Thermocouple mounting location?

[BigGunZ]

From what I can tell, lots of folks are mounting the thermocouple for the pyro pre-turbo. I saw in another thread (an e-mail from Cummins) that pre-turbo install can lead to turbo failure if the thermocouple fails (comes apart). My questions are...



What are the advantages of pre-turbo install and do those advantages outweigh the possibility of a probe being eaten by the turbo if it fails?



If mounted post-turbo, can boxes such as the Edge etc. be adjusted to allow and compensate for either pre or post turbo install?

 

[JonathanBurk]

I wrestled with your same question a short time ago, and I'm the one that posted the Cummins email I believe you're referring to.



In brief:



"Why do most recommend pre-turbo measuring?"



Pre-turbo is a more accurate temp. If you mount it post turbo you're going to have to just guesstimate by mentally reducing the temp a couple hundred degrees.

Example:

Pre-turbo pyrometers you want to keep it at 1100-1250 as a ceiling, but post-turbo you're going to have to shut it down earlier than that because you're not getting as hot a reading.



"Is there a product to correct the difference?"



I don't know of any products that will take the guess work out for you. Seems like then they could be liable if their guess doesn't work, because even a device isn't going to know the temp where it should be.



"What if the thermocouple breaks and goes into the turbo as Cummins said?"



They pretty much have to put that as a disclaimer. Get yourself a good reputable gauge & thermocouple from like Diprocol or ISSPro, etc. and their thermocouples are usually rated to like 2500 degrees+. Before your engine gets that hot you're gonna have a lot more damage than a thermocouple going into your turbo.



Just make sure you properly use the gauge to shut everything down. Close to 300 as possible to turn off the engine, and let it warm up for 30 seconds or so before taking off.



Someone correct me if any of this is wrong... I'm new to diesel myself and have been researching like a mad man these past couple of weeks.

 

[BigGunZ]

I've found an answer to this question on the Banks site... .



We might mention that some mechanics fear installing the pyrometer thermocouple in the exhaust manifold for fear the probe will break or burn off and blow into the turbocharger. Such a piece of foreign material entering the turbine would cause serious damage that could in turn break the compressor wheel of the turbo, sending broken pieces into the intake system of the engine where even more damage could occur. While the above scenario is scary, it is also unlikely. Today’s quality pyrometers feature thermocouples that are sheathed in stainless steel to prevent just such an occurrence. It is exceedingly rare to find a diesel mechanic that can honestly say he’s ever seen a thermocouple that has failed and fallen into the turbo on a diesel pickup or motorhome. It just doesn’t happen with a good pyrometer.

 

[BigGunZ]

As far as which location is better... .



"Whether the pyrometer thermocouple is mounted before or after the turbine is usually a matter of finding a suitable mounting location, or of convenience. It should be noted that when the EGT is measured after the turbine, the turbine outlet temperature at full throttle or under a heavy load typically would be 200º to 300º F. lower than the EGT measured in the exhaust manifold. The temperature drop after the turbo indicates the amount of heat energy in the total exhaust gas flow that was used to drive the turbocharger. The temperature drop through the turbine is also related to the total flow and speed of the flow through the turbo. At part throttle, under light load, such as cruise conditions, the turbine outlet EGT may be as much as 500º F. lower than the turbine inlet temperature, but the total exhaust flow is much less than at full throttle. At high turbine speeds (under heavy load) the exhaust gases simply don’t have time to give up as much heat energy as they speed through the turbine. This variance is why installation of the thermocouple in the exhaust manifold is considered more accurate. The EGTs discussed in the remainder of this article will all be turbine inlet temperatures. "