Low Engine Temp Since Cold Weather?

'92 3.8, 198,000 miles.

Since it turned cold, my van temp gauge willl not go above the 2nd mark. It usually stays between the bottom mark and the 2nd mark. I am not getting getting any heat. I've read some of the threads about the heat exchanger but mine was replaced within the last 2000 miles. FAn works fine. I've noticed it running cooler a little earlier and replaced my thermostat hoping that would do it. I guess not. Any ideas?

I had that problem early with my van, and I'll try to make a long story short.
My early findings with the fuel management computer is that GM had not cared to install a precise fuel ratio algorithm for "lower" temperatures, but just figured out a SAFE fuel input to ensure the engine starts - meaning very rich - and counting on reaching radiply higher engine temperature at which time a valid "table" of ratios would be used.
This came from the fact that the smell of exhaust at lower temperature proved to be "very" rich - I'm from the time of carburator and choke so I know that smell - and the fuel consumption goes with it.
AND......the engine temperature would keep low.
THe GM assumption that higher temperature would be reached fast enough to discard metering precisely that part of the operation is wrong in cold climates.

NOw....I have experience as a private pilot and one known fact with aircraft piston engines is that during climb, when engine is at full or nearly full throttle, we keep the MIXTURE control at RICH (yeah, we control that manually in aircraft) for the purpose, in part, of COOLING THE ENGINE WITH EXTRA UNBURNED FUEL....(plus preventing preignition ...etc...)
I applied that wisdom to my van (concluded that the engine was FUEL COOLED) and added a switchable resistor (2200 ohms ) in parrallel with the engine temperature sensor to fool the computer and make it believe the engine was warmer than real - once the engine was started normal and then switch the resistor in after 1 minute - so that the computer says "OK now, I can lean the mixture".
It DID work positively in ALL aspects:
- enormous gain in mileage for short treks (once the engine is warm, the value or the sensor totally overwhelms the added resistor, so no change on long runs)
- no rich smell
- WARMER engine MUCH faster

NOtice that if by mistake my temperature correction is applied before starting in cold weather, the sngine will simply NOT fire up, showing how much this reduces the fuel contents.

..sorry, that was long anyway....

GUESS WHAT!!!

The thermostat I bought and installed did not come with a gasket. I installed a thermostat without a gasket. Therefore, no seal and the water would slowly seep around the sides of the thermostat. All I did was go to a GM dealer and get a thermostat that had the gasket installed and whamo!!! Everything is perfect. I got heat and I got normal operating temp. whoopeeee....

SUper: Best way to get rid of a problem is to not have one......
Happy warm winter.....