The heat in my 98 tahoe blows warm but not enough for comfort . I flushed out every thing in cooling system and added new dex cool antifreeze and water and still no change in the heat what is the problem

Concentrated green .... any brand you choose. Then top off with water.

sometimes when you flush the system especially if you use a flush chemical and have a weak seam on the radiator, heater core, water pump, etc. any part of the cooling system it will cause a leak I have had it happen to me before, it sounds like the heater core is leaking which unfortunately is expensive to replace

Two things are possible. Air in the cooling system, or the system needs to be flushed. You didn't say what year your van is, but I'm sure it use dexcool antifreeze. Dexcool is the orange antifreeze recommended by GM for all their vehicles. The problem is that dex cool attacks gaskets causing gasket failures, especially the intake gaskets. It also can cause buildup in the cooling system causing overheating, or plugging up heater cores. We'll try the easy solution first.We need to get the air out of the system. First, the radiator needs to be higher than the engine. If it isn't, either use drive on ramps or raise the front end with a jack, Remove the radiator cap, put the heater controls on hottest setting, start the engine and let it run. When the coolant gets hot enough, the thermostat should open allowing the coolant to circulate. When it opens, the coolant level will drop in the radiator. Add antifreeze to make it full again. The coolant will drop again and may do so several times. Just keep adding antifreeze each time. continue to do this until the coolant level stabilizes. If the thermostat closes momentarily it will cause coolant to overflow. Not to worry, wait til it opens again and top off the antifreeze. Put the cap back on the radiator and check the heater for heat. If it' still not warm, you may have to flush the radiator.

You may have to flush the system again. Did you use a commercial flush such as Prestone Super Flush? Plain water won't remove the rust and sludge. The Dex-cool antifreeze that GM recommends for their cars is bad about forming a gummy sludge in the cooling system. It clogs radiators and heater cores. I would suggest another flush with the Prestone product. Follow the directions closely for best results. One thing that will help is. after you drain the radiator, refill with clear water and let the engine run until the coolant is circulating good, then drain it again. Do this three or four times. This will ensure that all the antifreeze has been removed from the engine block. When you refill the radiator, use a green antifreeze that is compatible with aluminum radiators and aluminum engine parts. Do not use Dex-cool. Dex-cool can also cause the intake gaskets to fail. Make sure the new thermostat is at least a 195degree unit and that it is installed correctly. you would be surprised how many thermostats get installed upside down. After refilling the radiator, leave the radiator cap off and let the engine run until the coolant is flowing. Keep adding antifreeze each time the coolant is pulled down into the radiator. Use full strength antifreeze because the water that is retained in the block will dilute it. A 50/50 mixture won't protect below freezing.

buy you a new temp sensor from the dealer not autozone,try that,my suburban did the same thing cause i got a cheap piece of **** sensor from az

you cannot mix dex and regular it will cause a gel affect you will need to get a coolant flush and change to regular dex is terrible it will be ok to do so

switch malfunction,blower not working,heating element burnt out.

It sounds like you need to service your cooling system. The cooling system may need to be flushed out due to dirty from corrosion. A sign of no heat in the heater and the engine is hot is low on antifreeze in the system. Check the antifreeze level first and add water just to get around to buy the things you need to service the cooling system. Buy antifreeze and a thermostat, drain the old antifreeze and replace the thermostat. Add new antifreeze with a 50/50 mix solution water/antifreeze. Too much antifreeze will gel and the cooling system will still run hot and to much water will boil over. Good luck. Keep me posted be glad to help.

The major reason for using dex-cool is that antifreeze is often neglected as a service item. If neglected, it becomes acidic over time which is particularly important with the use of aluminium in most major components which are served by antifreeze. Acid causes etching and premature failure of gaskets and permanent damage to blocks, heads and especially the radiator and heater core, which are not vert thick to begin with.
Since "normal" antifreeze acidifies faster than does dex-cool, mixing both together causes a change in breakdown rate...the more "normal" coolant added, the faster it breaks down.
Both coolants do not react chemically with each other and therefore retain the same ability to prevent boil over and freezing.
In reality, normal coolant can be used with little or no effect on components, provided that you change it every year. (that's where the EPA gets involved) They do not want people dumping this stuff into the ground, so they push for extended service intervals. Since dex cool has a longer service life, that's what they want you to use.
As far as how you chasnge the coolant, it is always a good idea to flush system during a change, regardless of antifreeze type. This removes solid particles which can plug radiator core. Radiators are much smaller than their older counterparts. Loss of even a small portion of cooling area can cause overheating. Engine running temps are also higher than older vehicles (heat=power output). Therefore most systems have a much smaller margin of error than before. What I find though is that regular flushing can also be bad for the system as the chems eat away at metal components in order to clean. I recommend regualr or dex cool antifreeze systems be flushed with water only, once a year, but retaining what you removed and filtering it through a coffee filter, using it during the year to "top off" the system. To retain effectiveness of coolant, use a hydrometer to check concentration, adding new coolant to bring reading to proper protection level.Then, every three years, do a complete chem flush and change entire batch. This keeps your system clean and the epa happy!

as long as the engine temperature is normal, i would suspect a clogged heater core, the dex-cool antifreeze is notorious for building up deposits in cooling system. have heater core flushed first to see if it makes any difference