No heat to cabin after changing thermostat

castnblast · **Joined:** Fri Oct 29, 2010 8:34 pm **Posts:** 18

Someone please help me out on how to restore heat to the cabin after changing thermostat.

Heating tube at top back of engine is warm. Heating tube at top front of engine (parallel to radiator) is not only cold, it doesn't appear to have any coolant in it.

I've tried running engine to operating temperature with heat on and coolant cap off.

I've tried popping the coolant vent (upper left hand corner of radiator) while engine was warm -- and all I got was a bunch of hot, sticky coolant all over me.

Does anyone have any experience or suggestions?

Many thanks in advance!

Castnblast

Squeeto · **Posted:** Fri Sep 02, 2011 11:15 am

Any chance you reversed the hoses on the viscous heater?
May not matter anyway but the short hose from the tstat goes to the left side of the viscous heater (viewed from the front of the truck).

warp2diesel · **Posted:** Fri Sep 02, 2011 11:21 am

There are two hoses on the top of the coolant recovery tank. The small one next to the cap is for over flow. The larger one is an air bleed to help purge the air out of the system. If the larger hose gets kinked or blocked, there will be air pockets in the heater core and cylinder head.
Another air bleed hose goes from the left side of the radiator, across the top, and back to the engine, maybe the thermostat. Check to make sure it is not kinked or blocked.

Squeeto · **Posted:** Fri Sep 02, 2011 11:40 am

Some on this forum have noted that with this truck, it seems easy to trap air in the coolant system.

I put this in for a different reason but it seems to help me clear the air out:

castnblast · **Joined:** Fri Oct 29, 2010 8:34 pm **Posts:** 18

I still don't have heat after changing thermostat.

What I've done so far: i) there's no air in the system (checked hoses for kinds and dealer did coolant flush to make sure no air in system), ii) the hoses to viscous heater (VH) are correctly attached, iii) the engine is not throwing any codes and iv) the air conditioning works fine. The engine runs smooth as silk at all speeds, gets up to running temperature quickly and stays there (i.e., one click below the mid point).

By the way, I have a GDE Eco Tune, so the VH only runs when air temp. is above 44F or coolant tem is below 131F. But there should be heat even if the VH is not running.

It's getting pretty cold here in the mornings now. Any more ideas you may have would be greatly appreciated.

Castnblast

papaindigo · **Posted:** Mon Sep 26, 2011 12:07 pm

First off the 2 silver tubes in the front of the engine over the radiator are AC not heat so ignore them. The heater core is supplied by the hose coming up out of the right (viewed from the front) of the viscous heater and running over the tstat back to a solid pipe going to a bit of hose at the firewall and the return line from the heater core is immediately below that line. Pop the plastic engine cover and they are easy to see.

Try this train of thought. There are only 2 reasons for no heat, assuming of course that the engine has been warmed up, 1) no or little coolant flow thru the heater core or 2) no or little air flow over the heater core and into the cab. So is the heater hose coming out of the viscous heater hot and is the return hose hot? If not you have no flow so look into why. I'll bet you have flow but if not pop the hoses into and out of the heater core and see if you can produce flow thru the heater core (NOTE I am pretty sure but not positive that there is no valve in our system that turns flow on/off to the heater core, at least I don't see one, but if there is then its functionality needs to be checked). If you cannot get any flow thru the heater core and that likely nonexistant valve is working then the heater core is plugged and likely needs replacement although you can try reverse flushing (water pressure but not too much applied to the outflow line might push the clog out) or pull the lines all the way back to the firewall to see if there is some sort of plug in the line. If flow is not the issue then your problem is almost certainly failure, not at all unheard of, of the baffles that direct air flow over the heater core (e.g. those baffles are not directing any air over the heater core) or a failure of the switches to "tell" those baffles to move. If this is your situation I cannot be much help as I do not know how the baffles work or how the switch triggers them but you will have narrowed down the problem and might look at the 2006 FSM (it's more complete than the 2005 FSM) for diagnostic hints. FYI I am ignoring a possible fan problem as you say the AC works hence the fan works and I therefore assume when your heat is in the "on" position the fan just blows ambient air temp.

racertracer · **Posted:** Mon Sep 26, 2011 9:19 pm

I experienced the same thing after I changed the thermostat and never found out what it was that caused the cabin heat not to come on or get warm. My jeep is at the shop now for a cylinder head replacement, all this happened after I replaced the thermostat, heat worked fine before the swap it just took a little while for the heat to come on.

