There was a time, long ago, when passenger vehicles used to be much simpler than they are today. There were many downsides of this era, safety chief among them, but there were some perks as well. They were in general cheaper to own and maintain, and plenty could be worked on with simple tools. There’s perhaps no easier car to work on than an air-cooled Volkswagen, either, but for all its simplicity there are a number of modern features owners add to help them with these antiques. [Pegor] has created his own custom engine head temperature monitor for these vehicles.
As one could imagine with an air-cooled engine, keeping an eye on the engine temperature is critical to ensuring their longevity but the original designs omitted this feature. There are some off-the-shelf aftermarket solutions but this custom version has a few extra features that others don’t. It’s based on a ATMega32u4 microcontroller and will work with any K-type thermocouple, and thanks to its open nature can use a wide array of displays. [Pegor] chose one to blend in with the rest of the instrumentation on this classic VW. The largest issue that needed to be sorted out was around grounding, but a DC-DC converter created an isolated power supply for the microcontroller, allowing the thermocouple to be bonded to the grounded engine without disrupting operation of the microcontroller.
The finished product looks excellent and does indeed blend in to the dashboard more than the off-the-shelf temperature monitor that was in use before. The only thing that is planned for future versions is a way to automatically dim the display when the headlights are on, as [Pegor] finds it a little bright at night. We also enjoy seeing anything that helps these antiques stay on the road more reliably as their modern descendants don’t have any of the charm or engineering of these classics.
Very strange.
For the Trabant and the air-cooled Robur trucks manufactured in the GDR, no temperature monitoring was necessary. Read small cars, trucks I dover personally many years.
The design was safe, so there was no need for fear.
Trabant…Safe…
LOL
Good one.
Why no temperature monitoring was necessary?
Because they didn’t have enough power to get too hot.
And if for some reason they did, and you managed to seize up the engine, it was a two-stroke motorcycle engine that was cheap enough to replace. Though chances are someone would just open it up, bang the piston loose with a block of wood, and off you went again, trailing blue smoke.
Oh now I remember how in early 1990s a bakery in my town had a Robur truck.
3000 kg load capacity and a 70 HP air-cooled petrol engine 😂
When fully loaded its max speed would likely be comparable to a bicycle.
With cars like these Eastern Bloc didn’t need any external enemies, its economy would grind itself to a halt anyway from gross inefficiency.
Until your fan belt failed. Deutz had a mechanical safety for belt failure.
Does he know the critical cylinder on his VW engine?
IIRC it’s left front that always burned exhaust valves…That’s where you want the temp sender.
I’d double check that, been ages.
I did bugs when they were super cheap, fun cars, not so much fashion accessories.
Modern ‘bug enthusiasts’ get angry when I talk about the number of German bugs I cut into Bajas.
They seem to think a Wolfburg was something special…
I don’t really like the digital dash.
Should have gone with something period correct if he wanted to keep the value.
Hopefully easy to remove.
Do you know why?
The oil cooler was right above the left front cylinder (#3 IIRC) and blocked the airflow to it.
Hey, I learned that on Mustie1 YT channel!
Mustie1 FTW!
Cylinder #3 is the hot one since it sits offset out of the stream of air. That’s why down the middle fan shroud conversions are nice if you can find them though pricey. I love putting T4 oil coolers on T1 engines and modifying the doghouse to fit. It makes a big difference on the oil temps.
Agree with the digital point, but that can be fixed by designing an analogue display, may not work well for one that small, would need a slightly bigger round display.
If he makes a new board, he should change things so the color temp matches the dash lights as well.
Also some beetles were equipped with distributors that retarded the timing of the #3 cylinder by 2 degrees to help it run cooler.
“I did bugs when they were super cheap, fun cars, not so much fashion accessories.”
Cool. HaD is making me start to want one. For the repairability and hackability, not the fashion accessory. That aspect makes me NOT want one.
“I don’t really like the digital dash.
Should have gone with something period correct if he wanted to keep the value.”
So… it IS a fashion accessory then. Just… a retro one.
In 2025 they are too old and collectable to molest.
They were great when you could butcher them, knowing that you could get another for under 1k$.
Granting the new one would also have a rusted out pan, but can’t have everything.
Times really have changed, there are people collecting K-cars, Fieros and Peugeots.
No accounting for taste.
Why not go full tilt and put an EGT in there as well?
Fixing up my old moped, I used a cracked thermocouple temperature gauge from a small aircraft. Cost fifteen bucks plus five for the 100 pack of clear discs, one of which I sanded down to glue in place of the cracked stock one. Works just fine. An exhaust has temp gauge would be better (especially on a two stroke), but this is fine for now.
I used to build and drive air cooled vw’s for many years VDO made a very nice analog cylinder head temperature gauge that used a thermocouple attached to a washer to read #3 cylinder temperature. And a 914 tach could replace the speedometer … A few other matching gauges made for a beautiful black face instrument dash.
Obviously he knows what he’s doing, but I’m a little confused. I’ve spent a bunch of time sticking thermocouples on the water pump and radiator inlet/outlet to assess the system cooling efficiency with different duct designs to the radiator, and when I’ve had the thermocouples in electrical contact with the metal of the radiator and engine, I’ve had all sorts of problems with bad readings and the uC resetting. Now I put down a piece of kapton tape, the thermocouple, and a couple more pieces of kapton to keep it in place, and that’s really reduced the issues.
Know what; i’m just finishing up my dual head cht gauges! Hackaday is like magic!
I have a old VW bug convertible from which i’m restoring the engine. Problem; its a tuned 1600 aircooled engine in a convertable (airflow issues with the roof down), and with the old decklid with limited cooling (looks great). So that is why I would like to have a checkup on the temperature.
Stock factory it would be of no issue
Bite the bullet and install the hinge spacers.
They look stupid, but are needed for anything other than a bone stock bug motor.
Also you need them to clear the replacement carburetor.
I you don’t know, the stock Solex will eventually burn the car to the ground, replace it ASAP.
As noted above, you only need one sensor, left front.
Bad things happen there first.
For most people, a temp gauge on an air-cooled motor is simply an anxiety generator and will distract you while driving. Maybe an engineer or mechanic type knows better, but there’s a reason they didn’t put them on everyone’s vehicle.
If you’re not familiar with airheads, try and make a gadget that will log the temperature during an average drive around town, then look at it and try not to become alarmed. It’s more difficult than you think.