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Replacement aluminum heater core low heat output idea

Rennat_2006

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Ive fallen victim to this one myself after my stock core leaking so bad i had no choice but to install a local parts store aluminum replacement. I honestly dont understand why there is a low output issue with these aluminum ones, obviously aluminum disapates heat better that copper but im my head im thinking this should be a positive thing in our situation here not the negative it has been shown to be. Ive got an idea im wanting to try to remedy the issue also but want some other members thoughts before doing so as to not harm anything else.

Heres how im looking at it...
Thinking about this as the engine coolant radiator to start with,Aluminum disapates heat better than copper, thats why aluminum radiators are so popular and tend to work better. In this case the airflow through the grill of the truck which then travels through the radiator pulls the heat out of the radiator and into the engine compartment which then goes out the fender liner openings, out below the engine, little out between hood and cowl, etc. This heat is not being harnessed for another purpose like we are trying to do with the heater core but principle is the same.
Heater core has airflow from the blower motor going into and through it then coming out into the heater box to be diverted to defrost or heater vents. Most of us that have had to install one of these aluminum cores now have low heat ouput to the vents be it defrost or heater. Why is that so with how well aluminum transfers/disapates heat? If we have the same temperature coolant (say 180*)going into the heater core be it an aluminum or a copper one and say the core temperature itself is 170-180* the airflow blowing through it should be "picking up" and disapating this heat as long as airflow is making it through the core and out which we know it is because i did not loose any airflow out the vents after my replacement. If airflow through the core had become restricted ld understand the low heat output as with the decrease of airflow at the vents.

Heres what im trying to figure out and hoping another member has this information.
1.) In changing from the copper core to the aluminum is the construction of the core internally different? Specifically thinking of these as a conventiinal radiator was the copper cores setup as say a "double pass" internal coolant flow routing verus these new aluminum just being a "single pass" and because of this coolant isnt being held in the core long enough to heat up the core itself to get the transfer of heat from the air passing through it? Again thinking of this as a engine radiator we have all heard of people upgrading from single to double or even triple pass radiators to make that coolant spend more time in the radiator with the airflow going across it to disapate that heat the coolant is carrying to help with engine overheating issues.

2.) What about some sort of restricter on the "return" hose out of the heater core going back to the engine or radiator wherever it goes essentially cutting down the flow rate some making the coolant spend more time inside of the heater core? The other question to go with this though would be how would this affect the rest of the cooling system of the truck is we were to cut back on the flow out of the core? If i had a coolant temp gauge on the blazer i would just go pinch the core outlet hose down some and test this theory but dont want to overheat some engine component by doing this.

I feel like im missing a piece of the puzzle here to fix our issue. The material of the core alone should not have made the heat output decrease as much as mine has. All of the late model vehicles ive worked on run aluminum cores and most have the same size feed and return size hoses which tells me they arent using a smaller hose on the core outlet to slow down the flow rate which may be the case in our setup with the slightly smaller hose. The same principles and basic designs apply with these later model cars and they have great heat output with aluminum cores unless the core itself becomes plugged internally.
 

ssdvc

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Don't forget, diesels are cold blooded to begin with. When the temps drop down into the 20's (and south of that). Heat in the cab will be tough to find, no matter how good the heater core is. That is why they made those Arctic heater kits and a lot of us that live in colder areas out winter fronts on our trucks. A friend of mine had the same issue in his diesel powered LandRover. He went out and purchased a small diesel powered cab heater off of ebay and never looked back. And his cab is now nice and toasty no matter what the temp is outside and he has a convertible top on his truck. He even found away to plumb it directly from his fuel line so he wouldn't have to deal with fill the tiny tank on the unit.
 

Mullaney

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Ive fallen victim to this one myself after my stock core leaking so bad i had no choice but to install a local parts store aluminum replacement. I honestly dont understand why there is a low output issue with these aluminum ones, obviously aluminum disapates heat better that copper but im my head im thinking this should be a positive thing in our situation here not the negative it has been shown to be. Ive got an idea im wanting to try to remedy the issue also but want some other members thoughts before doing so as to not harm anything else.

