Coolant temp sensor was just changed with no effect on the issue. The only thing I can see right now is because the fans are allowing so much cold air to go past them (on the sides) it is causing the engine to run cool.

 

Well block it in with cardboard and see if it helps.

 

Saskatchewan thermostat
I did that on my beater truck cause once I got to cruise speeds the temp would drop off

 

I have a near identical problem with my truck. Specs:

2002 Tahoe, 5.3 with all aluminum rad. However, switching fans will not solve your problem. I have 05+ fans, and am stuck around 170-180 in all situations. If I idle for what feels like hours, 200-210 can be achieved. I have blocked half the rad with cardboard, and of course the truck still takes all day to warm up, but wont cool off as much during cruise.

Like you, I believe the problem is the T stat, and I have a feeling we are both leaking coolant past it. You have replaced yours several times with the same result, but can we be sure its sealing to the water pump and to the T stat neck? I am certain our problems are the t stats leaking thru.

 

Fans were replaced this weekend but not really cold enough to see if it helped.

 

I have a 34" aluminum radiator with stock clutch fan, on a 1999 Silverado.
Similar situation, lower engine temp, 170*F. (40*F outside morning temp.)
Interior heat was at 90*F.
Changed thermostat, coolant, same heat.
Back flushed both sides, of heater hoses, at firewall.
I think, I got air, in the heater core.
I did run heater at full, with coolant reserve cap, off, 3,ooo rpms, then idle, repeated 3 times.
Needed to have truck, not level, front up higher.
Heater gets to 120*F, now.
Use a cooking thermometer, in the vent, to measure heater temp.

 

The only job the thermostat has is to open and close at a certain temp. It shouldn't matter how cold it is outside. The cylinder temp is high enough to heat the water in the block higher than 140* even if it is negative temps outside. Definitely a weird issue your having. What temp thermostat did you put in the truck?

 

Is this the Genesis Auto aluminum radiator?

 

My radiator is from Shepherd Automotive.
2002 Chevrolet tahoe All Aluminum Radiator

And to back up my theory of it being the t-stat:
When I did my cam, I replaced the OEM water pump with another AC Delco OE replacement. I did the radiator and 05+ e-fans at the same time as well. I reused my original thermostat neck and original thermostat.

As a result, I think I am leaking coolant past the thermostat. I mean, its more than a leak, it has to be a steady flow. And I was pretty certain that the old stat sealed to the new water pump, but mistakes do happen. You can't mix up the heater core hoses (differing ID's) and there is no way to put the rad hoses on wrong. And no, I do not have an external leak of coolant.

I have a truck with rear heat (Tahoe) and used a Service Bulletin I had found online to refill and bleed the cooling system, so I am at least 80% confident I did that part of the project correctly.

So in closing, the problem is either overcooling, which shouldnt happen because the t-stat should open and close accordingly. Or its a sealing issue allowing coolant to flow past the t-stat at some steady rate, thus severely slowing the warm up rate.

 

I'm having the same issue with my cooling system. Just did the 34" radiator and 05 efans and now it takes forever to get to temp. I changed the t-stat because I thought that was the issue as well. There is a definite liquid rushing sound in the heater core when I accelerate so I think there is an air bubble in the system and I plan on doing a full flush and using a this vacuum pump when I refill the system. http://http://www.amazon.com/UView-550500-AirLift-Economy-Refiller/dp/B000O3IGI6

Anyone use one?