motor oil: which type

freek · Post by **freek** » 19 Apr 2005, 02:34

Hi,
I own a CX gto turbo2 and a BX trd turbo. When these cars were produced life was easy. You could only chose a mineral oil of the right specification (and may be Mobil 1 synthetic). But today synthetic oil is usual in new cars. I thought that you can recognise the synthetic oil to their first SAE number which indicates the viscosity at low temperatures. The synthetic ones have a low number for example 0 or 5, I thought. But now I doubt that. For the last oil change of both cars I used Castrol Magnatec 10W40. The specification does not mention whether it is synthetic, semi-synthetic or mineral, but I think it is the first. And when this is true, did I make a mistake when I used before 15W40 mineral oil? A relative of mine owns a SEAT Alhambra 1.8 turbo and he said he made the mistake of adding mineral oil to the original (synthetic) oil, resulting in blocked oil pipes of sludge. So my questions are:
1) how can you recognize synthetic, semi synthetic and mineral oil? 2) is it allowed to mix different oil types with the same SAE-number? (and if so: why did my relative almost end up with a ruined engine?).
regards Freek

madmanbob · Post by **madmanbob** » 19 Apr 2005, 03:26

All three can be mixed but only give the protection of the mineral. The SAE number does little to indicate which type of oil you are using. The only thing is that synthetics normally have a wider gap between the two numbers. Mixing a 10/40 with a 15/40 will give you a 12.5/40. I go for the lower first number as the oil will only act like a 10 for the first few miles of driving.
I don't understand why your friend would think that adding mineral to synthetic would cause sludge as they will mix.
I also owned a CX DTR Turbo 2 at one stage, and used fully synthetic 5/40 diesel oil in it. Had this oil been available when the car was made then the oil change intervals would probably been extended. I used to change mine every 12000 miles, and had the old oil analyzed after a change once, it was found to be fully servicable and did not need changing.
There are many threads dealing with oil on this forum but my advice would be to use the most modern oil that you can get and change at the manufacturers recomendation. When I had my first CX diesel, a 2500cc 75 bhp version from 1981, Citroen said change the oil at 3000 miles but the best spec one could buy at that time was API CC. With the Turbo 2 and 120 bhp in 1990, API CE was around and Citroen recomended 600 mile changes. My C3 HDI 16 valve calls for fully synthetic and 12500 mile changes.

Kowalski · Post by **Kowalski** » 19 Apr 2005, 04:08

As you were correct in pointing out, SAE number has nothing to do with whether an oil is synthetic, mineral or a mixture of the two. Taking that a step further, the oil change interval also has nothing to do with whether the oil is mineral or synthetic too.
Additives are what gives an oil its lifespan whether they be pH buffer or detergent, once your additives are used up your oil needs to be replaced. Oil specifications have improved since you had your CX, but the improvements aren't purely down to the introduction of synthetic oils.
Having said all of that, synthetic oils tend to need less additives adding to them and do tend to come in lower viscosities than mineral oils but the latter is down to marketing rather than anything else.

madasafish · Post by **madasafish** » 19 Apr 2005, 19:25

Castrol Magnatec 10W40 = mineral oil.
Overpriced by up to 300% imo

arry_b · Post by **arry_b** » 19 Apr 2005, 20:05

You've got to pay for the branding and advertising somehow.....

madasafish · Post by **madasafish** » 19 Apr 2005, 21:05

I buy branded (Comma or other secondary makers) but much cheaper. Branding and marketing do not lubricate an engine better....

freek · Post by **freek** » 19 Apr 2005, 22:10

I did some survey myself and found out that Magnatec is not mineral (as stated by madasafish) the product guide of Castrol says 'A breakthrough in engine oil technology, Castrol GTX Magnatec is a synthetically based product containing esther molecules which provide 'unique molecular attraction'.
But I still wonder why my relative (which is a car technician himself) had very serious engine problems (no oil pressure!) after he topped up with mineral oil. The engine had a very serious sludge problem. Are there special oils on the market which do not tolerate other specifications?

