[HUMMERcustoms.com/TAZ]

Fubar sorry I did not follow the situation as You got further along. I did not think to check comments on the Pic section. Fubar, Allen programmed Your fans on the PCM He did for the dealer. He sets it for any rig that He is told will have electric fans. He set it to match what ever t-stat the dealer told Him You had. If going to 160 degree which I recommend He would reprogram it again or if He has a copy of Your program which He most likely does, He will be able to change the fan to match the 160 and swap PCM's with You.
The purpose of a t-stat is to get the engine to a temp that the factory wants before it opens and let's the coolant flow through the system and hold usually what ever the t-stat rating is. If the engine starts to cool down then a 190 t-stat will close till the engine temp is back to the 190 degree or higher. Well the same reasoning goes in why You run a 160 degree t-stat on the engine so that if You are having cooling problems or just want truck to run cooler to prevent detonation and yes an engine running to hot with the wrong grade of gas will have or can have detonation. The purpose of the 160 is so that the t-stat opens sooner than a 190 which allows the coolant to begin the cooling process sooner in this case 30 degrees sooner and it has to work with the fans as the fan has to be told that you need it to come on sooner with a 160 t-stat than a 190 t-stat. If You do not then You lose the efficiency of the t-stat and fan working together. The point is to not let it get hotter and have to let the fan work harder to keep the coolant temp low. Let the fans get as early a jump as they can starting to move the air through the radiator once the t-stat has opened to let water flow. Sooner water flows and sooner the fans blow You get cooler temps and everything runs better and lasts longer.
Same thing with many drag racing rigs. They will pull t-stat out completely and I had done on a 1968 Mustang that I raced and I had no t-stat, water wetter, and a higher mix of anti-freeze to keep it cooler so i did not blow a head gasket. Back in those days water wetter was just pouring some denatured alcohol into the radiator. Temp being to high can cause many problems but, one of those is a blown head gasket but, the real concern with cooling is to prevent detonation so that you can run bigger cams, carbs., and eveything else to get more HP.
The only place I would not be in a hurry to lower t-stat temp is in the case of a desiel engine. The fuel already has a high tolarence against combustion so cooler temp on it means jelled fuel if not careful. Everyone has their opinion and when You talk to people like LPE and other major engine and performance upgrade companies and they highly recommend 160 t-stat then it is just a matter of doing what You think You know is the right versus what some others say is the way to go. I personally have run a 160 t stat on My 5.3 Silverado with handheld tuning set a 93 octane runing 87 octane since 1999. Have not had any timing retard by nock sensor's and I did the same thing on the H2 for 12,000 miles and no problem's. So when i got MY sponsored HPTUNERS software i checked the way i was running and it should no problems with what I was doing and this software is at least as good as You can use. Once I up boost to 12 to 15 lbs. I have already seen on tuning that i will have to go up to 93 oct. fuel. Holding the temp low as possible to prevent detonation will no longer work by it self in running low octane and allot of timing advance etc.
Fubar it is MY feeling and many years of experience You have done the right thing by going to 160 t stat but unless the fan is programmed to work with it You do not get all the benefit. If or when you change t-stat call Allen and He will make arraingements to get you an adjusted PCM to work with the cooler t-stat.
There are going to be different and radicaly different opinions on all the different things in the workings of an engine from the oil pan to the carb. or fuel injection. BUt, it seems to Me to look at what the large companies do and recommend as in LPE for one and look at rigs that have followed a different MO and talk to as many as You can to see what is the predominate consensus amoung those who are and have dealt with this problem.
Fubar looks like You have done the things to correct the problem. I wish I had been smart enough to get My dealer to make My change to cover it under warranty instead of Me footing the bill but, I did not hesitate spending My own money because I had a problem with the AC not cooling and temp running to high on the gauge so rather than worry with it I spent about $500 to make the change and have never been happier with the temp. situation. So I hope Yours will be OK come next summer Fubar. Well Fubar My apologies for not thinking about checking quotes on the Pics board.
TAZ