CUCV Replacement Heater Cores - No or Low Heat Output Reason

jacksmad1

Member
48
5
8
Location
Columbia, TN
I had to replace my heater core back in the summer because my original core was leaking. It has just now gotten cold enough to start requiring heat and I soon found out I was not getting heat like so many others on the site who have replaced their original heater cores. I did not want to spend $120 or more to get my old core rebuilt so I went on a crusade to determine why I was getting no heat. I thought maybe I had an air-bubble somewhere in my system, so I bled all the air out and went through several heating and cooling cycles to make sure the system was full of coolant.

Still no heat....so then I got my infrared thermometer and measured the temperature on my crossover near the thermostat after driving for 10-15 minutes. The temp was running between 160-170 degrees, so naturally I thought my thermostat was stuck open, so I removed the thermostat and took it inside to check when it was opening in a pan of hot water. It started opening between 190-195 degrees, so the thermostat was not the issue (yes it is a hockey puck type) so I re-installed it, refilled the system, bled it, etc. So I then blocked my radiator with cardboard and tried again. The temp still only got to 160-170 degrees after a 10-15 minute drive. I checked my heater hoses temps then and the feed hose was around 160 degrees and the return hose was around 150 so hot water was getting to the heater core and there was a temperature drop on the return side. Now it was time to remove the heater box and look at what was going on.

I got my original replacement core from O'Reilly (both O'Reilly and Advance sold the exact same core). After much head scratching and comparisons I finally figured it out. Although we all know the replacement cores are made of aluminum and they are thinner, that is not the main issue. Aluminum is an excellent conductor of heat (i.e. aluminum cookware). The thickness of the core is thinner and would not have the same thermal mass or cross sectional area to exchange heat to the air, so I will give you that, but there still should be some heat.

So here is what I found. Look at the three pictures below. Picture 1 is the original heater core. Notice the left side of the core has a good seal against the board (the board represents the heater air box the core is mounted to). Now look at picture 2 of the heater core I got from O'Reilly (same as Advance had). There is a quarter inch gap between the core and the board! The air in your heater box will take the path of least resistance when going through the air box so 90+% of the air will actually go around on both sides, instead of going through the heater core and never pick up any heat!

It may be possible to block the air on the sides with foam or something but the better solution is to find a Spectra Premium heater core 94553 (I got mine from AutoZone). Look at picture 3. (Sorry I had to use a stock image, I forgot to take a picture of the new core before I installed it) The Spectra Premium core is still aluminum and about the same thickness as the core in picture 2 but it has filler panels on the sides of the core to seal it against the air box so all the air goes through the core instead of going around the core. I now have good heat in the cab even though the engine temp is still at the 160-170 degree range. The Spectra core was only around $28 bucks.

Hopefully this will help all of you have some heat without having to spend big bucks to get your old cores repaired.

old heater core side.jpgnew heater core .jpgheater core from az spectra premium 94553.jpg

old heater core side.jpgnew heater core .jpgheater core from az spectra premium 94553.jpg
 
Last edited by a moderator:

scottladdy

Member
538
4
18
Location
CT
Heater Core Question

... but the better solution is to find a Spectra Premium heater core 94553 ...
Thanks for the great post and the additional time to research this issue.

I need to replace the radiator in my M1008A1 and the water pump to boot. Small leak in the radiator and there is weepage out of the weep hole in the pump.

Over the summer I replaced all the hoses, thermostat, and radiator cap with the Stant self sealing model #10230 (as these are now recommended to reduce cooling system contamination) to both of my trucks. I also added a KAT's engine block heater #11612 to each, but the one in the pickup is bad and has a small leak. It also needs to be replaced (under warranty from NAPA).

Since I am going to this much trouble, I was thinking it would make sense to replace the heater core at the same time as well. How far behind can a leak be in the heater if there is a leak in the radiator? Might as well head it off at the pass, especially since the cores are pretty cheap in comparison to the cost of the antifreeze I will need to replace when I do the job. I had already landed on the Spectra Premium heater core as well as the Spectra radiator.

My question to you is, have you noticed similar heat output between the old and new cores? I realize it may be subjective, but any information is appreciated.
 

jacksmad1

Member
48
5
8
Location
Columbia, TN
Thanks for the great post and the additional time to research this issue.

I need to replace the radiator in my M1008A1 and the water pump to boot. Small leak in the radiator and there is weepage out of the weep hole in the pump.

