DON’T TOUCH THE RADIATOR CAP: A Mechanic’s First-Hand Experience That Nearly Ended in Blindness

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We work on cars and trucks all the time here at BestRide, and most of the time the most dangerous thing we do is put a car on jackstands. But in July, we heard about Peter McCullough’s story and wanted to get it out there as a cautionary tale for both shadetree and professional mechanics.

“I work as a mechanic in a small two-bay shop in northwest Houston,” says Peter. We’ve been in touch because Peter follows one of the same Facebook groups I do, and he’s always posting photos of the cars he’s working on.

The owner of the shop is Peter’s friend Derek and Peter had been working there on and off since November of last year. He fills in when necessary, and he also works on some of his own projects.

“I hang out up there often. Sometimes on dead days I’ll bring my own rides up to tinker with off on the other side of the shop,” says Peter. “I was working on my 1990 Mercury Grand Marquis. I brought it in as I was having some mild and random overheating issues that constant attempts at burping couldn’t resolve.”

Find a Mercury Grand Marquis at

Peter hadn’t spent much time driving it that day, figuring he put maybe a mile and a half on it before he parked it in front of the side bay door. He popped the hood figuring he’d let it cool down and went inside to talk with the guys in the shop for 10 minutes or so.

As he walked back to the car, he could hear a high-pitched squeal coming from the engine bay.

“It wasn’t showing any signs of overheating,” Peter told us. “I poked around under the hood but I couldn’t find the source of the squealing.”

Wisely, Peter grabbed an infrared gun to probe around the cooling system to read temperatures at different sources.

INfrared gun

An infrared gun consists of a lens to focus infrared thermal radiation on to a detector, and then converts that radiant power into an electrical signal, and displays the temperature of an object the gun is pointed at. It allows temperature measurement from a distance, without having to contact the object.

“With the thermostat housing reading 200 degrees Fahrenheit, I was a bit puzzled,”Peter says. “I probed around a bit more with my ear facing the engine bay, trying to find this squeal.”

Then disaster struck. “I got as far as the right side of the radiator, and simply touched the top of radiator cap. Boom, I found the squeal. The radiator cap few off from the plastic radiator tank, and I got a nice dose of immensely rusty water, antifreeze, and more rust.”


For those of you who remember basic science, water boils at 212 degrees. Coolant — as its name suggests — offers the additional cooling advantage of raising the boiling point of water. A common 50/50 mix of water and coolant raises the boiling point of engine coolant to 235 degrees.

Even that’s not enough to cool the massive temperatures of a running V-8 engine enough to avoid boiling, though. An automobile’s cooling system is under 14 to 18 pounds of pressure, thanks to the radiator cap, which raises the boiling point another 45 degrees.


Boiling water is enough to cause third degree burns. Boiling coolant can be deadly.

A radiator cap is designed to stay in place under pressure, but plastic radiator tanks and cap housings can fatigue over time. Radiator tanks and housings used to be constructed of brass, but since the 1980s, plastic is the material of choice.

The results of the explosion were immediate.

“Derek heard the loud bang and looked around for its source,” says Peter. “He saw a huge mist of vaporized, pressurized water in front of the second bay and ran over to check it out. I stumbled into the bay, not feeling any pain, but a bit dazed. His eyes meet mine and his face went pale.”

Derek thought quickly and his actions probably saved Peter from further consequences. “Without saying more than ‘Dude, let’s go’ he grabbed me just before I nearly passed out from the sudden onslaught of tremendous pain. I found out later that in that moment, he watched the skin on my face literally start to boil off. Sorry to be graphic, but it’s accurate.”

“Another guy who comes by the shop every so often recognized all the commotion and aided Derek in getting me into the cab of his truck and he raced over to the nearest ER clinic in record time.”

Peter McCullough Burns

At the ER, the staff worked quickly to clean Peter’s wounds and medicate him to keep the pain in check. “Thankfully, my glasses took the brunt of the hit from my eyes,” Peter says. “That’s the only reason I still have my eyesight, according to my doctor.”

Second- and third-degree burns are horrifically painful, and they leave the patient vulnerable to infection. Peter stayed indoors for 16 days, avoiding exposure to the sun’s ultraviolet rays that could cause even further pain and injury. “I pretty much slept the whole recovery away. I followed all the doctor’s instructions for wound care and it healed up without a scar or even any noticeable marks,” he says.

Peter Mc After

“As it turns out, a blown head gasket was the cause of the tremendous pressure that was built up in the cooling system despite the relatively low temperature,” Peter says.

It left him — and everyone who was in the shop that day — understandably hypersensitive to the hidden dangers of working around hot cooling systems, though. “All the shop hands who saw the accident go down are now all semi-paranoid of radiator caps now,” he says.

He’s exercising much more care when working on the cooling system. “While this was part freak accident, there’s still no excuse for having my head or tools or hands or whatever anywhere near a pressurized system,” he says. “Yes, we’re all guilty of cheating the unwritten (and sometimes written) protocols for automotive safety, but it only takes one time for your cheat to backfire.

“It’s a bit of a wake up call all around really, because there’s a lot more to being safe in a shop than just using jackstands and wearing non-slip shoes.”

For more on shop safety, visit Nationwide Insurance.  Thanks to Peter McCullough for sending photos and answering our questions.

Craig Fitzgerald

Craig Fitzgerald

Writer, editor, lousy guitar player, dad. Content Marketing and Publication Manager at