All Omegas are heavy powerful cras which are good for towing. The weakness with the petrol engines is the plastic cam-belt rollers which must be replaced when the cam belt is done, otherwise it can result in one VERY dead engine. There are a few stories of head gasket failures on the V6 models which can be expensive. Regarding the diesel engines, the 2.5 ex-BMW engine was good, BUT BMW stopped supplying them to Vauxhall because of the number of warranty claims over big-end failure (Vauxhall had modified the oil filtration system to suit the Omega). In a panic they dropped in the Vauxhall 2.0 TD engine from the Vectra, but with only 99bhp, it is underpowered. The newer 2.2TD is a better engine, but no-where near as good as the TDCi engines fitted to the new Mondeo's. Also, only the BMW diesel was available with an automatic gearbox, the Vauxhall units were manuals only.
