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CHT Nirvana (cylinder head temperature) gauge/sender FAQ
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pierrox
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PostPosted: Mon Jan 22, 2018 7:52 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

Thanks for your feedback!
Pretty neat the cut in the head, unfortunately the engine is currently where it belongs and I can't quite see myself doing that on location! But I'll keep this in mind for sure as engines tend to be removed once in a while.

I thought the black hose near the sender was some kind of heat shrinking tube, but clearly not.
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PostPosted: Mon Jan 22, 2018 9:10 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

I personally don't like the cut in the head, the technique will give about the same temperature reading as drilling a hole in the same location, but still involves the spark plug and thus the ring could be damaged when the plug is removed or installed.
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PostPosted: Sun Jan 28, 2018 2:42 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

Completely stupid question I know... what is a good head temp range? What is a warning temp?
I'm pretty familiar with oil temps as I've had gauges on most my VWs for ever, but head temp is a novelty for me!
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PostPosted: Sun Jan 28, 2018 3:01 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

pierrox wrote:
Completely stupid question I know... what is a good head temp range? What is a warning temp?
I'm pretty familiar with oil temps as I've had gauges on most my VWs for ever, but head temp is a novelty for me!


Does your engine run well? Take it for a half hour highway drive, and after the first twenty minutes, glance at the gauge every few minutes. Average out those numbers and you’ll have your target range.

I have found CHT readings to reflect ambient temperature significantly less than oil temperature readings.

The only way we can compare numbers is if we have the same sensor, installation, gauge, and engine. What is your setup like?

Robbie
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PostPosted: Sun Jan 28, 2018 3:40 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

pierrox wrote:
Completely stupid question I know... what is a good head temp range? What is a warning temp?
I'm pretty familiar with oil temps as I've had gauges on most my VWs for ever, but head temp is a novelty for me!


The temperature that gauge reads can and will vary a lot with the location of the "hot" thermocouple junction. The hot junction is not the ring, but just the crimp. The ring is for attachment only. If you stick the plug through the ring, bend the crimp up so it will fit down in the hole you are reading an average of the cylinder head temps and the spark plug temps, actually biased somewhat in favor of the spark plug temps. This will be about the highest temps you can register.

If you cut a groove or drill a hole somewhere in the head and epoxy the crimp in place you will be reading mainly the temperature of the metal of the head, which will be 20-40° cooler than what you would get if you used the ring under the plug. There is nothing at all wrong with reading the CHTs this way, but the results can not be directly compared.

If you buy a 10mm thermocouple ring and put it under a bolt in the early TSII sensor location, the crimp will be out in the air flow and read even lower. However if you drill the boss for the early TSII sensor location and epoxy the crimp into the head you will get a pretty good reading.

If you use the later TSII location you are going to be reading a much lower temperature still, while still meaningful, it may be 40-80° lower in temp than using the ring on the plug method.


Last edited by Wildthings on Mon Jan 29, 2018 7:21 pm; edited 1 time in total
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pierrox
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PostPosted: Mon Jan 29, 2018 9:57 am    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

Thanks for the feedback, it makes sense since the reading is not a complete absolute. I'll get on the highway to do some measurements!
I thought there would be data like for the oil temp, but I guess oil is easier to measure accurately!
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PostPosted: Mon Jan 29, 2018 7:07 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

I bought and installed the Mainline Sensors CHT kit available on ebay:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F161468474209

It is not a round gauge its a rectangle, but I'm ok with that. It's almost half the price, incredibly well made and has CJC built in.
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PostPosted: Thu Mar 08, 2018 7:53 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

Wildthings wrote:
I personally don't like the cut in the head, the technique will give about the same temperature reading as drilling a hole in the same location, but still involves the spark plug and thus the ring could be damaged when the plug is removed or installed.


