pulley couldn't move, but it probably isn't the best idea, could end up breaking the bolt the pole is against off the pump.

A tool like this will do the trick
http://www.ebay.co.uk/itm/Sealey-Viscous-Fan-Holding-Tool-Damage-Prevention-Vinyl-Dipped-Handle-VS095-/311311981224?hash=item487ba3daa8:g:-psAAOSwNSxU-2Yv
...or this...
http://www.amazon.co.uk/Laser-5591-Pulley-Holder/dp/B00BP7WSCK?ie=UTF8&keywords=viscous holding tool&qid=1459427686&

I dont think I will be trying your method Sloth but at least you used some initiative .

Cheers Ob , damn these tools are expensive , a cost I usually forget to figure in when replacing parts.

If you've got a grinder, welder and some scrap, you could probably knock one up for nothing :-)

Just drill a 10mm hole in the end of a lump of 1" steel bar. Don't drill in the centre but offset it to one edge. You can then put the head of one of the pulley bolts into the hole and rest the side of the bar against the shaft. That's my holding tool.....