Holden Problems

The backfire you are hearing is the gas igniting in the intake manifold, which is quite common with cars running on LPG. A random spark usually causes it, and the plug leads usually cause that. It's not the LPG. I'd take it back to the installer and get his help.

Have the diff mounts checked; they're likely to be the cause.

It sounds plausible that the wiring harness could be damaged and needing replacement. You can get your answers from Carsguide.com.au.

It's odd that these problems should start after you had the new radiator fitted. I would suspect that whoever did the work did it poorly. Take it to an air-conditioning specialist.

I am assuming the engine was a second-hand one and there was no guarantee on it or the work done by the mechanic. If that is the case you are relying on the goodwill of the mechanic to do the 'right' thing and have little other claim. The best thing to do would be to talk to the mechanic about your expectations and try to reach an agreement on the cost to carry out the subsequent repairs. If you can't reach a satisfactory agreement you could try your consumer affairs people, or take the mechanic to your small claims tribunal. If there was a guarantee on the engine or the work make a claim on that.

It could be the diff itself or the diff mounts. Check the mounts first, if they check out ok, consult a diff specialist.

The engine is overheating, that's the gauge is telling you. You need to have a mechanic check it; any number of things could be causing it, from a blocked radiator to a blown head gasket. It's nothing to do with the grille.

I doubt very much that it is the head gasket; I reckon you would have seen the engine temperature rise if it was a leaking head gasket. You won't know until you actually pull it apart and check it, but I would suspect it's the water pump that's leaking.

They shuddered when they were new, the problem is that they're not flipping over when they should at the top of the stroke and they're forced back across the windscreen against the grain if you like. Look at the blades and the way they are mounted on the arms and make sure they are free to change angle when they change direction.