I've recently bought a facelift 156 JTS and when it came to servicing I was planning to run 10w60. Visiting my local motor factors they were all out of stock, but in one place their catalogue showed 10w40semi as a "recommended alternative". Not wanting to jump in I went away to think about it.
I called Benfield Alfa in Newcastle to ask the opinion of the 'service manager' (accept that it could have been anyone on the phone in reality). I was told that 10w40 semi would be fine in a 2.0JTS. Apparently my owners manual should show 10w40 as an alternative oil, but my manual has suffered water damage and just my luck the relevant pages are stuck shut. Trying to pry them open has caused it to rip and I can't read anything.
Does anyone's manual mention 10w40?
I also considered the point that symon has already made, the JTS is a modifed TS, and from looking at diags I can't see any real difference in the lubrication system.
I also thought about the possibilty of Alfa changing the recommended grade to 10w60 only to address oil consumption, rather than engine modifications that would require a thicker oil. One clue would be if the engine ran hotter than a TS, which would be a good indicator that a thicker oil is neccessary, but my JTS runs at the same temperature as a TS (i've had 2 in the past and the wife currently has a TS).
Taking all this on board I decided to try 10w40 semi-synth. I accept that this will increase oil consumption and require more frequent changes, but I hope that it will improve engine lubrication and also the efficiency of the engine (a thinner oil is easier to pump) which will help with performance and economy.
I've now run 10w40 for 600 miles. It took less than a pint to top up, about the same it used on 10w60. Average mpg has increased from 29.9 to 32.4. The problem is that I also replaced the sparkplugs and air filter at the same time so I cant determine what difference anything has made in isolation. The engine is running fine on 10w40. Temperature is same as before and it sounds exactly the same. No evidence of low oil pressure when hot (you get a tapping noise when using too thin oil on an engine with hydraulic lifters). All this has made me feel confident so I plan to continue using 10w40 during my ownership.
Despite all this I will probably flush it again and refill with 10w60 when it comes to selling, simply because it may deter potential buyers if I say that I've used a different grade.
Has anyone got any experience of using 10w40 in the long term on a 2.0JTS?