My 2004 duramax engine temperature never reaches above 185 degrees weather low on anti-freeze or not. I have a chronic low coolant level message even when the resevoir still has some in the bottom. System seems slow to fill through the resevoir but I can't find any other place to shortcut that process what do you recommend?

the lowering on the temp gauge indicates a lack of coolant around the bulb of the temp sender unit or a lack of flow around the cooling system
could be from low coolant level or blockage in the coolant system from forming ice ( 16 degrees is -8 degrees Celsius which is below freezing point of water)
I suggest that you check the antifreeze ratio in the cooling system and it should be no less than 50/50 to water
any thing less than 50 % antifreeze in the water will allow the coolant to freeze up which may be your problem
coolant condition should be checked every season as it does deteriorate over time and the % ratio will drop
topping up with normal water is another method of lowering the % point
check with a radiator shop or dealer service center to get the correct % of antifreeze for below freezing conditions and keep it at that point

This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.
A code P0128 may mean that one or more of the following has happened:

• Low engine coolant level
• Leaking or stuck open thermostat
• Faulty cooling fan (running too much)
• Faulty coolant temperature (ECT) sensor
• Faulty intake air temperature (IAT) sensor

Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:

• Verify coolant strength & level
• Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
• Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
• Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
• If the above items check out good, replace the thermostat

you have all ready replaced the thermostat with the proper temperature opening thermostat(hopefully) and coolant sensor, you say you have to refill the coolant every 2 weeks this indicates that you either have a coolant leak that needs to be checked out and repaired or you are burning coolant which indicates a possible head gasket problem which will have to be checked. a low coolant level will set this code as there is not enough coolant in the engine to get the engine to operating temperature and stay there. these last suggestions is where I would start to look.

The water expands up to more than 9% when it freeze below 0 degrees Celsius. Due to this phenomena, during the extreme cold weather when the ambient temperature falls below 0 degrees the cylinder blocks of the automotive engines often burst or crack badly.
This damage can be prevented by using the antifreeze coolant in the cooling system.

white smoke is caused by-- water or anti-freeze entering cylinder . if in radiator or the overflow tank. it will look like a chocolate milk shake. check on oil dipstick for traces of water or anti-freeze. also, a bad head gasket will let water or anti-freeze in combustion area. head gasket symtoms if bad. Symptom #1: Chronic Engine Overheating
Symptom #2: Significant Drop in Coolant Level Symptom #3: Mixing of Coolant and Engine Oil
Symptom #4: White Smoke from Exhaust Pipe
popping of overflow cap Symptom #6: Air Bubbles in Radiator
Symptom #7: Engine Lacks Power GOOD-DAY!

Look for a crack in the block or head, a blown gasket, or a bad expansion plug*. I assume the water is your coolant. If that is the case, the level in the radiator will be low.
The coolant leak could be up higher - perhaps it's coming from the thermostat plumbing or the temperature sensor. It could even be a crack in one of the heater hoses. The worst case is the cracked block - in that case the engine is essentially junk. A leaky hose connection is the easiest to fix.
*Note on expansion plugs (AKA freeze plugs). These look like inverted jar lids pressed into the block and are designed to be pushed out if the coolant freezes so the expansion of the ice doesn't crack the block (freezing can happen if you don't have a proper anti-freeze/water mix in cold weather). If you don't replace your anti-freeze according to the maintenance schedule, they may rust out and cause a leak.

Well, I can't give you any specific information regarding your vehicle because you forgot to mention what kind of vehicle you have. (This is kinda important if you really want some help figuring out what is wrong with your car)

The "Generic OBD" of code P0128 is "Coolant Temperature Below Thermostat Regulating Temperature"

The most likely cause is a stuck-open thermostat, however, I have also seen defective Engine Coolant Temperature (ECT) sensors also cause this code.

will try to help. sounds like a low coolant problem,remove radiator cap w/engine running,being very careful,contents under pressure! suggest you start it after it;s cooled down, then proceed with radiator cap removal. you can visually check the coolant level in the radiator this way.as the engine warms, the coolant should start to flow around inside so you can see it moving. top the radiator off with proper coolant,anti-freeze,green.turn your heat on high while waiting on engine to reach it's operating temperature.top or fill coolant level to the top of radiator, replace the cap and check for proper coolant level on tha plastic jug, to the side of radiator,if low fill to warm level, you should be able to see proper coolant level on the side of the plastic jug.if this does'nt repair your problem you may have a bad thermostat in the engine.if you need instructions on thermostat replacement, please post you question for instructions, with engine size, year and make and model of your car and we'll be happy to help!!thank you for choosing fixya.com and we look forward to assisting you in the future.!!

First check your antifreeze level - especially if your car is equipped with the 3.4L engine. these are known for coolant leaks due to failed intake manifold gaskets. Coolant levels that are slightly low can cause poor circulation through the heater core and can "fool" your gauge sending unit into "thinking" that the temp is low when the engine is actually on the verge of overheating.

If the coolant level is OK when you check it, replace the thermostat.

P0300 is a code for multiple misfire. Which could be created to the P0128
P0128 PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat.
A code P0128 may mean that one or more of the following has happened:

• Low engine coolant level
• Leaking or stuck open thermostat
• Faulty cooling fan (running too much)
• Faulty coolant temperature (ECT) sensor
• Faulty intake air temperature (IAT) sensor

Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:

• Verify coolant strength & level
• Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
• Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
• Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
• If the above items check out good, replace the thermostat

Good luck and hope this helps. keep me posted, be glad to know your car is running 100% again soon.

Check the following :

BMW Code PO128
This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125
In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant

temperature (ECT) sensor reading, and the speed of the vehicle.

You will likely not notice any drivability problems other than the MIL illumination.
A code P0128 may mean that one or more of the following has happened:

• Low engine coolant level
• Leaking or stuck open thermostat
• Faulty cooling fan (running too much)
• Faulty coolant temperature (ECT) sensor
• Faulty intake air temperature (IAT) sensor

solutions
Past experience indicates that the most likely solution is to replace the thermostat. Verify coolant strength & level

• Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
• Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
• Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
• If the above items check out good, replace the thermostat