TheSamba.com :: View topic - CHT Nirvana (cylinder head temperature) gauge/sender FAQ

Thu Mar 15, 2018 11:08 am

pierrox wrote: 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?

There will be a large difference in numbers from plug to EGT monitoring; the big point I try to make clear is that a CHT gauge is best used for tracking trends on your personal engine. So if you mount the sensor on an exhaust stud, you should only compare numbers with yourself and other people that also have it mounted on their exhaust stud. You should learn what’s normal for your bus around town, on the freeway, or floored up a long hill. Once you know what your engine usually puts out, you can monitor the gauge for unusual readings. See a spike? Investigate.

I run a CHT gauge to monitor the following:
If a bag or towel is sucked into my fan, the temps go up instantly.
If I get bad gas and a little bit of inaudible pinging, the temps go up noticeably.
If I have a fuel delivery issue and the engine starts running lean, temps go up drastically.

All of those are catchable regardless of where you mount the sender. The only difference is how quickly the gauge responds, and how close to actual head temperature you get. Under the spark plug has proven to read most accurate with the fastest response times. I tried four other locations and settled on the exhaust stud because it’s easy to get to, consistent, VERY close to the spark plug in running conditions, and reacts very quickly to change in combustion temperature. One caveat includes idle timing: if you have a timing setting of 0 degrees or anything more retarded, you will see a temp spike at idle that does not actually exist in the cylinder head. This is from the spark happening so late that the heads are cooling off and shedding the heat and combustion reaction into the exhaust. As soon as you get moving again the spike subsides instantly.

Pick whatever location you want.
Robbie

Engines saved with a cht gauge: 1
Number of nice days ruined by scary numbers: 99

Thu Mar 15, 2018 11:17 am

Kinda off the subject but it proves the point. I heard some folks talking on a program who flew B-17's in WWII when they were brand new off the factory floor. These were mass produced aircraft where every wire, every rivet etc etc went in the same place using templates etc. Totally mass produced. The comment that the pilots all agreed with was that each aircraft had its own personality. Some had to be trimmed more than others, some had to be trimmed to the right, some to the left, some had a different feel or vibration than others. In a way it is the same thing many here have said about gauges. They are valuable for trending but when it comes to comparing to another VW bus, the numbers are in general only. Each bus and gauge set has its own personality.

Thu Mar 15, 2018 11:37 am

When using a ring under the plug, I have wondered how much the spark plug brand and heat rating for the plug could effect the CHT readings, as you are reading plug temperature as much or more than head temperature.

Thu Mar 15, 2018 11:56 am

asiab3 wrote:
Pick whatever location you want.

Thanks! It actually makes perfect good sense. Which exhaust did you pick? 3 seems the important cylinder to monitor, but then its exhaust studs probably get more cool air when driving than say cylinder 4?

Tue Mar 20, 2018 1:10 pm

camit34 wrote: 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.

Get it installed?

Wed Mar 21, 2018 4:45 am

Wildthings wrote: When using a ring under the plug, I have wondered how much the spark plug brand and heat rating for the plug could effect the CHT readings, as you are reading plug temperature as much or more than head temperature.

My gut feeling is that it wouldn't affect it much. Heat rating on a plug is a function of insulator length and affects the temperature of the very tip of the plug. Hotter plugs have more insulation and so the tip stays hotter since it can't cool as well. It shouldn't affect the temperature of the base of the plug very much. Most of the heat at the base of the plug is coming directly from the combustion chamber, and the heat migrating from the exposed electrode has got to be a drop in the bucket.

Mon Apr 02, 2018 1:25 pm

AircooledHome wrote:

Get it installed?

Just arrived last week. Gonna try this weekend to get my manifold / carb done so I will do this at the same time and reply back.

Mon Jul 02, 2018 10:02 am

asiab3 wrote: I tried four other locations and settled on the exhaust stud because it’s easy to get to, consistent, VERY close to the spark plug in running conditions, and reacts very quickly to change in combustion temperature

I'm finally getting around to installing this and then I wondered: by "under the exhaust stud" do you mean you removed the heater box and put the ring over the stud so that it's pressed between the exhaust gasket and the head or that you just removed one of the nuts that hold the heater box on and slipped the terminal over the stud so that it's between the nut and the flange?

