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CHT Nirvana (cylinder head temperature) gauge/sender FAQ
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ratwell
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PostPosted: Mon Feb 21, 2005 6:33 pm    Post subject: CHT Nirvana (cylinder head temperature) gauge/sender FAQ Reply with quote

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There was post today on the Type2 mailing list showing exactly how bad the VDO CHT gauge/sender is:

http://homepage.mac.com/ratwell/VDOGauges/CHT-revisited.txt [ed url 7/24/06]

I've been bothered by them for about year because there is simply no way to know what the real temperature the heads are at but it's a really important gauge to have. Gene Berg has a great writeup on how he hates them. They can't be calibrated and even if you could adjust it the technology is too simplistic to deal with ambient temperature changes. I've been using a Fluke DMM for my own readings: it's digital, dead accurate but not dash mount friendly.

Wouldn't it be great if there was a gauge with the following features:

- 2 1/16" (52mm) round size
- accuracy WITH cold junction compensation circuitry
- affordable

I finally found such a company in Dakota Digital [ed url 7/24/06]. I discovered them a few years ago when I was looking at a magazine article about their expensive beetle instrument cluster but I never went to their website to discover all of their other products (maybe there wasn't one at the time).

Not only do their gauges meet our basic requiements, they also have:

- digital display with night dimming
- microprocessor stabilized readings
- user adjustable flashing indicator

That's right. You can program it to flash at you when the gauge reads any temperature you desire between 300-600F. This is a miracle for bus owners: you no longer have to drive by the gauge: just wait for it to flash like a real idiot light!

The gauge is $109 without harness. Their harness only goes up to 14 ft. but they will make up a cutom length for you for an extra $5 (their wiring is thermocouple all the way to the gauge). Unfortunately, their ring terminal only fits under a 1/2" bolt so I decided to make my own harness.

If you purchase a new 14mm ring terminal or re-use your VDO terminal, buy a suitable length of k-type thermocouple from your local electronics surplus for 50 cents/ft. you be in CHT Nirvana for only a little more money than the VDO setup but for a lot more value.

I've tested this gauge simultaneously against the Fluke between 200-420F in the bus and the Dakota Digital gauge was only 5F higher throughout that temperature range so I know it doesn't wander. Because it's got the CJC circuitry, the gauge itself is also immune to freezing/heating and I tested that also in the house.

They also make matching OT and OP gauges. They aren'y exactly cheap but if you want to be warned when the oil temp is too high or the oil pressure is too low without driving by the gauges, these are the gauges for you.

It gets better: Dakota Digital uses VDO senders so you can re-use your senders with their gauges. I haven't bought either or these two gauges to prove it but that's what they tell me. Some of their gauges have programmable temperature ranges for maximum sender compatibility.

Their gauges are the old style with the mounting bracket on the back unlike the more modern VDO spin-loc hardware. Because of that I recommend you use the VDO rubber mounting plate instead of the metal plates.

Isn't this awesome? I chose the blue display with the black bezel.

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


Don't throw out your VDO gauges! VDO makes some really nice mounting hardware you can re-use. Smile
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Last edited by ratwell on Mon Jul 24, 2006 10:58 pm; edited 2 times in total
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PostPosted: Mon Feb 21, 2005 6:44 pm    Post subject: Reply with quote

*adds to "to-do" list, adds to budget*

SWEET!!!!!
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PostPosted: Mon Feb 21, 2005 7:09 pm    Post subject: Reply with quote

Hot damn!!! That is awesome! If thier gauges really use the VDO senders this will be a snap to swap my current gauges out. The price is worth the accuracy. I've always dreamed about an accurate HT guage. Digital to boot, and a warning light? Almost to good to be true! Very Happy Very Happy Very Happy I wonder, could you just uncrimp the ring terminal from the VDO thermocouple and recrimp it to one of thier senders? Richard, are you planning to get OT and OP gauges from them also? I'd love to hear if they are as accurate.
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PostPosted: Mon Feb 21, 2005 7:22 pm    Post subject: Reply with quote

Excellent news!

I admire your dedication and I marvel that you find the time.
I, for one, am glad you do.

Finally, a guage that seems to indicate real temperatures.
"Trending" be damned!

Good work Richard, your work may save some engines!

By way of a little background:

The term "Trending" refers in this case to guages which provide a read-out that means NOTHING other than a number you can use to compare to future numbers provided during similar circumstances. CHT guages get their temperature readings via a thermocouple. This is nothing more than a pair of wires which provide a number representing the DIFFERENCE between the temperatures at the ends. In other words, if the thermocouple is at ambient temperature (in your van) on one end and under a spark plug at the other, the guage will give you a number representing THAT difference. Unless you always have the same ambient temperature at the "cold" end, the readings don't mean much. To make matters worse, CHT guages driven by thermocouples seem to read the opposite of the actual conditions. In cold weather, CHT guages seem to provide higher readings than they do at desert temps.

