Shell Helix HX5 15w40 or Helix HX7 10w40

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As above,what would you recommend in an old carb Engine that doesn't do a lot of miles.I can get both Shell Helix HX5 15w40 and HX7 10w40 very cheap,however i have been unable to find the HX5 in 10w40.The car will only be used in summer,not long trips and temps between 12c and 28c.
 
Hi Ether,

Great question, I wonder the same thing myself. Here are some related threads:
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4566960/
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4146392/
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4293744/
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4583594/

As you know the Shell HX5 15W40 is a mineral oil rated API SN/CF and ACEA A3/B3.
The Shell HX7 10W40 is a semi-synthetic oil rated API SN/CF and ACEA A3/B4 plus it carries OEMs like MB 229.3 and VW 502/505.

Before reading the threads above, I would always go for the HX7, but after valuable input from various oil formulators here, I now find I'm double guessing myself.

It seems like it's harder to get B4 over B3 due to some deposit tests - making HX7 the pick. But it also sounds like most oils are developed as a matrix of various grades together, so that the HX5 would probably pass as a B4 (except for TBN) but it's aimed at a different segment of the market so they may undersell it so as not to steal sales from their more expensive products - making HX5 the best bargain.

Let me know when you work it out, I haven't yet.
 
I'll just add that guessing what they may have done when developing an oil does not equal carrying the official spec on the bottle - advantage HX7.

But a mineral 15W40 with SN & A3/B3 is a good oil, meets the exact requirements written down in my car's owners manual and is very cheap for me to buy. I know lots or people who run nothing but this oil for the full life of their car without any oil related problems - advantage HX5.
 
OP, I just found this

It's an old PDF from Shell (June 2008), so be warned the oil formula may have changed since the document was produced, but it does say "Shell Helix HX7 offers up to 24% more protection from oil degradation and up to 34% more shear stability than Shell Helix HX5."

Probably not important if you don't do a lot of miles between oil changes. But it's the only comparison of HX7 and HX5 that I could find.
 
SR5,Thanks very much for the detailed info.It seems to be very difficult to decide,or work out which is better,more so if you like trying different oils.I have for the last 20 years used semi synthetics in this car,but i am now thinking that the 10w40/15w40 mineral oils appear to be so good nowadays,and so cheap,that the sensible choice would be to just use one of these and be done with it.I am now also looking at the new Castrol GTX Ultraclean in 10w40 flavour,just to make the choice even more complicated.I think my main criteria in choosing an oil for this car would be something that is good at resisting fuel dilution,short trips,along with good cleaning and heat/shear resistance.
 
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