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  #1  
Old April 20th, 2011, 08:47 PM
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mark kellgren
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The "Increase your heater output" thread

Cheers to dave_lucas for inspiring me to finally get around and do this mod. This is the mod of enlarging the smaller than necessary bulkhead hole for the heater blower.

Tools I needed so far:
  1. 7mm wrench (heater control cables)
  2. 11mm socket/wrench (lower heater box bolts)
  3. small vice grips (to hold the lower bolts from inside...PITA!)
  4. 13mm wrench/socket for upper box bolts (they are secured by rivnuts)
  5. hose clamps (the kind for cutting off flow) for heater lines to box
  6. phillips screwdriver (for removing heater duct under wing)
  7. 10mm socket/wrench (for removing my webasto and coolant overflow)
  8. sheet metal nibbler (I need to get one at harbor freight tomorrow)
  9. metal file
  10. drill (needed to get hole started)
  11. dremmel with cutting wheel (to get hole started FASTER!)
  12. rustoleum paint or equivalent to treat the steel cut areas.

Family just headed out of town and weather is nice (now that winter seems to be gone) so this is THE time to do this well before next winter when the suck comes back. So far, this was actuallly easier than I thought! I came home and started at 5:30pm, and it's 8pm now and the heater box is completely out, and the hole partially cut.

Here's what I did so far:
  1. remove bonnet
  2. remove heater intake grill on wingtop
  3. remove coolant overflow and push to side (PITA! I have 2 rivnuts with your name on it beeyoch)
  4. remove webasto. I think that's the wiper fluid bottle for most of you
  5. loosen upper bulkhead wing bolt (makes it easier to pull out duct)
  6. unscrew duct from wing (under removed grill)
  7. remove duct
  8. clamp off hose lines and mark them so you get them back on correct lines
  9. remove hoses and secure away
  10. remove heater control cables (mark them to know where they go back)
  11. disconnect heater box wiring leads
  12. if you have A/C, drop the under dash A/C facia (5 screws...no sweat)
  13. put vice grips on nuts in passenger (RHS) footwell that secure the lower box bolts
  14. remove 2x 11mm bolts on lower box
  15. pull that byoch out! (the box that is)
  16. recover from stunned amazement out how much restriction there actually is
  17. wonder who the D***B A** was in Solihull on the design team that thought it was a good idea to leave it. (don't deny yourself this. it's going to happen, so just let the thoughts come).
  18. make a template from heater box outlet, mark the hole and start-a-cuttin!

Couple snags I hit along the way:
  • if you don't have a rivnut kit, if there was ever a time to get one, it's before starting this!
  • one of the two rivnuts on the bulkhead for the upper box bolts failed and spun with the bolt...SUM BEECH! I replaced that rivnut! FIXED
  • I also drilled out the lower heater box bolt holes on the bulkhead and put in rivnuts. This is a really, really good place for a rivnut. you can eliminate the need for vice grips going forward on the next box removal.
  • Did i mention that I'm going to put rivnuts on the wing for the coolant overflow? Oh yeah.

Last thing I did tonight was use a step drill and dremel to start opening up the cutting area. pretty easy, but once you cut through bulkhead, there also thin sheet metal from the heater ducting on the cabin side. It's also really hard to cut along the top and bottom of the cut area with a dremel, hence the nibbler to finish up.

Tomorrow I get the nibbler and start finishing up the hole. then reassembly.

