5w40 v 15w40

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subaqua

What’s the point
Location
Leytonstone
my old jeep Cherokee had a table in the operators manual that listed several grades dependent on environment. I kept 20w50 in it as I found that it stayed inside a lot longer than 15w40 , to be fair if it didn't leak it wouldn't have been a Jeep. best thjing was running it on LPG as the oil was almost as clean coming back out on oil change time as it was going in . ( might be due to changing the oil through leakage ;) )
 

madmadmax

Regular
Location
sheffiled
come on guy we could be talking about his/her pride and joy, oils do more than one job in an engine it cooles and dampens noise as well as lubrication so running a 5w oil will make the engine louder but will not change the running temp of the engine also you need to take into acount for how the car will be driven if its doing start stop and short distance so that it never warms up then drop down to a 10w40 (this is what i would be doing to the car if it came to me for a service as good quoltey 10w/40 oils are much easier to get hold of).

then thers the seals that have been skoed in minral oil all there life, going to a 5w will more than likley make them leack and once thay start the seal will have to be replaced also the thiner oil will mean the oil ring on the pistion will leave more there so it will burn oil which will contaminat the cat if its got one

hears some reading if you whant its abit more redabul than the kewenginering and is more geared with exsplaning whats going on rather than tecnical infomation
http://www.bobistheoilguy.com/motor-oil-101/

[QUOTE 3459126, member: 9609"]a 5w40 will still be far thicker than an sae40 at 100°c[/QUOTE] you got that mixed up the 5w/40 will be thiner than the sea40 @40°c not thicker becaus at 100°c thay will be the same thickness
 

screenman

Legendary Member
What ever you do don't take my advice, I am a high mileage 40,000+ per annum I buy cars at about 70,000 and sell them at about 185,000, services, well maybe sometimes, oil, well whatever I find knocking around I have even been known to use clean second hand oil. You might have guessed I am also in the motor trade and have been so all my working life. I have been known to do over 100,000 miles with no oil and filter change only top ups.

I know terrible, but cobblers shoes and all that.
 

madmadmax

Regular
Location
sheffiled
multi grade oils where made to make the oil thiner at colder temps so saying a straight s.e.a 40 is thiner at lower temps than a 5w/40 is wrong, i think you misinterpreted the graph in your link.

ok what if the car never gets to running temp then what? (bearing in mind running temp for an engine is betwean 80-90°C)

the 5w/40 will most likley be a synthetic oil, the synthetic oils have more detergents in them so thay clean all the deposits away from the seal and then you have a leack never seid dammage. the other thing that can happen is the seals exspand when exsposed to certen camicals mostley potrolium distilates that are some times in minral oils and not in synthetic oils so with the synthetic oils the seal shrinks back to its orignal size and there you have it a leack where ther was non befor.

burning oil is where and tear so the 5w/40 will accentuate whats allredey there and the clerances pistion to bore where desined for a 15w/40 so the oil scraper ring will leave more on the bore wall at warm up if you use a 5w/40.
 

albion

Guru
Location
South Tyneside
Reminds me of the history of 0W/40.
Mobil brought it out (mid 80s ?) demonstrating near zero engine, cold starting being the prime cause of knackered engines.
The problem for them was that Castrol had the deals with the manufactures so, what appeared to be an orchestrated campaign against decent oil.

With the repair industry worth billions, I can assume the outcome was that Mobil struggled, with the public being scared back into using standard really rubbish oil that you, back then, got from the likes of Kwik Fit.
 

Mr Celine

Discordian
ok what if the car never gets to running temp then what? (bearing in mind running temp for an engine is betwean 80-90°C)

Most cars run considerably hotter than this. 90°C is approximately the temperature that radiator thermostats begin to open at, and cooling fans don't normally come on until past 100. And that's the temperature of the coolant, not the oil.
 

gbb

Legendary Member
Location
Peterborough
Errr ……… I am the one who raised the issue of mileage. A higher mileage means the engine might be more worn i.e. bearings. A new engine is much tighter as it is …… new. I would still go with what the oil rating the manufacturer recommends.
Yes, you did. So did Screenman. :thumbsup:
Apologies, that sounded odd. I saw Screenmans post first, missed yours. Youre both quite right (IMO) to raise the issue of mileage
 
OP
OP
Chris S

Chris S

Legendary Member
Location
Birmingham
Thanks for all the advice - I'll just get the 15w40 that Nissan recommend. Halfords have sold out of 5w40 now anyway.
Just out of interest, is 'thickness' necessarily the same as 'viscosity'?
 
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