Sorry for the long post, but not everybody has been following this.

Thanks again Richard!
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PostPosted: Mon Feb 21, 2005 7:30 pm    Post subject: Reply with quote

Excellent info Richard. Thanks for finding and putting that together for us gauge junkies. I was thinking about putting together some new ones and I think this is going to be my next project after I get the interior back into the bus. Im gonna need those for my new engine.
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PostPosted: Mon Feb 21, 2005 7:30 pm    Post subject: Reply with quote

westy78 wrote:
Hot damn!!! That is awesome! If thier gauges really use the VDO senders this will be a snap to swap my current gauges out. The price is worth the accuracy

For CHT yes. When using the same VDO OT and OP senders, you'll have nice digital readings of whatever those senders read. Still, the flashing warning display is very cool.
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PostPosted: Mon Feb 21, 2005 7:49 pm    Post subject: Reply with quote

I've been wondering when the technology for reliable gauges would be made affordable to bus drivers.
They have been doing stuff like this for years in airplanes.

I have to say that I am not a big fan of the space age digital look. I would rather prefer a traditional gauge with an LED or something hidden in the face to warn of an impending overheat.......oh well, maybe someday.

Anyway, good find, I might have to consider them as an upgrade in the future.

It sure beats the $1500 buck that the EDM-700 costs. If you really want to know what your engine is doing, you get one of these.
Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Mon Feb 21, 2005 11:10 pm    Post subject: Reply with quote

Thanks Richard!

And I thought I was the only one out there looking down at that gauge and thinking "it can't be THAT hot!"

I will check them out and most likely get one. Summer is HOT out here in Arizona. Just paranoid of the worst case senario.
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PostPosted: Tue Feb 22, 2005 7:53 am    Post subject: Re: CHT Nirvana Reply with quote

Do you know if any one makes a 12mm ring sensor? I guess the 1/2" that comes with theirs is probably pretty close, within 1mm anyway. Thanks for the info.
Tim



ratwell wrote:
There was post today on the Type2 mailing list showing exactly how bad the VDO CHT gauge/sender is:

http://www.type2.com/~type2reflect/msg93971.html

I've been bothered by them for about year because there is simply no way to know what the real temperature the heads are at but it's a really important gauge to have. Gene Berg has a great writeup on how he hates them. They can't be calibrated and even if you could adjust it the technology is too simplistic to deal with ambient temperature changes. I've been using a Fluke DMM for my own readings: it's digital, dead accurate but not dash mount friendly.

Wouldn't it be great if there was a gauge with the following features:

- 2 1/16" (52mm) round size
- accuracy WITH cold junction compensation circuitry
- affordable

I finally found such a company in Dakota Digital. I discovered them a few years ago when I was looking at a magazine article about their expensive beetle instrument cluster but I never went to their website to discover all of their other products (maybe there wasn't one at the time).

Not only do their gauges meet our basic requiements, they also have:

- digital display with night dimming
- microprocessor stabilized readings
- user adjustable flashing indicator

That's right. You can program it to flash at you when the gauge reads any temperature you desire between 300-600F. This is a miracle for bus owners: you no longer have to drive by the gauge: just wait for it to flash like a real idiot light!

The gauge is $109 without harness. Their harness only goes up to 14 ft. but they will make up a cutom length for you for an extra $5 (their wiring is thermocouple all the way to the gauge). Unfortunately, their ring terminal only fits under a 1/2" bolt so I decided to make my own harness.

If you purchase a new 14mm ring terminal or re-use your VDO terminal, buy a suitable length of k-type thermocouple from your local electronics surplus for 50 cents/ft. you be in CHT Nirvana for only a little more money than the VDO setup but for a lot more value.

I've tested this gauge simultaneously against the Fluke between 200-420F in the bus and the Dakota Digital gauge was only 5F higher throughout that temperature range so I know it doesn't wander. Because it's got the CJC circuitry, the gauge itself is also immune to freezing/heating and I tested that also in the house.

They also make matching OT and OP gauges. They aren'y exactly cheap but if you want to be warned when the oil temp is too high or the oil pressure is too low without driving by the gauges, these are the gauges for you.

It gets better: Dakota Digital uses VDO senders so you can re-use your senders with their gauges. I haven't bought either or these two gauges to prove it but that's what they tell me. Some of their gauges have programmable temperature ranges for maximum sender compatibility.

Their gauges are the old style with the mounting bracket on the back unlike the more modern VDO spin-loc hardware. Because of that I recommend you use the VDO rubber mounting plate instead of the metal plates.

