Exhaust Gas Temperature gauge

Quote:

Originally Posted by rambada

Why would the EGT drop if it was dropped down a gear? Wouldn't the increased revs/workload increase the temp?

The only increase in workload is the increase in frictional losses due to the higher engine speed, which is minimal when measured against the work required to keep the train moving.
If you look at it from a power perspective, the lower the engine speed the more torque required to make the same amount of power. The only way to make more torque is more fuel and a bigger bang.

I see a coolant and oil temp difference of ~15 degrees C between 6th and 5th gear when towing at 100KPH on the flat. EGT difference is more like 70C and I use less fuel in 5th.
The engine is making the same power, it's just not working as hard on a per-stroke basis to do it.

Quote:

Originally Posted by rambada

Ok - ignorance about to show.

Why would the EGT drop if it was dropped down a gear? Wouldn't the increased revs/workload increase the temp? Or does the hot gas get blown out?

If the EGT drops with increased revs, then I assume this needs to be balanced out with coolant and transmission temps? Is this correct?

A high EGT is (generally) due to incomplete/substandard/poor/inefficient (call it what you like) combustion occurring, basically with too much fuel going into the combustion chamber ('cos your foot is flat to the floor) and lots of unburnt fuel still in the combustion chamber.

Some call it "over-fuelling", however there are other reasons for this such as faulty fuel pump/injectors, etc.

The 'easiest' way of causing this situation of high EGT in a passenger vehicle (we are not talking earthmoving equipment here) is by having your foot flat to the floor and the engine labouring at lowish rpm.

Essentially, by dropping a gear or two you are raising rpm and in the process causing a more efficient combustion process to happen.

I think pretty much the only time we'd be likely to get a high EGT is by driving our auto in "manual" and in the process not paying attention to which gear we are in, and then by allowing the engine to labour (as above) in too high a gear then you'll see a high EGT. We'd be towing a heavy load (and probably a hot ambient temp) to exacerbate the situation.

In my opinion, a high EGT is not a problem in the modern diesel passenger vehicle because its basically very under stressed, and the ECU's controlling fuel 'mixture' and other things do such a great job in controlling such parameters.

In the case of a D3/4, and other modern cars such as Scarry's LC200, I assume it would decide that the driver is an idiot and the ECU would message the auto to change gears accordingly??

Coolant/auto temps are less likely to be affected by higher rpm than the engine using lower rpm. They depend much more on ambient temp/load/ and duration of the 'pull' up the hill. We are speaking very generally now.

Having said all the above, I just remembered one of my boys just pre COVID was with his family towing his 21ft van with Nissan Navara (about 2014 model I think) on a very hot day heading south into Sydney from Newcastle.

He was driving the auto in "manual".

Climbing one of those steepish hills on that Expressway, without warning the engine management system shut the engine down to idling and he nearly sh.t his pants. He pulled over and long story short after idling for around 20 mins he managed to get going again. Not sure if it was due to high coolant or auto temp or high EGT. The ECU had detected the situation and acted accordingly.

Quote:

Originally Posted by Tombie

I have plenty of plates ready if people are looking to do this....

I just havent had time to pull my vehicle apart

PM sent. Cheers.

Quote:

Originally Posted by Tombie

I have plenty of plates ready if people are looking to do this....

I just havent had time to pull my vehicle apart

Looking forward to the complete DIY sheet complete with tools you’ll need to do this job. I’m keen to say goodbye to the EGR coolers.

Received. I’m off travelling for the weekend. I’ll revert upon return home