Over the summer I replaced all the hoses, thermostat, and radiator cap with the Stant self sealing model #10230 (as these are now recommended to reduce cooling system contamination) to both of my trucks. I also added a KAT's engine block heater #11612 to each, but the one in the pickup is bad and has a small leak. It also needs to be replaced (under warranty from NAPA).

Since I am going to this much trouble, I was thinking it would make sense to replace the heater core at the same time as well. How far behind can a leak be in the heater if there is a leak in the radiator? Might as well head it off at the pass, especially since the cores are pretty cheap in comparison to the cost of the antifreeze I will need to replace when I do the job. I had already landed on the Spectra Premium heater core as well as the Spectra radiator.

My question to you is, have you noticed similar heat output between the old and new cores? I realize it may be subjective, but any information is appreciated.
I would say the heat output is about the same, but it has been almost a year between using the old one since my leak occurred during the summer. Just be sure that when you install the Spectra core that it is centered over the opening in the air box for the core and that there is not a gap on either side so all the air has to go through the core and be heated. Good luck with your repairs.
 

Keith_J

Well-known member
2,972
70
48
Location
Schertz TX
Exactly what I found. The thinner cores are micro-finned, unlike the original. These thin, short fins are far better at giving up heat to air.

The replacement core I got for Tim's 1009 included foam to seal the core in the box. But I have not had the time to test it since installing. From my heat transfer industry experience, I know heating air with hot water requires large area on the air side. Which is the design philosophy on the compact heater cores.

But with this fin pitch, there is increased pressure drop over the core. ANY leak will bypass a large volume of air. And make it seem like the new core isn't working.
 

gungearz

New member
1,721
2
0
Location
northwestern indiana
Is it possible to run 100% antifreeze and not achieve adequate engine temps during the cold season...? What mixture are you running in your cooling system...? In colder temperatures, personally I think 50/50 is best for +0. Plus, taking in consideration that diesels do not heat like your standard petro automobiles. They tend to run cooler.... I'm glad your getting heat back out of it. That's what matters most...
 

jacksmad1

Member
48
5
8
Location
Columbia, TN
I am running about 50/50 mix. I checked it with one of the Prestone antifreeze testers and I was between 50-60% antifreeze. I will drive it more this weekend and let everyone know how it performs.
 

Keith_J

Well-known member
2,972
70
48
Location
Schertz TX
More than 60% ethylene glycol reduces freeze protection. Pure water is the most efficient heat transfer fluid, if you can keep it from freezing or boiling.
Indirect injected diesels tend to behave more like gasoline engines since the fire is mostly in the precombustion chamber. In a direct injected engine, the fire is in the piston which has a dish/bowl. The pistons are cooled by the oil.

My CUCV is fully warmed up after 5 miles in town. The heater is noticeably warm after just a mile without any idle warm-up.
 

K9Vic

Active member
1,261
2
38
Location
Fort Worth, TX
Thank you, I need to replace the one on my M1031 as there is no heat at all. It would be nice to get real USA made heater cores, but times have changed.
 

natemccabe

New member
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0
0
Location
Fairbanks, AK
Good tip, and something for me to check this weekend. I was already to just give up on heating my 1009. I am also asuming that the -30F temps around here are a major thing to overcome with such a large cabin space and such a tiny core.
 

jacksmad1

Member
48
5
8
Location
Columbia, TN
Just an update as promised.....went driving around this weekend with temps in the mid to low 40's out....actually had to turn down the heat to half or less to stay cool...so the heater core swap has worked well.
 

bimota

New member
211
1
0
Location
Campbell, CA
Anyone have issues with repeated heater core failures - leaks? I've put three heater cores in my M1031 this year and I give up - they last about a month and then start leaking. Something is causing a failure of the heater cores. New cap, no other leaks, straight forward install - any one have a diagnosis or solution?
 

Warthog

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Super Moderator
Steel Soldiers Supporter
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Sometimes if you have bad ground wires, the current will flow thru the heater core and radiator and make them corrode. Not saying that is your issue but is something to check.
 

Hasdrubal

New member
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Location
Vancouver BC
Interesting note, my ground wires are all good, clean and tight. Never had any electrical problems, yet when I had my radiator rebuilt, guy said it looked like I had some corrosion forming in the side tanks. My replacement heater core has been in for 6 years, tons of heat, no issues there.
 

Warthog

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Steel Soldiers Supporter
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Anyone have issues with repeated heater core failures - leaks? I've put three heater cores in my M1031 this year and I give up - they last about a month and then start leaking. Something is causing a failure of the heater cores. New cap, no other leaks, straight forward install - any one have a diagnosis or solution?

