Omega Buyers Guide (Part 1: Engines)

[laidback66]

Now I won’t bore people with the history of the Omega. If you are reading this, it is because you want to buy one of the great used car bargains out there.

This will be followed by a seperate guide for bodywork/transmission/interior etc.

Engines.
Obviously history is important and you should always try to get a car with a well documented history.
I don’t mean a service book either, that counts for nothing in my eyes (all too easy to forge). I want to see the receipts for the work done and parts replaced!
Always check engine over when cold , does it start ok, sound fine, no rattles/knocks?
After test driving do all the checks listed below again!

2.0 injection 8 valve.
Only a few of these around thankfully. While the engine is old and proven in the Carlton, it is simply not up to the job in the Omega. 113bhp is not really enough. These were manufactured as the absolute base model and short of being very, very cheap, have little to recommend. Avoid.

2.0 injection 16 valve Petrol. Ecotec engine 1994 –1998.
Major improvement over the old 8 valve engine. More power 134 bhp and generally good reliability.
Engine improved in 1998 with twin balancer shafts and other tweaks for better results.

Things to check/look out for on the 2.0 lumps:

Idle control valve & breather assembly. These cars often develop idling problems that also develop into hesitation and lack of power.
The cause is breather assembly. Over a period of time the pipes become clogged with oil and dirt. This affects the engines performance and will cause the rocker cover gaskets to start leaking oil as the crankcase fumes, unable to escape elsewhere, will force their way through the gasket.
Usual symptoms are uneven idling, revs are slow to come back down to tickover and hesitation when pulling off.
Easy fix, detailed in the Vectra (same engine basically) how2 section.

Cambelt! As with all Vauxhall petrol engines, the cambelt needs to be changed every 40k or 4 years (whichever comes first). On the 2.0 it is highly recommended the water pump is also replaced as it is driven off the cambelt.
Not a difficult job on these cars. An experienced mechanic should do it in under 2 hours.

2.5V6 & 3.0 V6 24 valve Petrol. Ecotec engine 1994-1998

2.5 gives a good mix of power (167bhp/ 167 lb/ft torque) and ecnomy (up to 38mpg on motorway) if driven sensibly

3.0 is noticably more powerful (207bhp/199lb/ft torque) and can be give up to 35mpg on a run. However, urban driving is not so economical.

In 1998 engine was improved in various ways, and is the one to go for if possible.

Excellent engines if properly looked after. Will do huge mileages.

Cambelt kit change: Most important thing by far! Whatever the year, of manufacture, the full kit (belt, tensioner, rollers) must be replaced every 40k or 4 years.
It may last longer, but if it goes (usually the tensioner that fails, hence change the whole kit) then expect to need 2 replacement heads!
Put simply. If you are looking to buy, and it does not have proof of change recently, allow £300 for replacement at a garage.

Rocker cover gaskets. Pull a plug lead from each side of the engine. If you see oil, then gaskets have to be changed. Quite a long job on the V6. Garage will probably charge £150-£200. There is a full how2 on here.

Oil cooler. Real pain of a job to do. Early oil coolers failed due to poor quality and were not helped by coolant not being kept in good condition. Later coolers are stainless steel. If replacing, make sure you buy a stainless steel one!
Dead giveaway is oil contamination of the coolant. You will see the water resemble brown goo!
NOTE: This does not mean head gasket failure!!
So many people and garages wrongly diagnose this and go changing the head gaskets.
Head gasket failure is very rare on the V6, and very expensive at a garage!!
Full how2 replace oil cooler on here.

Heater bypass valve. This is a little 3 way valve that controls the flow into the heater matrix.
Known to split and cause symptoms that have people suspecting head gasket again.
Symptoms are loss of coolant and system overpressurising (giving appearance of water overheating).
It is awkward to get at , as it sits at the back of the engine on the left hand side. Part itself is not expensive (around £25).
Can casue a secondary problem in the longer term. When it splits, it sprays water over the DIS (coil pack) . This leads to premature failure of the DIS pack.

DIS pack. Sits on left cylinder banks and when it starts to fail will cause car to start misfiring, especially under load. Check plugs and leads for faults first.
It will not produce a fault code though (fault codes explained later).
Normally will last way over 100k miles., unless heater bypass valve goes…
Note there are 3 different packs used on the V6. Engine number is required for confirmation when ordering replacement. Absolute swine of a job to replace!

Other points to check (applicable to 4 and 6 cylinder engines).

Oil. How does it look? Is it clean, signifying a recent change, or does it look more suited to sealing a flat roof?
Any sign of a creamy mayonnaise deposit in the filler neck or the dipstick?
If yes there is quite a bit, especially on the dipstick, walk away, head gasket is blowing (only really happens on the 2.0).
A small amount in the neck and on the filler cap signifies car has done only short runs recently (especially V6). A good longer run will get rid of this. Not a concern.
Get underneath, look at the oil filter, does the condition of that tie into the condition of the oil? How much oil is down there? Evidence of leaks?
These are a few things people do.
Oil is clean, but filter dirty as they have to regularly top oil up due to leak/use of oil.
Drain and refill oil but can’t be bothered to change filter. Sign of laziness, not good in car servicing!
Have actually done a proper oil and filter change just before putting car up for sale. However, it had been so long since the last change that the new oil is very quickly dirty. Again, be wary.

Coolant. Does it look like pure water?
If so, be very very cautious as this usually means the coolant is being regularly topped up. It should not need to be!
Is there any sign of contamination in the water? Look for the water being a dark brown colour. Also does it seem overly pressurised even though the engine is cold?
Any smell of gases in the header tank? These are signs of head gasket problems (2.0).
Ideally coolant should be a reddish or bluish (dependant on anti freeze used) colour signifying a 50/50 mix of water and anti freeze.

Power steering fluid. Should be reddish pink colour. If it is brown/black, it is seriously in need of change and may well be damaging the power steering pump.

Brake fluid. Should be clear. If not, it needs changing. Really it should be replaced every 2 years. I would look for this on the receipts.

Air filter. Always a good one to check. A dirty filter is very restrictive to the engine!

Pollen filter. On the passenger side of the car at the bottom of the windscreen is a flap in the scuttle (black plastic cover to stop leaves etc). Lift up this flap. In there sits the pollen filter, held in by clips on each side.
Pre facelift (ie pre ‘99) cars have a white (well it was once!!) pollen filter.
Post facelift (post ’99) cars have a black carbon pollen filter.
Facelift has an auto re-circ function on the climate which incldues an air quality sensor. It auto engages re-circ if anything nasty (smelly) is detected as such a carbon filter is requried to stop this facility permanently engaging.
Very easy and cheap to replace.

Also look to the bottom of that section. It is notorious for the drainage hole becoming blocked with dirt and sludge. This will then lead to damp (and smelly) passenger footwell, misting up of the windows, and, if left long enough, electrical problems as wires don’t like being immersed in water!
Easy fix, just clear drainage hole, but keep out of the path of the water!

Battery. How does it look? Old and worn, or new and fresh?
How are the terminals, are the connections clean and tight? No dodgy looking wiring coming off it?
Lift the cover to the fuse box, does that all look ok? No signs of heat damage?

Radiator. It should look clean with no signs of leaks. Any signs of white deposits around the connections signifying leaks?

Start car up. It should fire up immediately and settle to a smooth idle (if cold it will be much higher).
Listen for unevenness.
Rattles are not uncommon, EGR valve being a common culprit.
Low knocking sounds are really not good though and should prompt a hasty exit!

Many thanks to Marks DTM for his advice and input. Without him I would not be able to write this.