Isn't this awesome? I chose the blue display with the black bezel.

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


Don't throw out your VDO gauges! VDO makes some really nice mounting hardware you can re-use. Smile
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PostPosted: Tue Feb 22, 2005 8:50 am    Post subject: Reply with quote

How thin is the sender? I wonder if you could use it as a replacement for the spacer on temp sender II, seems the treaded part was small but I don't know the diameter, Just kind of thinking out loud I guess. Good post, I've never trusted my VDO gauge.
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PostPosted: Tue Feb 22, 2005 9:29 am    Post subject: Reply with quote

This rules. I am so *@##*@ sick of the VDO gage. In the morning at 50deg F my gage reads 150deg before starting. Thanks for the research Richard.
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PostPosted: Tue Feb 22, 2005 9:33 am    Post subject: Reply with quote

I've never ran a temp gage- Volkswagen never installed one for buses. Is this something I should consider for the future?
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PostPosted: Tue Feb 22, 2005 9:39 am    Post subject: Reply with quote

VWBusrepairman wrote:
I've never ran a temp gage- Volkswagen never installed one for buses. Is this something I should consider for the future?


Talk to Bottomend about the plastic bag over his fan guard. You can see that pretty quick on a CHT gage.
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PostPosted: Tue Feb 22, 2005 10:26 am    Post subject: Reply with quote

there was a newspaper section on my fan cover once- but it wasn't the funnies!
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PostPosted: Tue Feb 22, 2005 10:41 am    Post subject: Re: CHT Nirvana Reply with quote

Does anyone know the length of the VDO CHT sensor and lead that is made for the bus? I had to add a couple of feet to mine to make it reach the gauge. At $19.95 for the 14' sensor, it would be worth the extra $5 to get it the proper length the fisrt time.
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PostPosted: Tue Feb 22, 2005 10:46 am    Post subject: Re: CHT Nirvana Reply with quote

timmy74006 wrote:
Do you know if any one makes a 12mm ring sensor? I guess the 1/2" that comes with theirs is probably pretty close, within 1mm anyway. Thanks for the info.

I'm not sure what the overall size their sender is. I've only seen it in pictures on their website and been told the size of the opening by their tech support.

http://www.dakotadigital.com/zoom.cfm/-/PartNumber=SEN-11-6/zoom.htm

mightyart wrote:
How thin is the sender? I wonder if you could use it as a replacement for the spacer on temp sender II

No.

jberger wrote:
In the morning at 50deg F my gage reads 150deg before starting.

This gauge doesn't show a reading until 150F as well. They say the internal temperature of the unit won't allow colder readings (it's rated for 150-750F). Luckily once the engine has been running for 30 seconds, you'll hit that temp and then the gauge will be accurate from that point on.
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PostPosted: Wed Feb 23, 2005 5:48 am    Post subject: Reply with quote

Thanks a ton ratwell, just as I was looking for a CHT to put on my '73 when I go over the engine this spring! Found a sale they had, basically the same gauge w/a square face and only cost $55!! (minus sender) Snatched that sucker up quick! Now about this 'make your own sender' thing...could you whip up a 'guide for dummies' on that? Just need to know exactly how i'd go about that. Thanks again!
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PostPosted: Wed Feb 23, 2005 8:55 am    Post subject: Reply with quote

You just need a suitable ring terminal that fits under the plug, expose both of the thermcouple wires (strip off about 5mm of the insulation) and crimp them in the terminal so they are touching. That's it. Look closely at this photo:

http://www.germansupply.com/xcart/skin1/images/tech/cht/TIVSenderInstalled.jpg

With the right terminal and a NGK plug I find there is plenty of room to fit the terminal without altering the head. Luckily #3 plug is also the easiest to reach through the tin on a Type 4 engine (with overhead hatch of course).

The hardest part is finding the ring terminal. I have a few 14mm spares that can I probably mail out for $1.50 each to anyone in the US making their own harness.
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Last edited by ratwell on Wed Feb 23, 2005 10:02 am; edited 1 time in total
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PostPosted: Wed Feb 23, 2005 9:24 am    Post subject: Reply with quote

Quote:
You just need a suitable ring terminal that fits under the plug, expose both of the thermcouple wires (strip off about 5mm of the insulation) and crimp them in the terminal so they are touching. That's it. Look closely at this photo:


I thought the thermo couple ring is composed of two different specific metals, that produce known volts when heated. If so, how can we use a normal ring terminal?
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PostPosted: Wed Feb 23, 2005 9:32 am    Post subject: Reply with quote

Wonder if these would work
http://www.ultralightnews.ca/cht/index.html
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