Heat woes continue...

[MarkEagleUSA]

I posted a few weeks ago about some of my troubles. I thought I might have figured it out but that doesn't seem to be the case. We've been in the teens/low 20's this week and the truck is just not warming up. In fact, after being plugged in overnight, I start it, let her warm for 3-5 minutes, then head out to work. After about 2 or 3 miles I can get something out of the heater but by no means is it warm enough to be comfortable. After sitting all day at work (10-1/2 hrs) the ride home is unbearable.

We had about 2" of snow last night with temps around 22°. Got up this morning to plow and when I went outside I noticed the hood was clear of snow while the rest of the truck was covered. That tells me that the block heater and winter cover are both doing what they're supposed to by warming the engine and keeping it under the hood. I started the truck and let it idle while I brushed off the snow. Got in and started plowing the driveway. After about 10 minutes I was feel decent (not great) heat. Finished the driveway and headed out to the store. This is where it gets interesting. As I was driving along, the heat went almost completely cold. Temp gauge read 190-200 like usual. After another couple of minutes, warmth followed by cold again. Got to the store and was inside for about 30 minutes. Came out and the truck immediately was blowing warm-hot. A few miles into the ride home, cold aagain. When I got home I popped the hood and saw that the coolant tank was between the Min/Max marks so I don't think it's low coolant.

So I'm wondering... is this indicative of a bad t-stat, water pump, and/or air in the system? The temp gauge never goes over 210-ish, the fan kicks on at 200-ish, and I'm not losing any coolant that I can tell. I'm puzzled by the fact she blows warm-to-cold-to-warm. That seems to tell me it's a flow problem or an air pocket.

What is the best way to bleed the system on these trucks?

Is there any other troubleshooting I can do?

Thanks in advance.

 

[jgillott]

Are you sure the HVAC doors are operating correctly? I've had a lot of trouble with my 2007 with temp control issues over the years and now our 2010 1500 is giving us fits. Could be anything from a control head programming problem, actuator issue, or broken HVAC doors.

 

[MarkEagleUSA]

Are you sure the HVAC doors are operating correctly?

As far as I can tell everything is fine except the mode door for floor/defrost (very little air from the floor vents). While I supposed it could be a control issue, it really feels like a coolant flow problem to me.

 

[Tuesdak]

Check the heater core lines to see if they are the same temp. That would be a quick test of the coolant/clogged heater core side of things. An IR gun is close enough as they are kind of too hot to touch. I have had trouble even with Heater Treater doors not giving me heat and needing adjustment.

 

[B.G. Smith]

Had similar problem. The recirculate air door came off and fell down over the vent into the cab. All seemed to work pretty good until I got on the road and up to some speed then the broken door was allowing outside air to enter the cab and not going through the heater core/evaporator. I removed the blower motor and was able to remove and replace the door through the hole. Put in a metal door and metal drive adapter. Works great now. bg

 

[MarkEagleUSA]

Check the heater core lines to see if they are the same temp. That would be a quick test of the coolant/clogged heater core side of things. An IR gun is close enough as they are kind of too hot to touch. I have had trouble even with Heater Treater doors not giving me heat and needing adjustment.

I did check the hoses this morning. Upper radiator hose read 198, heater inlet was 189, outlet was 180.

I flushed the core a couple of weeks ago and it helped. I may try to flush it again tomorrow when I have time. If the core were clogged I wouldn't expect to get any heat (which is where I started). Today is the first day I noticed the warm-to-cold fluctuation which is why a thought it could be an air pocket.

 

[MarkEagleUSA]

Had similar problem. The recirculate air door came off and fell down over the vent into the cab. All seemed to work pretty good until I got on the road and up to some speed then the broken door was allowing outside air to enter the cab and not going through the heater core/evaporator. I removed the blower motor and was able to remove and replace the door through the hole. Put in a metal door and metal drive adapter. Works great now. bg

Replaced the recirc door a couple weeks ago. It is working properly now (checked this morning).

 

[MarkEagleUSA]

If the t-stat or water pump were bad I should see increased operating temps, correct?

 

[jgillott]

As far as I can tell everything is fine except the mode door for floor/defrost (very little air from the floor vents). While I supposed it could be a control issue, it really feels like a coolant flow problem to me.

I've replaced the doors on my 2007 twice since new. The last time I had heat issues, they were similar to what you described. It would be blowing hot, go to cold, back to hot again etc. Reprogramming the head fixed the issue for now.

