Combating Shutdown Heatsoak- I finally did something about it

Dec 10, 2013
Kuala Lumpur ,Malaysia
Some of you guys might have noticed I like to partake with the topic of engine shutdown heatsoak. I tend to have what EricTheCarGuy describes as excessive mechanical sympathy. This project has been almost a year in the making, and I finally got the system working, after a lot of thinking, design, mock ups, searching and online shopping, and lots of Youtube video learning.
Before I start , I want to stress that I suck at electrics and electronics especially the electronics bits. But I do have soldering experience thanks to my RC Car hobby. I have to repeat to myself several times which wire goes to where, and had to search on forums and Youtube videos to get ideas and understand concepts.

The system consists of :
1. A remote control relay, 12V powered.
2. A Programmable temperature controller with wire probe, max detect temp 120C, also 12V powered.
3. Automotive 40A 4 pin relay.
4. Three 80mmx38mm Ball bearing brushless fans, load draw 1A.
5. Many lengths of 20ga and 16ga wires, in black, red and yellow.
6. Tiny Switches
7. Compact fuse holders
8. Tight fit connectors 2 different types
9. Small Diameter cable trunking.
10. Own designed fan brackets and 3D printed housings and air ducts.

First the system inside the car. I pulled a + and - from the radio adapter connector which is always live and fused to the radio. Soldered a XT30 connector. Plugged the Wires to another XT30 connector which supplies power to the system. The Heart of the system is the 12V remote control relay. The 12V power mentioned earlier goes to this relay. Before it reaches the Remote control relay, it goes through a 1A fuse and a tiny switch, so I can cut power to everything when I dont want the system to be misused (car at mechanic or in some one else hands). The remote control relay will send 12V power to the Temperature control relay when I want it to , namely by pressing button A on the remote. The reason I used a remote control is so that I can turn on/off the system without opening the doors.
The temp controller then has its own relay which activates when the temperature detected (in this case the rocker head surface ) is above the set temperature. This temp relay also has a tiny switch wired after the relay so that I can cut power to the fans and use the system merely to detect the head temp.
Both these electronic modules are housed in a 3D printed plastic housing which is taped on the right side below the steering wheel, and It allows me to see the temp controller target temp and actual measured temp, as well if the relays are turned on.
The temp probe and the 16ga + wire from the temp relay is routed into the engine bay. The + wire is attached to pin 86 on the 4 pin relay, and pin 85 will go to ground. The + from battery goes through a 3A fuse to pin 30, and pin 87 powers the 3 fans in parallel. The fans then take each ground from the best ground point nearby. The fans are attached on brackets I designed that mount on the best available space I have. One fan is under the turbo and is the lowest placed fan , so it sucks in relatively cool air from below and blows it up to the hood surface. One exhaust fan is placed on the opposite end near the fire wall which will suck out and eject hot air through the small gap between hood and fender, I designed my own vacuum cleaner type ducting made with 3D prints.
One more fan is mounted ahead of the power steering pump and blows underneath the front turbo towards the fire wall. I am not too happy with this fan position so I turned it last night to suck hot air out and eject it through the radiator. I have not tested this latest configuration . The last 20+ cycles I tested was in the previous configuration, but what I didnt like about it was it was forcing the hot air out towards the lower part of the windscreen , heating the localized area of the windscreen to nearly 60C.
Overall the system works well and is not a terrible drain on the battery, but I am still doing some fine tuning. The system achieves its intended goal of quicky lowering peak shut off temperature under the hood which otherwise stays hotter for way longer. Now I am able to bring down a 91C head surface temp down to 57C in 1hr 30 mins. I chose 57C as it is a temp that isnt damaging to the wires and rubber hoses, and if I go much lower I would be running the fans for too long and may drain the battery too much. Initially I set it to 45C but finally settled on 57C.
For now I give a sneak peek of the brain of the system ,I will post up the youtube video by tonight.

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My Cherokee heat soaks pretty bad. To the point that it won't run if it gets shut off hot. Only Chrysler could make an EFI system that vapor locks. One neat thing with the Cherokee is it has a mechanical fan on the passenger side and electric fan on the driver's side. What I did was add in a dummy relay so I can control the electric fan when ever, but without setting a fan code. The electric fan will move air directly over the exhaust manifolds / catifolds and move enough air that it won't heat soak.

The downside is I have to remember to turn the fan off. But it does help. If we're on a trail and stopped, I'll turn on the fan for 10minutes and it'll flow enough air over the exhaust catifolds and keep everything cool enough post-shutdown that it won't heat soak.
Good for you. Of course the jokers and scoffers here will mock it, that is par for the course in this forum. You may want to add a flyback diode in parallel to you main relay, if you don’t already have one.
When I pull into the attached garage in hot weather after a highway trip I lift the hood and leave the garage door open for a couple hours or so. Cools off the engine bay and keeps the garage from staying hot for 1/2 day. Neighbours must think I have the most unreliable car on the block :D, having to lift the hood a few times a week.
I worked in a fleet type maintenance for a huge portion of my life. The secret is to keep the vehicle only until towards the end of the sweet spot in its life cycle then sell it and start over. When the engine is turned off , the fan isn't blowing, the Coolant circulating or the oil circulating. Brilliant work though . The secret to engineering things is simple, Just figure out a timer to run the fans.
does the radiator have an electric fan? Could you no add a relay to keep that turned on for a few minutes (say 10) after the vehicle is turned off.

Use a 555 timer and some circuitry directly connected to the battery. Also easy to add a termination circuit that turns the fan off if the battery is running low during the 10 minute cycle.
Serious question, what problem is this solving?
You know you can buy a Turbo Timer that will idle the car a set time even when the car is "Off".
Longer spark plug wire life, longer distributor life, longer battery life, longer rubber hose life, longer igniter -ignition coil life. The head stays a tad above 80C for more than an hour after engine shut off in tropical climate, not good for the spark plug wires which sits right on top. Besides, I am the type of guy who only drives older cars (like from the 80s).
Some cars are more susceptible to heat soak than others.

An econobox four cylinder driven gently won’t suffer.

A high performance car (horsepower comes from heat) with a crowded engine compartment will suffer. A V-12 twin turbo, for example, gets incredibly hot under the hood after shutdown.

My bud’s 1975 Mercedes 450SL had terrible wiring problems and rust as a result of heat soak. In the year, Mercedes put the cats (new for 1975) IN the exhaust manifolds, keeping all that heat right there under the hood, where it couldn’t escape. Under hood temperatures would soar on shut down. Naturally, we moved the cats to under the car, as was done in 1977 on, when we did the restoration.

The vent fan would be great on my V-12s. I love this idea. I just wish I could find room…
I remove the engine cover from each car and leave it on the garage shelf until the car is sold. It's there only for appearance; sound deadening is just a marketing spin. It retains heat at a time when shedding heat is a challenge for modern vehicles.