What’s That Smell

Written by Don Stewart | 30 June 2009

You’re riding along in your pony one cold morning with the heater turned on when suddenly the cabin fills with an odor that smells like antifreeze. The humidity inside the car shoots up and the windshield fogs over. The smell gets stronger and you feel like you’re in a steam bath. What just happened?
What happened was that the heater core ruptured and it’s spilling hot antifreeze inside your car. It’s bad enough to blow a radiator hose in the engine compartment but a blown heater core in the passenger compartment is far more gut wrenching. A radiator hose can be replaced in the field, the radiator can be filled with antifreeze mix, and you can be on your way. If you don’t have a concours engine compartment, that’s pretty much the end of the story. It’s messy, it’s inconvenient, but when it’s over, it’s over.

Not so with a blown radiator core. Yes, you can drive home or to a repair garage without a tow but that’s just the beginning. The real fun begins after you get there. But first things first. Let’s get the thing drivable with a quick fix that bypasses the heater. The idea is to create a coolant short circuit by re-routing the heater hoses.
Using a towel or large rag to protect yourself from the hot coolant, slowly and carefully loosen the radiator cap to relieve any residual pressure in the cooling system. Cut off the heater hose coming from the water pump as far away from the pump as possible. After loosening the clamp that holds it to the fitting, remove the other heater hose from the engine. In place of the hose you just removed, attach the hose you cut. Reuse the clamp to hold it securely in place. Now you can fill the radiator and drive home or to a repair garage. You won’t have a heater but you won’t have a leak either.
If you drove to a repair garage, just get out the money and have them fix the heater. It’ll be expensive and it’ll take a while. The core itself is relatively inexpensive but not the labor because they’ll have to tear the inside of the car half apart to get at the core. It’s best to make sure you’re at a garage that understands how to work on your pony. Otherwise, the mechanic may break some pieces while he learns how to take your car apart and put it back together again.
If you’re going to repair the heater yourself and you’ve never before done the job, make sure you have a service manual to guide you. And you also might want to call a mechanically inclined friend, preferably one who’s done the job.
This Pony Trick won’t go into the details of how to make the repair. The intent here is to describe some facts about heater cores. A core is just a miniature radiator working to keep you warm on cool days by radiating heat from the engine coolant circulating through it. A core failure is usually due to age plus normal wear and tear. Holes in the core’s thin metal tubes, for example, can be caused by rust circulating with the coolant. That’s because rust is abrasive and over time it can wear through the metal. Another source of failure can be blamed on repeated expansion and contraction caused every time the engine heats up and later cools down when you shut it off. At some point, those heat cycles can cause solder joints to fatigue and fail, resulting in a leak.
Speaking of solder, when cores are built, an acidic flux is used to promote adherence of the solder. Before it’s ever installed in a car, a brand new core can sit on the shelf and slowly eat itself from the inside out if the flux wasn’t completely washed out at the end of the manufacturing process. In that case, a relatively new core can experience a premature failure. There’s no way to predict this type of failure.
Leaks can also be caused by the harsh environment where heater cores live, an environment that’s significantly more harsh than where radiators lives. That’s because full coolant pressure from the water pump is directed to the small volume of the heater before the thermostat opens. Some high pressure flow also goes through the thermostat bypass hose when the engine is cold but the heater takes the real beating. If there’s a weak point in the core, it can fail during engine warm-up.
A core can be repaired with the same techniques used for full size radiators but replacements are inexpensive and probably more reliable than a repaired unit. So the best advice is to buy a new heater core any time the old one fails. Besides you don’t want to do the job more than once. It just isn’t fun.
On the other hand, if a replacement core isn’t available for your car, you can have the old one recored. Under the circumstances, it will be the best repair you can get and that’s exactly what you want.
It probably isn’t necessary to tell you this but I’ll throw it out there anyway. If you’re restoring a car or if you have the dash torn apart so that it’s relatively easy to get at the heater core, replace it. Don’t think twice, just replace it whether it was leaking or not.

Hoofbeats into the Sunset
Folks, I have mixed feelings about saying this but you’ve just read my last Pony Trick. Mary and I have some exciting new opportunities ahead of us and we need to free up some time to devote to them. The hours I spent researching, writing, and editing Pony Tricks was extensive so I’ve decided to redirect those hours to the new tasks. When things calm down, I may be back, if Todd wants me to fill some space.
It’s hard to believe that Pony Tricks appeared in 92 issues of the newsletter, dating all the way back to December 2001. Thanks for your positive comments about the articles. The column was fun to write and an overall enjoyable experience.
I need to say a special thank you to James Clegg, Jim Edwards, David Farmer, Dave Golf, Ed Milano, and Greg Sullins for writing or assisting with nine of the articles. Somehow, I came up with the other 83 on my own.
As for the name of the column, I wasn’t the one who thought it up. Brett Smith deserves the credit. Pony Tricks is a great play on words and it couldn’t be more appropriate. It covers any pony car subject that you can think of. When your thoughts wander to that Mustang parked in the garage, whatever’s going through your mind could be woven into a pony trick.
I hope someone in the club sees my exit as an opportunity to pick up the slack. It would be great to have the column continue under a new byline. When it comes to the guts of the Mustang; about 90% of my experience dates back to the first generation. But there’s any number of articles that could be written by someone more familiar with the newer generations. And certainly, there are an endless number of personal experiences that all Mustang owners could write about, experiences that define their life with the iconic pony car. It wouldn’t be hard to keep Pony Tricks going if one club member or several members would write articles for the column.
If we’re fortunate enough to see a new byline and that person wants a copy of the log that lists Pony Tricks’ articles from the past, just let me know. The log would help the new columnist avoid writing articles about tricks that have already been covered or it could serve as a basing point for expanding on previous articles.
I guess you can tell that I’m having a hard time cutting the string but the exclamation point at the end of the next sentence will get it done. Thanks, everyone!