Testing Heater Core for Heat Output

[xirdneh]

After replacing the heater core in my wife’s Tercel and not being satisfied with the amount of heat the new core produced I decided that before attempting the miserable job again I needed some way of testing the core to be sure it was going to put out the heat.
The local radiator shop could only test for leaks using a pressure test. He mentioned that there was no way to test for heat output. He also said that internal oxidation could slow the transfer of heat.
The first thing to do was find out what a good heat output temperature was. I shoved a temperature gage in the middle vent of several Tercels. Blower was set to one of the two higher speeds. Outside air temperature was in the 40’s. Set air lever to “RECIRC”. Water control valve checked on all to make sure it was fully open.

87 Blue car 158 deg (original core) 250,000+ miles
87 Blue car 155 deg (original core 300.000+ miles)
Silver 145 deg (original core) 250,000+miles)
Brown 135 deg (original core) 230,000+ miles)
White 120 deg (recent new heater core, car had better heat with old leaking core)
Yellow 122 deg (back flushed two years ago, brought back a bit more heat)
(checked for debris on top of core) (original core 230,000 +miles)
Grey 90 deg (owner checked for debris on top of core)(original core 200,000
+ miles)

For heat the testing contraption uses a 4 QT pressure canner with temperature gage and pressure gage. The heat element is Propane. The Tercel water pump with standard 4-3/4” dia. pulley is driven by a 1425-RPM electric motor with an 8” diameter pulley producing about 2399-RPM at the pump. A flow indicator is located just before the water pump inlet. It has a clear view window with what looks like a propeller inside that spins with the flow of water. Hoses are 5/8” diameter.
I used an entire Tercel heating assembly that includes the blower housing and heater core housing. I made a lightly insulated sheet metal duct and attached it to the housing output hole to imitate the middle vent configuration of the Tercel. It has a temperature gage located inside, a few inches before the vent opening.
The blower runs on 12-volt car battery and has a four-speed controller I picked up at a local auto parts store for $14.00.
The pressure canner inlet and outlet hose connections are located in the side of the pan about halfway between top and bottom. The pan is filled with water to the top of the pan keeping the inlet and outlet submerged so no air can enter the system.
Heater core “A” was used for the first test. (It’s a used salvaged core, same with “B”)
I carefully filled the system with water by tilting the pan in such a way as to let the water run into the pan inlet hose, down to the water pump and up into the heater core and up to the pans outlet (highest point). I had hoped this would minimize air bubbles in the system.
It took about 25 minutes to heat the water throughout the system to 200 degrees. I periodically turned the pump on for short periods during the initial heat build up.
When I was satisfied all the water in the system was near 200 degrees I let the temperature build up to 220 degrees and turned the pump and blower on (Full speed).
The room temperature was 40 deg as was the temperature at the vent opening.
The temperature of the water slowly fell as the vent air temperature rose. The steady water temperature drop slowed down to almost a stop at 190 deg and fell slowly to 180 deg which is the Tercel’s operating temperature. During this period the vent air temperature peaked and stayed at 142 degrees.
The systems water temperature continued to fall slowly and the vent air temperature began to follow suit.

Core “A” Water 180 deg Air 142 deg
Core “B” Water 180 deg Air 142 deg

“I need more heat Scotty!!!”

The 2600 Watt element was the most powerful I could get and was disappointed that I could not hold 180 deg water at high blower speeds. That’s why I had to do this at middle blower speed and be happy with the slow temperature drop between 190 and 180 deg.
I noticed the blower speed did not make much difference in air output temperature while testing the various Tercel's, so doing this test at middle speed should be fine.
Pressure gage never moved from zero.

Nothing ever goes according to plan. I had to change this testing unit many times before it finally produced something that works. The first two water pumps (salvaged) began leaking out of the bottom weep hole and took forever to begin circulating water. I’m assuming the seal allowed some air in and messed up the flow.
Still, getting the water to flow with a good pump was not a sure thing. The system was very temperamental and even after carefully filling the system in the manner explained earlier the pump had to run for several minutes before the flow indicator began to turn in fits and starts gradually building up speed. Mounting the pressure canner at the highest point made a huge difference. I picked up the pressure canner at the local Goodwill store for $5.00 minus the gasket. Ordered the gasket ($11.00 + 6 shipping)on line and had it three days later.