Kowalski · Post by **Kowalski** » 19 Apr 2005, 22:16

You can pay for branding and marketing if you want, personally I pay for oil when I buy oil.
R&D is a different kettle of fish, I'll subsidise that if it makes my car last longer, but flashy TV commercials and glossy magazine ads don't do anything for me.

ItDontGo · Post by **ItDontGo** » 19 Apr 2005, 22:58

Is it really going to make much difference what you put in it. If you find that the engine struggles to rev then maybe but I doubt that would happen even if you used water or washing up liquid.

Kowalski · Post by **Kowalski** » 20 Apr 2005, 00:48

In the 80s cars that did big mileages started to suffer from what was called black death at the time. This was a build up of sludge and grime in the engine that eventually would kill the engine. These days cars don't suffer from it, and they last for hundreds of thousands of miles, oils have improved and are critical to your engine.
The oil stops metal to metal contact, it cleans, cools and lubricates. It also has to deal with condensation, soot and any other products of combustion that get past valve seals or piston rings. Too thick an oil can end up damaging your oil pump in extremes, and too thin oil may mean your engine is unable to maintain enough oil pressure to keep your bearings from going metal to metal.
Oils are fairly critical, but there is not a massive difference between the best and worst oils, so its best to buy what you're happy using.

john alexander · Post by **john alexander** » 20 Apr 2005, 01:10

years ago I saw a morris 1000 which had been ran on castrol gtx It then was changed for duckhams , by the next day the engine was full of mayo and sludge. regards john

CITMAN · Post by **CITMAN** » 20 Apr 2005, 02:17

maganatec is actually semi synth. it aint fully synth by a long way. Not long ago I put magnatec in my laguna only to change it back to comma again as the engine sounded rougher.

Niek · Post by **Niek** » 20 Apr 2005, 02:53

Hi Guys,
I just want to sort of hook into the oil discussion (Yeah I know it's been talked about before but I'm still confused)
My xm has run for about 230000km and is still running good. It's always been on mineral oil for as far as I can tell. I've been putting Duckhams (probably semi-synth) into it since about 180000km. Is it safe (and is there any point) to upgrade to full synthetic say 5w/40 oil spec? You can always find stories about people who know people who've had very bad things happen to their engines when doing this sort of thing but although I don't usually believe nth hand stories it still makes you think. I'm sure some of you have sensible things to say about the subject. I'm very interested... (even just to find out what you people use)
cheers

arry_b · Post by **arry_b** » 20 Apr 2005, 03:51

I changed to 5W40 fully synthetic from mineral on my old 2.0 12V Mazda 626 at 170,000 miles. I did take the rocker cover off for a looksee before I did it and it was extremely clean, amazingly so.
No leaks, no problems at all.
The chap I sold it to is just about to take it through 200,000 miles with no new engine problems, four years later.

FrenchLeave · Post by **FrenchLeave** » 20 Apr 2005, 05:17

Synthetic oils are made up of two major constituents, esther (a sort of artificial castor oil that doesn't have its disadvantages) and polyalphaolefin (an artificial hydrocarbon but with a uniform molecular size). It flows better when cold, resists oxidation and is more temperature resistant than mineral oils. It is for these reasons that the oil change frequency is able to be increased. As it also has better lubricating properties it can be considered to be a Good Thing. Semi-synth uses mineral oil instead of esther, it is therefore cheaper and not quite such a Good Thing. As long as you choose the correct viscosity you can use either type in any engine, although if it's a gummed up old donkey you may find you have a few leaks when it frees up the sludged up parts. Those of you with long memories may recall that castor oil was considered to be superior to mineral oil and was favoured by the racing fraternity. Unfortunately it oxidised badly and had to be replaced at very short intervals - no problem with racing engines that were stripped after every race but no good for road cars.