With so much being said about exhaust tempatures (how high is to high) when Ford or International builds the PSD why is there not a pyro prope in the exhaust manifold that would start cutting back on fuel when it gets to the danger zone They do this with an over rev condition or downshift the transmission from overdrive if fluid temp gets to high and so on. could it be that the companys building gauge sets set the limits any one else have any differnt toughts?

 

You can bet that when the engine was developed, there were plenty of gauges in use. And by using them, they designed a fuel map for the stock program that would stay well on the safe side of maximum under all situations. That is where chip makers come in. They push the envelope closer to those limits, adding more fuel and thereby producing more power. But with many of the chips, it is possible to cook your engine and that is why, when one decides to go for more power, the first money they spend should be for gauges, so that they can regulate those temps by means of their right foot.

 

Carfunkel,

Well said and quite accurate also. More fuel and/or more air equals more heat.

Two things about pyrometers that might be of interest.
1. A pyrometer with the probe or sensor mounted upstream from the turbo is dangerous. Due to the very high temps and constant heating and cooling cycles, the probe can crack and break off and go into the turbo with disasterous results to the turbo nad possibly the engine. As for temperature readings, a sensor mounted upstream will read about 100-degrees hotter than a sensor-probe mounted downstream due to exhaust cooling in the turbo.

2. Pyrometers are a sensitive and notoriously troublesome device. The bi-metalic probe actually generates a tiny electrical current when exposed to heat. The current generated is somewhere in the one-tenth of one volt range at maximum temperature. The guage on the dashboard which is calibrated in degrees of temperature is actually a volt-meter with a scale of about one-tenth of a volt. In a laboratory under careful conditions this can be an accurate instrument. In a vehicle with vibration and constant exposure to oil, water, dirt, etc. is has been less than 100% reliable. You can end up trusting your expensive engine to a fairly in-expensive guage. None of the commercial over-the-road semi tractors sold today come standard with pyrometers anymore. (They can be specified as an option for aprox. $100.00.) Also, the conductivity of the wire between the pryometer is critical. The instructions always say to never cut or shorten the wire. The thermocouple in a household furnace or water heater is quite reliable because there is steady temperature, little vibration, and the valve does not have to differentiate between varying voltages.

It's much easier ,as Carfunkle said, for the manufacturers to design the fuel map for safe temperatures.

BobJonesSpecial

 

There was a thread recently about the possibity of the thermocouple mounted pre turbo breaking off and going through the turbo........no one ever had it happen or knew of anyone that had it happen if I remember correctly.

As far as temp. variance, people with two pyros (one w/ the thermocouple pre turbo and the other post turbo) have reported a 50-450* variance between the two. So, if your thermocouple is post turbo how do you know when 1250* is the safe max temp or 850* is the safe max. temp???.......you really don't.

I'll keep my pyro pre turbo so that I have accurate readings of the temps.........people who do run both say that their post turbo pyro is basically useless.....



Just my $.02

 

To answer DPMPSD's original question.

In a Powerstroke diesel I have never actually heard what the maximum recomended exhaust temps are.

In Heavy duty commercial over-the-road diesel engines the MAXIMUM was generally regarded as about 1100-degrees for a downstream mounted pyrometer probe. (usually mounted about 3-4 inches downwind of the turbo outlet)

You know, instead of calling it an exhaust temperature guage, it would actually be better to call it a piston temperature guage, or better yet, a piston SIZE guage.

Nobody really cares how hot the exhaust is unless you're worried about melting the muffler or something. It's the PISTONS we're worried about. For every degree they get hotter, they get bigger in diameter. When the piston expands to where there is no longer room for oil between it and the cylinder it scrapes metal to metal and severly damages both the piston and cylinder. It is also possible to melt or burn a hole in the top of a piston from excessive combustion chamber temperature. This is what we are trying to prevent by using a pyrometer.

The exhaust temperature maximum for a Powerstroke may well be less than for a HD commercial engine. It depends on what type of piston cooling devices are designed into the engine and other factors such as piston alloy and manufacturing clearances.

I would check with the pyrometer supplier for an actual temperature maximum relative to their installation.

BobJonesSpecial

 

In a PSD 1300* is the max. safe temp pre turbo.......or 1250* if you want to be on the safe side.

 

You will notice that absolutley NO commercial over-the-road diesel engines sold in the last 10 to 15 years have the pyrometer probe mounted upstream from the turbo. They are all downstream about 2 to 3-inches. 1100-degrees is considered the maximum safe limit.
I have talked to many drivers of "stock" commercial HD engines, and they report that no matter how hard they push it or how hot the day, they can't get the pyro over about 900-degrees. This shows the care and degree of saftey built in by the manufacturers.

Since fuel economy and long engine life are of such importance in commercial over-the-road trucking, there is much less talk of modifying diesel engines than there used to be.
Also, the electronics supplied by the manufacturer are getting quite sophisticated and difficult to modify. The computer on most current HD diesels actually keeps a permant record of all operating parameters. This can be downloaded in case of warranty claims. By the way. The warranty on new OTR engines is 5-years, 500,000 miles.

BobJonesSpecial

 

i am going chip my truck but i want to make sure i do it right so i dont tear it up .i am putting a pyrometer in i dont know rather to put it in pre turbo or not and max exhaust temps.

 

Most everyone here will agree go pre trubo and the max temp 1250. So far I haven't heard or read anything about the probe breaking off. It is possible, but fairly unlikely. Mine is pre turbo.

 

Mine is pre-turbo and so far so good. My truck is also bone stock and when towing up hill in the summer (9K pound trailer) I see 1250 pretty quickly. I would never know it were it not for the gauge. So don't let anyone tell you a stock engine's EGT's can't get too hot.

Frank

 

This is all hogwash. Yes a bone stock motor can easily burn itself up, even with all the cooling I have added to my truck, in the stock setting while towing my 5er I can hit 1250 quickly and easily if not watching my temps.

As for pre-turbo and post turbo, I have both. There is a huge diference betweenthe two, depending on speed, and load on the motor. The variances I have seen in my own personal truck are between 0and 400 degrees. Pre turbo is much more accurate and also real time monitoring. everyone should use the preturbo location if wanting the most accuraute readings.

As for the thermocouple cracking and breaking off. Old wives tail. I challenge anyone to give me hrdened proof of such an accurance. No I do not want to here a buddy of mine or a guy knew or my uncles cousins dog with a wooden leg who once.... I want first hand experience.

Gale Banks, who has forgotten more about diesel motors and EGT's vs cooling, then anyone of use will ever know, states that for the 7.3l 1270 degrees is the maximum safe number the EGT's should reach with a pre-turbo mounted thermocouple. I will take that to the bank. For me I keep her below 1150, just to be on the safe side. Good luck all

 

After working with thermocouples for over 25 years, exposed to constant 2500º+ F, I have a tendency to go with Fire Rooster on this one. I had no problem installing my pyro pre-turbo after examining the probe that came with my AutoMeter guage. It is designed quite differently than the ones you will find in your average 'household appliance'. Thermocouples can change voltage output after many years of service, but it will most likely outlive the dash guage many times over.

 

not quite sure how it could break off and go through the engine???? if mounted pre turbo the worst case would be it broke off and went through the EXHAUST side of the turbo no way it can get inside the engine unless it started sucking through exhaust and exhaust through intake "running backwards" in that case a broken pyro probe would be the least of your worries