The average car on the road today keeps its engine running at around 200 degrees Fahrenheit, but a racing engine runs around 280. Here’s the reasoning behind this, why teams run ice-water through their engines, and more fascinating facts about NASCAR engine cooling systems.

Stephen Papadakis, the owner of and the subject of our story last year , also runs an excellent YouTube channel that provides all sorts of insights into race car technology. In his latest video, “7 Things You Didn’t Know About NASCAR Cup Technology,” he gets into some hot, steamy NASCAR cooling system details:

There’s a lot of good stuff in that relatively short video, including a look at NASCAR air conditioning systems and a peek at how special machines scan race cars’ exterior profiles. Plus, there’s a fun fact about side skirts—namely that they are actually designed to be replaced, since they scrape against the track in an effort to optimize aero.

But the real good stuff is the talk about cooling systems. Papadakis explains that NASCAR engines run at around 290 Fahrenheit, or around 90F higher than a standard road car engine. This reduces required airflow through the radiator and allows teams to tape larger sections of their grilles shut. This is good for aerodynamics, since oncoming air hitting tape flows over the car and can contribute to downforce, whereas air that has to enter a radiator grille bounces around an engine bay and adds what’s known as “cooling drag.”

To prevent the water (and yes, it’s literally water, not ethylene-glycol-based coolant like what’s likely in your car) from boiling at these high temperatures, teams run their engine cooling systems at elevated pressures ().,

The video also explains that, during qualifying, teams tape their grilles completely shut to help maximize vehicle speed. In this condition, cooling drag is minimized and there’s more downforce, however as you might expect, the engines also heat up quickly. So after a few laps, to pull the heat out of the engines, teams hook their cars to an external “cool-down unit,” which flows ice water directly through the engine cooling system. NASCAR made a little video about this setup here:

Papadakis also mentions that, even during a race, teams have tape on their grilles arranged in such a way that set areas can be removed to precisely allow additional flow to the radiator. These bits of tape that can be strategically removed are called “tape pulls.”

It’s all fascinating stuff—so much so that I decided to give NASCAR engine designer Dr. Andy Randolph a call. He’s the technical director at , which designs motors for the Richard Childress Racing team, and he’s talked with Jalopnik of ; he knows his stuff.

“There’s this constant struggle that goes on between the engine community an the aero community,” he told me. “For drag reasons, [the aero folks] prefer to have no air go through the radiator,” he said. “For engine cooling reasons, obviously, we prefer to have a lot of air go through the radiator.” He did mention that there is a way to get the best of both worlds, and that’s called a ducted cooling module, which basically takes air that has flowed through the radiator and ducts it out through holes in the hood.

Teams used this setup, which yields reduced drag but still high volumetric flow through the radiator, at the All-Star Cup series race at the Charlotte Motor Speedway earlier this month (see below), and Randolph said there’s been some discussion about adopting the tech for the 2020 season. (The All-Star race tends to be a prior to ).

It’s not a perfect system, though, since the hot post-radiator air gets into the intake, which is located at the base of the windshield. Dr. Randolph explains:

...some of the hot radiator air exiting the hood ducts was subsequently ingested into the engine through the cowl. Our intake air temperatures were around 130F during the race which caused other engine durability concerns. Relocating the air inlet location is a fairly significant undertaking given existing designs of the air cleaner, intake manifold, and underside of the hood. For next season, either the ducts will have to be moved outboard enough to miss the cowl or the intake air location will have to be moved.

As far as the current setup, which incentivizes cooling system compromises in favor of drag reduction, Randolph admits that it’s a “reliability issue,” and that it’s expensive to design an engine to handle those elevated temperatures and pressures. In an email, he described how much stress those conditions put on engine components, saying:

Components that suffer from high temperatures include rod bearings (oil more likely to cavitate as it gets hotter), pistons (aluminum softens as the average operating temperature increases), valve seats (seat wear/erosion proportional to operating temperature), and cylinder heads (life shortened due to aluminum softening). Lubrication becomes problematic as oil film thickness reduces with temperature and in fact the oil itself begins to dissociate above 350F (engines smell like sulfur when disassembled due to oil dissociation). Bore roundness deteriorates, bolt clamping forces change (some increase, some decrease), chances of knock and/or preignition increase. Lots of bad stuff.