I can't wait to try this sucker out when I'm done. It can't be anything but an amazing improvement.
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  #2  
Old April 20th, 2011, 09:41 PM
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cool tech bit, had no idea that could be improved.
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  #3  
Old April 20th, 2011, 10:00 PM
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What are the sizes of the old and new holes? I've seen this before, but I remain skeptical as the bulkhead hole seems larger than the vent openings in the cab.
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  #4  
Old April 21st, 2011, 08:19 AM
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William Skidmore
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There is neat trick explanation on the CROC website for rivnuts. You need two nuts one that has been drilled out and a bolt and a wrench.
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  #5  
Old April 21st, 2011, 09:11 AM
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Now that you have enlarged that opening and made the airflow more efficient definately get the MUD-UK Defender vents. They are an amazing improvement over the crappy oem units and also have a side demister. I wish I had taken a photo of the oem vent next to the Mud vent as it would show how restrictive the oem units are.
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  #6  
Old April 21st, 2011, 09:31 AM
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Quote:
Originally Posted by kevkon View Post
Now that you have enlarged that opening and made the airflow more efficient definately get the MUD-UK Defender vents. They are an amazing improvement over the crappy oem units and also have a side demister. I wish I had taken a photo of the oem vent next to the Mud vent as it would show how restrictive the oem units are.
That has definitely been in the que!

------ Follow up post added April 21st, 2011 09:34 AM ------

Quote:
Originally Posted by Red90 View Post
What are the sizes of the old and new holes? I've seen this before, but I remain skeptical as the bulkhead hole seems larger than the vent openings in the cab.
John, not following the question intent? You can see the size of the intended hole in the picture, as I put the measuring tape across the hole size, so you can see the OEM hole and the full marked cutout size.

I'm not done yet, should be done today, but with what looks to be about 40% blockage removed, the flow can't be anything but dramatically improved, as reported by others that have done/inspired this mod.
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  #7  
Old April 21st, 2011, 11:45 AM
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I am missging something here.

The current openinig matches the dimensions of the heater core. All air must blow over the heater core.

It appears that the expanded opening will allow some air to bypass the heater core. As the heater core will be itself a flow restrictor, I assume the path of least resistance will be around the core.

Will you gain air flow but loose heat / BTU transfer?

Or are you going to put in a larger heater core?
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  #8  
Old April 21st, 2011, 11:57 AM
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Quote:
Originally Posted by Firemanshort View Post
I am missging something here.

The current openinig matches the dimensions of the heater core. All air must blow over the heater core.

It appears that the expanded opening will allow some air to bypass the heater core. As the heater core will be itself a flow restrictor, I assume the path of least resistance will be around the core.

Will you gain air flow but loose heat / BTU transfer?

Or are you going to put in a larger heater core?
there should be no opening around the heater core. That space should be filled with foam to prevent the path of least resistance. Having done this mod on several trucks is does make a signifigant difference in heater output/airflow.
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  #9  
Old April 21st, 2011, 03:28 PM
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Quote:
Originally Posted by 130Tdi View Post
there should be no opening around the heater core. That space should be filled with foam to prevent the path of least resistance. Having done this mod on several trucks is does make a signifigant difference in heater output/airflow.
What he said. I'm opening up the bulkhead from the 4.5" rectangular opening to 8.5" to match the 8.5" opening on the heater box, thereby removing the bulkhead restriction of airflow.

I just finished the install and did a sitting quick test....significant increase in flow rate coming from vents in the cabin....significant.

Now to adjust the control cables and reinstall the bonnet. I did add sound insulation between the bulkhead and the airbox; a big 9" wide matt of leftover Second Skin Luxury liner I had leftover from my soundproofing project. It acts as a defacto weatherstrip insulation closing up the gaps, and will further aid in diesel noise into the cabin, as well as quiet the heater sound. I have thought of putting some insulation on the heater box, but once my engine gets to temp by the webasto, there is no problem as is with heating the whole cabin. My sound and heat insulation project made it easy to warm the interior of a 110. Doing the roof alone makes a huge difference in cabin temp stability. Last winter, we went up the NC mountains for snow fun, and most of the trip was spent with the heater off due to the interior heat.

Webasto...she is nice, no?

More pics to follow.
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  #10  
Old April 21st, 2011, 07:39 PM
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Quote:
Originally Posted by Overlander View Post
John, not following the question intent? You can see the size of the intended hole in the picture, as I put the measuring tape across the hole size, so you can see the OEM hole and the full marked cutout size.