Heres how im looking at it...
Thinking about this as the engine coolant radiator to start with,Aluminum disapates heat better than copper, thats why aluminum radiators are so popular and tend to work better. In this case the airflow through the grill of the truck which then travels through the radiator pulls the heat out of the radiator and into the engine compartment which then goes out the fender liner openings, out below the engine, little out between hood and cowl, etc. This heat is not being harnessed for another purpose like we are trying to do with the heater core but principle is the same.
Heater core has airflow from the blower motor going into and through it then coming out into the heater box to be diverted to defrost or heater vents. Most of us that have had to install one of these aluminum cores now have low heat ouput to the vents be it defrost or heater. Why is that so with how well aluminum transfers/disapates heat? If we have the same temperature coolant (say 180*)going into the heater core be it an aluminum or a copper one and say the core temperature itself is 170-180* the airflow blowing through it should be "picking up" and disapating this heat as long as airflow is making it through the core and out which we know it is because i did not loose any airflow out the vents after my replacement. If airflow through the core had become restricted ld understand the low heat output as with the decrease of airflow at the vents.

Heres what im trying to figure out and hoping another member has this information.
1.) In changing from the copper core to the aluminum is the construction of the core internally different? Specifically thinking of these as a conventiinal radiator was the copper cores setup as say a "double pass" internal coolant flow routing verus these new aluminum just being a "single pass" and because of this coolant isnt being held in the core long enough to heat up the core itself to get the transfer of heat from the air passing through it? Again thinking of this as a engine radiator we have all heard of people upgrading from single to double or even triple pass radiators to make that coolant spend more time in the radiator with the airflow going across it to disapate that heat the coolant is carrying to help with engine overheating issues.

2.) What about some sort of restricter on the "return" hose out of the heater core going back to the engine or radiator wherever it goes essentially cutting down the flow rate some making the coolant spend more time inside of the heater core? The other question to go with this though would be how would this affect the rest of the cooling system of the truck is we were to cut back on the flow out of the core? If i had a coolant temp gauge on the blazer i would just go pinch the core outlet hose down some and test this theory but dont want to overheat some engine component by doing this.

I feel like im missing a piece of the puzzle here to fix our issue. The material of the core alone should not have made the heat output decrease as much as mine has. All of the late model vehicles ive worked on run aluminum cores and most have the same size feed and return size hoses which tells me they arent using a smaller hose on the core outlet to slow down the flow rate which may be the case in our setup with the slightly smaller hose. The same principles and basic designs apply with these later model cars and they have great heat output with aluminum cores unless the core itself becomes plugged internally.
.
@royalflush55 and the mention of a leaky airbox around the core might make a big difference and @ssdvc 's mention of cold blooded diesels is "the gospel" for sure.

My only contribution is to suggest that you were on to something when you mentioned a restriction on or at the heater core. A lot of other vehicles - like a plain simple old Chevy pickup truck - use (for example) a 3/4 inch inlet hose into the heater core and a 1/2 inch outbound heater hose.

Often times on big trucks or road tractors, there are valves on the motor block that can close off the water to the heater core in the summer. AND in the winter, you can restrict outbound flow from the core to accomplish (or try to accomplish?) a way to hold that hot water longer.
 

ssdvc

Well-known member
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CT
While the outbound flow restriction sounds good, wouldn't that prevent in coming circulation of what little fresh hot water is coming into the heater core? If fluid is moving outbound slowly, inbound wouldn't be refreshing the core with the hottest water available? At least that's how I think it would work. Maybe someone with a better education than I can correct me if I am wrong.

