Booked to travel in C class during August and the aircraft is a 737.

Do all the 737 have the updated short haul seats? Also, does LY still switch the IST routes to a bigger aircraft during the summer months?

Lastly, does anyone now which lounge LY uses at IST?

All the 737 have 16 updates craddle seats.
It does switch to a bigger a/c, but i think they already came out with the summer schedule so you can know what a/c you are flying. I actually flew a few months ago with a 767.

In August, all the widebodies are utilized for the USA, London and Far East routes. Those planes usually have a long layover in TLV between their arrival in the late afternoon and departure in the night. On busy evenings, they are used on short routes such as ATH, IST and LCA - especially before and after the weekends. If your flight is in the evening then you might get lucky. If your flight is in the morning - afternoon, the most you will get in case of an aircraft change is probably a 757.

I got really lucky and my TLV-IST was a 763 those C-class seats were very nice !

That's because they are Platinum class seats, which is great if you get them on a short hall or even medium hall like LHR but not great on the TLV-LAX route (vie YYZ) as they are not up to the standards of the new Flat bad or Flat bed style seats other curriers have on the route.

Clubman - Have you flown on the new 767 seats? They are actually very very comfortable. They are not full flat beds, but they are lie angled flat seats, with the same angles as on the AC and CO a/c. I actually think the 767 Platinum seats are more comfortabe then the LY First Class seats on the 777 and 744.
If you open the link and check out the first seats, the 7800 Sleeper Seat System, its the same seat but w/o the "Built-in privacy shroud."
http://www.weberair.com/businessmodels.html

BTW - The 7070 System is something like what LY has in the 777 Platinum but w/o such a good recline, and the 8080 System is very similiar to what LY has in First Class.

So far Weber has been the supplier of seats for LY, up until the recent order of Secma seats for the new J class seats in the 777 and 744.

I have flown on the 767 in Platinum class (ages ago though) although since most of my flights with Elal are TLV-LHR and other short hall, when I do fly the 767 its usually in Business Class configurations rather then Platinum.
I know that the 763's have different seats to the rest of the fleet (they are leather aren�t they?) but don't the 762's with platinum class have the same seats as the 777/747 platinum, or have they already been changed?

All the 767 have the new lie angled seats - same seats as in the pictures above.
In a/c, 4x-eaa and 4x-eab th pitch is 55' in the rest eac,ead,eae,eaf,eaj,eap the pitch is at 60'.

They are totally diferent then the seats in the 777 and or the 744. No two aircraft types ever had the sames seats. There were always different seats in the 777, 744, 742, and 767. Today their are still differences between the seats in the 777 and 744. That will chang soon after LY install the new flat seats - The new seats for the 777 and 744 are like the new ones installed in Iberia, Finnair and SAA (A340).

Agreed, they are much more comfortable than the flashier more complex seats they have on the 777s. In these seats I can sleep on my side and I'm not a small guy.