mixing oil grades??

[seanmcg]

quick question guys... ive always used castrol 10w40 for my fd3s, just checked it there and im running a little low, iv a tub of that \'ultimate rotary oil\' in the shed, think its 5w30, would it be wise topping it up with a bit of that? or just wait and buy 10w40? thanks

[col_fd3s]

shouldn\'t ever really mix oil grades, and definately avoid running it when low on oil, even if it\'s just once.

col

[pdtaylor18]

Agreed, just change the oil to that new rotary stuff, not good to mix oils.

[M@r]{]

I\'ve often wondered about this.  Even on an oil change you are not going to get all the oil out unless you start taking the oil coolers etc off to drain.  So when changing its always going to mix to a certain extent?  

I recently went from what I think was semi synthetic to a fully synthetic - it worried me about the semi left in the oil coolers but as I change my oil every 2 events it shouldnt take long for the semi to disappear.

[Prof]

{;626930\']I\'ve often wondered about this. Even on an oil change you are not going to get all the oil out unless you start taking the oil coolers etc off to drain. So when changing its always going to mix to a certain extent?
 
I recently went from what I think was semi synthetic to a fully synthetic - it worried me about the semi left in the oil coolers but as I change my oil every 2 events it shouldnt take long for the semi to disappear.

I think the same - you are always going to get some \'mixing\' when changing oil - and not all the old oil will be flushed.
 
Surely the oils will mix, it\'s not like you are mixing oil and water?

[col_fd3s]

The problem comes from mixing different brands or formulations of oil i.e. Mobil 1 and Castrol. In these situations the oil has different additives which may not mix well together. Different brands or types of oil have different additives some of which when mixed together can totally negate the protective effects of the additive on the engine or possibly even harm your engine.

col

[M@r]{]

Again though, unless somehow you completely drain all parts of your oil system then flush it through you will always get a certain amount of mixing.

I just work on the assumption that as long as the ratios are very different, something like 10:1 - ie 4000ml of new oil to 400ml of old / different grade thats hanging around in the oil coolers etc then it will be ok?

[seanmcg]

i left her at home and went an got castrol 10w40... just to be safe

[BlitzBoy]

LOL @ THIS THREAD, and all the internet expert twaddle spoken on it.
Prof is the only one speaking any sense on it.
Col do you work for an oil company or an oil technician? Mixing different Grades although not ideal eg 50:50 wont harm an engine, the worse thing to do is not change the oil regularly.
You will always have old oil left in the coolers and line when doing an oil change, Oil companies know this and factor this in when developing oil, at the ratios of mix its not worth worrying about.
As has been previously said its not like you are mixing water and oil lol

[Shiuko]

Sorry for the hijack, but col_fd3s could you please answer your phone?

[col_fd3s]

{;626956\']Again though, unless somehow you completely drain all parts of your oil system then flush it through you will always get a certain amount of mixing.

I just work on the assumption that as long as the ratios are very different, something like 10:1 - ie 4000ml of new oil to 400ml of old / different grade thats hanging around in the oil coolers etc then it will be ok?

granted you will always get some residual, doesn\'t matter how long you let it drain for, if your changing brands, or mineral to synthetic say then you should theoretically drain the coolers too. it\'s just good practice and as i said in my last post some of the additives when mixed can end up offering less protection.

the point sean asked in the 1st place though was about topping up from a low oil level, which could be over 1 ltr, in that case, i would say it\'s a definate no-no to mix oils.

col

[M@r]{]

Oi Mark, Prof and I are saying the same thing - so can you include me in your "only people making sense" group?  

LOL @ THIS THREAD, and all the internet expert twaddle spoken on it.
Prof is the only one speaking any sense on it.

[Shiuko]

Col FD3S, I need your address so I can go and pick up the car.

Give a ring to my mobile please:
07711669896

[Prof]

{;626965\']Oi Mark, Prof and I are saying the same thing - so can you include me in your "only people making sense" group?

In fact you said it first :King
 
I have to say after reading through a lot of the stuff that oilman put up ages ago, the bulk of the oil is going to be various base stocks, and the additives make up a much smaller proportion of that.  Given that some of these are likely to be common between the different oils, the only time I could see that a problem might occur, is if somehow you had acids and bases or acids and alkalis mixing and creating non oil soluble compounds giving \'ash\' or reagents that would react with metal or the seal materials in a non favourable way.
 
I tend not to mix brands - only because I like to know what\'s in the engine - but if it was an emergancy then I\'d put similar oil in for sure.  I change it every 3000 miles - which is about every 3 months in any case - so it\'s changed regularly.

[Aubec]

Timely thread for me, as I\'m about to replace the mineral oil which has been used to date in the engine for synthetic and had the same questions.
 
I\'d work on the same logic as you guys - so I\'m gonna just drain at the pan, fill up with synth and then change again with new synth before I go to the \'Ring in September - which will only be about 400 miles between changes.  I reckon that\'ll be enough to get the mineral content down to a bare minimum (like 1 in 100 or so), and at the next change in another few thousand miles it\'ll be like 1 in 1000.