RC nitro engines like to be pre-heated before they are started and so we do see plenty of solutions like hair dryers, paint guns, curling irons with a 3D printed adapter to fit the cooling head and the velcro things to wrap around the head.

A while ago I made a temperature controlled pre-heater with some simple Aliexpress temperature controller: Homemade engine heater - R/C Tech Forums which does do its job very well.

But I always had the idea to create something with a real temperature readout showing how hot the engine is.
I am well known with electronics but beside some school experience with Ultimade/Ultiboard (I have an original old DOS version with a special school licence) I do the most on just simple experimental PCB so I did design a schematic with some calculated components to make a steady heater at 100 degrees C (that is 212 F) and a simple LED bar meter.
In a very short time it became clear with the needed space I needed to go to a lot of SMD components double sided to get it within the 46mm round shaped PCB to make it all fit so I downloaded KiCad which has an awesome community and so within 2 days I had a good base to finetune.



When I was happy with the result I gave an order to JLPCB and in a week time I had 25 PCB's on the doormat. Not that I was planning to make that much but it was not the extra costs...



I started to assemble 10 PCB's





With my previous model I used a massive bar of aluminium and gave it the right shape on my lathe. This time I bought a fresh tube of aluminium with an ID of 55mm that will fit most of todays onroad cooling heads and did press in a 5mm thick plate to make it a nice cup. It is cheaper and much easier/faster to produce. Here a 1st test with just a 40w cartridge heater and the controller its sensor clamped on the cup, unless the bad heat connection to the cup it became quickly very hot.



And the 2 parts got compartments milled with a rounded tip mill bit for a maximum touching surface. Also a blue top panel was made. I have also black panels ready



So this is the temperature sensor in the middle of the cup that will be close at the glowplug to measure the surrounding temperature. The sensor is mounted in a piece of teflon which is a very good heat insulator so the sensor is not much influenced by the direct heat from the aluminium cup.



Tested with my FLIR. Problem with my head is that it is 50mm in diameter and so there is a huge airgap between the cup and the head but it did look promising. I have plans to make an adapter for 50mm heads.



Because the temperature inside did not go beyond about 70 degrees I had to adjust the scale of the LED bar which was by default 125. I could easily do a small invisible mod on the PCB.

Here a pic of an todays OS head fitting the cup nicely.



Here the parts for the total assembly. First I thought I could do it with an 8mm lexan disc as an insulator and on top the blue disc holding the electronics but with all the wires I came to the conclusion more space was needed so I added a 6mm dark colored lexan ring. The blank lexan part has a small hole that will get a fitting high temp rubber cable gland.





Off course the eye wants to see something so I made a LED strip all around in a slot that was made in the blanc lexan part which also indicated that it is on power and so hot.



First test on the track was promising. I still had no adapter made for my 50mm heads and so the engine did not get that hot.





With the cup getting fast on temperature it does take the readout up to 5 minutes to get to 50 degrees and then it takes another 10 minutes to get to about 70 degrees C so the readout is really measuring temperature changes close to the glowplug.

The idea is working but need to get some changes. First of all I need to make an adapter to bring all the heat closer to the head, maybe to raise the temperature a tiny bit from 100 degrees C to about 120. Also the used cartridge heater supposed to be 50 watt but on my power supply it shows as a 40 watt heater. I did see there are also 60 and even 70 watt versions to find so that could be something to try. Also some shrink wrap or a thin plastic sleeve around the cup will isolate the cup more from cooling from the outside, for that I can take off 2 to 3 mm of the OD of the cup to keep it small so it will fit though the body (with 53~55mm heads), the OD of the cup is w/o any work 60mm.

Other versions I have planned with all the parts I have prepared is beside a blue topdeck a black one and basically any wished color matching the body or brand colors is possible, not that I will start production to sell but I did look into orange because a good friend runs Serpent. Sadly because it is not a well used color it is not that cheap. Also the LED strip can be bought in all kind of colors getting it matched with the topdeck color.
I have made one topdeck to fit a small voltmeter as a readout to show a real temperature and I have one prepared with no readout as a simple version.