Fully v Semi

[j90xxx]

Not looking for recommendations or the difference between fully synthetic and part synthetic (we don't need to go into dynamic or kinematic viscosity or Newtonian fluid density), just an answer to the following.
I was under the impression (I used to work in the retail/commercial oil industry) that if an engine has been using fully synthetic oil, then under no circumstances should part synthetic be used. Damage could/would result.
A quick browse on http://www.castrol.com recommends Castrol Edge 5w-40 Fully Synthetic. A correct choice. But under the mid-range choice (Edge is the premium) they recommend Castrol Magnatec 10w-40 Part Synthetic.
What do Citroen themselves recommend?
I could be wrong, technologies may have changed in the 10yrs since leaving the industry.

[knobblywobbly]

... that if an engine has been using fully synthetic oil, then under no circumstances should part synthetic be used. Damage could/would result.

I can't/don't believe that this is true.

How would you know when buying a secondhand car what oil has been used in it, particularly if it had had a couple of owners.

[Coco]

... that if an engine has been using fully synthetic oil, then under no circumstances should part synthetic be used. Damage could/would result.

I can't/don't believe that this is true.

How would you know when buying a secondhand car what oil has been used in it, particularly if it had had a couple of owners.

I too have heard this said in the past, but no idea if it's true, or just a clever marketing idea

[Tomcat3]

Just to throw a spanner in the works aint it recommended to use 5/30 semi synthetic oil in the hdi engines now?

[knobblywobbly]

..... or just a clever marketing idea

Probably. A bit like saying you can't use car oils in a motorbike with a wet clutch because your clutch will slip, and pointing you to the expensive motorcycle-formulated oils. I've always used car oils in my bikes and never had any clutch slip.

[3rensho]

Their recommended oil, the Total Quartz etc. is just listed as a "synthetic based" oil in the lit. I can find. Can't really tell from that if it's fully synthetic or semi.

[j90xxx]

Ok.
In a nutshell (sort of...)
Citroen dealer.
Total Quartz 7000 10w/40 fully synthetic. (see * below)
Total website.
Total Ineo ECS 5w/30 fully synthetic.
Halfords website.
Mobil 1 0w/40 fully synthetic. (see ** below)
Shell website.
Shell Helix Ultra 5w/40 fully synthetic.

So 4 different grades of oil from 3 different manufacturers!

*Citroen dealer said that Quartz 7000 was fully synthetic, but reading on the Total website it is 'synthetic based'. Does that mean 'part synthetic'? Don't think 'based' means 'fully'?
**Halfords also recommend Castrol Magnatec 10w/40 part synthetic for the same vehicle/engine.

Back to my original question, fully or semi?
The Citroen dealer said it should be fully synthetic.
Then quoted me a synthetic 'based' oil...
Am I any wiser?
No!

[Ol'Jeffers]

Citroen only recommend Total Quartz Ineo ECS 5W30 for their HDi engines.

Other oils, however, are suitable. :-) ( As long as they conform to PAS PEUGEOT & CITROEN B71 2290.)

[j90xxx]

Not my Citroen dealer!

[Ol'Jeffers]

I did say 'Citroen'! That doesn't mean one of the witless dealerships who would love to replace your turbocharger
as they're short of work!! LOL!!!