And it appears that current flowing thru the heater core will cause issues.

http://www.steelsoldiers.com/showth...-resulting-in-leaking-of-heater-core-into-cab
 
Last edited:

CycleJay

New member
1,434
3
0
Location
Marietta, Ga
I had to replace my heater core back in the summer because my original core was leaking. It has just now gotten cold enough to start requiring heat and I soon found out I was not getting heat like so many others on the site who have replaced their original heater cores. I did not want to spend $120 or more to get my old core rebuilt so I went on a crusade to determine why I was getting no heat. I thought maybe I had an air-bubble somewhere in my system, so I bled all the air out and went through several heating and cooling cycles to make sure the system was full of coolant. Still no heat....so then I got my infrared thermometer and measured the temperature on my crossover near the thermostat after driving for 10-15 minutes. The temp was running between 160-170 degrees, so naturally I thought my thermostat was stuck open, so I removed the thermostat and took it inside to check when it was opening in a pan of hot water. It started opening between 190-195 degrees, so the thermostat was not the issue (yes it is a hockey puck type) so I re-installed it, refilled the system, bled it, etc. So I then blocked my radiator with cardboard and tried again. The temp still only got to 160-170 degrees after a 10-15 minute drive. I checked my heater hoses temps then and the feed hose was around 160 degrees and the return hose was around 150 so hot water was getting to the heater core and there was a temperature drop on the return side. Now it was time to remove the heater box and look at what was going on. I got my original replacement core from O'Reilly (both O'Reilly and Advance sold the exact same core). After much head scratching and comparisons I finally figured it out. Although we all know the replacement cores are made of aluminum and they are thinner, that is not the main issue. Aluminum is an excellent conductor of heat (i.e. aluminum cookware). The thickness of the core is thinner and would not have the same thermal mass or cross sectional area to exchange heat to the air, so I will give you that, but there still should be some heat. So here is what I found. Look at the three pictures below. Picture 1 is the original heater core. Notice the left side of the core has a good seal against the board (the board represents the heater air box the core is mounted to). Now look at picture 2 of the heater core I got from O'Reilly (same as Advance had). There is a quarter inch gap between the core and the board! The air in your heater box will take the path of least resistance when going through the air box so 90+% of the air will actually go around on both sides, instead of going through the heater core and never pick up any heat! It may be possible to block the air on the sides with foam or something but the better solution is to find a Spectra Premium heater core 94553 (I got mine from AutoZone). Look at picture 3. (Sorry I had to use a stock image, I forgot to take a picture of the new core before I installed it) The Spectra Premium core is still aluminum and about the same thickness as the core in picture 2 but it has filler panels on the sides of the core to seal it against the air box so all the air goes through the core instead of going around the core. I now have good heat in the cab even though the engine temp is still at the 160-170 degree range. The Spectra core was only around $28 bucks. Hopefully this will help all of you have some heat without having to spend big bucks to get your old cores repaired.

View attachment 401891View attachment 401892View attachment 401893
Hello,

Darn, I wish this post had caught my eye before I just replaced my heater core just a few months ago.
I am having a similar issue, I will have to go under there, and see if there is a gap, if there is perhaps I will use insulation,
or replace the core again with the spectra premium. Thanks for the post. and information.

Good night

CJ
 

ARYankee

Active member
1,961
3
38
Location
Benton, AR
Hello,

Darn, I wish this post had caught my eye before I just replaced my heater core just a few months ago.
I am having a similar issue, I will have to go under there, and see if there is a gap, if there is perhaps I will use insulation,
or replace the core again with the spectra premium. Thanks for the post. and information.

Good night

CJ
I replaced mine with one from Autozone. I used some weatherstripping on the sides of it to seal it in the box. It works great!
 

jacksmad1

Member
48
5
8
Location
Columbia, TN
On a scale 1 - 10, 1 easy & 10 hard, how hard was it to change the core?
Probably around a 5.

some of the nuts on the firewall are kind of difficult to get to.

to make it easier be sure and remove the glove box and have plenty of light so you van see what you are doing under the dash

with patience, which I do not have in abundance, you can do it.

also help to have something to stand on when working under the hood if you are vertically challenged like me...
 

ssdvc

Active member
572
28
28
Location
CT and MD
I used the Autozone Spectra unit and it worked great, even when it was 10 degrees out. Fairly easy job, just remember to retighten the hose clamps after two or three heat cycles.
 
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