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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Tue Jul 06, 2021 9:32 am Post subject: CHT gauge and Thermistor(?) |
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I got this CHT Gauge and the sensors with a Dune buggy project that I bought 10 years ago. The gauge was at least 15 years old then. No manufacturer markings on the gauge and I haven't seen the sensor clips since the 1980's. Is it worth using? Will any other sensor work with the gage? It has a rotary switch and 4 sensors so you can compare all 4 cylinders.
The Stewart Warner paperwork was in the box with 3 other gages. Oil pressure, oil temp and Amps. Those were SW. This one not sure.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Tue Jul 06, 2021 11:05 am Post subject: Re: CHT gauge and Thermistor(?) |
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BIGMIKEY wrote: |
I got this CHT Gauge and the sensors with a Dune buggy project that I bought 10 years ago. The gauge was at least 15 years old then. No manufacturer markings on the gauge and I haven't seen the sensor clips since the 1980's. Is it worth using? Will any other sensor work with the gage? It has a rotary switch and 4 sensors so you can compare all 4 cylinders.
The Stewart Warner paperwork was in the box with 3 other gages. Oil pressure, oil temp and Amps. Those were SW. This one not sure.
Mike T |
I was going to ask if its REALLY a thermistor and not a thermocouple...but yes...in the paperwork they say "thermistor".
So...pros and cons:
A thermistor...most average ones...operate to about 480*F. You can find more than a few now that operate to about 550-575 F
A thermistor is about 3X faster in response time...but its just not an issue for this application.
Long term accuracy....thermistors will drift or change with age and cycling about 0.2% per year...while thermocouples are about 0.03% per year. Really....this is not an issue in our application unless you are looking at EGT's.
The thermistor ....If over a decade of use, its off by +/-2% (it will be one or the other...not both).....thats 8* with a target of 400*. Significant but not life changing. If 400* is your "worry point"...392* or 408* is not catastrophic.
The Thermistor.....does not have the temperature compensation issue of thermocouples though....so thats a good thing!
I would use it! Test it with hot and cold water first. Looks like a nice part.
Ray |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Tue Jul 06, 2021 1:51 pm Post subject: Re: CHT gauge and Thermistor(?) |
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Well. Better news than I suspected I would hear. Thank you Mr. Greenwood. Now to determine the ideal location for the clip.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Tue Jul 06, 2021 3:03 pm Post subject: Re: CHT gauge and Thermistor(?) |
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BIGMIKEY wrote: |
Well. Better news than I suspected I would hear. Thank you Mr. Greenwood. Now to determine the ideal location for the clip.
Mike T |
I meant to say that a thermistor is about 3X SLOWER than a thermocouple.....but again its really not an issue. Ray |
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tattooed_pariah Samba Member
Joined: April 24, 2006 Posts: 2047 Location: El Cajon, CA
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Posted: Tue Jul 06, 2021 7:26 pm Post subject: Re: CHT gauge and Thermistor(?) |
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The best part of this for me is seeing that it looks like your gauge spans from 300-500F..
I have a digital thermocouple gauge and it seems like no one wanted to be held accountable for telling me what the safe operation range is.. My temps regularly stay under 300, unless I'm digging into the throttle doing 75mph+ for extended periods of time.. even then I think the highest I've seen is like 370F, so I guess I'm doing alright.. _________________ -pariah (just a novice from "that other VW site")
'72 Volksrod "Effigy"
"Never worry about stepping on people's toes. People who get their toes stepped on are either sitting down, or standing still on the job."
-Admiral Arleigh Burke, USN(ret.) |
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Culito 11010101
Joined: December 07, 2006 Posts: 5863 Location: Columbia Missourah
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Posted: Wed Jul 07, 2021 10:38 am Post subject: Re: CHT gauge and Thermistor(?) |
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At first glance it doesn't seem like that clip would give a very accurate reading. _________________ Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug
johnnypan wrote: |
...dont pay no attention to Culito,he's a cornhole.. |
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evanfrucht Samba Member
Joined: July 24, 2016 Posts: 2180 Location: Laurel Canyon, CA
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Posted: Wed Jul 07, 2021 11:13 am Post subject: Re: CHT gauge and Thermistor(?) |
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Ya, I noticed that as well.
Everyone always talks about how important it is to get a reading at the plug with the more common thermocouple based CHT gauges. Seems like attaching a heat sensor to a cooling fin might be counterproductive, but what do I know
Looks like a cool little gauge to me, I'd give it a shot. _________________ 1967 Bug ( the daily rod )
1964 Fury Wagon ( the pavement shredder ) |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Wed Jul 07, 2021 12:47 pm Post subject: Re: CHT gauge and Thermistor(?) |
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evanfrucht wrote: |
Ya, I noticed that as well.
