What Is Heat Soak? 

I drive my cars into the pool when I get home.

In the racing world, we call “heat soak” when your engine detunes due to heat. The super chargers and turbos get heat soaked, than you get lower power. So your best laps are always at the start before you get heat soaked.

I like to pop the hood when I get home. Then I can smoke my pipe and ponder the engine’s condition.

"Something in the back of my mind is saying, 'Eric, you're going to have to fix this, don't break it.'..." PREACH, Brother. Preach on...

Jaguar Rover tech here. Been seeing a lot of vehicles come in here to our dealership in the fine mid July Atlanta heat with leaking evap seals to breather hoses or purge valves. Particularly on early 2010 jag sedans. And as anyone knows that works on jag or rovers, they LOVE brittle plastic material for hoses. The smoke tester has been worked to death since early june. I've replaced 3 evap canister purge valves and 2 full throttle breather hoses just this week. And Its not even thursday yet

I sometimes do the same as you, leaving the hood open when I park in my fairly small garage after a longer trip or if I was running hard. Also even though I've got water cooling going to my turbo, I still let it idle for 10-15 seconds after coming to a stop just to help the center cartridge cool down a little bit better. It's small things like these that ultimately prolong the life of our vehicles. And when you add all these precautions up, it can mean driving your car for a year or more before it really *dies*.

You're worrying about the plastic materials in 10-15 years. Some times on hot days I pop open the hood and leave the garage door open with the 6.2L AMG just so the house AC won't have to deal with all that heat 😅

I do that too. Park the car in the driveway , pop the hood and let it cool before pulling it in the garage an hour later. I do that mostly in the summer. In the winter I do the same but in the garage and use that heat to heat the garage.

A few months ago I got a 2020 Supra. Something I noticed right away was how amazingly fast the engine came up to normal operating temperature, in probably half the time of any other car I've had. With a bit of investigation I discovered that BMW, with whom the car was jointly developed, has done a lot of work on actually retaining heat after the engine is shut off. I think they call it heat encapsulation. The purpose is to minimize warmup time and thus maximize mpg.

i like that “mechanical sympathy” lolz here in Arizona we have hear soak in june -September. (100F at night)

Good video Eric - thanks! I do understand heat soak as my summer fun time toy is a boosted Miata, and it runs hot... Being on the opposite end of the garage spectrum (theft prone, urban high rise parkade), I have to pretend I'm cleaning out my trunk, checking tire pressures or whatever else I can do to give my engine 15 minutes to cool off a little with the hood open. The biggest sacrifice to living in the city isn't the smallish dwelling, it's the lack of a private garage. Kudos to all of you out there who made it a priority to have a proper garage - much respect.

Hi Eric, Where I live is usually really hot and I also open the hood and put a floor fan facing the radiator. Even if the car is shut down if you can cool the water in the radiator it will cicle, slowly but it will because the “heat convection” effect. Some german cars a more effective system to allow the car to cool properly after shutdown, where the radiator fan keeps on for few minutes after the car is shut down. My father and I where able to recreate this system on my old ‘94 Civic. Basically you need to give direct power to one of the relay prongs in order to activate the circuit of the fan and water temp. What you want is keep the circuit alive after key shut down, the fan will spin until the temp is lowered and the fun will shut itself.

any one with a garage can install a fan on the floor that you drive over it facing the engine bay , that works for 15 minutes and shut off by it self after you park your car to cool down your engine , no need to open the hood or even turn on and off the fan . great idea .

I don’t necessarily raise the hood when I get somewhere. But what I have done particularly when the kids were little, if they were asleep. I’d leave it running with the AC on. I’m in the southern climate. There are times we run our AC at Christmas. But I digress, if we were parked and I had to run the car with the AC on, I would often raise the hood just to let the heat out. It tends to keep rubber components happier and the alternator and starter. Numerous occasions I had people ask me if I was having car trouble, “no I’m preventing them” ✌️

Also I consider the life of the rubber, plastic parts too. Hoses and all that. Really gets hot under the hood in the summer when shutting down. Good vid, thanks

I like to open the hood and connect a battery charger/maintainer. My AGM battery on my Honda Odyssey has a short life because of significant discharge when parked. I turn a fan on and leave the garage door open for a while if possible to get the heat out of the house.

