Another Oil Question or two

Hi, Having had my car serviced at Porsche (where they over filled it), I now need to top it up. They used Mobil 1 0w50. But as I have had a number of smokey start ups, I thought it wise to follow some advice and use 5w40 oil instead to top it up.. I assume you can top up with a different grade as long as they are both fully synthetic? And do I have to use a Mobil 1 5w40 (where I've heard this is sold as a diesel engine oil)?

Hi David. Not sure about mixing the grades - it probably won't matter too much BUT - are you sure that you need to? My 996.2 doesn't get too much use and there will always be a degree of blue smoke on start up after she hasn't been used for a little while. It seems to be part of the nature of the these flat-cylindered engines. There's no sump to speak of and the oil is likely to migrate around the bottom side of the piston rings when 'at rest' and you will then get the obligatory puff of blue smoke when you fire them up. The fact that the engine is also cold on start up up will also make a difference as everything is cold and contracted - which obviously then changes as she warms up and the rings, etc. expand with the heat and prevent further oil migrating in to the combustion chamber (which is why you get a little smoke). My engine is noticeably quieter also. This might be my imagination but I've seen Mobil 1 0/40 when it's hot and the stuff is about as viscous as water - not for me, thanks very much! I've run my engine exclusively on Castrol GTX Magnatec for the last seven years which has resulted in far less smoking on start up and she also generally uses less oil. This is a 10/40 semi-synthetic oil which a friend of mine has been running his 3.4 996.1 on for years - and he regularly takes it to the 'Ring and blasts around there - so I figured that it would be fine for my (considerably less) aggressive driving style [ ]. There will be those who will disagree with this though....... If you're not happy with what you currently have I would either make use of the oil you've already spent your money on in the understanding that she's going to behave this way and then consider changing the whole lot when the time comes - rather than mixing. Just my opinion, of course! Hope this helps. Adrian.

Adrian summarised and answered perfectly.

Porsches recomendation is 0w-40, haven't really heard of 0w-50 by Mobil1, nor 5w-40... ?? There's 5w-50 but that is usually for air-cooled engines or nordic countries with lots of cold starts.

Wrong way round Alex. 0W-40 is thinner at low temperatures and better for starting. You are correct that a lot of people prefer 5W-50 for the aircooled stuff, because it has to handle a lot more engine cooling than the water cooled cars.

True, I suppose it dates back to when 10w-40 was the alternative... ;-) I used to run 5w-50 on my car but then my local OPC changed to 0w-40 only, after some debate they checked with Porsche in Stuttgart and because of some the changes made with the latest Mobil1 products they now recommend 0w-40 for all models.

Hello, Topping up with different viscosity oil? I see no point just top up with whatever and when you change your oil next go for 5w. Its not going to change the viscosity to any benefit of what's now in there. Are you going by dip stick or dash and how long did you leave it before checking?. If not left long enough oil wont have drained back to sump, and sometimes if left standing for long periods and you check oil it can have drained from areas that it normally wouldn't so will read high. Thats why the 20 min oil countdown timer on dash and oil status should be read when engine is at operational temp. The recommended oil by OPC? Funny wonder if they put that sticker on the Deck for free or they got heaps of cash for it?.

Ahhh. I get you now. I wouldn't run 0W-40 in my 3.2. It would find all the leak points! Mine is pretty leak-free with 5W-40, and seems to be quite happy on it. Most of the oils in the Porsche Approved list are 5W-40, but for some reason they always factory fill and service with 0W-40.

Ill +1 on that. I dont run on 0w oils anymore in any of the cars I have owned that OEM stated 0w oils. Its too thin, Cars ive bought that have had it have leaked it if laid up for some time. Strange how the viscosity is supposed to be the same according to a lot of factors but personally I wont use it. And I think could cause more harm than good, Yeah the difference of operating range is only small but if you were in a swimming pool and the temperature changed by 5c you would sure notice the difference. However don't panic I wouldn't rush and do and oil change just because you have 0w-40w oil in your sump.

If I paid a bit more attention in school I could describe all the differences in oil brands and viscosity, but since I can't I can only say that the collaboration is a bit more than a sticker on the engine lid. ;-) All of Porsches testing is done with theese oils, and the feedback goes back and forth constantly. It's the same with Michelin tyres, they are tested with the cars from start to finish. It's pure developement all the way, not just branding. So if you've got a mate who's done this or that, or an indie whos done it to 10(!) cars they are still a couple of million miles behind in testing and experience. ;-) Just my 2p... ;-)

I think that you're right, Alex but there's a pretty strong school of thought that the less viscous oils (eg. 0/40's) are more suitable for environments like the one that you seem to live in! In other words; the more predominantly cold the atmospheric temperature is the thinner the oil you want - it's the same with blood; it tends to get a bit thicker when you get colder. Porsche seem to do a lot of their new-model testing in areas around the Arctic Circle - at least most of their promo videos that I've watched seem to be set in brass monkey environments! I guess that if they then base their (oil) findings on the worst case (or harshest environment) scenarios then any weather/temperatures more conducive to running a machine in is a only going to be a bonus! [8|]

Never the less, you'd want as wide a operating range as possible, even with the same top temp label (40) a 0w-40 oil will tolerate a higher temperature than a 10w-40 oil, so if you want to change to something thicker at least go with the 5w-50. (I put my car away when winter comes anyway.. ;-) ) I'm sure Baz has some meaningful insights if he's still lurking around here.

I rune my C2 and my wifes Boxster both on 5 - 40 with no issues at all, I run my C2 as my daily drive doing 25k per year, uses hardly any oil, no smoke, there is also less tappet rattle on cold mornings when using 5 - 40. I used to use 0 - 40 but I agree when its hot, its does not make you feel really good about it.

Cheers everyone. Very informative and re-assuring[ ] I'll change over to the slightly "thicker" oil at the next oil change. It was just the sight of my brother-in-laws face as I started my car outside his house and smoke came out. I am sure I could see him say to my sister " Daves bought another heap...." Thanks Dave

Hi Dave. Just to check: would you say that this was a moderate amount of blue-ish smoke that clears from the air quite quickly - rather than a larger cloud of white smoke that hung around for a while....? And that you don't get a similar 'effect' if you give her the beans whilst your on the move (nothing in your rear view mirror..?) Adrian.

Nope, it clears after a few seconds, and when opting to lose the Transit thats decided it wants a race there is no smoke either. [>:]It's just the start up's.

Good news! I recently had a similar situation with a guy in a Mitsubishi Animal 4 by 4! Yes, you read it right. [ ]

Two points 1)Castrol GTX magnatec is a highly modified MINERAL OIL for reference google mobil1 vs castrol court case from 10 years ago or so the judge ruled Castrol could call their oil semisynthetic as it is modified,that however doesnt make it a bad product. 2)there is so much misinformation about oils and viscosities and of course everybody has there own snake oil they swear by.this question always crops up in short SAE grades change over time the SAE grade recommended by your car manufacturer is current to the age of your car I would at the least use that grade and that grade alone,I dont see the benefit in mixing a higher spec oil ie 0-50w with a lower spec oil ie 5-40W.IMHO the for best informed opinion on oils I would go to the oilman who sells opie oils http://www.opieoils.co.uk/t-the-oilman.aspx smoking at start up is very common as long as it doesnt continue U R ok! Just to prove my point about it being a common question see pistonheads IanUK1 always writes knowledgeably http://www.pistonheads.com/gassing/topic.asp?h=0&f=48&t=1188435&mid=0&nmt=Oil+for+996