CHT Nirvana (cylinder head temperature) gauge/sender FAQ

[D/A/N]

[LazyLightning75]

I have an older dial style VDO CHT gauge that I want to hook up for kicks and giggles. I bought the 18’ Dakota Digital CHT sender wire in the pic below. The ring terminals will work on the gauge. Question for you - are you aware of any compatibility issues with the VDO gauge and the DD sender wire before I run the wiring? Will this mix and match work?

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1975 Riviera 1.8L FI

[Ebehne]

For the past year-and-a-half or so I've been running the DD CHT gauge on my '71 bus. I've got a relatively stock 1600 DP, 34pict3 carb, working thermostat/flaps, etc. The thermocouple hot junction is run under the #3 spark plug.

I do a lot of round trip journeys in the 180 mile range along the same route at various times of day. Most of the time I take the trip down during the day and the ambient temperature is relatively hot (80-90deg F) and then return late at night and it's much cooler (40-60 deg F).

My CHT readings are relatively consistent with other people on this forum using this same setup, but one thing that I have noticed is that my CHT readings seem to trend higher by about 20-30 degrees when it's cold at night and I'm running the heater. Has anyone else noticed this?

Thanks
Eric

[pierrox]

71 bus, so upright engine. That sort of makes sense since the heater "steals" air from the fan. In a way it's not so bad as the engine has to be within a certain temp to be happy.
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Our bus is on Instagram
instagram.com/biencuitbus

[Ebehne]

Yes it is an upright engine. I get what you’re saying, but does the heater actually flow more air through the heater tubes vs. over the cylinder heads when it’s on? I don’t think this is the case. Assuming that the thermostat is fully open (largest amount of air able to flow to the cylinder heads), all you’re doing by manipulating the heater control is either directing the air overboard or closing the flap in the heat exchanger boxes to send the hot air up to the cabin.

The only difference I can potentially see the heater making is that the cold outside air is going to be a better heat sink to pull heat from the hot exhaust/heat exchanges as compared to the cabin (particularly after the cabin/heater piping starts to warm up after 10-20minutes on the freeway).

[a-marshal]

Maybe not Nirvana but I'm quite pleased with my home made Arduino based gauge. If I acutally make version II THAT will be Nirvana.

For this unit I used an Arduino UNO, 3 Analog thermocouple amplifiers (Adafruit AD8495). a 1.3" OLED display (Adafruit product 938) and some
cheapo Type K thermocouples and wire from ebay.

I was pretty thorough in the testing.. after running through a bunch of other things I finally mounted the sensors to a destroyed head and put the whole thing in the gas grill and ran the temp up to 500 degrees.. I'm pretty confident that they are reading accurately enough.

The first photo is ambient temp the other morning..

and the second pic is today after idling in the driveway for 30 minutes or so as I messed with the carbs. As I watch the temps rise, they both top out in the 250 range with cylinder 3 running around 10 degrees warmer than cylinder 1. It takes Cylinder 3 5 or so minutes longer to get to temp and I'm not sure if that is due to the choke holding closed longer( which it is) or something to do with the thermostat flaps.

If I can find a colour display that I can read in the daylight I'll make version II, since I have some more space in memory on the Arduino I may add to the code .. a better data smoothing method for sure and maybe even another sensor or two ...
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-Ob. vehicle info....
1973 Westy w/ '74 1.8 liter / PDSI (type3?) carbs / 009 distributor / pertronix

[tommu]

[Beagledog1]

The link to German Supply’s write-up of how to install the Dakota Digital CHT sensor seem to be broke. Does anyone know where I can find that write-up?

[BUSBOSS]

[SGKent]

try at archive.org. They have some pages there. You may have to try different dates until you find one that fully loads.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Sleepnone]

[PatJr]

[ImAddicted]

I thought I had added to this thread but I guess I didn’t. I did the poor man’s CHT by piecemeal off eBay. I haven’t driven Ducky yet but has run extended in the yard and it has worked out well. I did the ring under the #3 plug. When tested before install it was within a few degrees of my candy thermometer. He gauge is pretty basic, just CHT and ambient.

[PatJr]

Thank You for the follow up
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1970 Transporter a orange one
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[EZ Gruv]

Since this seems to be the most complete thread on CHT install, I'll put my question (which I still have after reading many threads) here.

Where are people routing their thermocouple wire? Up through the spark plug hole seems like less than an ideal choice.

Photo during install:

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Eric
1977 Deluxe Westfalia - 2.0L FI Type IV, Completely Original
Photographer for HotVWs, VolksWorld, AirMighty, VW Camper & Commercial, Hayburner, and more.
My Photography Page.

[PatJr]

I just slip the cht ring over the top of the spark plug. I couldn't get a reliable seal between the spark plug and the head. I also just slit the plug boot so I could try and keep the cht wire away from the tin.

I don't think I get proper reading on that thing in any case. I have come to for cht ignorance might be bliss. TheEZGZ says he doesn't use a cht.
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1970 Transporter a orange one
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[SGKent]

many notch the head and take the wire out under the tin in a safe spot.

I found that the spark plug washer is tapered and that taper pushes the sender outwards until it is an oval, then it leaks. Taking the washer off, and using the sender as the washer gave me a better seal and stopped the distortion of the sender that occurs. Keep in mind that a hotter spark plug will result in lower observed heat temps while a colder spark plug will result in higher head temps. A colder plug tip conducts more heat to the head than a hotter plug tip. A hotter tip plug retains more heat in the tip.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[ewdb92]

[SGKent]

eric the problem I had is that the plug washers are not flat, they are wider in the center and taper to the outside. The ring has a little gap between it and the plug. That combination would expand the ring a little. After the plugs were removed about four ir five times the ring would be so expanded or ovaled it would leak. Since the head has a square shoulder, and the plug has a square shoulder, I just got rid of the sealing washer on the plug the sender is on. I know that it was leaking before I did this because I found carbon traces in the plug threads all the way up. That leakage will also cause the sender to run hot. To be 100% thoughtful on this subject, I am not sure if we are reading head temps or plug temps right at the head. Meaning an inch or two away head temps could be much lower.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[ewdb92]

I'll definitely be paying attention to this the next time I remove the plugs. Perhaps I have not taken them out enough times yet.

I agree on the error of temp we're measuring, so many variables(and opinions). I find even the temp of the weather makes a visible difference in the gauge reading. Which is why always focus on the trend. Once I knew where the head temp sat on various weather days, headwinds, and grades, I felt comfortable with the gauge readings and look for the abnormal ones.

Thanks for clarifying Steve.
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Erik
71 Camper
http://zerotosixtyeventually.wordpress.com/