I have noticed that our fans aren't that strong (even a newer replacement) and heated air flowing to the floor area only comes from the two little ports under the dash. A more powerful fan (I have no idea if that could be done) may help distribute more hot air. I did have my dash apart when I changed my heater core and when I put everything back together, I made sure to seal the core box really good and I took the time and wrapped all the gaps in the ductwork with metal HVAC tape. Worked pretty good and flow did increase a bit to all the outlets. I am now fairly comfortable when the temps are between 25 and 30F.

IMHO, if you want real heat in temps near or below 20F, a secondary diesel fired heater is the way to roll.
 

Mullaney

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While the outbound flow restriction sounds good, wouldn't that prevent in coming circulation of what little fresh hot water is coming into the heater core? If fluid is moving outbound slowly, inbound wouldn't be refreshing the core with the hottest water available? At least that's how I think it would work. Maybe someone with a better education than I can correct me if I am wrong.

I have noticed that our fans aren't that strong (even a newer replacement) and heated air flowing to the floor area only comes from the two little ports under the dash. A more powerful fan (I have no idea if that could be done) may help distribute more hot air. I did have my dash apart when I changed my heater core and when I put everything back together, I made sure to seal the core box really good and I took the time and wrapped all the gaps in the ductwork with metal HVAC tape. Worked pretty good and flow did increase a bit to all the outlets. I am now fairly comfortable when the temps are between 25 and 30F.

IMHO, if you want real heat in temps near or below 20F, a secondary diesel fired heater is the way to roll.
.
No doubt that the diesel fired heater would be better!

The fans in these trucks are pretty sad. The part that I remember from days gone by is that the "stock" heater sucked a lot. We would rip those out and replace them with a little cube about 10x10x10 inches (roughly). The blower motor in those units would throw dirt up off the floor and into your eyes if you weren't careful...

On the other hand, it isn't "factory". I do remember cutting a hole in the side of the box to plumb in the defroster...

----

I did a quick search and found something similar. Claims 12,500 BTU output and a 3 speed fan. I think we rigged them to one speed (high) and a toggle switch whick solved a lot of problems. Remembering that the switch was crap... AND this is 12v, so a little more looking is required for 24v.

The picture below gives a little more info and I imagine it might be found for less $$.

CabHeater.jpg
 

Skinny

Well-known member
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Location
Portsmouth, NH
I think it's an air sealing thing and not the material itself.

My truck takes a good amount of time to warm up but it will boil you out of the cab in the coldest of temps. The grille cover made a huge difference in keeping operating temp while going down the road. As in it actually comes up to temp. But I have no issue maintaining 160-180 degrees is sub freezing temps.
 

Rennat_2006

New member
20
16
3
Location
Idaho
You may not be getting a good seal between the new heater core and the housing. Therefore the air is not going thru the core but around it. You can add high density weatherstrip foam to get a better seal.
Your new aluminum core should produce more heat.
Mine had some foam/weatherstrip in the box with it which i installed so should have a decent seal. I could see this being an issue for other members though, thank you for the reply.
 

Rennat_2006

New member
20
16
3
Location
Idaho
Don't forget, diesels are cold blooded to begin with. When the temps drop down into the 20's (and south of that). Heat in the cab will be tough to find, no matter how good the heater core is. That is why they made those Arctic heater kits and a lot of us that live in colder areas out winter fronts on our trucks. A friend of mine had the same issue in his diesel powered LandRover. He went out and purchased a small diesel powered cab heater off of ebay and never looked back. And his cab is now nice and toasty no matter what the temp is outside and he has a convertible top on his truck. He even found away to plumb it directly from his fuel line so he wouldn't have to deal with fill the tiny tank on the unit.
That is a fact. Did some testing today and let truck idle for a half hour or so after a short drive, i dont think the thermostat was fully open to be honest. It was low 20's outside.
Shooting the heater hoses with a IR temp gun they showed between 105-115* about 6" out of the firewall. Thermometer sitting in the driver side defrost vent and the vent on the floor was showing 130*.

