As someone who has been operating vehicles in an extremely hot and dusty climate for many years, I will chime in with an example based on experiences of my own. I will focus on the Mustang GT Fastback Performance Package (Coyote 5.0L V8), as this is the newest vehicle in my fleet with 16,000 km (10,000 miles) on the clock.
Going against the OE recommendation of 5W-20, factory fill was dumped at the 1,500 km (938 mile) mark and replaced with Motorcraft 5W-50 and an FL-500S filter. This oil change was a complete mess - as soon as you started unscrewing the drain plug, oil started seeping out like water and the gushed out all over the place as soon as the plug came off. Until the vehicle is officially out of warranty, I will continue to have all maintenance done by the same dealership. Although I have had close contacts of my own at the dealer for many years, I prefer they regularly see the car for services and checkups.
Fuel wise, the vehicle runs Euro V rated 95 RON. As the local refineries are only capable of producing Euro II rated gasoline with an octane rating ranging from 91-95, Euro V is imported from the UK and is refined by Kuwait Petroleum International's refineries there.
At the 5,000 km (3,000 mile) mark, the oil and filter was changed along with the air and cabin filters. I still used Motorcraft 5W-50, but switched to a Fram Ultra XG10575 at this point. Although the dealership recommends oil changes every 10,000 km (6,250 miles) with Motorcraft 5W-20, I do a simple drain/refill at the 5,000 km (3,000 mile) mark along with new air and cabin filters. At the 10,000 km (6,250 mile) mark, the oil filter is replaced along with the oil and the usual air/cabin filters. Even with 5,000 km (3,000 miles) on them, the air and cabin filters are full of extremely fine sand particles. You feel a difference in the air conditioning as soon as the cabin filter is changed out.
At the 5,000 km (3,000 mile) mark with 5W-50, it'll still drain out watery, albeit more viscous, just not as watery and free flowing as 5W-20. With all that being said, I have heard other Mustang owners complain to service advisors about their engines ticking like a type writer and you can really hear it, almost like a rod knock. One of them I spoke to said he was running 5W-20 with ~18,000 km (11,250 miles). I, touch wood, have not had this problem.
Depending on the time of day, ambient temperatures this time of year range between the 120 °F - 130 °F. You're welcome to check out these articles:
Temperatures to hit Kuwait 68 degrees C. this summer (05/28/2019)
Kuwait and Saudi Arabia record highest temperature on earth (06/12/2019)
Kuwait City Makes Claim of 63 Degrees Celsius (06/14/2019)
Kuwait witness 62 degrees Celsius temperature, Trees and bushes catch fire (08/08/2017)
At the end of the work day, 16:30 hrs, the ambient temperature is between 120 °F - 122 °F. Coolant temperature on a "cold" engine that has been sitting for 9 hours will be in the 118 °F - 125 °F range. If allowed to idle, the engine will hit operating temperature within 5 minutes of firing up. If you wait for it to drop off high idle and drive off, you will hit operating temperature in about 2 minutes.
ATF, on the other hand, will be within the 125 °F - 130 °F range, and with a thermostat in the air-to-oil cooler, it'll hit about 190 °F within 5 minutes of driving. The 212 °F - 215+ °F range isn't far fetched and once in this range, the transmission may bang into gear when shifting from neutral to drive at the lights, for instance.
The other thing that doesn't get as much attention and really takes a hit in high temperatures is the electrical system. You'll get a voltage reading of 13.9 V at start up on a summer day (14.3V in the cooler months), but turn the AC and as soon as the cooling fan kicks in at full blast, you're looking at a voltage reading of 12.0 V at the battery post. Often I find myself turning off the AC, even in a one year old car, to help with engine cooling with the AC clutch disengaged. Not fun, even with tinted windows, but it's not long before coolant temperature exceeds 218 °F. If you really get on it at those temperatures, the engine will experiencing preignition and that is definitely not something I want on an engine this new, so I will baby it. The load on the electrical system and high engine temperatures get worse if you happen to hit traffic, particularly after sunset.
ATF and Differential fluid was also replaced at the 15,000 km (9,375 miles) with Motorcraft 75W-140 over the recommended 75W-80. The factory stuff was super thin in comparison.
This isn't a Mustang thing either, it's exactly the same with my Grand Marquis that has an electrical fan. The Envoy (although electroviscous), Explorer and Pajero have the added advantage of an engine-driven clutched fan and that still seems the way forward in hot climates.
Tires are another issue. The factory Pirelli P Zero (255/40ZR19) tires had to be replaced at the 12,000 km (7,500 miles). I run Goodyear Eagle F1 Asymmetric 3 (245/45R18) on the Grand Marquis and generally summer performance tires do not tend to fare very well in the heat, even if you drive sensibly.
In a nutshell, I haven't done any oil analysis to be fair so there is no "hard evidence" to back anything up. But I personally refrain from running thinner oils in this climate, even if the engine was "designed around it". There are no CAFE, fuel economy or emissions requirements in this part of the world and that's one less thing to worry about. My engine is not ticking like other folks' engines are, and yes I change oil much more frequently, but it works for me and I'm going to keep doing it. YMMV.