Are you losing coolant?

Is the coolant in the coolant bottle low after a long drive?

Any undetectable coolant leaks?

Air in the system was one problem.

If I had to do it over again, I would have the cooling system professionally filled using a coolant flush machine like the dealer has. The machine quickly removes air in the system and brings the correct level and ratio of fluid back into the system. It eliminates headaches.

The machine pushes new coolant into the engine and forces the old coolant out along with trapped air. Air in the system is not a good thing, it is difficult to remove and may cause trouble down the line because it prevents the engine from being properly cooled.

If the engine isn't cooled properly, especially in our red hot turbo charged engine where high temperatures are reached quickly, head gasket leaks and cylinder head warpage maybe the result.

If you haven’t already heard, our CRD engine has a weak spot, it's the aluminum cylinder head.

Many have experienced head gasket and or cylinder head replacement. $$$$$$

The cooling system in our CRD isn’t something to play around with, it is very serious business that should be maintained to specification and every leak must be resolved quickly. It takes less then a minute for a poorly cooled turbo charged engine to damage an aluminum cylinder head and gasket.

Find and fix your leaks before driving it.

If I knew then what I know now about the problems that arose from the thermostat change, I would have left the old thermostat in and life would have been good in a cold cabin, I would have been OK just waiting for the heater to warm up.

Racer

castnblast · **Joined:** Fri Oct 29, 2010 8:34 pm **Posts:** 18

Thank you both for the input. At the moment, I've got no coolant leaks; and I can only hope that the dealer properly flushed the coolant system. I saw the technician using the machine that you mentionned, Racertracer.

Papaindigo, I particulary appreciate your reasoning ... and wish the dealership was capable of the same. I'm going to begin working through your instructions. Fortunately, thanks to this forum, I have a copy of the 2006 FSM.

Still no heat and still no solution, but at least I have a thinking man's plan of action.

Thanks again, and will keep everyone posted.

Castnblast

castnblast · **Joined:** Fri Oct 29, 2010 8:34 pm **Posts:** 18

Update: drove the car at highway speeds for 20 minutes this morning; ran at operating temperature (a tick below noon on the gauge) for 17 minutes; popped the hood and this is what I discovered: both of the hoses running to and from the heater core were cold.

Last night, after running the car for about 45 minutes at operating temperature with a mix of highway and city, stop-and-go driving, it seemed like both hoses were slightly warm -- maybe this was because of the warm ambient air (i.e., not warm or hot water in the hoses) -- and that the hose going to the heater core was definitely the warmest.

Although I haven't taken apart the HVAC or done any electrical testing -- except to verify that the engine is not throwing any codes -- I don't believe that the air-blend door or actuator is malfunctionning. Why do I say that? Because I can hear something taking place in the HVAC when I switch from cold to hot on the dial in the cabin. There's a brief "switchover" taking place in there; and it strikes me that the air-blend door is moving because I think I hear a redirection of air current following the closing of some kind of mechanism.

So now I think I'm back to the issue of having air trapped in the heater core and the hoses leading to the heater core.

Any suggestions? At lunch, I'm going to go out to the Jeep again and check the larger hose on the coolant recovery tank to make sure again that it's not kinked or blocked. As noted by Warp2diesel, there will be air pockets in the heater core and cylinder head if it is kinked or blocked. I'll keep everyone posted.