Everyone always talks about how important it is to get a reading at the plug with the more common thermocouple based CHT gauges. Seems like attaching a heat sensor to a cooling fin might be counterproductive, but what do I know
Looks like a cool little gauge to me, I'd give it a shot. |
You could put that clip almost anywhere...even attach it with a screw right next to the spark plug under the sheet metal.
If you can get the thermistor range required fro that gauge....you can simply buy thermistors of a wide range of shapes and forms to attach to the leads. Ray |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Wed Jul 07, 2021 2:30 pm Post subject: Re: CHT gauge and Thermistor(?) |
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raygreenwood wrote: |
If you can get the thermistor range required fro that gauge....you can simply buy thermistors of a wide range of shapes and forms to attach to the leads. Ray |
Any hints on how I could do that? I will look the gage over and see if there are any part numbers. I tested my Oil temp gage in a pan of boiling water. Would the same test work for this? Hmm, unless the low number on the scale is higher than 212°.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue.
Last edited by BIGMIKEY on Thu Jul 08, 2021 9:03 pm; edited 1 time in total |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Wed Jul 07, 2021 2:42 pm Post subject: Re: CHT gauge and Thermistor(?) |
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[quote="BIGMIKEY"]
raygreenwood wrote: |
evanfrucht wrote: |
If you can get the thermistor range required fro that gauge....you can simply buy thermistors of a wide range of shapes and forms to attach to the leads. Ray |
Any hints on how I could do that? I will look the gage over and see if there are any part numbers. I tested my Oil temp gage in a pan of boiling water. Would the same test work for this? Hmm, unless the low number on the scale is higher than 212°.
Mike T |
Well.....thermistors are "resistors"....thermal resistors. So....take some ice cold water and put the thermistor in it. Check the water temp with an accuraye voltmeter with a thermocuple based temp probe. Write that down.
Then set your voltmeter to resistance and read the resistance across the thermistor. Write that down.
Then take maybe a spoon or piece of metal and put it in the oven at say....400°F. Check the temp with the tnermocouple and volt meter....write that down. Then check the resistance of the thermistot at that temp. Write that down.
So.....you now have resistance of thermostor at known temps across the range you need. You can call digi-key or look on their site......for a thermistor in that range.
Look for a ceramic one. Should be maybe $5. Usually about 5mm in diameter.....a lottle blister with two wires. Drill a small hole the diameter of the resistor next to the spark plug well in the head....and cement it in with either heat sink paste or JB weld. Solder the wires onto you leads. Ray |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Thu Jul 08, 2021 9:08 pm Post subject: Re: CHT gauge and Thermistor(?) |
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Thanks. I will attempt to do as you describe. Weather in Northeastern PA knocked out our power for 36 hrs. Wind, branches down everywhere. Hope to get back on this over the weekend.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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Culito 11010101
Joined: December 07, 2006 Posts: 5863 Location: Columbia Missourah
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Posted: Fri Jul 09, 2021 10:46 am Post subject: Re: CHT gauge and Thermistor(?) |
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Only reason I mentioned it is because with the clip, the thermistor is hanging out in the air. I would assume you want this flat against what you are trying to measure? _________________ Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug
johnnypan wrote: |
...dont pay no attention to Culito,he's a cornhole.. |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Fri Jul 09, 2021 8:40 pm Post subject: Re: CHT gauge and Thermistor(?) |
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Culito wrote: |
Only reason I mentioned it is because with the clip, the thermistor is hanging out in the air. I would assume you want this flat against what you are trying to measure? |
Yes.....this is a very important point. Out on the fins...just tells you a temperature that is far from the hottest point of the head. It does tell you something....but the question is whether what it tells you is useful....for an aircooled VW.
If the difference from the point where a sparkplug is is say....150* higher than out on the fin...and temps were "linear".....you "could" use the spot on the fin ....and say.....if the fin is 250* then you know the plug area is 400*....right?
The problem is that that only works on an engine that runs at constant speed and cooling airflow...like an industrial engine or "maybe" an aircraft engine.
