Broken Turbo

**Dougal** · 25th March 2014, 12:55 PM

Originally Posted by schuy1

I have been told that high RPM will give a lower EGT reading due to the highish through flow of gases, has a sorta cooling effect like when the fan kicks in with a radiator. loaded, low RPM, more fuel burnt, slower though flow of gases, causes the EGT to rise. That is why going down in the gears will lower EGT with a load.
Sound feasible? Thats what I been told anyway and it makes sense to my mind as thats what happens with a non turbo.ed motor, let it labour in a high gear loaded and the temp gauge goes up.
Cheers Scott

Sort of.
The airflow through your engine tapers off as rpm rises, fuel delivery (stock) is also tapered off to match.
But with diesels the burn speed is fixed and so higher rpm usually gives a higher EGT reading as fuel is still burning later in the stroke. At higher rpm the combustion temps can drop but measured EGT rises. This is okay.

On turbo engines the worst point is when the turbo is still spooling up. This is when diesels normally run the richest A/F ratio and hottest EGT. If towing you can often end up driving for some time in this dangerous place. It is made far worse by aftermarket tunes where they use extra fuel to try and spin the turbo up sooner.

The main reason EGT drops when you go down a gear is the load and torque required from the engine drops. The second reason is getting it away from the point where you turbo hasn't quite spun up.

**twr7cx** · 25th March 2014, 01:39 PM

Originally Posted by Disco Muppet

Unless you're at max GCM locked in 3rd sport trying to hold 110 up a hill, you're not going to cook it on a stock map.

If your so confident in the stock standard setup, supply a D2 and I will gladly demonstrate.

**Disco Muppet** · 25th March 2014, 02:17 PM

Originally Posted by twr7cx

If your so confident in the stock standard setup, supply a D2 and I will gladly demonstrate.

How about you give me a theoretical run down

Dougal, in my example I made a typo, meant to say 4th locked, i.e top gear. So the box would be labouring, under very high load from the engine, which is what you said

I'm aware that gearing down is what helps reduce EGTs.
So like I said, unless you're being really silly, I doubt you'll cook it on a stock tune, but that remains my humble and often uninformed opinion

**Dougal** · 25th March 2014, 06:36 PM

I wouldn't expect to be able to cook an as-new TD5 on a stock tune. But given ~15 years of sensor values drifting anything is now possible.

**bidds** · 25th March 2014, 09:36 PM

Which sensors are the ones that are most likely to influence this?

**bidds** · 25th March 2014, 09:44 PM

uestion:
Is there any value in putting a VNT into my truck (D2a) given I'm not going to mod the airbox, change the intercooler or remove the Mantec snorkel?

I'm in comms with BAS and td5inside and getting the impression that I might be best off just fixing or replacing the standard turbo.

I was planning to go with the S208-1 and a close-to or totally stock map. Jose' from td5inside is happy to do a map to suit.

Many thanks for facts, thoughts, opinions

**Disco Muppet** · 25th March 2014, 10:06 PM

If you tow alot, I'd go VNT + suitable map, Larger intercooler, extra trans cooler, and an EGT gauge.
That should give exceptional results.

**bidds** · 25th March 2014, 10:11 PM

How much larger should the intercooler be? Would the D2a version be considered usefully bigger?

**bidds** · 25th March 2014, 10:14 PM

Here's the compressor. Blades look very worn - stuffed bearing? The nut from the shaft was missing. Guessing that's in the intercooler somewhere.

Here's one view of the turbine. Blades look bent, with some chunks missing. Guessing they're embedded in the centre muffler - is that a drama?

Here's another of the turbine - I've rotated it a bit. Can more clearly see a large chunk missing.

Any ideas what this would cost (very roughly) to have fixed/reconditioned?

**bidds** · 25th March 2014, 10:31 PM

I was also getting symptoms of broken exhaust studs: occasional screech (actually, only once); 'turbo' whistle. On removing the turbo, I found nothing broken and only a nut missing at the very back of the mainfold and some evidence (soot) of a small leak next to it. I've loosened all exhaust manifold nuts and they've come off nicely.

Does this indicate that perhaps it wasn't excessive heat that killed the turbo? Just a worn bearing?

Would worn impellor blades mean poorer pumping ability and perhaps higher EGTs and coolant temps? I seem to recollect there being a reasonable amount of wear for a long time - looks to have much bigger gaps between the housing and impellor blades than images of new turbos.

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