Taking the temp.........

[chrisexv6]

I was surfing around Rayteks site this morning and stumbled on a chart listing different emissivity values of metals.

Now putting 2 and 2 together, I figured that when we measure down the glow plug hole of our engines (in my case the TRX 2.5), we are aiming at an area that includes (at least a little) aluminum.

Checking the emissivity value of aluminum (in the range that Raytek suggests for their mini-temp guns), its a whopping .1. Whereas the temp guns are set and calibrated at .95.

So, is there a hole in my theory that says measuring this way is not correct? Granted, if we aim directly at the glow plug (which is probably steel, right?) the emissivity is correct. But on the other hand, would aiming directly at the glow plug give a false high measurement, because after all the purpose of the glow plug is to STORE heat?

I'm confused.........I was going to return my Radio Shack temp gun and get another one (cheaper, off Ebay), but if its not going to be really accurate, whats the point?

All of this came about because for some reason my temp gauge reads REALLY high but my truck shows zero signs of overheating.

For reference, the emissivity chart is located here

Thanks!!
-Chris

 

[FastEddy]

The use of a temp gun is only to aid in the tuning process. It will give you a reference point to help you find a sweet-spot that isn't dangers for your mill.

You are absolutely correct in your thinking. If you have an accurate Quality gun you will see around 10-20 degrees difference in the head temps. your measurements should be taken at the plug, on the exhaust side of the plug and opposite the the exhaust side.
Doing this will give you an idea of the heat range you are in.

I will look for temps around 10-12 degrees cooler than my target temp before fine tuning. Once tuned to the sweet spot I will take the temp on the plug. Remember the plug retains the heat longer than the aluminum head. When you pull in to take a measurement the head has had a chance to cool off a bit so the plug will give me a more accurate reading. I like to add 5 degrees to my highest temp to be on the safe side.

If you try to bring the temps to the high limit when tuning you are looking for trouble. Running a sustained temp at the limit leaves no room for temps to spike while making a WOT blast. In fact thats what will hurt your mill.

The use of a heat gun is only to aid in tuning and to confirm you are in the proper range.

Its good to see someone that thinks about what they are doing and questioning what they don't understand.

-Ed

 

[chrisexv6]

Thanks for the info!!!

After an (almost complete) teardown of my engine, and re-sealing and loctite-ing of every screw that came off, my mill seems to be running better. After a couple WOT passes (with a half tank of fuel left) I was at about 250-260. Although, after a couple WOT passes with less than 1/4 tank those temps spiked up to 300 or so.

I guess Ill run her a little richer to try and keep those low-fuel situation temps down lower.

Thanks for the response!! The first thing I thought of when I got the temp gun was "great, now I got one..........but where do I aim it...........and everyone else out there, are they aiming at the same place?" And when using it I noticed major differences depending on how far off the top of the head I was (even 1/4" made a difference), or even what angle I had it at when I was rested right on top of the head. That was my clue that temp can't be the only tuning method, because it seems to be very imperfect depending on who is doing the measuring.

I'm glad to see a board like this where people actually applaud others thinking out loud and questioning things. Certain other boards (who will remain nameleSS <hint hint>) dont seem to give off such a good vibe.

Thanks again!!!
-Chris

 

[FastEddy]

All temp. guns have different specs. The farther away from the target you are the larger the sweet-spot is that will be measured. Consult the manufacturer of your gun to see what the measurement diameter is for different distances. Some of the less expensive units will measure a spot as large as a dime from just 1-2 inches from the source. others will read a spot 1-2 mm from feet. Knowing your gun will help give you a better idea of the readings you are getting.

On mine I can hold it about an inch from the top of the head and get a 2 mm spot for more accurate readings and if I hold it 8-10 inches away I will get an average reading of the head and plug 6-8 mm.

Know your tools and how to use them.

 

[Banshee]

i dont think this is too off topic and i didnt want to start a new thread so here is my question (maybe someone will see it)

i have a traxxas temp gauge and I'm not quite sure where to put it to read the temp. it is very similar to the MIP onboard temp gauge. it looks to me like you wrap the end around the engine somewhere and i tried in between 2 cooling fins but it doesn't fit. if someone reads this, let me know how to use this temp gauge correctly.