Nov 2014 I set the whole thing up again but used propane burner and fan on full speed in 40 deg workshop
re-tested the cores and got different readings
Cores tested on contraption (out of car)
Salvaged core "A" 130 deg
Salvaged core "B" 125 deg
Salvaged core "C" 127 deg
Salvaged core "D" 134 deg
New Vistapro Ready Aire (Brass) 399317 tested at 137 deg 11/2014

[ARCHINSTL]

WOW !
What a treatise! Thanks!
As "someone else" would write..... .. .. .. .. .. .. .. .. .. .. .. .. .. ..

While you have your apparati set up...would you mind measuring the length of the translucent spacer between the blower and the heater unit - and maybe add a pix of if from the other side? Since it is highly unlikely I will ever get the AC on Goldie to work, as at least the compressor is shot, plus the expense of the conversion kit and parts - I want to achieve the heat (and air velocity) that I recall my '83 had; the AC unit just obstructs too much air, and it's probably filthy as well (PO was a smoker); this would also help the "cooling effect" during the Summer.
I would not think that the blower or heating units themselves would be different for AC and non-AC cars, so I'm hoping I could just install the "spacer" in place of the cooling unit. Othewise I have to fab something from plastic pipe.
Tom M.

[Neu]

wow...absolutely wow.

[Petros]

Nice job! That seems like a lot of trouble to test a heater core.

My local radiator shop can bench test a radiator by running hot water through it, and pointing a heat sensor gun at various places over the surface to see if it has even heat, meaning none of the tubes are blocked. The sensor looks like a timing light but has a digital temp readout on the back, it reads IR heat pretty accurately off the surface it is pointed at.

It seems to me the same thing could be done with a core, run hot water through it, and after sweeping the temp sensor over it, you can compare different heater core surface temps. The higher temp on the face of the core, the more heat is being transfered out of the water to the surface of the core, meaning you will get higher out put temps. You can even do this with simple surface thermometers with a home set up.

Measuring core surface temps will not get actual in dash temps like your rig does, but you can at least compare cores to see which is better with a lot less effort.

Of course, you can also use your test rig to adjust or experiment with other aspects of the heat system (flow velocity, airspeed, duct size and shape, system air leaks, etc.) to see if you can get even more output from the factory heater than a new system.

Let us know what you find.

It is not that cold in Seabeck WA is it?

[Neu]

Nice job! That seems like a lot of trouble to test a heater core.

My local radiator shop can bench test a radiator by running hot water through it, and pointing a heat sensor gun at various places over the surface to see if it has even heat, meaning none of the tubes are blocked. The sensor looks like a timing light but has a digital temp readout on the back, it reads IR heat pretty accurately off the surface it is pointed at.

It seems to me the same thing could be done with a core, run hot water through it, and after sweeping the temp sensor over it, you can compare different heater core surface temps. The higher temp on the face of the core, the more heat is being transfered out of the water to the surface of the core, meaning you will get higher out put temps. You can even do this with simple surface thermometers with a home set up.

Measuring core surface temps will not get actual in dash temps like your rig does, but you can at least compare cores to see which is better with a lot less effort.

Of course, you can also use your test rig to adjust or experiment with other aspects of the heat system (flow velocity, airspeed, duct size and shape, system air leaks, etc.) to see if you can get even more output from the factory heater than a new system.

Let us know what you find.

It is not that cold in Seabeck WA is it?

You just pretty much said "hey..nice job, but instead of working for 10 hours on that.. you could just walk down to harbor freight, pick up an IR temp sensor and just run hot water through it...knowing the water's temp." this actually made me laugh.

[xirdneh]

While you have your apparati set up...would you mind measuring the length of the translucent spacer between the blower and the heater unit - and maybe add a pix of if from the other side? Since it is highly unlikely I will ever get the AC on

its 8.5 on firewall side (widest points) 6.25 on interior side (widest points)
i'm pretty sure you can switch them out
i am pretty sure i've done it before
as i always remove the A/C stuff from the Tercels i fix up
i remove it because the charge has been lost and it costs to much to get it working again
do not really need A/C around here anyway

[xirdneh]

Nice job! That seems like a lot of trouble to test a heater core.

Measuring core surface temps will not get actual in dash temps like your rig does, but you can at least compare cores to see which is better with a lot less effort.

