Car oil (for topping up)

Ommbiance

We have an (oldish) Ford and (older) Vauxhall. The vauxhall needs occassional oil top ups, and the Ford is near the minimum on the dipstick level.
In the respective handbooks Ford recommends 5W-20 (but states 5W-30 is acceptable. The vauxhall needs 5W30.  Searching on the various car suppliers webistes you can put you reg in and they will list compatible oils. But none of them come up with the same brand although when reading the spec they seem only subtly different.
So my question really is whether there is very much difference between 5W-30 oils, becasue I'd much rather buy one 5L can for both vehicles.
Any thoughts please?

fatbelly

I can't see you would go far wrong with a 5w30 from a decent brand

Goudy

Fords and Vauxhalls generally run on different specifications of oil.

They might be of similar grades (viscosities), like 5w/20 or 5w/30, but the specs are usually different.

Engine oil is usually quoted in the handbook by:
Industry standard grades, like 5w/30
Industry standard specifications, like ACEA, (Euro) API (American) or JASO (Japanese).
Manufacturers own specification, like Fords WSS-M2***-* or Vauxhall's GMdexos.

I suspect one will be something like ACEA  A1 and the other something like ACEA C1.

Check both handbooks, if they both can take 5w/30 ACEA A1 then you're ok.

Ommbiance

Thanks for responses.  I couldn't find one which matched exactly for both vehicles.  I'm pretty sure there's a little bit of marketing involved in all of this, and agree a quality brand would proably suffice, but in the end I did find an exact compatible oil (based on the WSS code) for the Ford, so have gone for that. 

Goudy

I'm sure there's more to the specs than marketing.

Generally (very generally) your ACEA oils are grouped in A, B and C (E is heavy duty oils)

Each has a number along with the different letters, but they mean different things.

A1/B1 oils are low friction oils.
A3/B3 oils low friction with extended drain intervals.
These will be very similar.

A3/B4 are low friction, high temp performance oils

A5/B5 are low friction high temp and high shear performance oils.

A7/B7 are low friction high temp, high shear suitable for direct injected turbo engines.

Getting these wrong can generally damage things like turbos as the oil lubricates and cools a very fast spinning bearing. 
You sometimes hear warranty claims on turbos being rejected because they have tested the oil and it's the wrong spec.


C grades are similar but the C stands for Catalyst compatible.
1, 2 and 3 relate to the amount of SAPS (Sulfated Ash, Phosphorus and Sulfur.) along with things like shear rates and temp stability.

1 is low SAPS
2 is mid SAPS
3 is also mid SAPS (but a higher shear rating than 1 or 2)

Getting these wrong can damage catalytic converts and particulate filters, along with turbos if the temp and shear rates are also wrong.

Obviously the Japanese and American industry standards have their own different ways of identifying the differences of spec.

The manufacturers try to make is easier for you.
They tell you the grade and their own spec code/number that you need. (and often a recommended brand, which is marketing).

This means you don't need to work through all the industry standard grades working out what you need, you just select the right grade that has the right manufacturer spec code/number.

The manufacturer will also usually give you the correct ACEA/API/JASO spec as well.
It will almost certainly be one of the ACEA/API/JASO oils and if it's the right ACEA/API?JASO spec without the manufacturers code, it will be ok.

Ommbiance

Thanks for a comprehensive answer Goudy; interesting and not something I've really given a lot of thought to in the past.   My conclusion is that it's not a good idea to skimp on oil for the cars as it's a relatively low cost item for the value it provides.