Pressure Testing a Heater Core

[Patrick B.]

Since replacing a heater core is such a tough job and now we have to worry about the quality of the replacement parts, pressure testing your new heater core prior to assembly is often recommended. I found an extremely simple way to do this at home. A 25mm bicycle tube that you can buy at Walmart for about $5 will do the trick. Cut a section of the tube with the air valve and put it on both heater connections using hose clamps. The tube stretches fairly tightly over both inlet and outlet nipples although they are different sizes. I inflated it to about 5 - 10 psi and dunked the core in a 5 gal bucket of water to watch for bubbles.

I tried to inflate it to 20 psi but it exploded with an impressive bang. I would suggest using a shorter piece than I did and wrapping it in duct tape to try for higher pressure. Make sure to test it first at 5 - 10 psi before venturing to higher pressure so you don't risk ending up empty handed. I think the low pressure test is sufficient to test for pin holes in a defective core.

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[Mike T.]

Re: Pressure Testing a Heater Core

Pat - That's a neat idea, I'm going to remember that one. I've had experience with faulty 'new' heater cores. One was so bad, it leaked before the engine was even fired up and provided pressure to the system. Learned my lesson on that one so always double check the core before installing it.

[Gary R.]

Re: Pressure Testing a Heater Core

I made one up using heater hose to copper pipe. Plugged one end and used a 1/2 x 1/4 npt adapter on the other. Installed a 1/4 npt fitting with a hose barb or quick disconnect and applied 15-20 psi. It was solid connected so there was no issue. Very good idea to check all heater cores these days.

[Brad K.]

Re: Pressure Testing a Heater Core

That's a GREAT idea......I just installed a new one on a '67 last week withOUT doing this....Fortunately for the time being it is leak free. I would absolutely HATE to have to do the job over again. It literally took hours to get the frustrating job done. The curved inlet and outlet tubes were very difficult to get back through the small holes in the firewall after securing the new core inside the fiberglass heater box. I will certainly use this method (if I ever have to do this job again!)

[Steve G.]

Re: Pressure Testing a Heater Core

Great idea for checking a new core before installing.

On a used core I would spend the few bucks a rad shop charges to boil and test it. Flushing with a garden hose won't always remove all the debris that the commercial cleaning process does. The amount of crud that accumulates in there is quite amazing, and once that has been cleaned out the probabilities of a leak increase significantly. Sometimes, it's just cooling system crud, sometimes it's the "stop-leak" that was poured in there that was fixing an old leak.
Steve

[Mike E.]

Re: Pressure Testing a Heater Core

I like the idea! Thanks!

[David G.]

Re: Pressure Testing a Heater Core

I use the same method for testing radiators. I hate doing a job twice.
Dave

[Joe R.]

Re: Pressure Testing a Heater Core

Speaking of heater cores and radiators the same principle of checking them before installation should never be left out! If your heater core or radiator has been out of the car for some period of time and not filled with a mix of antifreeze and water it will corrode and form pinholes. My advise would be to fill the heater core and radiator keeping them wet and free of corrosion while that restoration (maybe years) is happening. I would never want to see an original radiator that was dated to the car corrode and be thrown away.

JR

[Duke W.]

Re: Pressure Testing a Heater Core

Most radiator shops, which are getting rarer, will test them free. It only takes a minute or two. Last time I had one tested the test pressure used was 30 psi - double typical cap release pressure. That will blow any weak solder joints.

Just don't tell them it's new, but they might figuree it out.

Duke

[Joe R.]

Re: Pressure Testing a Heater Core

Yes, a radiator will test them for you. They will dunk them in the water with suds/acid and when you take your aluminum radiator home it will develop holes!!!!! Most radiators fixed in those tanks are brass/copper and soldiered but cleaned first with acid to clean the paint and brass/copper off so the lead soldier will stick properly. You can fill in the rest!!!!
Aluminum Radiator owners please beware!

JR

[Duke W.]

Re: Pressure Testing a Heater Core

The shops I used just dunked them in a water tank to test. Maybe they use a chemical tank to clean brass radiators/heater cores them prior to repair.
If an OE type aluminum radiator leaks, it's toast - can't be repaired. I figured mine was bad due to white deposits, and the test showed many tiny pinholes.

Duke

[Joe R.]

