300Tdi Fueling and EGTs

RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
javelinadave said:
Ben,
Your location is perfect but the probe may not be long enough. The tip needs to be mid stream. This is what I install in 300Tdi motors and is 100% compatible with VDO gauges.
https://www.auberins.com/index.php?main_page=product_info&cPath=5_22&products_id=145

EGTL1.jpg
Click to expand...


How did you connect the wires to the gauge? I'm wondering how we know the gauge is telling us the right temp without any kind of baseline to calibrate from, and whether or not the wire length has anything to do with the readings. My wire has about 8 feet coiled up behind the dash.
 
RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Can you provide a pic of how that bent probe goes in? I’m not seeing how it can be locked into the fitting at the blanking plate. Mine has a threaded cap on the probe. This doesn’t look like it could work with what I have and know of.

...I hope it’s just the challenge of doing these simple jobs through the internet, but this truck sure makes me feel stupid.
 
R

Red90

Well-known member
RBBailey said:
I'm wondering how we know the gauge is telling us the right temp without any kind of baseline to calibrate from, and whether or not the wire length has anything to do with the readings.
Click to expand...

They are thermocouples. The voltage produced tells the temperature. No calibration is required. Wire length does not matter. The only thing you want to avoid is wiring junctions that are not near the meter unless you are using specific thermocouple wire and junctions.

For the sensor, all you need to do is drill and tap a plate and thread in a compression fitting. There is no need for a bulky welded on coupling.

The one from Auberins above is a regular 3/16" type K thermocouple. Get the 1/8" NPT stainless compression fitting. Drill and tap a plate to 1/8" NPT. Screw in the fitting. Insert the thermocouple to the correct depth and bend as needed to get to the center of the gas flow.
 
RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
OK.... the problem I think I might actually have is this. See if this makes sense:

The fitting/adaptor to the blanking plate is threaded at something like M12-1, or 1/2 fine thread. The problem is, the thread in the blanking plate is either one of those threads as well. It seems to be one of those situations where the bolt fits the threads “almost” correctly enough to allow you to turn it in a thread or two, but then it starts binding. The two are mismatched. This caused the relatively soft metal on the blanking plate to give way to the hard stainless steel of the fitting. So now I have a blanking plate that is screwed up.
 
RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
The big end of the adapter that goes into the blank plate is M13.5-1, or .53 inches with a fine thread.

The small end that the probe screws down on is 10.9mm with a thread width that looks like it is 0.8mm, or .42 inches with a fine thread.
 
Napalm00

Napalm00

Technical Excellence Contributor
Buy a brass/steel npt pipe bushing at the hardware store for one size larger.

Tap the adapter plate for the correct size and tap the inner bushing for the new probe.

Will probably cost about $5


71zndF7LdUL._SL1204_.jpg
 
RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Ah, see, I really am stupid. I thought a measurement had to do with the diameter. Not in this case, I see....

Getting an NPT tap might at least allow me to reinstall as-is. However, it doesn't solve the problem of having the probe long enough.
 
RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Sorry to keep bugging, but I have some more questions that I'm having a hard time finding the answers to on my own.

  1. What temps should I really, actually see on the EGT at cold idle? For reference, I see none, ever, not till I start to drive. And even after a full drive at full temps it will eventually cool to about 250 degrees.
  2. How do we know that our VDO gauge is properly calibrated?
  3. Do we have any kind of consensus on the idea of mixing/matching/shortening the wire leads from the sensor to the gauge?
  4. How do I make the longer EGT probe work with the current blanking plate I have (assuming I can fix it when I get home on Tuesday and find the tap in the mail from Amazon)? I'm ignorant of how it will fix into place compared to how the one I currently have is fixed.
 
Napalm00

Napalm00

Technical Excellence Contributor
1. 0 is where I'm at cold idle , after driving will be anywhere from 200-400 depending on how hot the engine is. My exhaust also sheds heat Much faster than normal.
2. Factory calibrated, nothing to do here
3. You can shorten them but should use like metal terminals in perfect world. I didn't , it works just fine.
4. The new probe should come with a new compression fitting , remove old and put in the new one, nothing special
 
RBBailey

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
For #4: I'm trying to picture how it works, for too long have I simply bought parts only to realize they don't work the way I figured, or won't work at all -- is there a copper sleeve that compresses as you tighten? Is it then adjustable as to exactly how much of the probe you want in or out? Does this mean I will just use the 1/4 NPT I currently have?

For #2: If they are calibrated at the factory, wouldn't changing the probe, and the length (overall resistance) of the wire throw off that calibration?

Originally, I bought the kit because I knew that was the simplest way to have it all together from one end to the other -- Ha!


By the way, I measured the set up as I have it now (accounting for being able to actually thread the fitting into the bung) I only have about <1/2" of the probe clearing the back of the blanking plate.
 
Napalm00

Napalm00

Technical Excellence Contributor
#2 no it's fine , works fine, the probe isn't specific to the gauge

#4 don't know what you are getting the vdo probe tightens on a collet. Just screw in the new one
 
R

Red90

Well-known member
All thermocouples of the same type will give the same reading. Wire length does not matter. It is pretty much idiot proof.

With the new probe get a new 1/4? npt compression fitting. Throw the old stuff out.

Have a beer. Stop worrying about everything.
 
AdamSanta85

AdamSanta85

Well-known member
Uncle Douglas said:
My recollection is that the VDO thermocouple gauge combo kit specifically says not to cut the wires/change the length as it will change the resistance and throw the gauge off. I have a good sized coil of excess wire behind a couple of my tdi dash's for that reason.

Note on page 19-6

https://www.vdo-gauges.com/media/in...ckpit Int'l & Vision Pyrometer Data Sheet.pdf
Click to expand...

Yep. I found this out after I cut the wire from the side that connects to gauge. It's working but I don't really know if its correct. Meh
 
R

Red90

Well-known member
AdamSanta85 said:
Yep. I found this out after I cut the wire from the side that connects to gauge. It's working but I don't really know if its correct. Meh
Click to expand...

Cutting the wire will make zero difference. I've installed and setup a thousand thermocouples. At no point is the wire length considered. There are details to worry about if you need decimal place accuracy, but that has nothing to do with this application. It is pretty much idiot proof. You will read within a few degrees 100% of the time.
 
AdamSanta85

AdamSanta85

Well-known member
Red90 said:
Cutting the wire will make zero difference. I've installed and setup a thousand thermocouples. At no point is the wire length considered. There are details to worry about if you need decimal place accuracy, but that has nothing to do with this application. It is pretty much idiot proof. You will read within a few degrees 100% of the time.
Click to expand...

Fair enough. That being VDO says specifically not to.
 
Napalm00

Napalm00

Technical Excellence Contributor
They definitely say not to cut it . I cut mine as I didn't want tons of working coiled behind the dash. Works fine !

I figured that if it didn't work I could just ask for a replacement. If you are worried ,don't change it's length
 
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