Thread: very high egt

Originally Posted by paul-defender

The boost is 17 to 19 measured at the turbo and this has not changed over time. Perhaps i should be looking at what is happening at the inlet manifold. Not sure what pressures i should see there. Could the intercooler need a clean. Car has 140k on it. It may have always had high egt since chip i have only been able to see it recently

Boost sounds about right, it's possible it's just too much fuel.
To get the temps down you either need less fuel or more air (more boost and bigger intercooler).

Going easy on the right foot will give you less fuel.
Bet it goes well with that much fuel being thrown down it's neck. Does it light up tyres?

Originally Posted by Dougal

Boost sounds about right, it's possible it's just too much fuel.
To get the temps down you either need less fuel or more air (more boost and bigger intercooler).

Going easy on the right foot will give you less fuel.
Bet it goes well with that much fuel being thrown down it's neck. Does it light up tyres?

Can't say i try to. Think something expensive would protest. Does sometimes accidentally at intersections if very rapid take off is required to get into traffic but tc puts an end to that and away she goes.

Listen to Dougal, he's done a lot more study on hair dryers than almost anyone else on here.

FWIW, I've read that EGT's, combustion chamber and piston temps is an inexact relationship in diesels, contrary to what most people think or assume.

Higher EGT's may or may not start to create material changes in the pistons.
It depends a lot on timing, and ATM I can't rememebr which way it went.
I think if injection was more advanced it created higher piston temps, (and more NOx) but EGT's may remain sane, inject the fuel slightly later (relatively speaking) and EGT's may go through the roof but chamber and piston temps may stay OK.



Reducing back pressure post turbo can drop EGT's, but in my experience only in the region of 25* or so.

BTW, how much smoke is it blowing at 900* ?

Originally Posted by rick130

Listen to Dougal, he's done a lot more study on hair dryers than almost anyone else on here.

FWIW, I've read that EGT's, combustion chamber and piston temps is an inexact relationship in diesels, contrary to what most people think or assume.

Higher EGT's may or may not start to create material changes in the pistons.
It depends a lot on timing, and ATM I can't rememebr which way it went.
I think if injection was more advanced it created higher piston temps, (and more NOx) but EGT's may remain sane, inject the fuel slightly later (relatively speaking) and EGT's may go through the roof but chamber and piston temps may stay OK.



Reducing back pressure post turbo can drop EGT's, but in my experience only in the region of 25* or so.

BTW, how much smoke is it blowing at 900* ?

not as much smoke as you would think. slight haze but nothing like a land cruiser. it is noticable in the mirror but does not make things disapear. the longer you hold it the more pronounced the smoke.

Originally Posted by rick130

I think if injection was more advanced it created higher piston temps, (and more NOx) but EGT's may remain sane, inject the fuel slightly later (relatively speaking) and EGT's may go through the roof but chamber and piston temps may stay OK.

That's my experience too.
Advanced injection timing puts more heat into the cylinder head (and piston), higher nox, blacker smoke and slightly cooler EGT's. Makes for higher combustion pressures, higher efficiency but higher loads on everything.

Retarded injection blows more of the heat out the exhaust port and spools the turbo quicker.

How do the TD5's control injection timing? Fully variable by the computer?
It's a tribute to their injection design that you can potentially melt stuff without blowing black clouds.

Originally Posted by Dougal

T
<snip>

It's a tribute to their injection design that you can potentially melt stuff without blowing black clouds.

That's what I was thinking too

Originally Posted by rick130

Listen to Dougal, he's done a lot more study on hair dryers than almost anyone else on here.

FWIW, I've read that EGT's, combustion chamber and piston temps is an inexact relationship in diesels, contrary to what most people think or assume.

Higher EGT's may or may not start to create material changes in the pistons.
It depends a lot on timing, and ATM I can't rememebr which way it went. ?

Advanced = hotter, this is mainly due to the longer time the hot gasses are compressed against the piston

Originally Posted by rick130

I think if injection was more advanced it created higher piston temps, (and more NOx) but EGT's may remain sane, inject the fuel slightly later (relatively speaking) and EGT's may go through the roof but chamber and piston temps may stay OK.?

Its all in how aluminium ( or its composite) transfers\holds heat. If you retard the timing and EGT raises it inferably means that fuel is still burning the manifold.

Originally Posted by rick130

Reducing back pressure post turbo can drop EGT's, but in my experience only in the region of 25* or so.?

True, I posted before about back pressure pre turbo, or back pressure created by the turbo. The higher the back pressure the higher the temp. Rule of thumb plus 1 inlet temp for every 14psi.
you can get to the point where you have so much Gas flowing out and so much pressure that the cylinders will not scavenge IE the burnt gas can not get out, an indication of this can be the increase of the Ratio between drive pressure to boost, this can be misleading. With the hot gases not being able to get out the turbo cant push more air in as well, this leads to an increase in inlet manifold pressure or a better looking ratio between inlet and out let pressures. The way around this is a progressive waste gate, these are usually spring activated where the vale is opened by the pressure its self ( against the spring, spilling the hot gasses around the turbo and relieving the pressure in both the manifold and the cylinders. As the hot gas is always at a higher pressure than the inlet, it is essayer to relieve than to push.

Originally Posted by rick130

BTW, how much smoke is it blowing at 900* ?

Originally Posted by clean32

Its all in how aluminium ( or its composite) transfers\holds heat. If you retard the timing and EGT raises it inferably means that fuel is still burning the manifold.

No the fuel isn't still burning in the manifold (unless you're retarded enough to think flames out the exhaust are cool), it's simply the hot gas has lost less heat to the cylinder, head and pistons. So when it passes your probe it's hotter.

Originally Posted by clean32

True, I posted before about back pressure pre turbo, or back pressure created by the turbo. The higher the back pressure the higher the temp. Rule of thumb plus 1 inlet temp for every 14psi.
you can get to the point where you have so much Gas flowing out and so much pressure that the cylinders will not scavenge IE the burnt gas can not get out, an indication of this can be the increase of the Ratio between drive pressure to boost, this can be misleading. With the hot gases not being able to get out the turbo cant push more air in as well, this leads to an increase in inlet manifold pressure or a better looking ratio between inlet and out let pressures. The way around this is a progressive waste gate, these are usually spring activated where the vale is opened by the pressure its self ( against the spring, spilling the hot gasses around the turbo and relieving the pressure in both the manifold and the cylinders. As the hot gas is always at a higher pressure than the inlet, it is essayer to relieve than to push.

This is completely counter-productive on a diesel. Dangerously high EGT's are the result of not enough air which requires more boost. To get more air in requires more boost and higher drive pressures.
The result of the higher boost and drive pressure is lower EGT's. It can take some getting your head around.
The other approach will lock you into a vicious circle which can only end with the turbo bypassed and extractors fitted. Needless to say, performance will suffer and you'll still need to greatly reduce fuel.

Turbos thrive on exhaust heat, the hotter they are they more efficiently they run and the less drive pressure they require.

A wastegate that opens based on drive pressure will kill your boost when accelerating with a cold manifold but do absolutely nothing to help high EGT's.
This is because drive pressure drops with temperature.

If you could guarantee your turbo won't overspeed and your head gasket will stay put then welding the wastegate shut will have the best positive effect on keeping EGT's down.