Another heater output question - Defender Source
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  #1  
Old January 5th, 2008, 10:53 AM
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Gary Baxter
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Another heater output question

Yes, I have searched and this is a serious question. The temperature of my heater output falls drastically once I stop driving but with the engine still running. The flow seems the same but the temp is quite cooler. Since the engine temp hasn't decreased and the heater output flow hasn't decreased, why is the temp so much cooler? And more importantly, can I improve it?
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  #2  
Old January 7th, 2008, 11:46 AM
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Sounds like the thermostat is stuck open.
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  #3  
Old January 8th, 2008, 05:48 AM
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Gren Thomas
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Another heater output question

Hi Gary, if the engine temp does not change when you drop to idle (with engine driven fan) then it would not be an open thermostat, it could be a partially blocked heater matrix, damaged heater hose or in worst case worn water pump.

when driving the water pressure and volume of water forces hot water past damaged hoses into matrix and if the matrix is partially blocked or the fins are clogged then the volume of hot water will give you warm air.
however when idling the pressure and volume passing the matrix is reduced and the air drawn in by the heater motor is enough to cool the reduced amount of water getting to the matrix giving cooler air out of the ducts.
sound plausible?

try sitting at idle with the rpm up to see if the heat goes up or down with rpm if it does i would pull the heater matrix and take a good look at it.

Have fun & let us know how you get on
Regards
Gren
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  #4  
Old January 8th, 2008, 12:35 PM
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Thanks Gren. The engine temp does not change at idle and your explanation makes perfect sense to this newbie. I'll rev the engine at idle and see what happens.
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  #5  
Old January 8th, 2008, 02:06 PM
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Robert Bees
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Heater

I'd like to know what the optimal heat output of a 'new' LR heater would be in a D90. Even with everything setup correctly and dialed in right, it seems that the heater output could never keep up with heat loss (particularly in a ST and here in the fridgid north). Is there a replacement solution akin to the one for Series trucks that works better ? God knows there's enough heat GENERATED under the bonnet....
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  #6  
Old January 10th, 2008, 06:54 AM
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HI Robert,
There are a few things you can do, I have found that the foam surrounding the matrix in the heater box breaks up over time allowing air to get around the matrix without picking up any heat.
It is a case of removing the heater box and drilling out the rivets holding the box together and repacking the matrix, however since you have gone that far you can replace the matrix for a thicker one made from ally which has a much better heat transfer they are expensive but it works.

I have also found an air ram works well on the wing to push a little more air through the heater

regards
Gren
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  #7  
Old January 12th, 2008, 06:49 AM
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Finally got around to trying this out. The heater output temperature definitely increases when I rev the engine while stationary and decreases at idle. I'll crack open the workshop manual and see if this is something I should take on. Thanks.
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  #8  
Old January 13th, 2008, 06:32 AM
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How'd you make out there Gary?
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  #9  
Old January 13th, 2008, 07:42 AM
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With great anticipation, I pulled the truck into my garage and got out my workshop manual. I quickly determined that I needed to remove the heater unit to examine the heater matrix. After reading the first two steps of that process:

1. Remove bonnet and disconnect battery
2. Remove radiator bottom hose at radiator union and drain cooling system,

I put the manual away and went for a nice hike instead.

Gren, thanks for your response; it helped me understand the issue. Matt, I'll call you tomorrow.
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  #10  
Old January 13th, 2008, 07:54 AM
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I just usually skip steps like that. You can swap a heater box without draining the system by just pinching off the hoses with vice grips or clamps, but you do need to remove the bonnet. Removing the bonnet get pretty familiar once you replace the clutch cylinder, heater box, wiperblades, etc.
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  #11  
Old January 13th, 2008, 12:57 PM
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My heat worked wayyyyy better once I replaced the water pump.
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  #12  
Old January 13th, 2008, 08:03 PM
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Alex Lapidus
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Has anyone tried the trick I read on this forum of simply removing the piece of foam that is apparently right behind the vents in the cab? Sounds too easy to be for real.
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  #13  
Old January 13th, 2008, 10:18 PM
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What piece of foam? There are some foam seals in the system, but nothing thats going to increase output by its removal.
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  #14  
Old January 14th, 2008, 05:58 AM
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I think he's referring to this mod and it does increase output through the vent:

http://www.defendersource.com/mod/blow.html
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  #15  
Old January 14th, 2008, 06:35 AM
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Yes, but that recommendation is a bit mis-informed, because the flaps are supposed to be controlled by one of the slider controls. A bit of a bad design because the control cable is poorly anchored in the sheetmetal underneath the plastic shelf. This strips out of the hole and then the flaps wont operate. The foam is merely the "seal" on the flapper doors to prefent airflow when they're closed, so removing the foam isnt going to help anything at all. Removing the ducts is subjective.

In the pix you can see the cable that runs down through the tray to actuate the flaps. Also, if you look closely, you can see how both flaps are attached to the same long rod, so the wimpy cable actually has a lot of work to do resulting in a weak point (especially when the panel rots out as in the pix). I replaced the panel with a piece of stainless.

Sadly, this only relates to airflow, and has nothing to do with your hot/cold flashes. So all my ramblings have been completely off topic.
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  #16  
Old January 14th, 2008, 09:30 AM
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Gary have you checked your thermostat? It could be stuck open.
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  #17  
Old January 14th, 2008, 11:12 AM
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J. Michael McCaig
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A good tool for diagnosing heater and and cooling problems is a "point and shoot" infared thermometer. You can aim it at the thermostat housing and radiator hoses to check the thermostat. It's great for finding a cool spot on a radiator meaning a clog. Point it at the supply and return heater hoses and you will get an idea whats going on with the heater. You should get at least a 20 degree drop between the supply and return if the heater matrix is functioning properly.
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  #18  
Old January 14th, 2008, 07:23 PM
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What does it mean if your heater matrix makes noises like running water under the dash when you accellerate? Is it really clogged up or is there something else going on? I thought there was some air in it somehow.

On the second topic here is an idea for enlarging the heater output, I checked it out since mine is all over the garage in pieces and the bulkhead opening is REALLY small compared to the potential given the opening the heater actually has. I'm ging to cut mine open some more.

Look about half way through the page.

http://www.eastcoastrover.com/97.html
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  #19  
Old January 14th, 2008, 10:38 PM
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I decided not to cut my dash when I had my truck apart. I honestly have never had a problem with the amount of airflow or heat, save only for the period of time before the tdi warms up.

I've had other cars make gurgling noises while driving, but only ones that had heater cores inside the dash. It meant the cooling system needed to be bled, usually a bad heater valve, but the Defender doesnt have a heater valve.
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  #20  
Old January 15th, 2008, 07:31 PM
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Naw it's my Disco that's acting up, my D90 project is about 50% together 50% on the floor of the garage.
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