Pyrometer Limits

[slp20045]

I just Installed my new aubers digital pyrometer and was just wondering if anyone new what the safest hi temp should be for a 93 model 7.3 idi

 

[Goofyexponent]

1200*F...max. Any higher for more than a second or so you can crack pistons, burn holes in the pistons. They are the component in the engine with the lowest melting point.

Is your truck a turbo or N/A engine?

 

[fuzzy1626]

Depends on where the probe is mounted also. Pre turbo (manifold)/Post turbo (down pipe)?

 

[lpennock]

Banks says to keep it under 1050 with their sidewinder turbo kit. That is on the hot side of the Turbo. I would try to say below 1100 for a NA.

 

[OLDBULL8]

I would think the hottest and most accurate exhaust temp. would be when the thermocouple is mounted in the exhaust manifold at #8 cyl. #6 and #8 fire consecutively.

 

[MIDNIGHT RIDER]

I would think the hottest and most accurate exhaust temp. would be when the thermocouple is mounted in the exhaust manifold at #8 cyl. #6 and #8 fire consecutively.

Seeing as how these engines will start with only one or two working glow-plugs, and considering what was just stated about cylinder #8, why not replace the #8 glow-plug with a pyrometer probe ??

Aluminum melts at around 1400*, right ??

 

[matt-jenkins]

Just Curious, Lots of cummins guys can get there trucks up past 1400 degrees for short periods of time(as in no more then 10 seconds)
Why is 1200 degrees the magic number in an idi?

 

[LCAM-01XA]

Seeing as how these engines will start with only one or two working glow-plugs, and considering what was just stated about cylinder #8, why not replace the #8 glow-plug with a pyrometer probe ??

That is a very good question - what is the thread of the K-type thermocouple? The glowplugs are 10mm fine pitch IIRC, and they have flares to seal against the heads...

 

[cetanefreek]

Just Curious, Lots of cummins guys can get there trucks up past 1400 degrees for short periods of time(as in no more then 10 seconds)
Why is 1200 degrees the magic number in an idi?

I've buried a 2000* pyro in a cummins before with no ill effects, although that was a purpose-built sled puller, I've also seen D-max's and powerstrokes go just as high with no damage. it's surely not good for things but it can be done, only in short bursts, so yes the melting point of aluminum may be around 1400, but it's not being exposed to that heat continuously, and there is also cooling through the bottom of the piston in the form of oil splash.

I would say part of the reason for the lower EGT guideline in the IDI's is the lack of a piston cooler oil-jet.

 

[fuzzy1626]

I would say part of the reason for the lower EGT guideline in the IDI's is the lack of a piston cooler oil-jet.

I thought they had them.

 

[The Warden]

I thought they had them.

They do have them. Every IDI has oil cooler jets spraying oil onto the bottom of each piston...which IIRC is part of why the oil pump puts out such a high volume of oil at such a low pressure, and also why there's so much oil vapor in the blow-by gases.

I'm honestly not sure why the Cummins and PSD guys can get away with such high temps...maybe the alloy their pistons are made up of can accept a higher temperature? Or maybe they're just playing Russian roulette with their engines and getting lucky? I've always been told that 1200 F (or, more specifically, 1250 F ) was the maximum safe (pre-turbo) temperature for ANY diesel engine, although even on an IDI I think it's "okay" to go a bit higher for a second or two.

Personally, I don't let my pyro get above 1000 to 1100 for more than a couple of seconds....OTOH, my thermocouple's mounted in the up-pipe going into the turbo, so while it's still pre-turbo, the exhaust has had a chance to cool a bit...

 

[1994IDI]

I believe aluminum melts at 1220 degrees. But the pistons are not pure aluminum, so you can probably run it higher. But like Warden said, its kind of russian roulette. It just depends on if you want to take the chance. Seems like the exhaust manifold would be the closest you could get to reading the actual temperature inside the cylinder, which is where you need to know the temperature at. Guys have had good luck with the #8 cylinder, so that is where I put mine, and try to keep it below 1100 just to be on the safe side.

 

[Jake S.]

Cummins are also direct injected. That a is big difference. The heat is in the bore, not in the head. To the OP, 1250 would be the safe limit that we see not to cross, sustained for minutes, I would stay below 1050.

 

[MIDNIGHT RIDER]

That is a very good question - what is the thread of the K-type thermocouple? The glowplugs are 10mm fine pitch IIRC, and they have flares to seal against the heads...

Type "K" thermocouples can be had in 1/8-NPT, 1/4-NPT, and many are designed threadless, to be inserted in a purpose-built threaded adapter to fit whatever.


As for Cummins EGT recommendations, Cummins themselves recommend a continous 1250* ( or was it 1200* ?? ) to be a safe rule of thumb for the B-series engines.

Mine often sees 1300*-plus when cresting a grade with a load.


When I see it is gonna go past 1250*, I drop a gear, increasing RPMs, and the EGTs drop to managable levels.

My probe is located in the manifold where all six come together; just ahead of the turbo.

 

[cetanefreek]

I did not realize the IDI had cooling jets, sorry. like I've said before, I'm new to the 6.9/7.3 world.