I've been doing this for years with my 13 F150 Ecoboost. On hot days I'll come home and park in my garage and pop the hood. It's damn hot under there... I do mostly for the sake of all the PLASTIC hoses, tubes, intakes, etc.... I also open my hood after I've towed my #7000 TT and get to my camp site and get it unhitched... I pop the hood and the heat just pours out of it.. I've had some "truck fan boys" come up and say to me.... "Well, I guess your FORD is overheating because you have to open the hood on it".. I say, "No, it's just that it is HOT out and it ran fine and never came close to overheating, but I'd like to get the "heat soak" out from under the hood"... They look at me like I'm from Mars and I just say, "This is just what I do, thanks for your concern.." Mitch

I've been doing the same thing for years. I occasionally open the hood of the Vette after driving. Usually open the hood of the Camaro, rarely open the hood of the Crown Vic, and almost always open the hood of the BMW to dissipate heat and prevent heat soak. BMW parts are plastic and expensive to replace and it runs very hot with a 219 °F thermostat, all aluminum block. The Vette runs really cool with a 160 °F thermostat and cast-iron block, but those wires and rubber hoses are pretty brittle after 27 years of age. Camaro runs pretty normal with a 195 °F lots of plastic parts with aluminum engine under that hood. The P71 served years as a patrol car and is pretty robust with extra cooling capabilities, so it can take a hit.

I'm used to people reffing to heat soak as loosing power on a hot day, usually, in a car with an aftermarket intake.

Having my headers ceramic coated made a huge difference in heat soak. Much lower temperatures now.

On non modified customer cars, not an issue today. I can remember one customer complaint of "slow crank" on a SAAB 900 back in 1985, that is it. My "junker" a 1994 Lesabre shows no heat soak symptoms even here in the Tucson summer (109F was the high yesterday 7/12/2020) Now on modified cars,heat soak can be a problem.That coked up oil sludge picture made me think of the Toyota oil sludge problem from 20 years ago. Toyota settled a class-action engine-sludge suit in 2007 that covered an estimated 2.5-million Toyota and Lexus vehicles made between 1997 and 2002. In that case, Toyota agreed to repair sludged engines for up to eight years from the time of purchase.

Here's a reverse. My grandpa(born 1897)when he was roofing would put a blanket on the engine of his truck in winter to keep it warm.

Keep engine clean. Repair any fluid seepage/leaks that attract dirt & gunk buildup; all that acts as an insulator, holding in damaging heat. High-temp ceramic paint helps to dissipate heat, think of a coffee mug. Fuel in the injectors & rails can also boil, depositing varnish over time, just as Eric mentioned oil coking.

Got a kick out of this, I have the same issue with machinery love / concern. Although, mine is two fold. I park ALL my cars inside to protect them period. In addition, I open hoods (especially on my older classics) to elevate pressure on lifting / pop springs and associated gas lift rods etc. This includes rear hatches as well, and T tops, so rubber seals are not compressed, Simply cover with ultra soft cotton sheets draped over each to minimize potential dust.

Before OEM's got heavy into turbos and learned how to make the engines live "turbo timers" were all the rage with aftermarket turbo kits. They would keep the engine running for several minutes after you turned off the key to keep the oil circulating while the engine cooled down.

1) Got a 2000 Prelude (original owner), never heard the fan stay on after engine shut off, had an issue on a '96 Civic where the fan wouldn't shut off after taking it up a mountain, dealer fixed it 2) I know the engine bay in my 'Lude is hot because the hood gets pretty warm but I never popped the hood on my car to cool it down. The engine has 191K and counting, got a chance to look at the inside of the head when replacing the exhaust cam cap seal, it was pristine, no oil sludge buildup. I am usually pretty punctual about oil changes (mostly Castrol 5W-30 dino juice, anywhere between 3-4K)

I had an old Mercedes that would run hot after getting off the highway on my way home after work in the summer. Eventually I started popping the hood once I got to my block to get extra airflow in and as soon as I got home I’d leave the hood up and go in and unpack all my stuff and head back out later to close it. Now in my Miata I open the hood every time I finish driving hard or for a long time whenever it’s hot out. I’ll also leave the key in the run position until the cooling fan turns off and then I’ll close everything up.

