Using a Temp Gun as diagnostic tool

[Mr. P.]

Where can I (we) learn more about using a temp gun this way, as a diagnostic tool?

Mr. P.

[banjo]

You can use it on the headers to find which one is cold. This indicates the cylinder is not firing, or down on performance.

Handy tool to quickly track a bad cylinder down.

[Mr. P.]

Can you use a temp gun on a dyno to verify cylinder-to-cylinder fuel distribution problems??? If so how much variance should one expect to see between exhaust port temps? +- 20 degrees? +- 200 degrees?

[k-star]

I check the tube temps on every engine that I run on my stand. I mark the same distance out from the flange on every tube. I use 1”, no reason that’s just the distance I came up with.

I have not spent a lot of R&D time to figure out what it all means. I do know that any engine family with a dual plane intake will very way more then with a single plane intake. I have had some small Chevys with a 175 deg difference with a performer intake on them.

I also just shot my first set of coated headers and the numbers were way low.

If you want to see something amazing, watch the temps with retarded timing…

Keith

[cpmotors]

If you want to see something amazing, watch the temps with retarded timing…

Keith

Slightly off topic-
Buddy of mine lives across from a body shop. Guy has him build a '69 Yenko Camaro clone. Has local engine shop build a 540.(their first) The owner and body man get it started on their own. I stopped over a few days later to check in. Asked how it ran, little rough they say. Started looking it over closer, motor has stock chrome V/Covers with loom mounts. Loom mounts are almost completely melted on top of V/C's! I says looks like it got a little hot. The owner replies the headers were glowing red on break-in!! I checked the timing for them, was way retarded. They had to replace most of the pistons a month later.

[Mr. P.]

OK so here's a hypothetical for you -

Gen-III LS motors: in trucks we have lots of failures of the #7 piston, and nobody can really explain why. So, if on the dyno I can measure the header primary on that cylinder and compare to the others and lets say (I suspect) that it is running hotter than the others, does that mean I can fatten-up the #7 injector with one that flows like 5% more fuel to richen that cylinder and even-out the cylinder-to-cylinder fueling? I don't want to risk #7 detonation like all my friends and colleagues have, we've lost many motors this way and it's thought because of manifolding that the #7 hole gets more air than the rest...

Mr. P.

[David Redszus]

InfraRed temperature measurement is very useful for many applications but some limitations do apply.

The IR temperature measurement relies on the emissivity of the material.
A dull black surface (called a black body) has a higher E value than a chrome or polished surface. A rubber tire has a value of 1.0 while polished aluminum has a value of .07. The readings will not be the same even if the targets are the same temperature.

To measure header wall temperature, it is a good idea to paint a black target spot on the header using high temperature paint. This will increase the accuracy of the IR measurement since the E value will be the same for each header pipe.

Exhaust gas measurement using wall temperatures is very inaccurate since the headers can have nodes where standing waves will induce local hot spots that have nothing to do with gas temperatures.

It can be used to measure inlet runner, carb, and underhood temps.

[MadBill]

To David's point, check out any set of chromed headers that have been run hard. As expected, they will be purple right at the head, but usually in other locations too, e.g. start of collectors, outside of tight bends, etc...

An alternative to an IR gun is heat-sensitive paints, e.g.: http://www.bjwe.com/tempil/0tempil.htm. A stripe of the right grade (available up to 2,000° F.) in matched locations on each tube will give decently accurate down-the-track temps for modest cost.

[Simonracing]

I've used mine for 7 years now to dianose tuning problems while working on individual runner intake engines.

From setting idle mixture, tracking down a clogged idle jet or bent throttle blade, to performing before and after load carb sync check, to be sure heat induced throttle linkage hysterysis is minimal. Then dumb-as-a-post simple stuff like "which one of these rascal holes isn't hitting" without burning my hand on the header tube or banging my elbow against the body work after pulling a plug boot and getting shocked <tell me you've never done that...>

I don't like tuning without one

[xanadu]

Possible Hi-Jack but in the interest of the question. I used my heat gun
on a set of Ceramic coated Headers (V8 after 10-15min warm up) and
found the LH side to be 175F on all pipes 2in from flange and the RH side to be 205F. Using a single plain with 750. Could the ceramic coating cause a variance in readings? As in one side being coated or polished up different? Engine has just been run in on the dyno. Have used a wideband AFR on each collector and both read as identical as one would expect.

[PhiloM5]

Question for Simon Racing.

You say you use the IR temp tool to set the idle on ITB setups. I have ITBs on an early model M5 and in the past used a vacuum gauge to set the idle bypass. But on ITBs, as you probably know, the vacuum gauge method is not that great because of cylinder pulses at low rpms. And measurement by vacuum doesn't address cylinder efficiency.

So if i use the IR method at the header, in-line six, if I find a high or low number shown I increase air bypass or decrease bypass ? My guess is if a cylinder is hot I would decrease the idle air bypass to fatten up that one cylinder. But not sure.

Thanks for the help.

Phil
_________
88 M5

[af2]

You are trying to get a # with a IR gun off a round tube??

[mike walsh]

Kind of a different use, I shoot exhaust manifolds on diesels alot to prove out to customers that my valve job isn't their problem, then explain that the cold cyl. is not cooking(no fuel) due to a bad injector. Did that today in fact! Boy does it piss them off!

My question??? Are you guys checking temps at idle?
I have always checked them at 2000ish during engine break in(cam) watching for any temp. spikes, or dead holes, and I also watch water temp with the I.R. gun.

[uncle paul]

Last week I had to go on a service call for work and to trouble shoot the job we rented a Flir Thermal Imaging camera. So the other night we had a BBC on the dyno and I took some pics.
The Flix camera I had works great but they are not cheap. We rented from here.
http://www.globaltestsupply.com/

[ijames]

To add a little to what Dave said about emissivity, the E of masking tape is very close to what they calibrate the guns to (I think most assume E=.9) so put a little piece of tape on the surface you want to measure and check it there. Of course it won't stand up to headers, sigh . Even if a coating changes the actual reading you can still compare from one pipe to another to see if they are they same, so it is still useful. An IR gun is also useful to check if a catalytic converter is working or not - take a warm up drive and then check the pipe temp in and out of the cat, if it is working right the outlet temp should be at least 100F higher than the inlet.