Help me with two EGT probes...

[esommer2500]

I tried to search for threads about running both pre and post thermocouples into one gauge with a switch to toggle between the two. I found one thread that was somewhat helpful, but I still have some questions.



1. Where can I get JUST the thermocouple and wire lead?



2. The thread I dug up noted using a DPDT switch. Why so? Couldn't I just get a switch with two leads in and one out to the gauge? Any other important switch considerations?



3. Does anyone know of or have a wiring diagram for this application?



I should be getting my truck back from the body shop in a couple of weeks, they have really made some progress on it. I am planning on moving the gauges from the pillar to the cupholder area, as I feel that they partly contributed to my accident in the pillar location. I am also planning on getting a painless wiring kit from geno's and maybe thowing in some XM and one of Rob T's famous center consoles. I got lots of other stuff to do too, we'll save that for later.



Any information you might have would be greatly appreciated. (On the gauge setup or anything else ) TIA.



Eric

 

[skobylenski]

As far as I know, most of the places that sell pyros sell just the thermocouple and wire sets. I know I've seen them. Can't help you with the rest, but when someone can I'll certainly be listening, as it seems like a good idea to get both readings, don't ask me why, maybe it's because it gives me one more switch



Good luck with you project! Can't wait to see the final outcome.



Scott

 

[y-knot]

What you want to do isn't very difficult or new. I wish you would have said what type gage you plan to run, there are way too many to guess. I monitor both pre and post turbo exhaust gas temperatures, and I choose to run with the Autometer Ultra lite series gages. If you want to use two probes and one gage, you need to get yourself a double pole double throw switch, also known as a DPDB. They are available at most electrical store, Radio Shacks, hardware stores, ect. If you go to a Hardware store, some list them as a 240v, 15 or 20 switch, same thing and just another name.

On the back on the switch, there will be (3) sets of terminals(two top, two middle, two bottom) Take the two wires from probe 1. and attach them too the top two terminals (most probe wiring is red & black, so observe proper polarity, attach all wires the same,IE red the black). Now take the wires from probe 2. and attach them to the bottom terminals, the same way you did the top. Now on the middle two terminal, you will need too attach two wire that go from the switch to the gage. If hooked up like described, when the switch handle is UP-you are seeing probe 2. When it is DOWN-you are on probe 1. If your switch has a center position, that is OFF, no reading.



I have several gages hooked up like this, they are usually items like rear end temp, and trans pressure. Items I have no need to constantly monitor. I went with two probes and two gages on the EGT's. I did want to monitor both, and I wanted instantaneous readings. The extra probe is about 1/2 what the whole thing cost, that might or might not make a difference to you. I just went on and got two full EGT gages, I like watching the two change as load and speed change. I also like observing the difference when the E-brake is on or off. Buy having two same make, model probes and gages, the validity of the results is enhanced, and verifiable. Your switch and one gage will work just fine, but you might want to consider the two gage type install? I find it interesting, but then again I have been told by more then one. I am a strange bird.

 

[esommer2500]

I'm currently running Autometer Ultralite series EGT and boost gauges.



Do you connect the leads from the thermocouples to the switch and then use some other wire to run to the gauge? Or do you cut the two thermocouple leads to the same length and use one of the extra pieces cut off to run to the gauge?



If I understand the EGT correctly, the thermocouple provides a certain voltage compared to the heat registered. Do I need to be concerned with dissimilar metals, etc. in the switch itself? Will the resistance of the switch have any NOTICEABLE effect on the readings? I'm not concerned with anything less than 50* of difference.



I will have to go back and check for prices of what a thermocouple will cost vs. buying an entire new gauge.



Thanks for the help so far, keep it coming if you can!



Eric

 

[y-knot]

Your trying to read way to much into this, you are not inventing something new. Yes the leads from the probes go to the switch, and from the switch to the gage, you will need a couple of short lengths of wire. Just keep the connections tight, and the polarity from all the wires the same . I would not cut the wires from the probes, if you have much extra, just bundle it neatly and tywrap. This set-up will work fine for you, I just thought you may want to view the two EGT gages because they are pretty interesting. It really gives you an appreciation for what is going on in that area. Depending on what you have already done to your truck, you will see how the 4" system influences EGT's, How different plates, boxes, intake air systems affect manifold temperatures(if you switch after the probes a installed). Their is alot of BS on this site, I think many only repeat what they have been told, This arrangement will allow you to verify, and even quantify the benefits on your new engine performance parts. Good luck.

