Pyrometer Placement
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Senior User
Joined: Oct 2002
Posts: 320
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From: outside of HoustonTX
Pyrometer Placement
I've seen people on here recommend putting the pyrometer probe before the turbo since this will be the hottest exhaust in the system. But since the purpose is to protect the oil in the turbo bearings, wouldn't it be better to place the probe after the turbo to insure that the turbo itself had cooled down to a safe level instead of just the gas going to the turbo? It seems to me that chunk of spinning metal would be a good thermal well that wouldn't cool off nearly as fast as the exhaust gas. Or is the difference negligble?
Elder User
Joined: Aug 2002
Posts: 772
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From: Salem USA
Pyrometer Placement
[updated:LAST EDITED ON 22-Nov-02 AT 12:54 PM (EST)]I've heard both answers:
Pre-turbo - hottest gasses
Post turbo - add 200 degrees to the reading, most have been worried about what would happen if the probe melted and got sent through the turbo, so they go post. But if they are adding 200 degrees then what they seem to be after is the pre-turbo temps.
Haven't heard of this happening, I'll probably mount mine pre-turbo.
Pre-turbo - hottest gasses
Post turbo - add 200 degrees to the reading, most have been worried about what would happen if the probe melted and got sent through the turbo, so they go post. But if they are adding 200 degrees then what they seem to be after is the pre-turbo temps.
Haven't heard of this happening, I'll probably mount mine pre-turbo.
Posting Guru
Joined: May 2001
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Pyrometer Placement
A pyro is not only to protect the turbo bearings but to keep from melting pistons, valves etc. Pre turbo is where you want to be. 1250*F is the max you want to run at and you don't want to shutdown until 300*F or less to protect the turbo bearings.
Les
Les
Posting Guru
Joined: Dec 2000
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From: Western Colorado USA
Pyrometer Placement
I have seen 2 probes go bad and melt/break off, fortunately they were both installed post turbo. I prefer post turbo for that very reason, a probe through the turbo is a guaranteed catastrophic turbo failure.
Elder User
Joined: Aug 2002
Posts: 656
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From: South of you
Pyrometer Placement
On the BIG diesels, the pyro is mounted post turbo. They then measure true exhaust gas temps. Don't know if the PSD is different, but the BIG engines is where my expertise lies.
Post Fiend
Joined: Jan 1997
Posts: 23,165
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From: Enjoying the real world.
Pyrometer Placement
For a post turbo, any pyro will do. For a pre-turbo use a competition class pyro as it can withstand higher temps and will not have the probe melt off. The best, IMHO, is both pre and post. This tells you how much the turbo is absorbing.
Posting Guru
Joined: Dec 2000
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From: Western Colorado USA
Pyrometer Placement
Isn't 2 pyros getting a little carried away though? Most of the time the main function of it is to let the driver know of any internal engine problems that are creating extra heat and to get it fixed before more damage is done. A good example is when an injector starts dumping extra fuel, this will show as higher than usual temps.
If the fuel has been turned up, then it's usefull to keep track of the exhaust temps while doing any hard pulling. I have read many post both here and on other sites where people swear that any temp over 800 post turbo is certain doom for the engine with any other opinions resulting in a flame war, hence I no longer state how high I let mine run. I will say that if I don't run it hard once in awhile, the exhaust will start to become higher pitched. After a hard run, it drops back down to a lower pitched tone. I am not sure why, probably the results of the turbo starting to cake with carbon.
If Cat is willing to warranty an engine for 500K with a pyrometer mounted post turbo, that's good enough for me.
If the fuel has been turned up, then it's usefull to keep track of the exhaust temps while doing any hard pulling. I have read many post both here and on other sites where people swear that any temp over 800 post turbo is certain doom for the engine with any other opinions resulting in a flame war, hence I no longer state how high I let mine run. I will say that if I don't run it hard once in awhile, the exhaust will start to become higher pitched. After a hard run, it drops back down to a lower pitched tone. I am not sure why, probably the results of the turbo starting to cake with carbon.
If Cat is willing to warranty an engine for 500K with a pyrometer mounted post turbo, that's good enough for me.
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Elder User
Joined: Aug 2002
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From: Salem USA
Pyrometer Placement
So for those of you with post-turbo mounted probes are you adding 200 degrees to the gauge reading?
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