Verify EGT Temps???

[Barry]

Friday I replaced my US Gear guages with a new set of Isspro EVs. I am satisfied that my boost is the same but my EGT guage is far higher than my other guage. Almost to the point that I have a heat problem. ( which I know I don't)



How do you VERIFY EGT. Temps?????

 

[Gary - K7GLD]

That can be pretty tough without a known calibrated temperature source up above 1000 degrees...

 

[johnrv4]

I've noticed the same thing with other trucks

I've had VDO Vision series gauges in '98 and my '01, and my EGT's are always lower than my friend's trucks that have the same mods and Isspro gauges. I know that one of them is not accurate, but I haven't figured out which ones are off. I'm thinking about putting Isspro EV's in my '97, and I'll do a comparison(if I can) with the VDO gauges and try to figure it out.

 

[RustyJC]

Barry,



Here's a handy reference for output voltage of a Type K thermocouple versus temperature (reference junctions @ 32 degF):



70 degF = 0. 843mV

100 degF = 1. 521mV

150 degF = 2. 667mV

200 degF = 3. 820mV

250 degF = 4. 965mV

300 degF = 6. 094mV

350 degF = 7. 207mV

400 degF = 8. 316mV

450 degF = 9. 432mV

500 degF = 10. 561mV

550 degF = 11. 703mV

600 degF = 12. 855mV

650 degF = 14. 014mV

700 degF = 15. 179mV

750 degF = 16. 350mV

800 degF = 17. 526mV

850 degF = 18. 705mV

900 degF = 19. 887mV

950 degF = 21. 071mV

1000 degF = 22. 255mV

1050 degF = 23. 439mV

1100 degF = 24. 622mV

1150 degF = 25. 802mV

1200 degF = 26. 978mV

1250 degF = 28. 149mV

1300 degF = 29. 315mV

1350 degF = 30. 475mV

1400 degF = 31. 628mV

1450 degF = 32. 774mV

1500 degF = 33. 912mV

1550 degF = 35. 043mV

1600 degF = 36. 166mV



If you have a DC millivolt power supply, you could pick a temperature and input that voltage into your gauge as if it were coming from the thermocouple. You should then get the appropriate reading on the gauge. If you don't have a power supply but do have a good digital voltmeter, you can use this table to convert the voltmeter reading to thermocouple junction tip temperature for a given condition and then compare that to the gauge reading at the same condition.



Rusty

 

[illflem]

Simple way to do a comparison of two pyros is to just remove the t-couple and hold the probe in a candle flame. The yellow part of the flame is generally 885°F. You may not get this exact number due to factors such as elevation, any wind, type of wax, etc. but you will be able to compare one gauge to another. You can also set the probe on a bare light bulb to do much the same.

 

[Barry]

This is going down hill fast... ... ..... The tech at Isspro has been very helpful. He faxed me a bulletin they had that gave instructions as to how to adjust the "gain" in the amplifier. So when you are all done, and the needle does what YOU want it to, how do you know it is accurate??????????????? I don't know about yours, but my pyro is more than window dressing.

 

[Wheaties]

I think illflem has the right idea. You need to calibrate the thermocouple-amplifier-gauge as a whole against some reference standard, preferably something that is well in the range of EGT's you'll expect. Using two reference points well apart is even better.



RustyJC is also right, and that's a very handy chart I'm going to cut and paste for my own reference, but it only addresses the gauge's response to the thermocouple. You may need to find out if the thermocouple is putting out the right voltage at a given temp.



Matt

 

[RustyJC]

Originally posted by Wheaties

RustyJC is also right, and that's a very handy chart I'm going to cut and paste for my own reference, but it only addresses the gauge's response to the thermocouple. You may need to find out if the thermocouple is putting out the right voltage at a given temp.

Matt,



Since a Type K thermocouple generates its output voltage from the junction of two dissimilar metals (chromel and alumel), they tend to either work or not - there's very little to go wrong with them. They will either go open (a lead or the junction will break) or the two wires will short together somewhere along the lead (in which case you will read the temperature at the point of the short). If you still have doubts, you could check the output voltage on the bench at room temperature with a digital voltmeter - the voltage should read about 0. 843 millivolts. Then immerse it in boiling water - the voltage should read about 4. 0948 millivolts.



Rusty

 

[Wheaties]

Thanks Rusty,



I suspected that was true of k types, but I'm no expert on the subject. This would mean that a k-type will always behave predictably regardless of make over its entire life. Other types of transducers may not be so consistent You've also answered another question I had, and that's that they generate a voltage and are not a resistive (if that's a word) transducer.



I have SPA gauges, which I love, but have always felt the EGT may be reading a bit low. I just don't seem to make the temps that everyone expects. I have also been told that it isn't a good idea to remove the thermocouple once it's installed. Is this true?



Thanks for the info

Matt

 

[HoleshotHolset]

MTE: Don't tell me that we have to remove your exhaust manifold at a wrench day.....



Makes you wonder why your EGT's have always been sorta low... .



Even if you're off a few hundred degrees - most people look at the gauge and say: "Whoa Nelly! - It's gettin' hot in here!!" :-laf



I doubt any of the old farts will enjoy that reference like us youngin's.....



MTY

 

[Wheaties]

Sorry MTY , but I can't afford the ATS manifold at this time. It will have to wait till Muncie... . how about 4AM on Sunday night?



I don't know, maybe the pedal doesn' t go all the way to the floor like on other trucks. Maybe it's timing. Maybe the amplifier on the k-couple is in need of adjustment. Mr Leonard pointed one of those hi-tech infrared (?) temp/radar detectors at my manifold and it was within tens of degrees of the gauge. I just have to wonder... .

 

[LSMITH]

Brandon once suggested the best way to handle EGT's if one is not towing. He said to put a piece of tape on the gauge face that reads 1000* and call it good... .....

 

[Wheaties]

LSmith,



That works for me! But what do you do when they read lower than you have a right to expect?

 

[LSMITH]

If towing I would try to do some of the testing Rusty suggested, the man knows his business or swap gauges with a buddy for a week or two, not too hard to do.

 

[HoleshotHolset]

MTE: I will never forget our friend Joe's late night / early morning manifold swap.



MTY