Best regards and thanks again,

Castnblast

racertracer · **Posted:** Wed Sep 28, 2011 10:37 am

My experience exactly.

We need help deciphering this issue, this may have been one of the reasons that fried my cylinder head and gasket.

papaindigo · **Posted:** Wed Sep 28, 2011 1:50 pm

Ok here is what I can tell you after a brief run around the block starting on a cold engine, with the heat on and ending at about 1/4 on the temp gauge. The main line from the tstat to the upper fitting on the radiator is hot near the tstat and cold at the radiator, the line from the viscous heater to the firewall (from there to the heater core) is hot, the return line to the odd Y fitting by the tstat is slightly less hot, the line from the tstat to the viscous heater which is hard to reach under the turbo>intercooler hose is hot (Note my viscous heater relay is pulled so the viscous heater is doing nothing). When I say hot I mean there is no doubt about it especially since the engine block is only slightly warm. In addition there is no sound in the cab when I switch the HVAC control from cold to hot or back although I do get a sense, with the HVAC fan on high that air is being moved in a different internal direction.

I also did a run to full operating temperature with the heater off. At the end of that run all of the above hoses were really hot. I'm also 99.9 percent sure that there is no valve in the heater core flow as 1) I cannot see one; 2) I cannot find one on the parts list; 3) there is an oblique reference in the manuals that implies there is none; and 4) after this run I switched between cold and hot and back and the air temp change was immediate which it would not be if the coolant flow was valved.

My initial reaction is you have narrowed things down to no or little coolant flow thru the heater core. It's not impossible that this is related to air in the heater core circuit although IMHO I'm inclined to doubt it. All modern pressurized coolant systems are designed to self purge air into the overflow or coolant tank (ours in on the firewall and functions both as an overflow tank and top part of the radiator in the sense that our radiator cap is located there). Of course that assumes the hoses running to/from that tank are not blocked. I know you are going to check the big hose but to check for complete circulation you need to confirm that the fluid level in that tank goes up on a hot engine and down on a cold engine. If so that system is ok. If not something is blocked.

I'd be inclined on a COLD engine to get the turbo>intercooler hose out of the way; pull the tstat to viscous heater hose off the viscous heater; pull the heater core return hose off that funny Y fitting, mentioned above; and apply a modest flow of water to where you pulled the hose off the viscous heater. If there is no flow out of the return line something is plugged up between those 2 points. If there is flow you will have purged any possible air so put it back together and see what happens. FYI Squeeto's picture earlier in the chat, installing one of those fittings may have some benefit for quickly bleeding air, refilling the system, and possibly flushing (I suspect the latter is true but have not tried myself. I imagine you can get the fitting alone but I know you can get it as part of a Prestone flush and fill kit for under $10.

What I don't know is if there is any possible tstat malfunction that would result in no or little flow to the heater core. I only mention this because your problem started after a tstat replacement.

racertracer · **Posted:** Wed Sep 28, 2011 7:30 pm

papaindigo wrote:

What I don't know is if there is any possible tstat malfunction that would result in no or little flow to the heater core. I only mention this because your problem started after a tstat replacement.

Pap, I am thinking that it may be a possibility because when I was experiencing this problem, I went ahead and removed the new thermostat and replaced it with the old failed one and cabin heat returned even if it took a half hour.

How would we check for a thermostat malfunction?

papaindigo · **Posted:** Thu Sep 29, 2011 8:39 am

I've sent an email to kap as he knows more than anyone I know about how our tstats work. Best I can say is, per MrMopar, the very bottom port (aluminum fitting) is the by-pass port connected to the water-pump inlet, the large plastic port connects to the viscous heater, going then to the heater core, and the small port is the de-gas flow (constant air bleed). I don't know of any way, short of a gross manufacturing error, resulting in the port being plugged, that our tstats could fail to deliver flow to the heater and bypass ports. That said if the coolant level in the plastic tank goes up on a hot engine and down on a cold engine then you know there is flow through the de-gas port. How to check for actual flow from the heater port? Hm; I've suggested how to check for obstructions to flow downstream from that port thru the viscous heater/heater core/back to engine based on the assumption that the tstat is providing flow. About the only way I can think of to be sure that flow is being provided without removing the tstat would be, on a cold engine, to disconnect the hose from the tstat to the viscous heater, loosen the connection to the tstat port just enough so the hose could be rotated to point up, carefully and briefly idle the engine and see if coolant shots out of that hose. Of course you could disconnect the hose coming out of the viscous heater, which is easier, and do the same thing.

