Alternative location for Cylinder Head Temp Sender, Considering one of the #3 Cylinder exhaust studs Options

[Dave_Darling]

Is this sensor for the gauge, or is it for your microsquirt?

If for the MS, the stock thermistor-type sender in the stock sender's location should be more than good enough. Since the ring-under-the-spark-plug sender is a thermocouple, and generates voltage instead of changing resistance, you'll have to program the MS differently to use that for warmup enrichment.

If it's for a gauge, then the spark plug sender is the way to go.

--DD

[worn]

I had the same issue with the 12mm plug and got some excellent support from "The sensor connection" guys. They worked with me sending back & forth several CHT's and finally got it right with a 12mm ring that will actually fit down in the recess on the head. Mind you, it's still a tight fit & you have to carefully bend up the tab, but their 12mm ring is a true 12mm, not 13mm as some vendors are supplying. No vested interest, just have had great service from these folks:
http://www.thesensorconnection.com/index.shtml

Sorry but I am reviving this old thread. I want to install the CHT under the spark plug like all the cools kids have. So is this the one to get or have there been better solutions? I am preparing myself for the idea of dropping the engine to perform the modification on the head. That's not the only reason to drop the engine. I need to install the crank sensor for my Microsquirt conversion too.

Thanks All!

The issue is that it can be difficult to properly thread a spark plug into the head, and it is even harder with a copper ring around the plug threads. Tradition has used such an instrument to measure head temps, so using number three spark plug has become a kind of standard. Is it etched in stone? Heck no! The factory made a special drilling for its own cylinder head sensor, but it is something that can be related to the experiences of others. Hmmm, my cylinder heads melted away at xyz degrees. George can correct me, but my recollection is that when I called AA he said that a CHT gauge would “just scare me”. And it has on many occasions, but the motor still runs…
Moral of the story is that the instrument will allow you to start making measurements. These can come in useful. It certainly tells when you stress the motor, and when you let it rest. It is summer while we have it. Good luck!

[913B]

Is this sensor for the gauge, or is it for your microsquirt?

If for the MS, the stock thermistor-type sender in the stock sender's location should be more than good enough. Since the ring-under-the-spark-plug sender is a thermocouple, and generates voltage instead of changing resistance, you'll have to program the MS differently to use that for warmup enrichment.

If it's for a gauge, then the spark plug sender is the way to go.

--DD

Yes it is for my Microsquirt conversion.
Ok that is good to know I can use the stock CHT. I also acquired this CHT from the dub shop. So between the 2 hopefully I can get my MS to work. I think I was overthinking the CHT part.
Thanks DD!

[Dave_Darling]

I don't know what kind of sender that one is from the Dub Shop. It might very well be a thermocouple, like the ring sender that goes under the spark plug.

Check on what the MS system expects to see for warm-up enrichment. Most cars that I know of use a thermistor in the coolant circuit.

Again: Thermistors are things that change resistance with changes in temperature. Thermocouples are things that generate voltages based on the temperature difference between their "cold" side and their "hot" side. Something that is set up to look at resistance will work poorly if at all when fed a voltage, and something that expects a voltage will not work when fed a resistance.

Make sure the sensor is compatible with the expected signal.

The stock CHT sensor will likely require some extra calibration to be done in the MS to get the enrichment right. The resistance range might be different from what the default setup expects, and it is likely that using HCT instead of coolant temp will throw things off to some extent. Check through the setups that people have used for MS on aircooled motors to be sure.

--DD

[GregAmy]

DubShop makes that thermocouple/thermister-thing for tuning warm-up on the Micro/Megasquirt. It's intended to be inserted under one of the engine tins screws (I use the one behind the #3 intake manifold). It's not intended as an accurate measurement of CHTs in the context of how we discuss them and the allowable temperatures.

One major advantage to that sensor is that it already has the pull-up built in, so all you have to do is wire it up to the MS (5V, ground, sense). It's the easy button for the purpose of managing engine warm-up and enrichment. Works great.

I also installed a standard K-Type thermocouple under the #3 plug to be used for tuning purposes, to ensure I'm not running too lean or hot. I ported that into the Microsquirt's ADC7 input via an Adafruit amplifier. It will not provide feedback to the ECU for corrections but I can log the data and later compare it to trends to see if I'm getting too hot (good so far). It can also provide warning limits if I'm using the ShadowTuner dash on an Android tablet.

So Ted, I suggest moving forward with the DubShop sensor for warm up enirchment and then work later toward adding the CHT for info.

[bbrock]

I just noticed the Dub Shop has a Type 4 version of the sensor that I didn't notice a few months ago. Looks like the difference is just that it has a larger hole do it can be mounted in the stock sensor location. Here is the description:

Modified GM coolant temp sensor for Air-Cooled VW use. The Type 4 sensor has a larger hole so it can be mounted to the factory location with a 10mm x 1mm bolt or you can use an intake manifold stud if you wish.

This is not meant to act as or replace a proper cylinder head temp sensor

[913B]

If I am not mistaken it goes on the tin screw and not the actual location where the factory CHT goes, but maybe I am wrong? (IMG:style_emoticons/default/confused24.gif)

[930cabman]

Contrary to what the experts are saying, I will be installing a new CHT gauge sensor in the factory location. Autometer setup. I will be able to monitor a "normal" reading vs an "elevated" reading.

[Dave_Darling]

DubShop makes that thermocouple/thermister-thing for tuning warm-up on the Micro/Megasquirt.

Well, that is great and means that all of the cautions I mentioned above are meaningless! Sounds like it's pretty much plug in and go!!

