Im going to install a EGT gauge. What is a better setup, Pre-turbo or Post.

 

IMO pre-turbo, this post will draw many different views....

 

The concern that some folks have with going pre-turbo is that the probe may become brittle over time, break off and be fed through the turbo and thereby destroy it.

Most commonly the probes are rated for temps far higher than will be seen in a pre turbo installation and the likelyhood of probe breakage is remote. But everyone has their own tolerance for risk taking . . .

The argument for pre turbo installation is that the temperature measured is the actual temperature seen by the turbo and that the response time is very quick.

The argument against post turbo is that depending upon exactly where the probe is installed and what the load condtions are, the measured temperature could be off by several hundred degrees from the actual turbo inlet temperature.

After actually holding the probe in my hand for a bit and considering the probe breakage risk, I ended up going with a pre turbo probe installation because I didn't feel that the risk was high.

 

I installed an EGT on my '02 F350. After speaking with several manufacturers and reading endlessly for weeks I decided to go with the before install. The temp difference between before and after was too great to chance.

 

As PSD60 will attest, you will probably melt your pistons before screwing up your turbo. That is why the exhaust manifold is the best place to put the thermocouple.

 

Absolutely. Even though there are plenty of technical explanations for this, common sense is all that is needed- the pistons are aluminum; the turbocharger turbine is stainless steel. Not even bothering to mention that the piston sees the actual COMBUSTION temperatures, which is even somewhat hotter than the EGT's.

 

Pax. side Exhaust manifold here. Plus it is a whole lot easier to install.

 

Really, at what temp do you think the pistons melt at? After talking with Diesel Dynamics in LV as well as other shops, and, after reading the following at PortaDiesel I made my choice. Here is the text, you decide for yourself


w a t c h i n g y o u r e g t ' s


Exhaust Gas Temperature (EGT) is a good indicator of your engine's performance. Accuracy in Exhaust Gas Temp (EGT) is very important. The turbo doesn't make heat; it absorbs the heat and uses the exhaust pressure. As the exhaust is blown across the turbine blades, the blades spin at incredible speeds. The shaft of the turbine wheel is slaved to the compressor wheel so they spin together. When you spool up the turbine, the compressor turns as well. Generally speaking, the faster it spins, the more boost the turbo will make. The problem comes when you're trying to turn the turbine too fast. To do this, it takes a lot of heat and pressure. If you get the turbine too hot, it can damage the turbo. At 1270 degrees F, the tips of the turbine blades begin to blow. If you get them too hot, they'll straighten out or even melt and you'll ruin the turbo. The factory Garrett turbocharger will pull all day long at 1250 degrees, but in our opinion, 1270 degrees is the DO NOT EXCEED temp for sustained use.

There is contradictory opinion and advice about the best place to install the temperature reading device (thermocouple) that supports the pyrometer, but there is no disagreement that watching EGTs with a graduated gauge is a good thing to do.

EGT's will run about 300 degrees F at idle to 1400+ degrees F under an extreme load (such as merging onto the interstate with 25,000 lbs.) Normal running temps will be between 500 to 900 degrees F. With EGT's at 600 degrees F, the 7.3L engine wis operating at its peak efficiency. Complete combustion is being achieved and converted into usable horsepower and torque as efficiently as possible. Maximum fuel mileage is achieved at this point. Above 600 degrees F the engine gets wasteful with the fuel due to load demands. Below 600 degrees F and you lose efficiency (Power and Torque). So when you're out on the road, pay attention to the gauge. If EGT's start to creep up, simply ease out of the throttle.

Some publications dealing with EGT temps favor Turbocharger Inlet Temp (TIT) and not Turbocharger Outlet Temp (TOT). This suggests that the thermocouple should be mounted Pre-Turbo (in the exhaust manifold) and not Post-turbo. (in the down pipe) In their view, if you choose to mount the thermocouple in the down pipe, EGT readings will be inaccurate. With the thermocouple in the down pipe, the gauge reacts more slowly and is reading the TOT which is lower than the actual temp of the turbocharger. The difference between TIT and TOT can be as little as 50 degrees F to as much as 400 degrees F under a heavy load.

Other experts point out that installing the thermocouple in the exhaust manifold, ahead of the turbo, raises the possibility of the thermocouple breaking loose in the heated air stream and damaging the turbo. With greater accuracy goes greater risk.

One expert gauge manufacturer suggests that mounting the thermocouple in the downpipe and watching for a sustained temperature of 1050 F, is just as good as mounting in the pre-turbo position. Logic would suggest that if the temperature can vary as much as 400 degrees from the input to output side, then the sustained TOT temperature to be watched for under extreme load should be more like 870 F (1270F "straightening" point minus the possible 400 F variation.)

The most convenient installation of the thermocouple for a TIT application is in the lowest point of the driver's side exhaust manifold. The manifold itself is made of a high silicon cast iron and is very easy to drill and tap. There is a place on the manifold that makes for an easy installation and since it's the lowest point of the exhaust manifold, the metal chips are easy to clean out. (Greasing the drill bit to capture and contain any loose metal chips does not seem to help much. Some owners drill with the motor running to blow the metal chips out in real time.)