I'm not done yet, should be done today, but with what looks to be about 40% blockage removed, the flow can't be anything but dramatically improved, as reported by others that have done/inspired this mod.
What are the opening dimensions of the bulkhead hole? If it is already larger than the vent holes in the cab, making the bulkhead hole bigger will make not difference as the vent holes in the cab will control the flow rate.

------ Follow up post added April 21st, 2011 05:53 PM ------

Quote:
Originally Posted by Overlander View Post
What he said. I'm opening up the bulkhead from the 4.5" rectangular opening to 8.5" to match the 8.5" opening on the heater box, thereby removing the bulkhead restriction of airflow.
OK, so the stovk bulkhead hole is 4.5X4.5= 20.25 square inches. The vents are 2"x2.25" Two of them gives 9 square inches. Less than half the opening of the bulkhead. The restriction will be 95% controlled by the interior vents and if you want more flow that would be the place to look.
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  #11  
Old April 22nd, 2011, 05:18 AM
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Because the stock opening is a restriction to flow in relation to the size of the heater core, the larger bulkhead opening is going to allow air to flow into the interior plenum at a higher volume per time unit. That will have the effect raising pressure in the plenum, which will result in more air exiting the vents per time unit. Not an exponential increase, but measurable.

And you are right, enlarging the vents would increase the volume of air moving too.
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  #12  
Old April 22nd, 2011, 07:43 AM
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Quote:
Originally Posted by TS888 View Post
Because the stock opening is a restriction to flow in relation to the size of the heater core, the larger bulkhead opening is going to allow air to flow into the interior plenum at a higher volume per time unit. That will have the effect raising pressure in the plenum, which will result in more air exiting the vents per time unit. Not an exponential increase, but measurable.

And you are right, enlarging the vents would increase the volume of air moving too.
That is exactly what I am experiencing now: much higher pressure. When i move my air displacement lever down to open up the lower dash holes (for example) that allow air to pass through my A/C facia, i can actually feel a strong stream of air on my legs and feet. That did not happen before.
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  #13  
Old April 26th, 2011, 02:37 AM
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Does this fix apply to 90's as well?
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  #14  
Old April 26th, 2011, 02:59 AM
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It should do, 90's and 110's (and 130's) all use the same bulkhead with the same pressings on them.
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  #15  
Old April 26th, 2011, 08:47 AM
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Quote:
Originally Posted by kevkon View Post
Now that you have enlarged that opening and made the airflow more efficient definately get the MUD-UK Defender vents. They are an amazing improvement over the crappy oem units and also have a side demister. I wish I had taken a photo of the oem vent next to the Mud vent as it would show how restrictive the oem units are.
They are a bit expensive
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  #16  
Old April 26th, 2011, 09:19 AM
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higher pressure =defroster that actually is putting out air pressure like other makes and it actually gets warm given there isn't the huge blockage inches from the heater core. This is how you fix the "weak"heater that everyone complains about.

On early bulkheads they made the cutout for the steering column and heater the same so these two could switch from side to side. On later "sided" bulkheads the difference is that the steering column hole is smaller. IMO the heater box opening size was a design flaw up to the tdci trucks
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  #17  
Old April 26th, 2011, 05:29 PM
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They are a bit expensive
I know, but they are worth it. The oem vents look pretty bad when held up next to the Mud units plus you get a side window demister.
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  #18  
Old February 25th, 2012, 05:55 PM
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I like the idea
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  #19  
Old February 25th, 2012, 06:18 PM
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When i did this to my 110 I took the lower dash off and cut from the inside. Removing the lower dash only took about an hour. I was working on the inside of the bulkhead anyways (soundproofing) so I was taking stuff apart anyways so it made sense to do it that way for me but it seems a little less complicated.
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  #20  
Old February 25th, 2012, 09:49 PM
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My Defender seems to have a perfectly adequate heater, is it a diesel thing?
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