To help increase engine durability, Randolph says his teams uses special coatings, alloys, and sealing materials. And the cooling system uses high-temperature o-rings and threaded connections in place of rubber hoses. But of course, this all adds cost.

I was curious to know if running these engine at higher temperatures yields any improvements in thermodynamic efficiency, and Dr. Randolph broke it down to me, saying that the answer is technically yes, but the higher temps actually reduce overall power due to increased intake temperatures:

Yes, there is a slight efficiency advantage because heat loss to the fluids decreases. However, there is also a power loss because the increased structural temperatures cause the intake air temperature to increase when it passes through the intake manifold and cylinder head ports. Decreasing air density with high temperature leads to reduced inducted mass and reduced power. So yes, the engine is slightly more efficient at making power, but it makes less power due to reduced mass flow. Fuel flow decreases accordingly as the mass flow decreases (closed loop feedback maintains a constant air/fuel ratio).

The former GM Powertrain engineer also talked about the cool-down unit (there’s one shown above, made by ), and how it can combine with the elevated engine temperatures to cause all sorts of trouble. “The rapid changes in the various metals in the engines...the expansion and contraction,” he told me, contribute to “a lot of stress on the head gasket” and “on interfaces between journals and bearings.” He mentioned that aluminum pistons in cast iron bores can also be an area of concern.

As an example, he explained that cold water from the cool-down unit might flow around the cast iron block, while the aluminum pistons might still be somewhere close to the oil temperature at the end of a hot run—so, around 320 to 330 Fahrenheit. This huge temperature delta, and particularly the wildly different thermal contraction rates of mating components, puts various components at risk of scuffing or even seizing. It’s for this reason that, according to Randolph, engine damage that could yield premature engine failure later down the line often happens during use of this cool-down unit.

“It’s kind of a sickening sound when they hook it up to the cool-down unit,” Randolph told me, describing a loud cracking between the head and block as the gasket shears. He told me about this in further detail via email, saying:

The head gasket contains multiple layers which can shear [against] each other. There can also be relative motion between the gasket and head or gasket and block without tearing the gasket. All of this is bad! The gasket continues to seal because as the engine heats up and the block and head expand (head more than block because it is aluminum), the bolts effectively tighten. In other words, the aluminum bolt column in the head expands more than the steel stud when heated, thereby causing fastener torque, and hence clamping load, to increase. Sealing concerns are highest when the system is cold.

Randolph says that his team’s engines use 100 PSI pressure relief valves, which bring the boiling point up to around 335 F, though he says engine temperature is usually lower than that, and is set not by a thermostat (since there isn’t one in these engines), but simply by the vehicle’s airflow. “The amount of cooling is set by number of square inches of grille opening,” the NASCAR engine expert told me.

That airflow can be altered via the tape pulls that Papadakis mentioned. Randolph told me they’re usually narrow horizontal or vertical strips, which can be pulled off to achieve a given temperature reduction if the car gets too hot. “If we’re running 300, we will normally make a change to make that cooler,” he told me, telling me that 280F is a more reasonable steady state temperature.

Of course, the engine doesn’t always run at its ideal temperature. For example, during a caution lap, when vehicles are driving slowly, engine temperatures rise due to a loss in airflow. In pit stops, there’s also a temperature spike.

It’s in these two conditions, Randolph told me, that a NASCAR engine tends to experience its highest temperatures, but there are other times when the airflow-limited engine cooling system can be put to the test.

Daytona and Talladega can be tough, particularly when cars are bunched up close to one another. The vehicle behind another one might experience less drag, but that also means less airflow to the radiator, and if the car spends enough time in sitting on another car’s tail, that could cause issues. “It’s so hot that you have to pull out of line and essentially give up your position to avoid having catastrophic incidents,” Randolph said.

Still, despite the cost and complexity, the setup can work well. “As long as you can maintain the water in liquid form,” Randolph told me, “you can do an okay job of cooling.” But boiling has to be avoided, as steam pockets that can cause major issues like cracking, melting, and distortion. On top of that, exhaust valve seats and spark plug seats can get so hot that they can yield pre-ignition. And this degraded combustion can significantly reduce engine life.

It’s fascinating stuff, though clearly incredibly stressful for NASCAR engine designers who are constantly tasked to make do with less and less airflow. Just to eke out a little more speed.

It is, of course, increased intake temperatures that yield reduced power, not reduced intake temperatures.