I've been reading around about this and it's unclear if it's a bad idea or not to install the Dakota Digital temp sensor ring under the #3 plug while the engine is in the bus. On a Type 1 motor there's no way to cut a notch in the head or remove the tin and get everything just right without pulling the motor. Yet it looks like folks have installed the sensor ring under the plug without a problem. Is there any technique to use that can "guarantee" a problem free installation with the motor in place?
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PostPosted: Thu Mar 08, 2018 11:29 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

I ended up drilling and tapping an M3 hole into the cylinder head on #3. I also had the luxury of doing this with the engine out for a rebuild. I will have to see if I have a photo of this.
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PostPosted: Fri Mar 09, 2018 9:59 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

AircooledHome wrote:
I bought and installed the Mainline Sensors CHT kit available on ebay:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F161468474209

It is not a round gauge its a rectangle, but I'm ok with that. It's almost half the price, incredibly well made and has CJC built in.


Thank you for the heads up on this.
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PostPosted: Sat Mar 10, 2018 2:13 am    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

camit34 wrote:
AircooledHome wrote:
I bought and installed the Mainline Sensors CHT kit available on ebay:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F161468474209

It is not a round gauge its a rectangle, but I'm ok with that. It's almost half the price, incredibly well made and has CJC built in.


Thank you for the heads up on this.


No problem. I have been testing it on my brand new 1776. It works really well and typically I hang between 75-85c (167-185f) and it only gets hotter than that when I shut the engine off and airflow quits. Haven't tested it on a summer day though.
Can't change it to read Fahrenheit though, gotta contact them and ask about that. (very responsive customer care)
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PostPosted: Sat Mar 10, 2018 10:39 am    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

AircooledHome wrote:

No problem. I have been testing it on my brand new 1776. It works really well and typically I hang between 75-85c (167-185f) and it only gets hotter than that when I shut the engine off and airflow quits. Haven't tested it on a summer day though.
Can't change it to read Fahrenheit though, gotta contact them and ask about that. (very responsive customer care)


Nice! mind reporting back once you figure the the temp change? I ordered it last night so not sure how long it will take to get here but if it arrives and has directions how to change it, I'll let you know.
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PostPosted: Sat Mar 10, 2018 11:18 am    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

neena wrote:
Wildthings wrote:
I personally don't like the cut in the head, the technique will give about the same temperature reading as drilling a hole in the same location, but still involves the spark plug and thus the ring could be damaged when the plug is removed or installed.


I've been reading around about this and it's unclear if it's a bad idea or not to install the Dakota Digital temp sensor ring under the #3 plug while the engine is in the bus. On a Type 1 motor there's no way to cut a notch in the head or remove the tin and get everything just right without pulling the motor. Yet it looks like folks have installed the sensor ring under the plug without a problem. Is there any technique to use that can "guarantee" a problem free installation with the motor in place?


There are several different casting styles of T1 heads. I made this graphic years ago which illustrates the difference, but I have since discovered that three different countries of manufacture all make deep and shallow plug wells, so ignore the country labeling. The info is still correct though.

Image may have been reduced in size. Click image to view fullscreen.



Add to the depth issue, that DD has managed to slip some QC out the window when it comes to their ring senders. They used to be a snug push fit around the spark plug, and now they leave a few mm gap between the threads and the sender ring, almost guaranteeing a leak. I chased high head temps for six months before discovering the plug well leak issue, and then the new sender didn’t fit right, so I fixed it to an exhaust stud and said “that will catch a lean-out.” And it will, too. So mine is more of an EGT gauge (which DD sells the same gauge for with a different label) but it does the job of catching plastic bags sucked into the fan and otherwise ruining a nice day’s drive.

Robbie
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PostPosted: Wed Mar 14, 2018 3:31 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

Robbie....thanks for the info. Now how the heck does one go about taking off the crush washer? Or is it sacrificed for a replacement one?

Here is what my DD ring looks like on the plug with the ring flush to one side of the plug (not my hand!). There's a gap for sure. Is this what you're talking about being a possible leak spot? Looks like it could be problematic.