Also known as the car cowboy, hell yeah brother, you're on the Eric The CarGuy RU-vid channel!

I have a couple of inexpensive fans I use when I park in the garage. 1 facing the engine bay and the other points out the garage window.

It's when you're as cool as Eric, you're so cool you can soak up the heat.

Thanks for the Space Cowboy part, Eric. I really need a humor pick up today. You are not alone on the "mechanical sympathy" element either. I treat rental cars well, so you can imagine...

I have used a huge belt driven 60 inch fan to remove the bulk of the heat from few of my vehicles while they were outside to cool them down after I drove it to start maintenance

I love the way you think. Still babying my 96 Integra I bought new.

I was aware of the occurance, but I had no idea it had a name. Thanks for the insight, thanks for the video, and thanks for being Eric The Car Guy. Long live ETCG.

This guys a true og I've been watching his channel for a minute now

I have a fan running on low speed blowing near the car 24/7 to keep air circulating in the garage. And I have the same problem as you when pushing the car. I worry a lot about things breaking. The good thing is that means my cars tend to last a very long time. Bad thing is I normally run the engine in low rpm and don't enjoy the car like other people who rev their car on a regular basis.

I live in Florida. I open my hood on all my vehicles every time I take them out, not counting when it's cold, which is rare.

The problem with opening the hood when you get home is you wear out the hood latch and release cable and eventually break it. Ask me how I know about that :)

I first became aware of heat soak, when I'd park a older Camaro with the starter directly under the right exhaust manifold.. It would seize up the starter till it cooled. I sorta fixed it with heat shields and other insulation, but I do get the idea. My old Turbo Corvair spider, would cook the oil in the bearing bushing once it "Spooled down. A good reason to run synthetics in newer turbo cars. Something else I wanted to ask you is " What do you think about leak down test and could yo do a video on it and how it can not only spot engine wear but indicate where it's coming from".. Blown head gasket, rings,valves/intake or exhaust. Just a thought. Your old pal Sela....Stay relatively dirty.

I actually noticed my sister's MK4 Jetta fans staying on when I turn it off. I knew it was to lower engine bay temps, but I thought it was just a VW thing. My 7th gen has never done that though, either way Cool vid!

My dads 92 accord will run the fan even with the key off, until the temp switch reaches its break temp. When I installed electric fans on my old cars I also wired them up such that they bypassed the ignition switch. Letting the temp switch break the ckt when the temp goes down. Its a little awkward to hear the fan running when the car is off and locked, but I feel like I'm helping the heat soak issue.

I think it depends on the vehicle and driving conditions prior to shutdown. My Tacoma 4-cylinder has gaps around the hood (not sealed) and no heat/sound insulation underhood so I don't even think about extra cooling for that. However, the 1995 Corvette would probably benefit from extra cooling after shutdown for several reasons: -- the 1990s Chevy LT1 was designed to run hot for emissions purposes (electric fans don't kick on until 228F) -- the iron block holds a LOT of heat -- the hood is partially sealed at the wheel wells and the firewall. If the car has been idled before shutdown, the big iron block could be 228F or hotter when it stops running, GAH. (If it's been moving along with some airflow it usually stays between 190-205F.) So I know for sure that everything under that fiberglass (FRP) hood cooks for hours after shutdown... the vacuum lines for the cruise control have become rough and brittle, the hood is still very hot 2 hours after shutdown, and the temperature inside the garage increases approx 10-15 degrees F after I drive that car. (The Tacoma does not cause such an increase in garage temperature, maybe 5 degrees F at most.) The problem with opening the Corvette hood is that the hood release cables are known to wear and break after 25+ years -- this car has emergency cables installed, but still I want to preserve the originals as long as possible and extra wear/tear is not desired. My solution is to place a small fan on the ground in front of the car and run it for 1 hour but I only bother with this if the engine temp is above approx 215F when shut off. I have machine sympathy as well. I bought these vehicles because they are excellent for doing exactly what I need and they are mechanically robust... and they will last nearly forever the way I treat them. Yes I get on the gas occasionally because that's good to clean out carbon. Thanks Eric for the thoughtful video.