Mon Jul 02, 2018 8:03 pm

Just realized that the person I asked about sensor placement said of themselves

"In the woods for the next two weeks."

So is there anyone other than asiab3 running a Dakota Digital CHT ring terminal off an exhaust stud and if so, how so?

Mon Jul 02, 2018 9:32 pm

neena wrote: asiab3 wrote: I tried four other locations and settled on the exhaust stud because it’s easy to get to, consistent, VERY close to the spark plug in running conditions, and reacts very quickly to change in combustion temperature

I'm finally getting around to installing this and then I wondered: by "under the exhaust stud" do you mean you removed the heater box and put the ring over the stud so that it's pressed between the exhaust gasket and the head or that you just removed one of the nuts that hold the heater box on and slipped the terminal over the stud so that it's between the nut and the flange?

It would create a leak between the gasket and the head. I'm pretty sure asiab3 is talking about putting the ring terminal under the nut that holds the exhaust on.
Tcash

Mon Jul 02, 2018 9:54 pm

The thing to keep in mind when using a location other than under the #3 plug is that you lose the ability to compare numbers to what others have been able to gather. Knowing the motor build as much as possible combined with knowing your numbers from the same location as others makes it a bit easier to know where you may really be at.

Thu Jul 05, 2018 8:40 am

This probably belongs in the stupid question thread but can the sender ring terminal be installed under the no.3 spark plug with the engine cover tin in place?

Thu Jul 05, 2018 10:14 am

SevenOaks wrote: This probably belongs in the stupid question thread but can the sender ring terminal be installed under the no.3 spark plug with the engine cover tin in place?

Yes but it is easily damaged and you can't see it to confirm that something has or has not gone wrong, which is main reason I prefer drilling a hole in the head and JB Welding the thermocouple crimp in place.

Thu Jul 05, 2018 4:06 pm

asiab3 wrote: mnskmobi wrote: Thrasher22 wrote: On a semi related note, has anyone else had difficulty getting a good seal when installing a CHT on a spark plug? I've tried putting one on #3 a couple times following the German Supply instructions, and get crap compression when its on.

Yes, indeed! It gets worse when the sender ovals out. :evil:

I have had success with taking off the spark plug compression washer, putting on the CHT sender and reinstalling the compression washer.

Two comments, which seem to get neglected:

1- some heads have incredibly deep and narrow plug wells. This will never allow the sender crimp to coexist with a spark plug socket. See here:

2 - if you bent the sender the wrong way, the issue gets compounded. This picture shows up in this thread every few pages, but someone usually has an epiphany…

http://www.itinerant-air-cooled.com/viewtopic.php?f=46&t=9835

Thu Jul 12, 2018 3:36 pm

I did manage to get my CHT gauge and sender installed last weekend thanks to the great tips in this thread, especially that drawing above that shows the proper bend to apply to the ring terminal. The install under #3 went slow and smooth. My maiden voyage with the gauge was just a round-trip to Home Depot and the high reading was 361 so it appears that it was installed correctly. Thanks all!

Mon Jul 16, 2018 7:51 am

What's everyone seeing as a reading when they first turn on the ignition (not start, just have ignition on)?

Mon Jul 16, 2018 8:07 am

samwise wrote: What's everyone seeing as a reading when they first turn on the ignition (not start, just have ignition on)?
Whatever the outside temp is........

Mon Jul 16, 2018 8:49 am

x2

you should see the ambient temp inside your exhaust when you first turn it on before trying to start.

If you do not, it's possible you have the two wires mismatched. On a LOT of them the yellow goes to red and red to yellow, I don't know why, but mine was like this as well. Typically when you get them wrong it'll read too cold, like WOT at 80MPH will read 320* for some, which is way wrong obviously.

Mon Jul 16, 2018 3:19 pm

97 air temp, DD gauge says 117 - bus sat in sun all day

Mon Jul 16, 2018 4:21 pm

airkooledchris wrote: On a LOT of them the yellow goes to red and red to yellow, I don't know why, but mine was like this as well.

That only happens if the harness is backwards. The offset *must* match up the colors. If your offset only works red > yellow/yellow > red, turn the whole harness around end-for-end, then it will be correct. Oh, and enjoy the additional 30* added to your once-wonderful readings.
Colin