Exhaust Gas Temperature Measurement

[Tuftythesquirrel]

Can anyone let me know where is the best place to mount an exhaust gas temperature measurement probe (thermocouple). As in, should it be close to the cylinder head, the turbo inlet or turbo outlet. There appear to be pro's and con's for each.

 

If its close to the head or turbo inlet, you would probably get a more accurate reading of the gas temperature, but if ever the probe broke off, it would damage the turbo. Accordingly, truck manufacturers seem to mount them on the turbo outlet. That's fine for a standard installation, where your losses are known and even though your reading is possibly 200-300 Deg C cooler than the actual exhaust gas, you can compensate accordingly.

 

In our case, where there are lots of variables e.g. maps, turbos, manifolds etc. this is not so easy to do.

 

Can anyone advise of their own experience? and what readings they obtained.

 

Cheers.

[coskev]

To do it really accurately you would have one probe in each leg of the manifold coming off the head!

But to get a average with one sensor it needs to be mounted where the four legs of manifold collect together just before turbo.

[vrs180]

Kev has said it all really.

The manifold is usually drilled and tapped as close to the cylinder head as possible/practical.

The only issue is that If the EGT probe were to ever disintegrate then fragments of the probe will almost certainly damage the turbo charger turbine wheel.

However all EGT probes are designed to slowly burn away and in theory will stop working long before they degrade to a state were they could potentially disintegrate.

[octyal]

However all EGT probes are designed to slowly burn away and in theory will stop working long before they degrade to a state were they could potentially disintegrate

 

 

. Unless you buy a cheap Chinese one of course. As said, as close to the exhaust valves as possible is best, which in real life isn't always possible. Why do you need an EGT probe though? Only usually needed on older TDi's where the fuelling can only be set by messing directly with the injection pump settings. On an ECU controlled setup, there wouldn't really be any need for one as the fuelling is more accurately measured, and the ECU map wouldn't allow the fuelling to run away that much to create excessive EGT's