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Well the switch I use is supposed to come on at 170, so if you are using an adjustable unit then I would shoot for that or a little less. I used the $20 option that you mount to the radiator hose. It has been there for the past 4 years with no trouble, kicks the fan on when needed. If you want to use your a/c then you need the relay as well it cost about the same, but you probalby knew all this. Again I would shoot for 160-170 I don't think you can kick the fan on too soon the sooner the better, however my truck temp runs right were it should yet the fan doesn't come on that often. This upgrade won't throw your a** back in the seat but it will make your truck seem to perform better or at least it did for me and ever post I have read on this subject says something similar, would definitely do it all over again. Good luck the hardest part will be getting the fan clutch off.
Thanks for the advice. One says a little lower, one says a little higher, but both about the same as the t-stat. Anyways, I will be using a 180 or 190 stat (need the heat in the cab up here ). I don't have a fan clutch. I am running an older engine with a carb, and I have the direct bolt on flex fan. I just need to unbolt it and use smaller bolts to re bolt the water pump pully to the pump. Thanks guys.
Upsss! if your are planing remove stock fan and install a electric fan thinks are a bit different:
Install Switch at water pump inlet connection and set up it to 15ºF lower than T-stat. This is the best configuration based on my experience.
There is an optional configuration: install switch at engine block, where is installed gauge temp sender (3/8" NPT), setup it to 5ºF higher than T-stat opening point. This conf. works better than any other.
I wrote a big spill on my opinion then deleted it. It is all up to the user, these things run pretty efficent cooling wise if everything is in good shape, so you have some room for personal discovery. Later
Originally posted by SPROCKET Really makes no sense having them come on before the T-Stat even opens, I personally like it to warm up faster and run better.
Well, it depends on switch location, remember temp. at engine block where gauge sender is locate is always 3 to 10ºF lower than temp read at t-stat elbow connection (Where EFI temp. sender is located) This is a typical behavior of inline engines 6L and 8L.
Guess it really depends where you're installing the temp sensor and what you're using to measure the temperature. I installed both temp sensors before the water inlet on the readiator and used a laser thermometer to get the actual temp.