Occasionally my mazda runs the fans after the engine is shut off and I like hearing it because it gives a bit of peace of mind

Huge problem on Jeep XJs... heat soak messes with the fuel injectors and if you have been driving, turn it off and then back on within a few minutes, the engine runs rough and throws codes. Some guys install relays to keep the cooling fans running. Probably a smart idea...

My name is Eric as well, and i totally do this. Well i did boost my car so after every drive, pop that hood for like an hour.

This reminds me of a PROTIP: If you're driving along and see your temperature gauge creeping up, turn your heater to full blast and then pull over at the next safest place. Check for traffic before exiting the vehicle to pop the hood and cool that baby down. The reason for turning on the heater is the heater gets heat from the engine. This can buy you a bit more time to safely exit the racing surface... I mean... the road

Eric, you are very kind to your machines, kudos to you!

Since i installed Long Tube Headers on my truck, there is much less Heat Soak in the engine bay. I dont have header wrap, the stainless steel just cools off much faster than the stock manifolds. The block and heads are aluminum, so that helps too

I agree with your assessment of the oil ‘coking’ issue, but I’m sure regular oil changes with modern oils helps to mitigate that issue. My concern with regard to ‘heat soak’ is the affect on the rubber and polymer parts under the hood, i.e., connectors, water and vacuum hoses, and belts... particularly those vehicles that have timing belts. All belts are affected, but the timing belt is more vulnerable because of its shrouded location and contacting all the steel and aluminum gears and pulleys, idler, tensioner, right up against the front of the engine block which are conducting heat away from the engine internals.

Heat soak can also mess with electronics too. Materials being hot affects how they conduct electricity. First thing I do with old vehicles is clean up electrodes and grounds and give the engine a good wash. Dust and oil all over your block can be a surprisingly good insulator, i've had weird electric problems go away after a good clean up.

Drive a fair amount. Get home. Turn the engine off. Pop the hood. Grab a seat. And listen to the exhaust manifolds crackling as it cools down. *pure bliss* Aside from that, heat soak is a very real problem with my '64 dodge. After driving for a while, then shutting it off to go buy sumthin at walmart, come back start the engine and it stalls as the carb got "overcooked" by the heat soak.

Heat soak is what happens here in Florida when you step outside. 😜 Edit to add: at 2:43 I call it mechanical empathy. Same concept. I have it too.

I definitely do the same leave the garbage door open, have a few beers & think about god only knows what. Maybe watch ETCG1. Winter I do the same but keep the garage door closed because it's free heat for my garage.

Eric what a beautiful background 2 beautiful integras.

Mechanical empathy/sympathy - what makes your cars last.

Love your work and videos! Can't forget the 🎂😊 I also really like the videos where you explain a specific topic, keep up the great work👍👍

I’m the same way. My show car runs hot. Whenever I take it out, and get home, I always open the hood. It’s an act of kindness for all the horsepower I expect from my engine 😊

My Audi has a system where it uses an electric radiator fan and an electric pump that turn on to circulate coolant through the turbos after shutdown. Only kicks on if its a certain temperature after shutdown.

Defiantly during pitstops and after the race we run the radiator fan with the car off. And pop the hood off of pitlane.

i definitely open the hood after a drive. My car has aftermarket fans that are wired to a switch panel (with relays of course) and I let those run after the car is off for some time.

I do exactly the same.... even more important on old cars running modern fuels contaminated with ethanol to prevent vapor lock.

My friend who tunes Subarus taught me that heat soak makes things difficult when tuning on a hot summer day because the engine heats up the intercooler and aluminum intake, which are both on top of the engine in Subarus, which raises intake temperatures, increases knock, etc. Sometimes I drive a car he's road tuning and we avoid stopping to prevent heat soak from interfering.

Yeah so true- living in here in New York City we get beak poked by the pidgeons all the time during the hot summer months.

Thanks for explaining this to me. New to tuning and this word is used a lot .

I usually just wait for the fans to stop running when I park, if I can.

Oh my gosh, now I know what that's called, machine sympathy LOL I have that as well and have tried to explain it to my racing friend who didn't. Too cool...thank you! P. S. Steve Miller rocks! Nice reference at the beginning ;)

Hence all the generators running airmovers/carpet dryers in the paddock at Track Days. Not to mention aftermarket Turbo Timers.

