Thread: EGT sensor - upsream or downstream of turbo?

It's a bit of a catch 22 situation of where to install the probe. Before the turbo you know virtually how hot exactly the spent gases are exiting the engine and therefore a better picture of the temp pistons/valves are subjected to, but the downside is the possibility of the probe breaking and falling down into the turbo and destroying it. After the turbo you have not a worry of a probe breaking and causing any damage, the downside is you just don't know the temps especially if they are around the critical area that will cause irrepairable damage, you are guessing(temp drop over turbo is generally considered to be approx. 200C). Momentary high temps you can get away with, but sustained high temps, you will cause damage.
I wonder if the truck manufacturers only install the probes after the turbo for longevity, as these engines are put under a lot of stress, for long periods. I have seen plenty of cases where the turbo lets go and most of the sump oil ends up down the side of the trailer blown out of the exhaust, and they don't want a case of a broken probe causing this.
I have an Autometer gauge and the probe is installed before the turbo (they recommend installing it before the turbo) the probe is a 3mm thick probe, but the 6mm probes are generally considered more robust, but they don't react as quickly with temp changes, mine is virtually instant when you floor it or lift your foot.

Have you come across a probe that's broken? Talk of it is rife on the net but I can't really see it happening. If the temps are hot enough to melt the probe then you'll be needing a new engine and turbo anyway.

I also swapped from a 6mm probe to 3mm to get a faster response. With the 6 I could do a run to 100 km/h and the needle would keep rising well after I'd backed off. I think I might have unwittingly hit 900 deg C a couple of times, but the big probe was too slow to catch the peak.

For curiousities sake I plan to run the 6mm probe downstream to compare measurements with the 3mm upstream.

Originally Posted by Dougal

Have you come across a probe that's broken? Talk of it is rife on the net but I can't really see it happening. If the temps are hot enough to melt the probe then you'll be needing a new engine and turbo anyway.

I also swapped from a 6mm probe to 3mm to get a faster response. With the 6 I could do a run to 100 km/h and the needle would keep rising well after I'd backed off. I think I might have unwittingly hit 900 deg C a couple of times, but the big probe was too slow to catch the peak.

For curiousities sake I plan to run the 6mm probe downstream to compare measurements with the 3mm upstream.

thats what we need more of! facts! there too many mate of a mate stories on forums. this is why i tried both positions.

cheers phil

Originally Posted by Dougal

Have you come across a probe that's broken? Talk of it is rife on the net but I can't really see it happening. If the temps are hot enough to melt the probe then you'll be needing a new engine and turbo anyway.

I also swapped from a 6mm probe to 3mm to get a faster response. With the 6 I could do a run to 100 km/h and the needle would keep rising well after I'd backed off. I think I might have unwittingly hit 900 deg C a couple of times, but the big probe was too slow to catch the peak.

For curiousities sake I plan to run the 6mm probe downstream to compare measurements with the 3mm upstream.

Nope, never ever heard of one that has broken, but I'm not saying it hasn't happened. But that is the "whats the worst thing that can happen if I do this" scenario. I doubt the probe would ever melt, before you reach the critical temp of the probe you wouldn't have an engine left. The probe would possibly fail due to fatigue. I think my probe is rated to 2200F which is about 1200C, don't think the Tdi will get to those temps.
With the 3mm probe I find that even a small lift of the throttle allows me to see the reduction in EGT,almost straight away.

Originally Posted by pawl

Nope, never ever heard of one that has broken, but I'm not saying it hasn't happened. But that is the "whats the worst thing that can happen if I do this" scenario. I doubt the probe would ever melt, before you reach the critical temp of the probe you wouldn't have an engine left. The probe would possibly fail due to fatigue. I think my probe is rated to 2200F which is about 1200C, don't think the Tdi will get to those temps.
With the 3mm probe I find that even a small lift of the throttle allows me to see the reduction in EGT,almost straight away.

same with the td5, just move the throttle and the temps drop almost with the pedal

now that i know what it dose with the trailer on up big constant hills i wont look at it as much.

cheers phil

cheers phil