It is not that cold in Seabeck WA is it?

rarely gets below 20 deg here
but the 120 deg output is not enough with temperatures below 34 deg
it takes about 14 miles to feel some good heat
and it never gets toasty

[takza]

Not sure why you can't get heat...My heater core is probably original at close to 250K...and I've only back flushed it once in 55K. When temps are 20F or above...once the car is warmed up...I usually don't need the fan running at all. Sometimes we see -20F...then I run the fan on 2 or 3 for sure.

[xirdneh]

I tried to buy a new heater core at the local Napa and the two cores from two different companys (Napa brand and Ready Aire 399317)turned out to be the same core. The length and width were the same as the originals but the thickness was half of the original. It was designed to fit in the Tercels original housing having ends that were the same thickness as the original. Just the radiator portion was cut in half. Since i'm trying to do a comparison test here I need the original core.
The core i bought for my wifes car (White) was Ready Radiator brand that matched the original. I would like to get one made from a different company.
Does anyone know anything about these thinner cores?

[toughtercel]

that one of greatest engineering idea to creative the differents of heat , that show someone is enjoy himself, to have fun of different ideas , just want to add few tips about heating system , from the past there a lots different cars/truck didnt realize "the faster the fan blower turn , the more cold air produce or blowing out " 1983 tercel have i think 4 speed fan switch while later one (85-87)have 5 or 6 speeds switches .
secondly my first car was 1983 heater was'nt hot enough and reason is control linkage(cable) attach to shutter or heater valve not fully open , once tried with plier fully open lots of heat come out but it self move closing postion ( less heat) but i own 86 works great then bought 85 same work great the bought another one is 83 back same problem "linkage problem "

[takza]

3 main things control the heat output:

* good hot coolant flow..check thermostat and heater valve...adjust the valve control cable?

* non clogged core...backflush it?

* air going thru the core...adjust the air doors?

Next to last resort would be to use a chemical to flush the coolant system. If all else fails...replace the core?

[xirdneh]

3 main things control the heat output:
* good hot coolant flow..check thermostat and heater valve...adjust the valve control cable?
* non clogged core...backflush it?
* air going thru the core...adjust the air doors?
Next to last resort would be to use a chemical to flush the coolant system. If all else fails...replace the core?

In my case of the white car (produces 120 deg) I did replace the core. Did not get the same heat output as the old leaking core.
I did the fill the system slowly and burp thing with radiator cap off even though I did neither of those things to the Blue car after a head gasket replacement and it produces 155 deg.
Either the core (looks just like original equipment) is bad or I have an air bubble in there somewhere. I sure wish there was a way to check for air bubbles.
I started this whole testing thing because I want to know everything there is to know about heater cores. It was fun to build and tweak the testing contraption and operate it.
As simple as this contraption is (minimal amout of hose) I'm finding out how tedious it is to get water to flow through it.
No matter what technique I use to fill it with water it still has to run for twenty minutes or so before the bubbles work their way to the highest point and water flows in fits and starts during that period eventually reaching top flow.
As noted the two used cores reached a high of 142 deg.
I ended up buying a new aftermarket aluminum core and tested it last night. I could not get it to go higher than 122 deg (even while running 210 deg water through it and blower on lower speeds). It did take a noticably longer period to drop air temperature output than the used cores (with blower on high).
Maybe an air bubble? Ido not know. What does it all mean? I do not know that either.
Frustrated in Seabeck I am.

[splatterdog]

And to think I've been called a mad car scientist......

[Petros]

I am not sure I would use an aluminum heater core, they can be reactive with many common rad chemicals and start corroding away. I know Subarus use aluminum heaters, and they are notorious for leaky cores. And like the Tercel, the Subaru heater core is a major job to replace. I think I will pass.

[toughtercel]

back in the mid 80's i use to work "RADSHOP" and other radaitor shop as well , most mechanic and "I" perferable (1) copper tubes and fins , (2) two tubes instaed of single wide tube AND (3) metal tanks instaed of plastic tanks , so i bought it at toyota dealer , not bad for $150.00 for radaitor (all made of copper/two tubes/and metal tanks) , private auto parts (LORDCO/NAPAS) some do have and some they don't , ESPECIALLY for example " rear axle diff. bearing" are hard to come by , at private auto parts sell bearing without sleeve so toyota dealer have them all and way cheaper now that weird , the point is , it is nessary to waste time driving few different auto parts store and compare the price and quantity.