Hopefully kap can offer some more informed thoughts.

Squeeto - your picture of a T fitting in the viscous heater to heater core hose is exactly where an identical fitting would be placed to use the Prestone flush and fill kit. I've used those kits before and they work just fine to flush all the old coolant out and, since the T is at a high point in the system, they allow a system refill/top off with the correct amount of antifreeze and virtually no air in the system. However, my experience has always been on systems with a traditional radiator cap and an overflow bottle working off a hose fitting adjacent to the radiator cap. Our systems are different in that the plastic bottle on the firewall is a combination of the top of the radiator with the radiator cap and an overflow bottle. Do you have an opinion on whether one of these kits would work on our cooling system?

castnblast · **Joined:** Fri Oct 29, 2010 8:34 pm **Posts:** 18

I found the problem and now have heat in the cabin.

All the input I received helped me narrow the problem down to a lack of coolant flow to the heater core. Having studied everyone's suggestions and having acquired a working knowledge of how the coolant was supposed to flow throught the thermostat, I went out to the Jeep prepared to gently flush some coolant through the heater core. What I determined is that the dealer had incorrectly attached the thermostat: the hose from the heater core output was attached to the viscous heater input, and the hose from the EGR was connected to the thermostat.

I switched it around so that the heater core output went to the EGR, and the thermostat went to the viscous heater input. I got heat almost instantly.

Neither the first dealer who installed the thermostat, nor the second dealer who performed the coolant flush noticed the error. In fairness, I didn't notice the error, either, but I had no idea how it was supposed to be connected (or that the dealers would somehow mess up on something like this).

Thanks to all of your help, now I know how it is supposed to be done.

Thanks again.

Castnblast

papaindigo · **Posted:** Thu Sep 29, 2011 4:05 pm

Now that's entertaining. When stoutdog installed kaps tstat and we installed my new OEM tstat there was no problem keep the hoses straight given their lengths and curves. Someone really worked to mess things up but I'm glad your problem is solved even if the immediate cause of no heater core flow was not on my radar screen.

kapalczynski · **Posted:** Fri Sep 30, 2011 6:59 pm

Hey Guys, thx for the email. Always glad to help. I've actually been working w/ castnblast through messages the last several days shooting him ideas and he just messaged me today he got it fixed right after I got the message from Papaindigo. Gratz on finding the issue and glad u got heat!

mark.kapalczynski@yahoo.com if anyone has anything else that comes up.

- Mark

Squeeto · **Posted:** Sat Oct 01, 2011 12:42 pm

papaindigo wrote:

Squeeto - your picture of a T fitting in the viscous heater to heater core hose is exactly where an identical fitting would be placed to use the Prestone flush and fill kit. I've used those kits before and they work just fine to flush all the old coolant out and, since the T is at a high point in the system, they allow a system refill/top off with the correct amount of antifreeze and virtually no air in the system. However, my experience has always been on systems with a traditional radiator cap and an overflow bottle working off a hose fitting adjacent to the radiator cap. Our systems are different in that the plastic bottle on the firewall is a combination of the top of the radiator with the radiator cap and an overflow bottle. Do you have an opinion on whether one of these kits would work on our cooling system?

You can flush coolant system including the heater core with the thermostat closed (ie. coolant too cold to open it) while the truck is running. It is good for acid washes- if the truck is running, you no longer worry about acid staying in stagnant sections of the system.

No heat to cabin after changing thermostat

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