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PostPosted: Wed Mar 14, 2018 3:45 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

neena wrote:
Robbie....thanks for the info. Now how the heck does one go about taking off the crush washer? Or is it sacrificed for a replacement one?

Here is what my DD ring looks like on the plug with the ring flush to one side of the plug (not my hand!). There's a gap for sure. Is this what you're talking about being a possible leak spot? Looks like it could be problematic.

Image may have been reduced in size. Click image to view fullscreen.



see:
SGKent wrote:
We had abnormally high temps... and pulled the plugs and sender in the process. The sending ring was already elongating from one use. Looking at the plug, the NGK used has a flat shoulder but the crush washers are thicker in the middle and narrow towards the outside... I think that because the sender is loose enough around the plug, the crush washer not only grabs it but pushes it out, elongating it, allowing it to leak a little. I cut the crush washer off and uses the sender to seal it to the head. Temps dropped about 50F to 75F. I believe it was seeing gasses escape through the threads.

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PostPosted: Wed Mar 14, 2018 4:19 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

The crimp is the hot junction, so the thermocouple is reading the temperature of where the crimp is at and not the head temps. It is getting radiant heat from both the head and the spark plug and since radiant heat transfer is a cubed function (IIRC) then it is coming closer to reading the plug temperature than the head temperature. If you cut off the crimp and glue it into a hole drilled in the head you will be reading the head temperature with no influence for the hot spark plug. If your head has the boss for the early TSII location that is a pretty good spot to install the hot junction.
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PostPosted: Wed Mar 14, 2018 5:04 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

That gap is incredibly leak-prone. I wasted a few senders figuring that out.....

On my personal bus I run it on an exhaust stud and forget about it. But if you desperately want to measure at a spark plug, try finding a proper 14mm ring terminal and soldering it to the bare wire tips of the thermocouple wire.

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PostPosted: Wed Mar 14, 2018 5:04 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

Wildthings wrote:
The crimp is the hot junction, so the thermocouple is reading the temperature of where the crimp is at and not the head temps. It is getting radiant heat from both the head and the spark plug and since radiant heat transfer is a cubed function (IIRC) then it is coming closer to reading the plug temperature than the head temperature. If you cut off the crimp and glue it into a hole drilled in the head you will be reading the head temperature with no influence for the hot spark plug. If your head has the boss for the early TSII location that is a pretty good spot to install the hot junction.


I forgot to mention that it's a VW of Mexico single port head so there's no provision for TS2. I don't know if that complicates or simplifies things. We were hoping for an installation with the motor in place. If the engine gets pulled then there's bunch of configurations to use. Would it be crazy or stupid to trim the outer part of the ring so that it turns out to like a more rounded version of the kind of terminal below? The wire-to-ring junction would be preserved and the terminal could sit flush to the plug. But there would be less surface area of the ring in contact with the head and plug. Bad idea?

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PostPosted: Wed Mar 14, 2018 5:39 pm    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

on the VDO sender the cold junction is at the end of the braided shield at the plastic coupler. The hot junction is crimp at the ring. The problem on the T4 head is it is very hard to find a good spot to mount it other than a plug, unlike the T1 head. The crush washers have a cross section where they start thin at the outside, get thick, then get thin again at the inside. This shape allows the crush washer to push outwards on the ring as it crushes, expanding the ring. If the ring is used as the sealing washer, then the elongation stops.
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PostPosted: Thu Mar 15, 2018 1:52 am    Post subject: Re: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

asiab3 wrote:
On my personal bus I run it on an exhaust stud and forget about it.


SGKent wrote:
The problem on the T4 head is it is very hard to find a good spot to mount it other than a plug, unlike the T1 head.


I haven't installed mine yet and I'm not dead set on the plug. What's the temp difference on an exhaust stud? Where else is a good place on a T1 head?
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