My Suburban temp gauge is pegged and no heat inside.

When the temp. gauge pegs hot what was the real temp of the engine ? Hook up a scan tool that can view live data to see what temp. sensor is reporting to the PCM / ECM , use a Infrared Thermometer to test temp at the engine . GM had instrument cluster gauge problems , bad stepper motors that control gauges . I replaced bunchesof these because people thought vehicle was overheating . 2003 to 2006 gm vehicles .

If the radiator was blocked you would have a very hot motor. I am thinking that the wire to the temp sender unit has broken or fallen of and is shorting out somewhere as this sends the gauge to full overheat. If ok replace the temp sender unit as it probably has a internal fault.

need to change the heat range of ur themostat

Having a blocked heater core will not make the engine over heat. You will just not get any of the heat from the fluid that would normally be pushed through the heater core because your core or cores are blocked (I think you have two cores if you have a rear heater.). The engine does not need your interior heater cores to keep cool. When you select "heat" on your console, either a valve opens up and allows fluid to move through the lines to your heater cores and or an air duct opens to the cores to blow air across them...

Did your heater work before your work?

Does the gauge stay pegged or does it fluctuate?

If your gauge now fluctuates after your work, it would indicate to me that there is air trapped in the engine or bubbles passing by. The air does not cool the engine block as well so the temp will rise quickly. It will then cool a bit as the coolant splashes by. If your gauge is staying hot and never moves, it could mean: you are missing a lot of coolant, trapped air near the temp sender, or your thermostat is not opening. A closed thermostat would make the gauge go all the way hot and stay hot. The thermostat can be checked with a pan of boiling water on the stove. When boiling, put the thermostat in the water and check to see if it opens. It is also important that the thermostat is installed in the correct direction. The temp sensor much be on the engine side. I am also assuming your pump shaft is not sheared and is still connected to the impeller and it is spinning as well. You can take your belt off and move it by hand to see if you feel any resistance. If you are sure the thermostat is opening and the pump circulating, I would then check and see if you have air in trapped in your system. I looked at my Uplander and noted a lot of hoses and metal pipes at a higher level than the filler neck of the radiator. Perhaps, when you filled your system back up from the radiator, that a lot of air got trapped in the upper part of the engine and the heater lines. I also saw that there were little brass valves near were the hoses connect near the pump and on the driver side. I would suggest running the engine and open and close the little brass check valve on the divers side to see if you have fluid or just air coming out. I wouldn

aFTER A HEATER CORE WENT OUT THE 454 OVERHEATED. hEATER COR REPLACED TEMP GUAGE STUCK PAST 160. cOOLING WORKS FINE NOW, TEMP GUAGE JUST PEGGED ON HIGH
wHAT NOW.....

You may have been given the wrong thermostat. Either way, you can try a hotter thermostat. If the water pump has never been changed it might be time for a new one. I've already had one that was so old that the propeller inside had the fins rusted completely off and the bearings were so bad it was messing up the timing of the motor. The truck wouldn't idle. And guess where alll the rusted off propeller chunks ended up. . . that's right. In the radiator, heater core and the thermostat. I flushed that truck for three days in both directions to get all that scrap out of there. Good Luck. And if you still have the old thermostat you can always throw that one back in, just to see what happens.

must have screwed up your temp sensor,could have plugged your heater valve,if you do replace the sensor get 1 from dealer not autozone, also low coolant level will affect the heater!

Sounds like there may be an air pocket in the system.
Try 'burping' the system. If this still doesn't fix the problem, check the temperature of the heater core hoses (in and out) The inlet should be fairly cool, the other should be piping hot. If they're both cold; the heater core has an internal blockage.

Next, replace the thermostat with a winter (180-195 F) derivative.
Bleed the system accordingly, and keep me posted!

Why do you need to know where the temp sensor is. It sounds like it is working properly. Check for thermostat not opening completely, or a clogged radiator.

jt\\it could be the water pump or the thermostat giving you problems