Another great video. I picked up an Alpina B7 (2013) recently and the "hot V" configuration with the turbos between the heads in the "V" causes most of the problems with this type of car. I've been opening the hood since I got the car, but I try not to drive it when it's really hot due to the superheating effect on the garage.

I only bother worrying if I've been driving the car hard. Then I'll give it a minute or two to idle if I didn't give it a few minutes of gentle driving before parking. Cooled oil and coolant can do way more for cooling a block than any amount of Texas air.

My accord definitely doesnt get that treatment. Been doing it for about 2 maybe 3 years and it fine. Gets redenned up once every few months and then turned off for another few. Reason for letting the heat soak in it is to let the moisture go away. Then a reasonably air tight cover is put over it. Car is all original bar an alternator, clutch, brake disks, spark plugs, filters, oil, tyres and an ignition which was accidentally damaged in 2003. 99 accord, f18b2 engine, manual 5 speed. 230k miles too and still starts (after months of sitting) like it was only running yesterday. That car has never failed to start ever and has never left me or my family stranded. Very little rust too which is surprising for that generation. It got undersealed multiple times. Interior is almost perfect. Hondas have to be some of the most under appreciated cars in existence

My accord runs the fan when I get home and turn it off I've always liked that about it

My owners manual for a 03 VW GLI says that after cruising on the highway, NOT to abruptly shut off the engine, but to let it run for a couple minutes to avoid "hot spotting" I assume certain parts become deferentially hotter, and having the water pump run allowed things to even out upon cooling

That mechanical sympathy thing, thats definately what i do lol. I cant bring myself to beat my vehicles no matter how new or how old and crappy they are, i dont even like having them rev high

Biggest thing that comes to mind for me with heat soak is vapor lock, and heat soaking an intercooler

I completely understand everything about heat soak, but it hasn’t affected my car as much, mainly because I live in Canada, where it’s cold 6 months out of the year. In these summer months, they may be an enemy, but in the winter months, they aren’t as much, since they dissipate more quickly during the winter time.

I sympathise with your mechanical sympathy, mine extends to my tools.

Big engine + tiny chassis + over sized radiator. My diesel doesn’t even turn the fan on. Not even going through Death Valley @ 115f. I do worry about my turbo. But I have a variable turbo with semi-manual control. So when I’m a mile or so from home I set my turbo to “wide open” In the hopes that heat flows out

Like most people, after a long run where the engine has been up to operating temperature, I give the car a minute or so at idle so that hot oil is not coating through my turbo.

FIRST ETCG1 VIDEO EVER ACTUALLY ON MY BIRTHDAY!!! YAY!!! Thanks Eric lol

Toyota landcruiser 75 series 1HZ 4.2 diesel with a denco turbo 10 psi boost with a turbo compensating injector pump ..... they can defeat the cooling system during high load slow driving ie 4wd in sand fully loaded, everything gets too hot and with a flir you can see the hole engine bay is the same temp. But I now run 3 thermo fans that can run after shut down with 1 between the radiator and the condenser and the 2 one pulling from the back of the rad and the the 3rd is on the inter-cooler drawing air in from the bonnet, also there is a Davies Craig Water Pump set up with this config I can keep the engine under 100 deg c and the intake manifold at 30 deg c.

If you have a turbo timer it will help a lot. It keeps the engine running after you take the key out and leave to allow the cooling system to cool down the turbo.

Seriously doubt it is an issue, Eric. I've lived in Phoenix AZ for 2 decades and we would park hot cars inside the garage, close the garage and not bother with anything. This on 115F days. (yep, that garage would feel loverly after a while) No coking and no issues at all. You just have to make sure your engine oils are changed on schedule. The only thing I do is to let aq turbo charged engine run for a few minutes to give the turbocharger some cool down.

Love your videos, keep 'em coming! Didn't know about heat soak.

Supercharged and turbocharged engines are especially vulnerable to coking. In my case, the only "boosted" engines that I own are in my 5 semi tractors. I've had each one fitted with a pre-lube system to circulate oil through the engine and turbo before a cold start, as well as after shut down. My drivers know that they will face my wrath if they don't use them! As far as heat soak, I'm a simple man. All of my personal vehicles, especially the ones with small block Chevys and headers, have heat shields over the starters!

