Hello all! I'm "new" to the forum. I've been combing through the threads whenever I need helpful tech info, but this is my first time posting.


I have a heating issue (surprise, surprise). My heater comes on hot once the truck is warmed up only if I haven't used it in a while. Then after about 10-15 secs of hot air it begins cooling off!


I've recently had my radiator replaced, and this issue began immediately afterwards. When I was leaving the shop I realized I had no heat at all. I took my truck back to the shop, and they said there's no air trapped in the cooling system. They did, however, notice the coolant leaving the heater core was substantially cooler than the coolant going in. They recommended replacing the heater core.


Well, I consider myself a "thrifty" guy that can turn a wrench. So, I found out how to flush the heater core on this forum. The next chance I got I flushed the heater core by running water through it backwards and forwards until clean water came out. Then I put fresh Dexcool until it flowed out of the heater core return. Then I ran the truck for a while (10-15min after warm) with the heater all the way on and the radiator cap off while reving the engine and occasionally squeezing hoses. Lastly I topped off the coolant in the radiator and in the overflow (to the hot line). Then put the radiator cap back on.


Wouldn't you know it! The heat worked for about 2min... Then it cooled off. Now I have the issue I described in the beginning where the heater will blow hot for a little bit, then cool off.


Help! It's gonna get very cold again soon in Oklahoma!!!

 

Are both heater hoses hot while its blowing cool air? Another common problem of leaky vacuum likes that will cause it to blow cool.

 

I had a similar problem but mine never got warm all the way. I tried flushing using just water with little success. I dumped a container of CLR in the core, let it sit for a few minutes then flushed it and black water came out. I have had good heat ever since.

 

I'll have to check again, but I only have my slightly calibrated hand. Usually the inlet hose is warm-hot and the outlet hose is less warm, but never "hot".


Tell me more about the vacuum lines...

 

I may try this. I planned on giving it another flush today since it's warm out, but wanted to try cleaning it too. I've seen someone else use CLR to clean the inside of the heater core.

 

They sell heater core flush but it is like $20 - $25. I think CLR is like $6.

 

Here's an update:


Yesterday I flushed the heater core again with water.
Per Tajohns34's suggestion, after flushing I filled the heater core with an off-brand "CLR" I purchased from The Dollar Tree for $1/bottle.


*Of course using the off-brand was my choice, not Tajohns34's suggestion. I was comfortable with the product though because I'd used it before and it performed (and smelled) the same as CLR.*


I used two bottles to be sure the heater core was full, and let it sit for about 8-9min.


Then I flushed the heater core again with water. I noticed a little more dark crud coming out than there was when I just flushed with water.


Lastly I refilled the heater core with Dexcool, reconnected the hoses, and ran my truck with the radiator cap off and heat on while revving the engine and squeezing hoses to "burp" the system.


The heat not only worked, but it was hotter than it was before I had my radiator replaced! Ran the heat for quite a while yesterday with no changes. Ran the heat this morning, and it's still working!


Thanks for all of the help!!!!

 

Awesome. Glad you got it working.

 

Me too! Thanks for the tips!!!