 

[DonFitzwater]

If the t-stat or water pump were bad I should see increased operating temps, correct?

Tstat failure almost always leads to a cold running engine. Water pump failure usually leads to a water leak and or overheating.

Silly question, have you removed the radiator cap to check water level? My 06 had developed a slow leak under the exhaust manifold and the overflow tank never dropped due to a loose fitting small hose that connects the tank to the radiator neck.

 

[MarkEagleUSA]

Silly question, have you removed the radiator cap to check water level?

Yes... radiator is full and overflow tank is where it should be. I'm confident there is no coolant loss.

 

[MarkEagleUSA]

I've replaced the doors on my 2007 twice since new. The last time I had heat issues, they were similar to what you described. It would be blowing hot, go to cold, back to hot again etc.

I can see the blend door moving to and staying where it needs to be. Recirc door works fine. The mode doors don't have any affect on hot or cold.

Reprogramming the head fixed the issue for now.

By "head" do you mean the controls? How does one go about reprogramming that?

 

[jgillott]

I can see the blend door moving to and staying where it needs to be. Recirc door works fine. The mode doors don't have any affect on hot or cold.

By "head" do you mean the controls? How does one go about reprogramming that?

Yes, I mean the controls. I had to have the selling dealer do it for me.

 

[MarkEagleUSA]

Yes, I mean the controls. I had to have the selling dealer do it for me.

Ok, that's what I thought you meant. Since I can see the recirc door working properly and the blend doors are in the right positions based on the heat knob position, I don't think it's the controls...

 

[Ozymandias]

The system bleeds itself because inlet is low on the core an outlet is high, so air is pushed out of the core always.
Only if someone mixed the hoses under the hood there can be an issue.

 

[MarkEagleUSA]

Tstat failure almost always leads to a cold running engine.

Would that be indicated by lower temps on the gauge?

Is the heater core is plumbed off the block, meaning the warm coolant passes through it regardless of the position of the t-stat?

 

[MarkEagleUSA]

The system bleeds itself because inlet is low on the core an outlet is high, so air is pushed out of the core always.
Only if someone mixed the hoses under the hood there can be an issue.

I can't find a definitive answer and the FSM doesn't seem to specify... is this the proper heater hose connection? Feed to top port, return from bottom.

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[petersonj]

Yes... radiator is full and overflow tank is where it should be. I'm confident there is no coolant loss.

DonFitzwater makes a good point in making sure the radiator is full. A slightly low coolant level in the engine block is a classic symptom of low heat output from the heater core, especially when driving down the road. The level of coolant in the radiator may appear to be full, depending on how it was checked. I know that I would want to be absolutely sure that there are no leaks.

I believe the most accurate method to check for coolant loss is to let the truck cool for several hours. This allows time for the coolant to contract and for the coolant in the overflow container to be drawn into the radiator. Before starting the engine, remove the radiator cap and check the coolant level. The radiator should be 100% full. If it is not, you have a coolant leak. If this is the case then top off the radiator with coolant and go for a test drive and see if the heater performs better.

If the heater performs as it should, you have now only to find the cause of the leak. If this is not the case, or you have already done this, please disregard this post.

- John

 

[MarkEagleUSA]

I believe the most accurate method to check for coolant loss is to let the truck cool for several hours. This allows time for the coolant to contract and for the coolant in the overflow container to be drawn into the radiator. Before starting the engine, remove the radiator cap and check the coolant level. The radiator should be 100% full.

I checked this morning after the truck had been sitting since early afternoon yesterday... coolant was up in the radiator neck where it has been every time I've checked it. Other than a varying level in the overflow tank the radiator has never been low.

If this is not the case, or you have already done this, please disregard this post.

- John

No need to disregard... you never know when you might have overlooked something or have just been too dense to figure it out.

According to the temp gauge, it doesn't run hot or cold... seems to always be just below the 200° mark. That combined with what's already been said seems to rule out the t-stat and water pump. Unless my heater hoses are connected wrong (pic above) the problem needs to be in the core itself in which case I just need to make it through the winter, pray for a stretch of 50°+ weather, or move to a warmer climate as I don't have any inside work area to take this any further before spring.

 

[Ozymandias]

According to this https://www.moparpartsgiant.com/par...-heater-plumbing-heater.html?Diagram=00i68958 then the lower one is the inlet and the upper is the returnline.

And yes was pretty hard to find with google.