Looking to monitor CHT's

[youngnstudly]

So I am trying to gather as much info as possible regarding the setup and components used to monitor cylinder head temperature. Although I realize this is a very simple principle (my nieghbor calls it "60's Go kart technology), I am completely new this so excuse the newbie questions. I wasn't able to find the answers to all my questions.

For starters, I would like to run one gauge in the glovebox, with a 4 position switch next to it, and 4 seperate harnesses and thermocouples leading to each cylinder. I want to be able to monitor each cylinder individually (for peace of mind, but it's also quick for troubleshooting my Webers and ignition). My plan was to route everything to the right side of the engine compartment and run the individual harnesses in seperate looms (or sprinkler tubing) through the roof (as the factory ran it's harness on the opposite side of the car), and have the harnesses exit right at the glove box.

As I understand it, the Thermocouple's can not be cut or modified in any way, but I am getting mixed answers on modifying the harnesses themselves (that run from the thermocouples to the gauge). I am also unclear on how the switch hooks up to the gauge or how I can make use of the 8' leads supplied with the typical switch. I want to keep all the thermocouple connections in the engine compartment, and run each harness with no connections or breaks (through the roof) to the switch in the glove box.

1) Can I use different brand components together successfully?

2) Can I make up my own wires to go from the gauge to the switch using the proper terminals?

3)Can the leads for the harness(es) be modified in length from 8' to (say for example, 14')? Obviously I can't use an 8' harness to go from the thermocouple to the switch or gauge. I need more like 10-13' so I am short more than a few feet.

4)What is the difference between "TSO" and "non-TSO" when it comes to these gauges and components (besides price??? ).

This what I am looking at buying (I'd like to keep it on a budget of $250 or so):

Gauge- http://www.bobsgauges.com/servlet/the-61/Cylinder-Head-Temperature-Gauge/Detail

switch- http://www.bobsgauges.com/servlet/the-895/Westach-Thermocouple-Switch/Detail

Thermocouple- http://www.bobsgauges.com/servlet/the-838/Westach-Under-Sparkplug-Ring/Detail

Thanks for the help!
Andy
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[Stripped66]

MGL TC-1

http://www.chiefaircraft.com/airsec/Avionics/MfgJR/MGLAvionics-SmartSingles.html

This gauge will handle 4 thermocouples (I bought mine from Dakota Digital...any J, K, or E-type thermocouple works), don't bother messing around with a switch, splicing, etc.
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[74 Thing]

A lot of Westach gauges here

http://www.aircraftspruce.com/menus/in/westach_cht.html

[Alexander_Monday]

Questions 1 - 3 = maybe. Depends on the specific way the system is designed.
You can get all kinds of goofy things happening if you mismatch.

Way too much to try to explain unless you have an through electronics background to
begin with, and if you do start here http://www.omega.com/temperature/Z/zsection.asp



Question 4 = http://www.faa.gov/aircraft/air_cert/design_approvals/tso/

P.S. Either get a temperature compensated system, or know where the 2nd junction is and what gauge variances happen when it changes temperature.
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[Ian Godfrey]

I've been down some of this recently.... if the gauge is to be accurate then the thermocouple wire has to be continuous from the sender to the gauge, which in your case would be 4 pairs of wire. For switchable systems using one gauge i would look at light aircraft set ups eg Westach which have switchs for 4 cylinders into one gauge or quad gauges. (4 gauges in one).
I ended up with single dakota digital gauge with a sender on #3 cylinder. They supply thermocouple wire in lengths up to 18 ft. Most of the thermocouples are to go under spark plugs but I opted to drill an extra hole in the head near the spark plug but into the meat of the head just outside the bore. It is extremely accurate, within 2 deg C. of my infrared gun. (i did testing on my engine stand, so i could reach different parts of the head) by comparison, my VDO gauge was 50 Deg C. out. (they are non temperature corrected).
Oil temp is an obvious one, the VDO gauge is only 10 deg out, but I have ordered a dakaota one to compare, though they seem to use the same sender. Put the sender in flowing oil, the bottom of the sump is much cooler. You want to know where it is hottest not coldest.
Next, a tuning device... a wide band AFR gauge or EGT gauges to correct mixture, I am using a Tech Edge AFR, which is probably the cheapest of the really accurate ones, and allows easier tuning of all throttle openings compared to using an EGT gauge. You also need some numbers..... I am aiming for oil max. 220 F, CHT under 300 F, max 350 F under extreme load. AFR 13:1 WOT, leaner on idle and cruise. Every engine is different as are fuels, oils etc. so do lots of research. There are also many opinions. good info at thesamba.com/vw/forum/viewtopic.php?t=293837

[miniman82]