--DD

[bbrock]

If I am not mistaken it goes on the tin screw and not the actual location where the factory CHT goes, but maybe I am wrong? (IMG:style_emoticons/default/confused24.gif)

They are selling two versions. One that goes on the #3 tin screw but another special for the Type 4 that has a larger hole to bolt to the stock CHT sensor location with a 10mm bolt. Same sensor, just modified with different size holes. Doesn't seem like it would matter which you use, but I like having the option of using the stock location. Feels cleaner somehow.

[GregAmy]

I went with the one on the engine tin screw because:

- It's outside the engine tin, so very easy to access - like, right there; and
- It doesn't matter where it is, since you're going to be managing/monitoring/editing your warm-up sequence based on what the sensor shows over time.

I do not, not, not suggest you use this sensor at the stock D-Jet true cylinder heat temperature. It should ONLY be used for ECU warm up sequence.

All of the years of collective "true" CHT evaluation and limits (such as Raby's recommendations) are based on a specific thermocouple (Type K) installed in a specific location (under the #3 spark plug).

If you try to use the D-Jet location in lieu of all of that collective knowledge, then you are setting yourself up for potential problems (that location is likely to be simultaneously neither as not, nor as responsive, as under the spark plug).

Of course, if you want to install both, and develop a stastical program to demonstrate correlation between the two, then everyone that follows you would be your biggest fans...

[Frank S]

I run a thermocouple under spark plug #3 and a BMW CHT sensor in the stock CHT sensor location with MS.
I'm using Lens heads with the ceramic inside and the black outsidecoating.

Both Sensors report the same temperature with a little advantage in reaction time on the under the spark plug sender.
However temps are always within 2% of eachothers reading, which is neglectable.

Will take the car for a spin today and can post a pic later...

[GregAmy]

I run a thermocouple under spark plug #3 and a BMW CHT sensor in the stock CHT sensor location with MS.

Would love to see that correlation! It would thus be an excellent alternative (and easier to install) location for monitoring engine safety. I've got the correlation data for the under-the-tin-screw versus spark plug and it is decisively not a good spot for The Raby Recommendations.

But if your correlation between CHT boss and spark plug proves strong, then let me offer a secondary reason why this is not a good place for using that boss for Mega/Microsquirt (or any EFI) warm-up: because it's historically shown to not be a good place for measuring D-Jet warm-up.

D-Jet has a problem with warm ups. The prevailing thought is that the CHT sensor warms up quickly and causes the the D-Jet to lean out too fast, well before the engine itself is ready for it. As a result, we have this "hole" where the engine fires up nice and rich, but soon leans out because the CHT is telling it to; idle and driveability suffer. VW/Porsche tried to fix it with a resistor and a retune, and even today we battle it by putting in steel spacers to reduce the rate of thermal rise.

The DubShop sensor in an engine tin screw near the intake manifold solves this. This location warms up much more gradually and slowly, and offers a much wider band of time to fine-tune the engine warm-up. I can start the engine foot-off with it dead cold with ambient temps in the 30s (I don't use drive the car colder than that) and it'll immediately settle into a solid idle, and core that idle all the way to full engine warmup (I use ignition timing to manage it).

My "full warm" point is 160F, and it takes about 3-5 minutes of light local driving to get there, depending on ambient. That's plenty of time to get the long block warmed up, the oil flowing nicely, and about the time I get to the interstate on-ramp. And given this wide range of time/temps to get there, I have a lot of flexibility in tuning to improve driveability.

For reference, on a typical highway drive the engine tin screw "CLT" (how it's logged in Microsquirt) is about 75-100F lower than the spark plug CHT. Whereas the CHT at cruise is ~330, the CLT is ~240.

I've read where some people use oil temps for warm-up enrichment management, but I suspect that this rise is a little TOO slow. I do want some compromise where I can reasonably inferentially measure the combustion chamber temps and still have a wider band of time than the spark plug. Plus, where would you measure it? If you kept your stock oil temp gauge you'd need to tap in somewhere to get oil sump temps.

So for all these reasons, I prefer the engine tin screw for EFI input, and the spark plug (or maybe the CHT boss?) for true CHT monitoring.

GA

[Frank S]

The MS doesn't care if you use Mario's sender or the one I'm using or if under engine tin or in CHT location. You just need to adapt the WUE settings and it will run fine.

Here before engine start:

[Frank S]

And here warmed up:



You need to look for coolant temp.

This correlates up the highest temps I have ever seen 183°C
Just if you push it really hard like WOT uphil the under the spark plug sender will show a max of up to 4°C more for some time and then the other one will catch up. You never miss more like this 4°C in spikes...

It's working absolutely flawless.

But again, I'm not using the OEM heads!

[Mark Henry]

...
I do not, not, not suggest you use this sensor at the stock D-Jet true cylinder heat temperature. It should ONLY be used for ECU warm up sequence.

All of the years of collective "true" CHT evaluation and limits (such as Raby's recommendations) are based on a specific thermocouple (Type K) installed in a specific location (under the #3 spark plug).

If you try to use the D-Jet location in lieu of all of that collective knowledge, then you are setting yourself up for potential problems (that location is likely to be simultaneously neither as not, nor as responsive, as under the spark plug).

Of course, if you want to install both, and develop a stastical program to demonstrate correlation between the two, then everyone that follows you would be your biggest fans...

I totally agree, I use the Micro 1000 CHT, besides the quality it looks a lot like a VDO gauge. For CHT I won't use anywhere but under the plug. The Djet sender, like my SDS uses, is just a rough ballpark for warm up.

[Frank S]

I have the under the spark plug thermocouple at cylinder #3 anyway, just saying it is reading exactly the same values as the other sensor...

[bbrock]

I am probably going to MS my engine over the winter and this thread has been super educational. Thanks everyone! (IMG:style_emoticons/default/beerchug.gif)