mixing different oils???

[kevpope]

Hi

Just bought a 4.2 Cerb, previous owner was using semi synthetic 10w40, it needs a bit of oil in it and I want to use fully synthetic 10w50 (PH Forun research indicates Silkolene pro-s is the favorite).

Does anynoe know if it's ok to mix them, or should I stick with the semi synthetic 'till the next oil change in 4k?

Thoughts?

Cheers

Kev

[Storer]

Don't mix would be my advice. Either buy some semi-synthetic to top up or do an oil change to your preferred oil.

[QuiteQuietCerb]

i ve been told by various mechanics that you could mix oils but not different types i.e. you cannot mix synthetic with semi or mineral, and also you cannot mix 10w-40 with 10w-50 you could mix 0w-40 with 10w-40 (basically the second number has to be the same)

[kevpope]

ok, that sounds cool, thanks for the advice, looks like i'm buying some castrol magnatec aswell as my silkolene then.

[rev-erend]

I hate to contradict these other opinions but I asked the same question to Opie oils and his reply is that all oil is a mixture.

You take a base oil and add addatives.

The old addage - any oil is better than no oil..or low oil.

There is also the fact that adding top up bu volume is a very small amout compared to an oil change.

[kevpope]

did you email opie or call them?

[rev-erend]

No - just posted it on their thread on the main TVR gassing section..

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Edited by rev-erend on Tuesday 19th August 15:27

[Cyclone1]

rev-erend said:

The old addage - any oil is better than no oil..or low oil.

True, but for the sake of spending no more than £15 on alitre of the right stuff then don't mix.

As has been said, mixing of the viscosity is not that much of an issue in small amounts, but mixing from one type of oil to another (e.g. None synthetic to synthetic) is not a good idea as the molecular structure of the oil is different and therefore acts/reacts differently under pressure and temperature, this is probably less pronounced on mixing semi with fully synthetic.

Jules.

[kevpope]

Cheers fellas,

Have emailed opie, will see what they have to say.

Jules, you are right of course, the cost of a couple of litres of semi to see me through to the next oil change is much better that shagging the engine by running the risk of mixing.

[rev-erend]

kevpope said:

Cheers fellas,

Have emailed opie, will see what they have to say.

Jules, you are right of course, the cost of a couple of litres of semi to see me through to the next oil change is much better that shagging the engine by running the risk of mixing.

I would say that's the right choice (what I would do..)

[Nefarious]

rev-erend said:

kevpope said:

Cheers fellas,

Have emailed opie, will see what they have to say.

Jules, you are right of course, the cost of a couple of litres of semi to see me through to the next oil change is much better that shagging the engine by running the risk of mixing.

I would say that's the right choice (what I would do..)

Ditto.

As an aside, this thread inspired me to give Opieoils a ring to ask about the best oil for a 4.5 Cerbera, as a couple of folks, whose opinions I trust, have suggested that Mobil 1 0w40 is "way too thin". Guy at Opie said he was 50-50 between Mobil 1 0w40 and Silkolene Pro S 10w50, but decided on the latter in the end as it would "quieten the bottom end down a bit". That said, he also said that the AJP runs quite cool, and so the oil viscosity tends to stay a little above the quoted numbers - but I forgot to mention that I run a cooling chip too (so probably run even cooler than standard).

TBH, I'm even more confused than before I picked up the phone. The only thing I've decided is that I'm doing nothing until service time.

Edited by Nefarious on Tuesday 19th August 19:47

[kevpope]

The chap from opie email me back and suggested silkolene pro-s 5w40. He also said to stick with the semi 'till oil change time.

[aychbawdy]

Storer said:

Don't mix would be my advice. Either buy some semi-synthetic to top up or do an oil change to your preferred oil.

Adding regular oils to synthetics helps very slightly....hot temp. will still degrade the cheaper
oil, in some cases .

[brogenville]

Semi-synthetic or fully synthetic, they all come from the same place, as are both based, one way or another, on mineral oil. With that in mind, mixing the two wont cause any problems at all. Whay you will get in the end is an oil that will have some of the properties of one oil, and some from the other oil you're mixing with. As you're intending on mixing one perfectly decent oil with another perfectly decent oil, the resulting mixture, whilst admitadly not 100% ideal, will be perfectly acceptable. The only down side is that you choose one oil for the particular lubrication characteristics it offers, and by mixing it with another, you'll obviously be introducing slightly different characteristics.

At the end of the day, whenever you change your oil, you'll always be left with a fair amount still in the engine, no matter how hard you try (expecially so in the cerb with its oil cooler). With this in mind, oil manufacturers have to ensure that the oils they make are safe to work with each other.

Whilst not exactly the same question, attached below is an extract from an answer to a technical question given to an oil engineer from Shell:

"There is no scientific data to support the idea that mixing mineral and synthetic oils will damage your engine. When switching from a mineral oil to a synthetic, or vice versa, you will potentially leave a small amount of residual oil in the engine. That's perfectly okay because synthetic oil and mineral-based motor oil are, for the most part, compatible with each other. (The exception is pure synetics. Polyglycols don't mix with normal mineral oils.)
There is also no problem with switching back and forth between synthetic and mineral based oils. In fact, people who are "in the know" and who operate engines in areas where temperature fluctuations can be especially extreme, switch from mineral oil to synthetic oil for the colder months. They then switch back to mineral oil during the warmer months.
There was a time, years ago, when switching between synthetic oils and mineral oils was not recommended if you had used one product or the other for a long period of time. People experienced problems with seals leaking and high oil consumption but changes in additive chemistry and seal material have taken care of those issues. And that's an important caveat. New seal technology is great, but if you're still driving around in a car from the 80's with its original seals, then this argument becomes a bit of a moot point - your seals are still going to be subject to the old leakage problems no matter what newfangled additives the oil companies are putting in their products."