heat sometimes, not others
 

new to site, let me know if i'm not doing this right


I have a 2005 chevy Silverado 5300 v8, 4x4 ext cab


I had my truck overheat a month ago out of nowhere after getting a coolant temperature hot warning. I started by replacing the thermostat, then noticed a leak and replaced both gaskets on water pump. temperature normal but still no heat. i flushed heater core, topped off fluids, and drove the vehicle everyday for the last two weeks. I had heat for a few days, and then ambient. sometimes when turning on heat, get heat for a few seconds and then ambient air. then a couple days later had full heat again. have burped the coolant system also.


I have noticed on days when the outside temp is above 50 I have all the heat in the world. but when driving to work in the morning and it's only 40 out, there is barely any heat at all, even at normal operating temp.


coolant system is an overflow bottle with cap; no radiator cap


does anyone have a clue? any help would be greatly appreciated.




this next part is just an FYI, no question about what's written below.
during the summer, typical Silverado a/c issue I've heard, is when the a/c starts blowing hot air after awhile or after adjusting high or low blower setting, but turning off the ignition and restarting resolves the issue. also have the same issue with driver's side heated seat turning on all by itself when it's humid or raining all on its own

you may still have air in the cooling system. do you get more heat when you raise and hold the engine rpm to 2000?





your a.c problem may be low refrigerant levels or a tire a.c compressor. start by confirming the proper refidgerant level.

do you think burping the system needs to be done repeatedly?

do the test I suggested as its a good indication of low coolant/ air in the system.


Modern vehicles cooling systems should be vacuum filled. Manual filling requires multiple thermocycles to get rid of trapped air. Even them, it can still be a problem.


your problem can only be; either a bend door problem or heat transfer problem from the cooling system.

• thanks, i'm working all day today, I will do first thing sunday morning and let you know

thanks for your support and I will keep you posted

make sure your a normal operation temp when you do this

just an update from driving to and from work today, had heat all the way to work and when I got off work.


will do your suggestion tomorrow i'm off all day so I should be able to get some progress and get back with you.


thanks again for all of you assistance

further info
 

are you still out there?

So does the bypass in this picture indicate the new hose goes from the water pump and sweep around the engine to the three way junction, or does it go all the way to the firewall to the inlet/outlet pipes of the heater core?

The picture unfortunately cuts off the view.
https://cimg5.ibsrv.net/gimg/chevrol...f7e103197f.jpg

If it goes directly to the inlet/outlet I am wondering what happens to the flow when you cut out the three way junction?

I assume you are stopping the flow getting to the rear heater core if you bypass the three way junction and connect it to the pipe that comes out of the front heater core pipe at the firewall?