 

[C. Harlan]

Whoa! never cut the excess wire! it is solid state wire, and needs to be left! just coil it up like Y knot said... . I have lots of excess wire, but have it zip tied up in the firewall... also, do not kink it. . roll it gently. . Kinks in solid wire, will eventually break it! keep this in mind. I am about to tackle what you are doing as well. . more gauges!!! arrrggghhhh!!!!!!



-Chris-

 

[esommer2500]

you are not inventing something new.

Wasn't trying to, I know it has been done before. Just trying to pick up what I felt to be relevant information.

I just thought you may want to view the two EGT gages because they are pretty interesting.

I really would like to have two EGT gauges and a bunch of others. College has seemed to put a hampering on my budget, though.

Whoa! never cut the excess wire! it is solid state wire, and needs to be left! just coil it up like Y knot said... . I have lots of excess wire, but have it zip tied up in the firewall... also, do not kink it. . roll it gently. . Kinks in solid wire, will eventually break it!

I didn't cut the wire when I installed the gauge the first time. I know it needs to be a certain length. I just wondered about the connection from the switch to the gauge. Will a 14 or 16 standard wire work for the length from the switch to the gauge?



I apologize if this all seems redundant or scrutinous. I just like to have a feel of what I am getting into. Thanks again.



Eric

 

[y-knot]

It isn't and don't get me wrong, your questions were relevant and I suppose form your perspective appropriate, I probably would have ask something very similar at your age. The 14-16 gage wire will work fine, just use the same type for each lead, and cut them the same length. If I remember right I paid about 120 for the Autometer EGT gages, and I think a probe was 60-70 bucks, so there is a bit of a difference there.

 

[ronco]

I bought my Autometer gauges last year at Geno's. I ordered an extra thermocouple at the time to facilitate what you are doing. I remember only paying sixteen dollars for the extra thermocouple at that time. I did not get the other, long wire needed between the thermocouple and the gauge though. You might try Autometer directly to see what they can do for you!





Ronco

 

[illflem]

The problem that can happen if you use a cheap switch is that some use nickel plated terminals. When copper wire and nickel are connected together they make electricity, your gauges will read too high. The thermocouple (probe) works in exactly the same manner, the copper nickel interface produces more voltage as the temp increases. All the pyro gauge is a voltmeter that measures milli-volts, just a tiny bit of extra voltage will throw the readings off. A quality switch with copper or brass terminals is not unusual and not much more money.

Just don't use a switch that has shiny silver terminals.

 

[esommer2500]

The problem that can happen if you use a cheap switch is that some use nickel plated terminals. When copper wire and nickel are connected together they make electricity, your gauges will read too high. The thermocouple (probe) works in exactly the same manner, the copper nickel interface produces more voltage as the temp increases. All the pyro gauge is a voltmeter that measures milli-volts, just a tiny bit of extra voltage will throw the readings off. A quality switch with copper or brass terminals is not unusual and not much more money.

That's what I was looking for, and remembered hearing from you before, Bill. I just couldn't find it in the search mode. THANKS!



I really would like to just run two EGT gauges, but I am moving the guages to somewhere like the cupholder location, and I don't think there is enough room for three in that spot. Gonna have to check into it.



Thanks again for everyone's input.



Eric

 

[JPereira]

Two guages one probe?

I already have a Autometer pyro on my truck. I am purchasing the TST box with the guages built into it. Has anyone ever ran two guages ooff one probe at the same time? Can I connect up the two guages and just use one probe?



My Autometer I installed pre turbo just outside #3 as it was the easiest to get to. I will probably add another pyro at #6 if i cannot run both the Autometer and TST from the existing pyro probe.



Like the detuning feature on TST if temps get to hot without having to rely on my brain and right foot reacting quick enough.



Thanks, Jeff