I use a swivel fan to dissipate heat with hood up in my garage. Fan is positioned about 6-8 feet away from car.

I'm so glad i don't have to deal with heatsoak in a prius. Well i do but not to the boiling water extremes (like in a regilar car).

There's a pretty steep hill I need to go up to get to my house, and I always have my foot in it pretty good going up it. As I get to the top, I let off the gas and try to coast as long as I can to get everything cooled off before I kill the engine once parked. I'll let it idle for a minute before I shut it down, too, on super-hot days. I run Amsoil in most of my vehicles, so I don't worry too much about internal heat. Things would have to be burning hot to coke up Amsoil Signature Series oil. My Silverado is past the point of me caring too much about it - been a lemon since even before it rolled off the showroom floor! At 102k miles now, so I figure I've got 30k more miles before the engine fails, either from a stuck AFM lifter, broken valve springs, walked cam bearings, or any number of the other failures this engine suffers. I definitely won't go above and beyond to keep heat out of it. The replacement engine will get better care than this one. If I had an engine like the Fairmont, I most certainly would open the hood! That's a giant aluminum bank account right there. 😁😜

I usually let my car idle for about 5 minutes after a long drive. Turn off the AC and most electric consumers that puts a load on the engine. It's not the most efficient way to cool the engine, but at least it circulates the oil while it cools down a little.

Ironically, some people call me the "Doctor of Love!"

I know the engineers at Honda thought about it when designing the cooling system to run the fans up to 30 minutes after switching off the ignition, but 30 minutes seems like a long time to leave a fairly high amperage circuit running on a series of cars that only run a 51R-C battery, something that does not have a lot of capacity to begin with. Just my thoughts.

Outside air is moving faster at driving speeds, = lower air pressure outside = hot air from engine will be pulled out at driving speeds. Also hot air rises. I pull out the winter rubber seals for the summer.

3:32 I actually do that hehe. I open my hood and just sit in the car on my phone for a while before going home

I do that when I have to work on the car right after I just drove it

In the 03 Chevy Cavalier I had for my first car the fans would keep running after I shut the car off, until either the temperature was below a set point (can’t remember what temp that was) or the timer maxed out (witch was something like 20 minutes I think..) Now I daily an 03 Silverado witch was not the same unfortunately because from the factory it came with a mechanical fan. But I really liked the idea of fans running after I shut the vehicle off IF it is over a certain temperature, and I was also interested in the idea of having electric fans in general because I do haul often and things can get a little toasty if I’m really pushing it when it’s hot outside. So after a couple years of owning this truck I swapped in a larger factory radiator and factory dual electric fans, from a newer model HD truck so they bolted right up. After a little tuning the fans are now controlled by the factory ecu and I also programmed them to run after the truck is shut off, IF the coolant temperature in the block is over 210 degrees. (Since I have dual battery’s that are not connected to one another when the truck is off I did not set a timer, they will just run until either the coolant temperature in the block drops below 180 degrees, or theoretically until the main battery dies but I doubt it would ever get THAT hot though to where the battery would die before the engine was cool enough)

Hood risers? Maybe? I just park in garage, pop the hood, turn on a fan on medium speed and hang out in the garage. I'm already in the garage for hours after work so it's cooled down by the time I go inside the house.

Eric, it might make for a very interesting video to graph your IAT sensor on a drive starting with a cold engine. Then make a stop for a few minutes to allow heat soak to take effect on the intake manifold etc. Then go for another drive and keep graphing. I was super surprised to see my IAT temps jump from 100 to 145 after running into the grocery store.

Finally a video on my birthday! Thank for the cake lol

If ive been driving hard then id take a minute of not driving so hard and actually follow tge limit as to cool it down or park it and let it idle a bit before killing it

Thank you for sharing your thoughts on this subject.

@ETCG1 Do PLEASE remind folks, that if propped open with object that bypasses the safety latch, to prop open high enough to notice or some other reminder, so as to not HOOD SLAP the windshield 😮😖 which is scary and expensive!