My Techedge wideband has 3 EGT channels built right into it, you just plug in your K-Type thermocouples and go. It's got built in temp compensation, and the software is user friendly (I use a program called winlog, not the one they supply). IMO wideband O2 and EGT logging are the 2 most powerful tools to have in your box when tuning an engine. I don't even look at CHT anymore, because I know as long as the belt's on the heads are just fine.
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Build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=212747

[youngnstudly]

I appreciate all the replies! I originally considered using a quad guage from one of the reputable companies, but the guage alone is out of my price range so I scrapped that idea. I have been looking at a few of the single and dual gauges that are temp. compensated and so far Digital Dakota appears to be one of the best for the money, and their thermocouples (or "temperature senders" as they call them) are the most simple and cost effective. The problem I have with them is they don't make a quad CHT gauge, nor does it appear that they offer a switch of any kind to use, and to top it off, the sender accepts a 13-14mm spark plug so I don't know if it will be too loose for the 12mm plugs I am running. And I thought this would be simple!

As for the other items mentioned, I've been sicker than a damn dog for the last week and I really need to do some fine tuning on my engine (which only has approx 40 miles on it!) and I was anticipating spending the entire weekend breaking in the engine ( ), but here I sit-sick! My plan is to install a CHT gauge and use it to monitor my engine, and later (once my pocket book recovers from the new 2276 and trans I bought ) buy a Wideband. I also have a VDO oil pressure gauge to install but I haven't had time. I still need to get an oil temp sender and hook my gauge up as well. Any other input would be appreciated. Thanks again.

Andy
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[Unkl Ian]

[miniman82]

Here's where I buy my thermocouples: http://tscsensors.com/egtmp0720000ssnmuffl.html

They have 72" wires, long enough for most apps.
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Build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=212747

[Ian Godfrey]

Another sight to look at for switchable gauges...
http://www.tangerineracing.com/engine.htm#EGT%20and%20CHT%20Instruments

[Tbirdusa]

Anyone used on of these for CHT monitoring?

Stick on High Temperature Type K Thermocouple Probe:
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[miniman82]

[Sigurd]

I would be wary of anything "stick-on", like it's removable/temporary?

[youngnstudly]

So I finally got some gauges for my car but I bought the CHT gauge off Ebay (new in the box) for $140 shipped. It is a Westach quad gauge which means it doesn't have temperature compensation. But hey, it was over half off, plus I found out that Westach is like 5 minutes from my house (go figure!)! I was able to get all of my parts from them, plus I bought an air temp gauge as well, and even got a tour of the entire place (yeah, it was cool! ). So now, a couple more (probably stupid) questions for you guys!

First off, should the thermocouples have any protective housing or (heat shrink type of material) over the braided cable? Second, I was planning to run the 4 thermocouples to the dash through the passenger side roof channel (opposite of what the factory did on the left side of the car with the wiring harness) and I would like to mount the air temp sensor next to the rear window (inside of the roof channel) where I plan to have my cold junctions. I assume (yes I know what it means ) the thermocouples (bare) can't touch each other in the engine compartment?

Is there a better place to have the cold junctions and air temp sensor? I would like to have them out of the engine compartment when mounted, but I still need to be able to disconnect the thermocouples if need be, so I thought I would make a bracket (or use a V-8 plug wire seperator) to hold them in the roof channel, along with the air sensor. Any (better thought out) ideas? Still learning here .

Andy
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[donmurray]

I now understand the Dakota CHT gauge wire from the sensor should not touch, or be close to, other wires. Has anyone experienced bad readings from running the wire with others? Bad numbers that were corrected by routing differently? I've got mine running under the drivers side channel cover with all the other front to back wiring and hate to think I'll get wrong numbers after all that work and expense.
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[Randy in Maine]

Not an issue for me.

[mondshine]

I use Westach gauges in a couple of cars.
In my Beetle, the thermocouple wire (only on #3 for me) runs parallel to the big harness at the top left if the engine compartment.
The cold junction is behind the rear quarter trim panel, above the voltage regulator.
The gauge is calibrated to the 48" thermocouple wire, so you cannot make it shorter; however there is no problem making it longer. Westach sells an extension harness, but you can make your own. 20 gauge wire is plenty adequate. To connect to the thermocouple wires, I prefer the European style terminal strips that look like this:

Radio Shack sells them.
Good luck with your project, Mondshine

[drmiller100]

an electrical voltage is created by the temperature differences between the ends of the wires. One end is near the gauge, the other end is in the cylinder head.

The voltages are VERY small.

However, I believe you can put switches as long as the switches have no resistance, and the switches and the extra wire is at the same temperature as the ends of the thermo-couple wire.

[Randy in Maine]

Of course in real life a single cylinder head temp gauge will do nicely.

No real need to monitor all 4 in a daily driver that I can think of anyway.

[mondshine]

Westach sells the switch, http://www.westach.com/gauge_images/254-4F.jpg
if you really think it's necessary. Monitoring all four might be overkill for a daily driver, as Randy stated.
Good luck, Mondshine