Re: Pressure Testing a Heater Core

Duke,

Your radiator sounds like one that has been removed and allowed to dry out for an extended time. They end up with small white scabs that are actually holes because of the corrosion. Thats why I cautioned everyone to fill them back up with a 50/50 mix while their restoration is taking place. I hate to see an original radiator go to waste cause the repo radiators can be spotted from several blocks away by a judge that is blind. I have repaired a few radiators using the refrigerant epoxy supplied to AC/heater repairmen. Fixing those with a couple of holes will extend their life for a while.

JR

[Steve G.]

Re: Pressure Testing a Heater Core

Duke,

Your radiator sounds like one that has been removed and allowed to dry out for an extended time. They end up with small white scabs that are actually holes because of the corrosion. Thats why I cautioned everyone to fill them back up with a 50/50 mix while their restoration is taking place. I hate to see an original radiator go to waste cause the repo radiators can be spotted from several blocks away by a judge that is blind. I have repaired a few radiators using the refrigerant epoxy supplied to AC/heater repairmen. Fixing those with a couple of holes will extend their life for a while.

JR

The small white spots that look like calcium deposits are the silicates that leach out of the antifreeze. I had never heard them to be responsible for the leaks, but they are known as the primary cause of blockage in the tubes. This, and the fact that with any reg glycol anti-freeze the corrosion inhibitors have become in-effective is the reason that the manufacturers (car and a/f) tell you that your antifreeze should be changed every 2 years. Whether you drive the vehicle or not. If you're storing your cooling system parts with a/freeze in them you need to change it every two years. A properly cleaned radiator or heater core is fine stored dry. Have it properly cleaned out before you store it instead of before you want to use it. It's the deteriorating antifreeze that becomes corrosive.

Silicate free (Dexcool) and other long life coolants allow for a 5 year interval.

In the corner of the shop here is a 63 Avanti that had the same anti-freeze in it for the past 20 some years and hadn't probably run 2 hrs in those years. When I took the t-stat housing off to fix weepage/leaking all around it the recess for the stat was nearly corroded right off and the large pits in the ball of the housing were so deep I could have pushed a screwdriver through them. This is the old antifreeze at work.

Getting people to change their antifreeze on time has always been an industry issue. If it was green and clear, it was assumed it was okay. They would change it when it turned brown with rust. By that time it was too late. The bottom of the block was filled with rust and the frost plugs were rotting through. The silicates leaching out was a major cause of water pump failure.

Steve

[Duke W.]

Re: Pressure Testing a Heater Core

Duke,

Your radiator sounds like one that has been removed and allowed to dry out for an extended time. They end up with small white scabs that are actually holes because of the corrosion. Thats why I cautioned everyone to fill them back up with a 50/50 mix while their restoration is taking place. I hate to see an original radiator go to waste cause the repo radiators can be spotted from several blocks away by a judge that is blind. I have repaired a few radiators using the refrigerant epoxy supplied to AC/heater repairmen. Fixing those with a couple of holes will extend their life for a while.

JR

Nope. My ...316 radiator was toast after about 12 years, and there was a reason. St. Louis did not install the upper mount rubber grommet. I knew it was loose up there over the years, but failed to investigate further. It wasn't until I bought an AIM that I realized the grommet was missing.

Without the grommet, the radiator was not electrically isolated from the engine, so what I had was an iron-aluminum galvanic cell and aluminum is the sacrificial material.

That's why the three rubber mounting grommets (two on the bottom, one on top) should be replaced when a new aluminum radiator is installed, and it's not a bad idea to use a meter to ensure that the existing radiator is electrically isolated. If not, it needs new mounting grommets to keep it from being eaten away by galvanic action.

Duke

[Gary S.]

Re: Pressure Testing a Heater Core

FWIIW: Took the original radiator out of my 67 small block in 1993 to do a full body off restoration. Filled it full of Sierra brand antifreeze, plugged all holes and hung it on the wall in my garage. For the first time since, took it off the wall last summer and put my airhose to it...not sure of the pressure, but way more than I should have. No leaks. Mounted it to my rolling frame and refilled it. Started the motor and no leaks. In the past I bought four dated C2 small block radiators that did not leak....after setting empty about five years, they all leaked. Expensive lesson on aluminum radiators.