Thread: 300TDi EGT probe position?

Originally Posted by johntins

I ask as well, what wrong readings are you getting? Does the boost part work ok?

Stupid question, possibly, but it's not 24V is it?

no not 24V

Originally Posted by AK83

I guess the other thing to check for is the cabling from probe to gauge.
If it's going through the firewall via an access hole that is bare metal, maybe it's chafing the wire and shorting out or something like that.
Continuing on from this, maybe the wiring has been placed next to some high voltage/high current wire, which could affect it's reading in some way.

Out of interest, what sort of 'wrong' reading are you getting?
ie. is it low or is it too high.

You said that it's located on the cast section, two inches higher than the flange.
Is that the egr/blanking plate flange, or the manifold to downpipe flange.
I doubt that it's getting too hot and melting. Looking at the specs for an average K type thermocouple, they're good for up to 1300°C.
Of you're getting a melting probe, then you've probably melted all your valves and pistons and ... well everything!

If it's mounted 2" higher above the downpipe flange/joint, this means it's mounted after the turbo wastegate, which (IIRC) means that temp readings can be about 200°C below those you get from before the turbo.
(ie. if the accepted max limit for an EGT reading at the EGR blanking plate = ~700°C, then the accepted limit for after turbo EGT temps = ~500°C).

the readings are erratic and very changable and almost everytime you back off to idle it zeros.
it is mounted in the cast downpipe 2in up from the flange that bolts to the exhaust pipe

Sounds like a bad connection/earth or damaged insulation.

IMG_0789.jpg
This is where the probe is located

Originally Posted by johntins

I ask as well, what wrong readings are you getting? Does the boost part work ok?

Stupid question, possibly, but it's not 24V is it?

i have video now but gotta work out how to get it here

Well for starters the split corrugated tube is going to suffer quite quickly from the heat, another good reason to use the blanking plate and keep the probe shielding away from contact with anything hot. Assuming the probe is properly connected at the gauge I'd be looking very carefully at the earth and power connections for the gauge.

With the erratic reading, can't help other than what the others said too .. so maybe a cut wire or an earth connection(but you already said that an elec had a look at it too)
Could be that the gauge hasn't got any dampening to slow down the change rate at which the needle(assuming it's a needle type gauge), so it flickers wildly as the temp range varies.
My gauge is digital, and it changes rapidly with movement of the throttle at low temp ranges and then backing off from high temps.
That is, if I'm on the freeway and the 300 tdi is struggling a little up a hill, as the EGT temp gets to about the 450-500 range, it's change rate slows down. Still struggling and rising and say it gets to 600+ degrees, if I continue on it only slowly rises higher. But if I lift a little, it's drops rapidly(maybe 50-ish degrees in a second). If it's at say 600 and I reach the crest of a hill and back right off the throttle, it'll drop down to 400-ish in no time.
So could just be the design of the gauge you have.
I remember a Kenworth I used to drive use to have the same 'immediate spiky movement' in it's EGT gauge.

One other question: does it behave the same up a long hill climb in top gear, where you've got a fair bit of throttle going(in top gear)?
This is where you should get less erratic readings. It should start to climb in temp quickly, then taper off as it approaches a certain temp(this temp will depend on fuelling and other factors).
Because you're probe is after the turbo you probably want to keep max EGT at about 500°C. But irrespective of that, it should climb quick then slowly get to a certain max temp and not produce an erratic behaviour.
Wastegate is going to impact on the behaviour too tho, as you build turbo pressure the wastegate is closed to start with and as turbo pressure builds up, wastegate starts to open more and more, dumping hotter gasses from the turbo.

Is your turbo boost pressure nice and smooth? does it feel like it's surging in any way? Can you hear the turbine whistle?
Johntins asked too .. does the boost gauge work fine(ie. not erratic)?

Originally Posted by bigcarle

the readings are erratic and very changable and almost everytime you back off to idle it zeros.
...

Zero at idle wouldn't surprise me actually.
At idle, I'm seeing about 100°C give or take 50-ish. it depends on how it was run before hand.
Start and idle, it usually sits at about 50-100C.
After a run on the freeway and then idle, it can sit at about 100-150C while idling.

SO if the theory that the lower part of the pipe (after the turbo) gives you a reading of about 200C less than that upstream of the turbo, then a reading of zero could be normal.
I'm not 100% sure what the resolution of the probe is(ie. at what temp range it actually starts to register), but if the probe starts to register from about 50 or so degrees, and the exhaust temp after the turbo is at about 50° then a zero reading is likely.

I'd say you're best way forward from here would be to source a bung to fit the probe(they're usually 1/8th NPT or something like that), or find a ready made EGR plate with a bung already fitted.
Also find a blanking bolt to fit your current probe mounting bung, to blank that part off.
Once you have those bits ready to go, you'd then fit the probe to the EGR plate, and blank the current port.

I'd reckon it'd cost you about $20-ish in those parts and about 30mins of your time ... depending on how difficult the plastic protected wiring has been tied down.

Originally Posted by bigcarle

i have video now but gotta work out how to get it here

Best way to do that is to upload it to utube or somesuch and link to it.