When i have some time im going to go drive into town and back (20 miles) and check temps again everywhere then see what it does at a idle. I think its safe to assume especially at the current temps the coolant temperature at idle is cooling way off after a short period of time below tstat temperature. My 2006 duramax is barely holding 150* at low speeds and idle right now.
 
Last edited:

Rennat_2006

New member
20
16
3
Location
Idaho
.
@royalflush55 and the mention of a leaky airbox around the core might make a big difference and @ssdvc 's mention of cold blooded diesels is "the gospel" for sure.

My only contribution is to suggest that you were on to something when you mentioned a restriction on or at the heater core. A lot of other vehicles - like a plain simple old Chevy pickup truck - use (for example) a 3/4 inch inlet hose into the heater core and a 1/2 inch outbound heater hose.

Often times on big trucks or road tractors, there are valves on the motor block that can close off the water to the heater core in the summer. AND in the winter, you can restrict outbound flow from the core to accomplish (or try to accomplish?) a way to hold that hot water longer.
These are setup with 2 different size hoses also.

Being a heavy truck and equipment mechanic this was my exact thought process behind restricting the return line out of the heater core to the radiator. Never used the valves on the semi's in the winter, we just would shut them in the summer to keep any heat out of the core.
 

Rennat_2006

New member
20
16
3
Location
Idaho
While the outbound flow restriction sounds good, wouldn't that prevent in coming circulation of what little fresh hot water is coming into the heater core? If fluid is moving outbound slowly, inbound wouldn't be refreshing the core with the hottest water available? At least that's how I think it would work. Maybe someone with a better education than I can correct me if I am wrong.

I have noticed that our fans aren't that strong (even a newer replacement) and heated air flowing to the floor area only comes from the two little ports under the dash. A more powerful fan (I have no idea if that could be done) may help distribute more hot air. I did have my dash apart when I changed my heater core and when I put everything back together, I made sure to seal the core box really good and I took the time and wrapped all the gaps in the ductwork with metal HVAC tape. Worked pretty good and flow did increase a bit to all the outlets. I am now fairly comfortable when the temps are between 25 and 30F.

IMHO, if you want real heat in temps near or below 20F, a secondary diesel fired heater is the way to roll.
Yes you are probably exactly right. My thought was possibly these aluminum cores are letting coolant flow through too quick and not disapate any heat and possibly restricting the flow some will increase the temp of the core. For example if they are a "single pass" where the copper core are "dual pass" which would make the coolant spend more time inside of the core.

That does remind me i need to wrap where the ducts meet the heater box, mine did not fit well at all and had like a 0.5" gap between the box and the defrost ducting if i remember right. This gets me wondering if the air pushing through the ducts is pulling in some cool air as it passes through this gap, kind of the same cooling effect those goofy looking exhaust tips do on the DPF equipped trucks.
 

Rennat_2006

New member
20
16
3
Location
Idaho
I think it's an air sealing thing and not the material itself.

My truck takes a good amount of time to warm up but it will boil you out of the cab in the coldest of temps. The grille cover made a huge difference in keeping operating temp while going down the road. As in it actually comes up to temp. But I have no issue maintaining 160-180 degrees is sub freezing temps.
I really need to get some sort of coolant temp gauge on this thing to be able to monitor, i hate these idiot lights.

Mine has a brand new GM OEM thermostat and after i short drive around the block then idling for a half hr or so checking temps im pretty sure it wasnt up to thermostat open operating temps. Upper hose was warm but you could hold on to it with no issues bare handed. I thought about blocking off some of the radiator or fashioning up a winter front but as hesitant without a actaul gauge.
 

cucvrus

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Jonestown Pennsylvania
I drove a CUCV for over 20 years as a daily driver. Fact is several CUCV's over the years. Many I had were bare bones. I even removed the jute padding from inside on the firewall and had a bare painted floor or Line X. I had aluminum heater cores in a few and brass / copper ones in a few others. Almost all had more then enough heat. When I had heat issues and everything else was in check I looked at head gaskets. I found a head gasket issue on every CUCV that I was having heating issues with. Most times it was the compression ring at the head gasket on several of them.

