Lower Radiator Hose Not Getting Hot

I’ve got a 1999 Tacoma Prerunner 2.7L with 395,000 miles on it. I’ve got a new radiator, new water pump, new thermostat, new heater core, and a new heater control valve. The truck has never run hot on me or anything of the sort but my heater only blows “warm” air. Not nearly as hot as it should be. On cold days (I live in NW Florida so I mean temps in the 30s) when the heat is on high the temperature seems to be lukewarm. I thought the thermostat may have been the cause of this issue so I replaced it but this didn’t solve anything. I also thought the thermostat may have been the problem because I noticed my lower radiator hose was cold to touch even after running the truck with the heat on for over an hour. I tested my old thermostat in boiling water and it was actually working properly. So even after a new thermostat I’m still not getting hot air and the lower radiator hose is still not getting hot. Any idea of what the Issue may be?

 

Heater core? Your lower hose is not suppise to be hot. It sends the cooler coolant back to the engine. The top one is suppose to be the hot one.

 

I just put a new heater core in a few weeks back. The top one is hot but the lower should be getting somewhat warm though correct?

 

might need to do a system flush. They make some prestone kits that do this. I had a lot of trouble with one of my ex's Grand Am's doing this - they are notorious for cooling system problems. After I flushed it a few times the heater somewhat worked. Try that.

 

Clogger radiator? Can take it out and run water through it to see if it's clogged.

 

when she is cold take the radiator cap off and start her. If you see coolant flowing this means the thermostat isn't closing all the way. After a minute or 2 the water in the top tank should start to circulate, thermostat is opening.

any one of these is adequate to test temps. There is a small possibility that the thermostat bypass line is clogged and not allowing water into the heater core. https://www.google.com/search?q=Tac...g#imgdii=putX3DyDb3mjzM:&imgrc=Jp9Fj9mBoDwbrM:

 

Your first issue is looking at your radiator hoses instead of your heater hoses if you're looking for a heater related issue. I really hope you didn't replace all those parts trying to fix the heat issue.

These 2 sides to a heater, water and air. Check the water side first, if it's not thee it's air side.

 

Forget about radiator. If your engine is not overheating you are good. Forget about thermostat. If your engine can get to operating temperature within few minutes from start it's good.

Only two possible reasons your vents are not getting hot air: the heater core does not have sufficient flow of hot coolant or heater core does not have sufficient flow of air.

First one is easy to test. Turn off the blower motor put heater control on hot and run the engine. If both hoses going to geater core are hot the flow is there. If not then there's a blockage in heater core flow: valve not opening, pipe going from the engine or core itself.

If core lines are hot turn blower at full. If return line from heater core becomes cold there is not enough coolant flow through the core. Might be partial blockage same as above. If return line is still hot but the vent air is cold then problem is in the air flow in the heater core (leak, flap not operating ).