The engine oil is kept separate from the combustion chamber by the valve seals and piston rings, either of these may be worn out.
These are seals placed on moving parts so the more miles the car has on it the looser they become, several things like letting your oil level fall too low, or operating at too high rpm can cause premature wear of these seals.
In some instances a faulty pcv valve can allow oil to enter the intake manifold when crankcase pressure is too high so check it out as well.
The coolant capacity for a Vectra is approximately 7.2 liters. That would be roughly 1.9 gallons of Vectra coolant capacity.
Vauxhall Vectra wiring diagrams: http://www.pdfoo.com/resultpage6~vauxhall-vectra-wiring-diagrams.html
The starter is burning.
depending on the engine size it is about 4.5 litres of 10w40 , i would recomend a least a semi-synthetic oil , as this leaves a nice coating on the internal parts of the engine and reduces wear and damage when engine is cold
i would 50/50 it just to be on the safe side as you dont want anythign to freeze up.
Possibly a problem with one of your belts?
Oil leak or the engine is burning oil.
Likely something to do with the Cam angle sensor...other symptoms are engine stalling (even with autotrans) and rough starting.
The presence of black smoke from exhaust when engine is first fired.That sign could also be an engine running too rich.
Vectra is 5 stud, Nubira is 4.
I had this problem with mine, then the engine management light would come on. Turned out to be the crankshaft sensor. (Cambelt off job)
Oil that has somehow gotten onto the manifold of the engine will produce this smell. Any oil leak in and around the engine will produce this.