If you are interested check out the thread that led me to this major project. It all started with no heat and steam out the tailpipe on a rainy cold day. Good Luck.

 

Rennat_2006

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Location
Idaho
Dont see any steam, excessive pressure in cooling system, or loss of any coolant so far so i feel like head gaskets are ok at this point.

Attempted to do some more testing today but that got cut short after developing a small leak out of the middle of the radiator when i got into town today. You can see something hit the radiator in the past(probably why the grill is missing) and it started pissing fluid out of the area of some smashed fins today. Hoping to get radiator pulled here soon and taken in to be cleaned out and repaired.
 

cucvrus

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Well that will do it. Low coolant and a hole in the cooling system will prevent the heater from working at optimum efficiency. That is a pressurized cooling system and must be full and pressurized to operate as designed. Every GM I ever owned had little or no heat when the coolant was low. Good Luck.
 

Rennat_2006

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Location
Idaho
Radiator has been replaced with a b850 autozone unit, very surprised when it showed up all aluminum. Did have some issues on install, top radiator mounts were not even close to thick enough and just let it flop around and the low coolant sensor would not fit. It had been a super long day and was about 10:30 in the evening when i was doing the install, rad installed and finalizing hose connections and such and sensor would not go in far enough to catch threads. Without looking inside i just assumed there was a weld goober inside of the fitting and would knock it off with a drill bit quick and easy, yup im sure you know where this is going...drill bit through the first plate of the oil cooler later my blazer will now have a external oil cooler mounted behind the grill.
Rubber mounts were easy enough fix with some mudflap/belting material glued to the core support to take up the gap.

I have gotten some more run time to test the heater output more. Driving down the road with some RPM heat doesnt seem to be any issue, stop and idle for a few minutes though and this thing cools off like a typical diesel and you can definetely feel the difference. I have noticed twice now after 5-10 mile drives in middle teens temperature this new radiator will actaully be frosty on the passenger side half of the radiator behind the grill. Definetely need to setup a winter front for this old gal but a little hesitant to do so without a temperature gauge.

When i have some free time i will run into town and back again and heat gun everything to get actual heater output, heater hose temps, and try pinching down the heater core to radiator hose to slow down the flow some.
 

Mullaney

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Radiator has been replaced with a b850 autozone unit, very surprised when it showed up all aluminum. Did have some issues on install, top radiator mounts were not even close to thick enough and just let it flop around and the low coolant sensor would not fit. It had been a super long day and was about 10:30 in the evening when i was doing the install, rad installed and finalizing hose connections and such and sensor would not go in far enough to catch threads. Without looking inside i just assumed there was a weld goober inside of the fitting and would knock it off with a drill bit quick and easy, yup im sure you know where this is going...drill bit through the first plate of the oil cooler later my blazer will now have a external oil cooler mounted behind the grill.
Rubber mounts were easy enough fix with some mudflap/belting material glued to the core support to take up the gap.

I have gotten some more run time to test the heater output more. Driving down the road with some RPM heat doesnt seem to be any issue, stop and idle for a few minutes though and this thing cools off like a typical diesel and you can definetely feel the difference. I have noticed twice now after 5-10 mile drives in middle teens temperature this new radiator will actaully be frosty on the passenger side half of the radiator behind the grill. Definetely need to setup a winter front for this old gal but a little hesitant to do so without a temperature gauge.

When i have some free time i will run into town and back again and heat gun everything to get actual heater output, heater hose temps, and try pinching down the heater core to radiator hose to slow down the flow some.
.
It isn't nearly as fancy as the snap on radiator covers, but cardboard in front of at least half of your radiator will help the problem in cold weather.
 

LT67

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Bowdon, GA
The heater core in my 85 M1008 had to be replaced. The replacement heater core was aluminum. The new unit will still roast my butt inside the cab.
 
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