You really need to get the probe point very close to where the sparkplug is. If you can get it there...whether its a thermistor or a thermocouple....is not really a big deal. Ray |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Sat Jul 10, 2021 9:17 pm Post subject: Re: CHT gauge and Thermistor(?) |
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Some Internet research revealed this gauge is a Radatron. Apparently a vintage item. Several threads address it n the accessories forum and the Vintage speed forum. No consensus was reached on where to put the sensor. I'm putting it as close to the spark plug as I can get it. I'll see what it tells me.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Thu Aug 05, 2021 6:30 am Post subject: Re: CHT gauge and Thermistor(?) |
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I have the Radatron cylinder head temperature gauge installed and working. I have 2 of the 4 thermisters installed on #3 & #4. The thermister clip on #3 is installed about 1" away from the spark plug on a close by fin. The one on #4 is installed under the head on the 2nd fin in from the cylinder top. I tested by taking a 1/2 hour drive in my local area. Hilly 2 lane roads avg speeds in the 40mph range up to 55 in places with occasional stop. The needle struggled to reach 270°F. The highest I saw it read was maybe 290°F on a 1 mile uphill grade which I took in 4th gear at about 45 to 50 mph. But it cooled right back down to sub 270°F when I got back to level road. Oil temps at the same time were steady at 170°F. switching back and forth from the #3 to #4 showed #4 running maybe 50° hotter.
Car is a 1973 standard beetle with 4spd 4.125:1 trans. 1600 otherwise stock, Dellorto 36 carbs with 30mm venturis, 9164.2 emulsion tubes, 180 airs, 122 mains, 60 idles and 50 pumps jets. 009 distributor.
Thanks for any comments.
_________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue.
Last edited by BIGMIKEY on Wed Aug 18, 2021 12:36 pm; edited 1 time in total |
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raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21474 Location: Oklahoma City
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Posted: Thu Aug 05, 2021 8:20 am Post subject: Re: CHT gauge and Thermistor(?) |
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BIGMIKEY wrote: |
I have the Radatron cylinder head temperature gauge installed and working. I have 2 of the 4 thermisters installed on #3 & #4. The thermister clip on #3 is installed about 1" away from the spark plug on a close by fin. The one on #4 is installed under the head on the 2nd fin in from the cylinder top. I tested by taking a 1/2 hour drive in my local area. Hilly 2 lane roads avg speeds in the 40mph range up to 55 in places with occasional stop. The needle struggled to reach 270°F. The highest I saw it read was maybe 290°F on a 1 mile uphill grade which I took in 4th gear at about 45 to 50 mph. But it cooled right back down to sub 270°F when I got back to level road. Oil temps at the same time were steady at 170°F. switching back and forth from the #3 to #4 showed #4 running maybe 50° hotter.
Car is a 1973 standard beetle with 4spd 4.125:1 trans. 1600 otherwise stock, Dellorto 36 carbs with 30mm venturis, 9164.2 emulsion tubes, 122 mains, 60 idles and 50 pumps jets. 009 distributor.
Thanks for any comments.
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Yep....thats too cool of a reading. The problem with mounting either thermistors or thermocouples.....is that they need to be out of the airflow.
The actual welded hot joint of a TC needs to be in contact with the hot metal/surface you want to read....and shielded from cooling airflow.....which can cool the sensor point fast.
Same with a thermistor resistor point. Ray |
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AlteWagen Troll
Joined: February 23, 2007 Posts: 8498 Location: PNW
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Fri Aug 06, 2021 2:14 pm Post subject: Re: CHT gauge and Thermistor(?) |
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AlteWagen wrote: |
Isnt that gauge the one they recommend in the how to hot rod book? If I remember correctly they put the 'clip' underneath the head in the small fins above the chamber. I think there is even a pic of the sender. |
Good catch. It is that gauge. They show the old style senders too. The kind that screwed in between two fins. Looks a lot like a Corvair Cylinder head temperature sensor. I wondered if one of those would work so i checked. Unobtainium.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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BIGMIKEY Samba Member
Joined: September 24, 2007 Posts: 1102 Location: North East Pennsylvania
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Posted: Wed Sep 01, 2021 2:16 pm Post subject: Re: CHT gauge and Thermistor(?) |
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Here is where I mounted the thermistors for the Radatron Cylinder Head Temperature gauge installed in my 1973 beetle. These are mounted in the position specified in the instructions. Head is #1 and #2.
Selecting between the 4 sensors I get maybe a 30° difference between the 4 positions. I suspect that I am not seeing the true CHT. But I don't know for sure. I have 3 different other devices to use to measure temperature. A tire/brake pyrometer, A laser thermometer and a Multi-meter that can measure temperature.
Mike T _________________ BIGMIKEY
Deserter Series 1 project.
https://www.thesamba.com/vw/forum/viewtopic.php?t=787047&highlight=
1973 Beetle Driver, Marina Blue. |
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