Temp gauge all over. no heat,sometimes

[tooslowtahoe]

99 tahoe. from the title my temp gauge is all the place during most driving cycles. when i remote start the vehicle after about 10 mins or so when i get in temp is about normal and the heat blowing is warm to hot so no problem there. after driving for a while 10 mins 30 mins whatever at some point the temp gauge will go all the way up and the heat will turn cold ice cold air is blowing at this time. just before the gauge gets all the way up it will then just fall all the way back down still blowing cold air at some point the gauge will go back to normal and the heat will be warm to hot again. this cycle happens several times while im driving city and highway.

Any ideas what would cause this.

 

[Tricky's_Limitedhoe]

Possible stuck thermostat, would change that first or bad temp sensor. How is coolant level? Make sure it's not leaking anywhere and check passenger floor board to make sure it's not heater core, or bad radiator.


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[tooslowtahoe]

coolant level is good has been the same level for weeks now so i dont think its leaking no wet carpet so i guess ill try the thermostat and temp sensor since both are next to each other, guess i check the wiring to the sensor too

 

[twomanymontes]

Sounds like the thermostat is stuck open. Sitting at an idle the air flow through the radiator is minimal, once you start to drive, more air flow and RPMs, it cools the coolant faster causing the heat to drop off.

I'd try replacing that first.

 

[TruckinAin4Sissies]

You said "gauge will go all the way up and blow cold" I'd guess you have air in the (coolant) system.

The ONLY way I was able to bleed out the air was the following:

* Front tires on ramps
* Remove radiator cap (when cold)
* Run the engine, heater on high for 10 minutes then shut off
* Monitor coolant level, topping off as it needs it (over 20 minutes)
* Repeat until you cannot add anymore

Overall process took me about 3 hours






TA4S

 

[TylerZ281500]

bleeding coolant system is easy. ive done it many times and should cure you blowing cold moving guage issues

open hood, take of rad cap, turn on truck, turn heat on alll the way, let her idle till the thermostat open and such you can see all the bubbles come out, then top her off while the amount gets lower. turn vehicle off to reinstall cap.

its easy to test thermostat but i dont think thats the case. also if the system isnt pressurizing properly it could be allwoing air in through your radiator cap.

 

[tooslowtahoe]

thanks guys i have one of those funnel things thats made for bleeding the coolant system ill try that also replace the radiator cap looks like its had better days. thanks again