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Coolant flow direction

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bretto View Drop Down
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    Posted: 23 Jan. 2016 at 5:03pm
I'm installing a water heater in my M38 and wondering if the return goes to the water pump port or the head port at the rear.  My logic tells me it shouldn't matter which one goes where as its just a heat exchanger, but there is an arrow on these Mutt heaters of the direction of flow.  Doesn't make sense to me but I will install like it shows.

Pic courtesy of RICKG (hope you don't mind)



Edited by bretto - 23 Jan. 2016 at 7:42pm
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Mark W. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 6:23pm
The flow should come from the water pump to the heater and return cooler after going through the heater to the head. Least that would be my understanding of the flo direction.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rus Curtis Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 6:53pm
My understanding is since the bottom radiator hose goes into the pump and the return hose from the engine exits the thermostat housing before returning to the radiator, the pump pulls or sucks the coolant into the engine.
 
If that logic is correct, then the return for the heater should be the pump connection and the inlet should be the head. 
 
 
 
 


Edited by Rus Curtis - 23 Jan. 2016 at 7:00pm
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bretto View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bretto Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 7:41pm
No matter how I hook it up, its going to flow thru the heater core one way in respects from the firewall side. I guess the question here really is, is there any logical reason to have the return on the bottom of the core?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RICKG Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 8:56pm
Hi Bretto. We know the coolant flow as regards to the eng and rad. We know that the flow out from the eng to heater is the fitting on the rear of the head and the flow back to the eng from heater is to the WP fitting. Look at your mutt heater-as installed in our M38s-is not the data plate upside down? Meaning that as purposely built and installed in the intended vehicle (mutt) the inlet tube would have been to the top of the core.  That's my logic anyway my inlet stub is at at the top of the core and it exchanges heat just fine.   (disclaimer: the mil spec TM for hot water heater on M38 shows inlet stub on bottom)Confused 

Edited by RICKG - 23 Jan. 2016 at 9:10pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 9:07pm
  Yes. The hot water, as it's heated in the engine, tends to rise and flow thru the upper hose to the radiator. (early cooling systems had no pump, they relied on a principal called thermosyphon [sp]. Hot water rises, cool water falls.) As the water cools in the radiator, it falls and re-enters the engine thru the lower hose. The same way, as water cools in the heater core (it's really just a small radiator) it tends to fall, and will return to the engine thru the return hose.
  Now. Having said that, I remember that the heater hoses on GM cars "cross". The upper hose from the intake manifold (would be from the head on the Go-Devil) goes to the lower heater core pipe, and the return is from the upper core pipe to the water pump......Confused  and cross-flow radiators wont thermosyphon, so it doesn't matter which way you flow them because they must be pumped,,,,,,
  I guess it doesn't really matter,EmbarrassedWink but if the pipes are marked, I would hook them up according to the way they are marked. Inlet from head, outlet or return, to water pump.   BW
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RICKG Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 9:29pm
Thanks for that TS. Keep in mind we are taking a VN era mutt heater and installing it UPSIDE-DOWN on a M38. Therefore the heater core stub marked "flow" is now at the bottom. I, with good results, ignored the "flow" stub marking on the heater core and installed the flow hose (from head) to the top stub. Then as you confirmed the hot enters the top of heater core, settles to bottom of core after heat exchange then returns to eng via WP fitting.

Edited by RICKG - 23 Jan. 2016 at 9:32pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bretto Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 10:44pm
Originally posted by RICKG RICKG wrote:

Thanks for that TS. Keep in mind we are taking a VN era mutt heater and installing it UPSIDE-DOWN on a M38. Therefore the heater core stub marked "flow" is now at the bottom. I, with good results, ignored the "flow" stub marking on the heater core and installed the flow hose (from head) to the top stub. Then as you confirmed the hot enters the top of heater core, settles to bottom of core after heat exchange then returns to eng via WP fitting.


Wacko

So all this up and down talk is getting me dizzy.  I know this heater installed in a M38 is flipped from its intended installation into a Mutt.  Ive actually flipped and brass riveted mine back on as you did.
So you just connected your hoses opposite of what the arrows say?  That seem most logical as this unit is flipped over from its original design.

In this pic, it has the flow arrows on both pipes.
Now speaking in the Mutt world, everything is  upside down in your pic.  The water from the head would go thru the top pipe and out thru the bottom, this would go along with the arrows.  Now speaking from the M38 world and having everything installed the way its laid out in the pic, if we wanted to follow suit to have the coolant from the head enter the bottom, then we would connect that hose to the bottom (opposite of flow arrow stickers).
Right?  Or am I just confusing to?  Hell it probably doesn't really matter.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote bretto Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 11:05pm
This settles it.  Taken from the TB 9-2855-37 M38 Hot Water Heater Kit

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 46Willard Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan. 2016 at 11:15pm
I think a lot of heater cores flow from the bottom to the top to help eliminate the possibility of air bubbles in the heater core. I think either way should provide adequate heat. Many modern cores have inlet and outlet on same end of core and have a tendency to plug up and cause poor heating. Common problem with Dodge pickups.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 12:03am
I was wrong.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 1:33am
  Are the two pipes on the core the same size? On GM cars, the heater inlet hose from the intake manifold was 5/8", while the return to the water pump (later on, to the radiator) was 3/4". Why, what difference did it make? I have no idea, that's just the way it was.Confused  BW
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bretto Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 8:34am
Yes they are the same size pipe.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RICKG Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 11:25am
Sheesh! My own pics prove (once again) that I'm full of "it". I did follow the arrows so my inlet is the top tube. Opposite the TM. I'll defend myself by saying the install was over a yr ago and I'm now feeble of mind.Ermm 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bretto Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 4:50pm
No problem there. I'm about full myself. Anyhoo, I put the head port to the bottom tube per the tech bulletin. We'll do a thermo test in them Black Hills to see if there is any difference. I'd bet you there will be absolutely 0 difference. I'm working n getting my pics together. I will post them up here and over on the WMJ page.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote bretto Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 7:03pm

















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Post Options Post Options   Thanks (0) Thanks(0)   Quote RICKG Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 7:53pm
Your bracket is perfect-well thought out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan. 2016 at 8:29pm
Nice

Chug A Lug
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