Truck heater not getting as warm as normal

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I just replaced my thermostat and it didn't make any difference
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Stacy, I got a bad new t-stat, yrs ago. Ever since then I test new one in a pot of water on the stove with a thermometer.

It was a one time thing. But I just feel better knowing, before I install it.
 
noheat, I'm wondering that same thing but not really sure how to check it. It's all hidden inside the heater box or whatever it's called and controlled by an electrical actuator that is screwed on top.



EddieS'04, I've done that in the past too but I didn't do it with this one.



Here's a little update. My gas mileage on this last tank of gas dropped from around 17 or 18 where it normally is every time down to 12.5 mpg. I did have a good bit of idling while looking into this cooling problem though. The driving was the same type and speeds. Makes me wonder if something is wrong that is causing the drop in mileage and heat temperature. Also, while driving on the highway last night, I decided to kick it out of overdrive and let the RPMs ride a little higher. I heard a little bit of gurgling which would normally indicate air in the system. After a few minutes with the RPMs higher, I got pretty good heat again. After putting it back into overdrive though, it went back to being barely warm. So, is my water pump not moving enough water, or is my heater core partially clogged, or is there still air in my system or is it something else? Any guesses or suggestions?
 
I think you should backflush the heater core as has been discussed previously, then have the coolant replaced. If you aren't able to do it yourself, then have it done at a competent shop. Winter in Minneapolis with no heat is No Bueno. Your test drive with higher RPMs tells me you're getting some flow through heater core, but not enough at lower speed.
 
First things first. Check the coolant level. If it is low, you will not get enough flow through the heater core.



Next check the vacuum doors that control the heater blend door under the dash. broken hose or vacuum leak can cause the door to not operate properly and that shuts off the air flow thru the heater core.



If everything is working OK then look check the engine thermostat and cooling system for problems like a clogged heater core. Flushing may or may not solve the problem, but it would be the next step before you start replacing parts.



...Rich
 
"noheat, I'm wondering that same thing but not really sure how to check it. It's all hidden inside the heater box or whatever it's called and controlled by an electrical actuator that is screwed on top."



Stacy, I haven't tried it, but I think a borescope-type inspection camera on a flexible boom - that might do the job. Something like this:
 
Stacy, you said coolant level was OK. This may be a stupid question, but you meant both the radiator and expansion tank, right?
 
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Vic, yes, coolant level is fine in the radiator and the expansion tank. I haven't had to add any and the levels have stayed the same so there aren't any leaks. I just replaced the thermostat a few days ago so that shouldn't be a problem. I'm pretty sure that my temperature blend door isn't controlled by vacuum hoses but rather an electronic actuator that sits behind the glove box. I've looked at it but have not removed it and I'm not sure of any way to check it to see if it works or not (I don't have access to an inspection camera as noheat suggests). The heat working pretty good at high RPMs leads me to believe that the blend door is fine. I think a heater core flush is probably in order but I'm just dreading it in the cold weather. Thanks for all the responses. I'll post some updates in a couple of days after I try the heater core flush.
 
The gurgling sound at high rpms in the heater core is the clue here. There is obviously an air lock there, what is causing it is another story. The heater core could be partially plugged. There is also the chance that the water pump is not flowing properly but this would be accompanied with other symptons also which you don't seem to have. What really has me thinking about this though is that none of your hoses are hot. I can see the upper radiator hose not being really hot if it is that cold outside but the heater hoses should be quite hot...unless there is a big restriction in the core but usually at least one of the hoses is still hot. What I would do in your situation is cross the hoses at the heater core. This may be somewhat challenging as the hoses are different diameters if I remember correctly. This will cause the coolant to flow through the core in the opposite direction and if the core is not totally plugged should result in you having heat. The only downfall with doing this is if it works is that now you know that the core is plugged and it is only a matter of time before it plugs again (it will probably last the winter though) which means that you have to pull the dash out to replace the heater core which sucks.



If you decide to cross the hoses at the heater core take care when removing the hoses as they usualy weld themselves onto the heater core fittings and the fittings are thin and will bend very easily. Also do not pull too hard on the hoses as you can harm the heater core. Best is to remove the clamps and then slightly push and twist the heater hose until it breaks free of the heater core fitting, then it should be easy to remove.
 
Ok, here's an update. Last night I used an air hose and reverse flushed the heater core just as the video on the ericthecarguy.com website. I saw a few specks of debris but not much at all. It was mostly clean looking coolant. I then used a bottle of Prestone Radiator cleaner to fill up the heater core and let that soak. I flush all that out with distilled water and filled the heater core up with fresh coolant. I bled the air out of the system using a funnel like ericthecarguy recommended. This seems to have fixed my problem. I'm not sure what was actually stopping up the heater core or blocking the flow as there was very little debris that came out. The heat gets hot now though and I'm happy. Now I have to deal with my PCV valve that was hanging loose and there are no tabs in my valve cover to hold it in. I noticed that when I was waiting for the air to get out of the system. That could explain my severe drop in gas mileage. Thanks for all the suggestions and help.
 
Eureka! Glad you got heat now - makes the drive up North much more comfortable. BTW, I stumbled across ericthecarguy a few months ago - he's got great repair videos and website. Very useful for us DIYers.
 

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