The best location for installation of the thermocouple for a TOT application is in the downpipe as close to the turbo as possible.

This article is based on our own research through the trade literature, and discussion with gauge manufacturers. You will generally find that neither the manufacturer of the truck, the engine, or the various manufacturers of pyrometers take a public position on where to put the thermocouple. Neither do we. In short, watching your EGT's is highly recommended if you operate under heavy load. And just as in deciding how fast to drive, there is risk and reward in deciding where to place the thermocouple. We hope that the information presented will help you to reach a reasoned conclusion on your own. If you need additional information, you should consult your Ford dealer

 

If you don't believe me, check my gallery. I have 5 melted pistons and a perfectly untouched turbocharger. That says enough for me.

 

YUP you sure have done that...no doubt here.....still amazed you did not do all 8!!!

 

I'm glad I didn't...3 of them got me home

Congratulations on the 10k posts

 

I have yet to hear from anyone who has had a first hand experience with a thermocouple break off and damage the turbo. I have asked repeatedly. All I get is "I know a guy who said .....". Anyone out there have a thermocouple break off and damage their turbo? I have yet to hear from someone first hand tell me they straitened the exhaust blades on a turbo from overheat. Seems to me they would fry the exhaust vanes that direct the exhaust onto the turbine wheels. Haven't heard from anyone yet that has had first hand experience.

The only first hand experience I have heard is from PSD 60L Fx4 who destroyed his pistons and engine before any damage happened to the turbo. That article is interesting but all hearsay and "I talked to this guy..." and "the experts said....".

 

Actually, what happened is reverse, Matt blew up the motor so bad that a piece of piston damaged the thermocouple...as it went fling by…. headed for the tail pipe as fast as it could
Probably moving at o-say-100 MPH as it went by the poor thermocouple


and thanks on the 10k

 

and the piece of piston didn't destroy the turbo? Hmmmm. Maybe you need an EGT to protect the engine?

 

All I can say is I don't need to have cancer first hand to know that smoking can cause it. How do I know that? Because of "hearsay" and "experts" and research tells us so. I listened to several dealership mechanics, several independent mechanics, several parts dealers as well as Gale Banks and PortaDiesel. I hate to quote mere "hearsay" and "the experts" Once again but if you want to dismiss one of the premier "experts" as "hearsay" go ahead. You can read the following from Gale Banks and make your own decision.

What is the best location for the exhaust gas temperature probe on a turbo-diesel?
This question is tougher to answer than you might think. There are two ways to measure exhaust gas temperature on a diesel engine: before the turbo (turbine inlet temperature); and after the turbo (turbine outlet temperature). When reasonably convenient, we recommend measuring the turbine inlet temperature, because this is the hottest—and most meaningful—temperature when evaluating the engine's performance. But when there's not a convenient place to put a probe in the turbine inlet side of the exhaust, the alternative is to mount the probe after the turbocharger, measuring the turbine outlet temperature. But this also presents a problem. The outlet of the turbo on the Duramax engine, for example, is shaped awkwardly, and the factory turbine outlet pipe is a very non-concentric shape to accommodate the outlet, so once again, there is not a good place to install a probe until about two feet after the outlet of the turbo. By going that far downstream, the integrity of the measurement is sacrificed.
Perhaps the best recommendation is to drill and tap a hole in one of the exhaust manifolds, and install a threaded pyrometer probe in there. Just be VERY CAREFUL about not getting any metal chips in the manifold, which would cause damage to the turbocharger. About the only way to be sure of this is to pull the manifold off of the vehicle to do the drilling and tapping.

Can failure of the exhaust gas temperature probe damage the turbocharger?
This is a highly debated issue. Some of the sentiments that surround this question date back quite far. Before diesel engines became widely popular in pickup trucks, the main use for diesels was in the long-haul trucking industry. Years ago, when truckers began to use pyrometers on their engines, the most logical place to position the probe was in the exhaust manifold ahead of the turbocharger, because this was the hottest portion of the exhaust stream. But the earliest probes that were used had exposed junctions, and the weakness of this design would sometimes fatigue and fail under the high heat conditions. A failed probe would inevitably cause expensive damage to the turbocharger. The solution to this problem was to move the thermocouple downstream of the turbocharger, thus avoiding the potential damage to the spinning turbine wheel. Knowing that the temperature would be lower in that location, it was expected that the operator would compensate for the difference by an appropriate amount.

Today, the thermocouple probes that are used are commonly sheathed in a stainless steel shell that is impervious to the type of failure that an exposed junction thermocouple might experience. This makes it safe to install upstream of the turbocharger. At Banks, we typically prefer to mount the thermocouple upstream of the turbo, but this is not always convenient. In the case of the Ford Power Stroke, we opted to provide a bung in the turbine outlet pipe rather than having the customer go through the difficulty of drilling and installing a probe in a location that is hard to access. Our testing shows that the maximum allowable turbine inlet temperature of 1350 degrees is equivalent to 1050 degrees on the turbine outlet side, so that is our recommended maximum temperature when measuring in that location. The temperature differential may be broader at lower temperature ranges, but the temp that we are most concerned about is at full power.