The temperature gauge should read somewhere in the middle third of the scale when the truck's warmed up. You should be getting SOME heat by the time it reaches the one-quarter mark, though.

If the no-heat problem started when you swapped out your thermostat, or shortly thereafter, the thermostat would be the very first thing I'd suspect.

I wouldn't worry too much about blowing a head gasket with a standard 195-degree thermostat. That's the OEM temperature and the engine was built to operate in that range. You usually don't blow out head gaskets unless the gauge is pegged or very nearly so.

 

Mine rests just above the second line and it's in good working order. Literally at the bottom of the first third. I'm also running a 180*. When It had the 195* it ran just slightly hotter than that. I think it varies from truck to truck.

Always test your thermostats on the stove, in a pot, with a thermometer to make sure they work properly. That way there's no guess work involved.

 

i've had this same issue for a while myself. for me i know it's a restriction in the core. i've flushed it and gotten decent heat now. i just don't want to pull the dash you can use a pressure washer to help clear it put then hook the hosed up backwards and see what you get. you aren't trying to seal all the pressure in. it's the air that gets sucked in with the water as it rushes in that breaks it loose.

 

Mine had the same issue. The heater core was mostly clogged up. Take your heater hoses off and flush the core out with a garden hose. Alternate side of flow and repeat till you get a good clean looking and full flow of water through it. After that reinstall the heater hoses on the opposite ports on the heater core to have the circulation reversed through the heater core. My heat was hotter than ever after that.

 

one point that should be made on the flushing is that if it's plugged up it's possible that the inside of the core has corroded. you could make it leak by taking out the crap that held it together. that's unlikely though. i haven't had that happen. usually what i've found looks like clay and most of the time i can get the customer to own up to putting stop leak in it hoping to avoid a radiator replacement or head gaskets (not sure how the stuff worked but it claimed it would seal a head gasket or cracked head lol) and that stuff has cost ppl alott of cash.

example
it was a 2007 cad cts if i remember correctly and they had the normal bars stop leak in it. the issue started off as a shrunken o ring... the end was
$1500 for labor on the heater core (big big big job) and $350 for the core.
$350 for labor on a rad and the part was $500 (was made of gold or some crap just for the northstar apparently)
then i had to pop out the core plugs to clean the walls of clay from the coolant jackets around the cyls and flush the hell out of the system. needless to say he doesn't use stop leak anymore for anything and he tried to get reimbursed for it. no go they have on the label a smalll print legal thing that basically sais "we are not responsible for damages".

BUT he has heat now

the morall is pay attention to what comes out and if it's a clay substance flush the entire system. and most liekely what ever they put it in for was replaced already so you shouldn't have a rad leak. to date i've only ever seen it plug the heater cores and radiator. maybe slowed down a leak at best. i quit using it when i was 16 because i was very cold afterwards.

 

I replaced the radiator first because it sprung a leak. Then the water pump went and I figured might as well replace the termo as well. After all that it ran cooler and winter hit and that's when I noticed the cold heat. It could be that I didn't flush it just drained whatever I could and

 

I replaced the radiator first because it sprung a leak. Then the water pump went and I figured might as well replace the termo as well. After all that it ran cooler and winter hit and that's when I noticed the cold heat. It could be that I didn't flush it just drained whatever I could and then filled it up and ran it without the cap on or maybe it did gunk up the core.

 

Take your thermostat out and check it on the stove with a thermometer. Then you can at least rule that out, if it's operating correctly. Besides the thermostat, all you changed was the radiator and water pump right? I can't see either of those making your truck run colder than it should. Unless maybe you got a hose mixed up or something lol. Hope you get it figured out.

 

you don't have to pull the thermo out if you have a infrared temp gun. just aim it at the thermo housing (in our case as close as you can on the hose) and assuming you have a 195 therm you should see 195-210 on vehicles. since you'll be on the hose and not the housing itself it may be a bit cooler but aslong as it's over 180 you should have plenty of heat. also you can grab the heater hoses and one should be hot as **** and the other should be notably cooler but not cold. if it's cold then you have a blockage of coolant flow. if they are both equally hot then i would suspect that you have air flow issue. the main point is that if the engine is above 180 you should have heat. i normally look for 120-140 from the vents on a customers car no matter what thermostat they have. anything below that indicate a problem in my eyes.

one other trick is if you think the engine is staying cold use a hose clamp (like the ones that pinch it off) and let idle for a few mins with the heat on and see if it starts to warm up some. just watch the temp gauge so you don't boil it.