Heat Sometimes Blows Hot, Sometimes Luke Warm

[NeWyoRksPLaYaZ]

sup guys, so recently its been getting really cold out and ive noticed that the heat isnt at as hot as should be. First off if the car sat overnight and i go start it and leave it started with the heat on full blast, it will still blow cold even if the car is fully warmed up(at operating temps), for ex I started my car this morning and let it idle for a solid 10 mins with the heat on full and when i got in my car the heat was blowing luke warm. If i drive for about 30 mins, then it starts to get hot and toasty, is that normal on old cars or could it be a bad heater core?

I did however notice a tiny puddle of coolant a few days ago under my car near the crossmember motor mounts, almost in the middle of the car but towards the back on the engine, like behind the tranny almost? it was a small puddle but i havnt seen it lately so i thought maybe it was something else because i did a drain and fill after i changed my thermostat and maybe there was too much coolant and that was the weak spot where it leaked out? im still a noob at this so any ideas are greatly appreciated. thanks in advance

i also wanted to add that if i start driving on the highway again i notice it start to get cooler but its not so bad as in the mornings or cold starts. Also if i dont go on the highway at all or drive for a while, it doesnt get hot..last night i went to cvs and its a about 10 mins each way and the whole drive there and the drive back, the heat wasnt hot just luke warm

 

[salvageddsm]

its low on coolant for the heat to work top it off, then presure test your cooling system to find the leak

 

[Talondvr]

Could be blockage in the heater core. You could try to back flush it to see if it will dislodge anything. Do you smell coolant driving down the road at all? Stock cooling system (fans/radiator)??

 

[NeWyoRksPLaYaZ]

dont smell coolant at all while driving or standing, and i have no a/c so i only have one fan. also stock radiator..ill try topping off the rad when i get home and see what happens.

 

[Pwrtrip75]

Someone could have put some "stop-leak" in it also. My sister did that to her van that leaked coolant, then the heater quit working. ive had luck back flushing them. Or thermostat could be sticking open.

 

[Talondvr]

X2 on checking the thermostat. Does it take a while for the gauge to read normal temp. When I blows hot/cold does the temp gauge change at all with it?

 

[johnovision27]

Get your car up to operating temp, crank the heater inside and then pop the hood. Find the 2 coolant tubes that go from the thermostat housing to the heater core (to the firewall, under the intake piping) and make sure they're both hot. Warm won't cut it. You should only be able to hold on to them for a couple seconds before burning yourself.
If one or both are warm, then you have a heatercore blockage and good luck with the swap. It was the first thing to go into the interior when the car was built, and there is NO easy way to get it out.

Also, to check and see if your thermostat is working properly, get it to operating temp, and then check the 2 rad hoses. they should be pressurized and the rad will be hot.

If it came from the back of the engine, check the hoses going into the underside of the throttle body, as well as those going to the firewall. They tend to break down over time and start to crack. If you're lucky, you'll just have to replace those hoses

And TOP UP YOUR COOLANT AND OVERFLOW BOTTLE!

Good luck.

 

[rEclipserGST]

I have replaced everything besides the heater core. Will try to backflush it one more time before replacing the heater core.

 

[Pwrtrip75]

Are the radiator hoses even hot?

 

[Rsawd95dsm]

check turbo coolant lines mine were old and failed and my heat wasnt working well till I found that issue

 

[NeWyoRksPLaYaZ]

Ok so I checked out both hoses and they are hott like very hot..its not leaking coolant anymore either..also coolant was topped off already..thermostat is working properly and heat still sometimes blows hot. Maybe its just really cold?

Thanks for the help guys, I really appreciate it.

Turbo lines are brand new since turbo is only 2 months old. Hmm

 

[Pwrtrip75]

Water pump maybe? Start it up cold with the radiator cap off... Let it warm up and see if there is any movement of the coolant.

 

[Cassanova122407]

Maybe u just have an airpocket top off coolant and check around turbo lines for leaks then burp the system top off again.

 

[NeWyoRksPLaYaZ]

its been working normal all day so far, maybe it was just being moody like a typical dsm

 

[johnovision27]

Far fetched, but perhaps the cables that control the hot/cold mix are damaged. If you turn the hvac selector quickly, you should hear a slapping sound from the vents. Aside from that, perhaps your thermostat is being temperamental. If it is stuck open, then it'll take forever for your car to heat up.

 

[Abe'sGST]

like mentioned above try burping your cooling system, most likely when you changed your coolant and poured new coolant in, air got trapped in there, good luck

 

[92AWDHX40]

Check the firewall for leaking it could be the heater core.