What EGT is safe? (1 Viewer)

[OM617YOTA]

1996 1kzte Prado

No concern in normal driving, but can top 1200f accelerating to highway speed if I try, and can top 1350f if I'm really giving it the beans on a long uphill run. Completely stock factory tune as far as I know, and I wouldn't expect Toyota to engineer anything that would burn down their engine, but it does make me wonder if these engine's habit of cracking heads might have something to do with high EGTs in factory tune.

I know hitting higher temps for a few seconds isn't a big deal, but folks tow with these in hot climates. I could easily top 1350 for minutes at a time if I was towing. Glad I have an EGT gauge and would know to take it easy and not burn down my engine.

What do you all consider a safe continuous EGT?

Edit: thermocouple is pre-turbo.

 

[Dougal]

High EGT on an indirect injection engine causes head failure long term. There are no short term failures as the pre-combustion cups can't melt.
High EGT on a direct injection engine causes piston failure (cracking) long term which is very rare these days. Short term problem is pistons melting.

How hot is too hot?
On direct injection diesels I've hit 900C (1650F) in moments of inattention and have run 750C (1380F) sustained for minutes at a time. I have since rebuilt that engine for unrelated reasons and the pistons were totally fine.
750C is totally safe if it is a true and accurate measurement. If your probe is too short or in a cold spot it is not going to give you a good measurement.

Indirect injection diesels, particularly japanese ones, run too rich with the factory tunes which is one reason they tend to crack heads. It's like they're scared of boost.
The 1HZ (no boost obviously) runs very rich at full load but you're never going to get a high EGT reading from it as with no turbine the exhaust rapidly expands and cools.
Running these engines with more boost keeps combustion cooler and reduces the thermal expansion/contraction that causes head cracking.

Basically if your IDI or mechanical DI engine is running clean (no smoke at all) at full load you haven't got an EGT problem. It is possible for unit injector and commonrail diesels to run hot and clean.

 

[AirheadNut]

People always say 1250°F maximum, but I think that can be taken with a grain of salt. 1250°F maximum sustained is probably more reasonable. My tuned OM617a would easily hit 1350 under heavy throttle and would run 1100+ when bucking headwinds on the highway. My tuned TDI usually runs 1000-1100 on the highway, I generally keep it below 1300 when pulling hills but have run it above 1300 for miles at a time when I had a combination of bad injectors and a rich tune. The hottest I’ve seen was about 1680 on a dyno pull, that was just for a moment. VW specs that turbo for 1682 max inlet temperature, but they don’t say for how long.

 

[GTSSportCoupe]

I figured out the hard way that 3 hours of 1000F is too much for a 2LTE. That said, I was 15-18psi (intercooled) full fuel the whole time. Foot to the floor basically.

I was towing 4500lb camper at 110 km/h (70mph) in 35C (95F) weather. Pissed about things that day and kept my foot in it knowing full well I was pushing it. Coolant was about 250F+ the whole time (waterless coolant). I can only imagine what oil temps were!

Oil cooling of piston crowns was not sufficient for cylinders 1 and 4. Quite possibly they were getting less air and running richer/hotter than 2 and 3? I managed to crack pistons 1 and 4, and simultaneously crack cylinder head between valves at cylinder 1 and 4 too (not enough that it went into coolant).

For those that know about 2LTE failure, what I did hasn't been done before afaik. Generally when the head cracks it's progressively worse from front to back of the motor (back is hotter). I can't find any record of anyone cracking 2LTE pistons (3L, yes).

So, either my Pyro was not working right, or simply the extreme conditions were too much for the motor.

Anyhow, got me a used (OEM new model) head, and popping a couple used 2LTE pistons in. Will go a bit easier on it this year. Eying up 200 series with 5.7l now for towing.

So lesson learned for me; if other parameters are extreme enough, even 1000F can be too much.

 

[OM617YOTA]

250f coolant temp for three hours! No wonder it had problems!

 

[Dougal]

I figured out the hard way that 3 hours of 1000F is too much for a 2LTE. That said, I was 15-18psi (intercooled) full fuel the whole time. Foot to the floor basically.

I was towing 4500lb camper at 110 km/h (70mph) in 35C (95F) weather. Pissed about things that day and kept my foot in it knowing full well I was pushing it. Coolant was about 250F+ the whole time (waterless coolant). I can only imagine what oil temps were!

Oil cooling of piston crowns was not sufficient for cylinders 1 and 4. Quite possibly they were getting less air and running richer/hotter than 2 and 3? I managed to crack pistons 1 and 4, and simultaneously crack cylinder head between valves at cylinder 1 and 4 too (not enough that it went into coolant).

For those that know about 2LTE failure, what I did hasn't been done before afaik. Generally when the head cracks it's progressively worse from front to back of the motor (back is hotter). I can't find any record of anyone cracking 2LTE pistons (3L, yes).

So, either my Pyro was not working right, or simply the extreme conditions were too much for the motor.

Anyhow, got me a used (OEM new model) head, and popping a couple used 2LTE pistons in. Will go a bit easier on it this year. Eying up 200 series with 5.7l now for towing.

So lesson learned for me; if other parameters are extreme enough, even 1000F can be too much.

View attachment 3871834
View attachment 3871835
View attachment 3871836

I reckon your Pyro was out. It's almost impossible to get that much boost with EGT that cold.

 

[GTSSportCoupe]

I reckon your Pyro was out. It's almost impossible to get that much boost with EGT that cold.

Possibly, but it would have been like that from new, because I've never noticed a change. Here's the story:

My Stock 2LTE: Easily hit 1200F on hills even in the city. Totally pathetic. I believe now it's the emissions equipment which kill these motors; specifically the throttle plate which limits air (design to draw in EGR gas). As others have noted, the Euro version 2LT-II without emissions is a much more reliable motor with fewer head issues.

My Tuned 2LTE: With each of these changes, I saw progressively a drop in EGT. Removed throttle plate, highflow dump/exhaust, efficient intercooler, as much air as possible (waste gate disabled), more fuel (but limited by 10mm pump). Now very hard to hit 1000F under the most extreme conditions (fuel limited because only 10mm pump). It's been like that for 12 years now.

My theory on the piston damage:
- fuel mix coming out of the pre-cup is hotter than the average cylinder temps that I measure in exhaust stream. It's easy to see on these pistons this is the case. I believe this is why 2LT pistons have a cooling gallery in piston crown while 2L/3L NA engines don't. Localized heating caused piston failure in my case, because I was pushing my IDI well beyond it's design intent.

All 2LTE pistons look like this with a mushroom showing where hot fuel mix comes out of pre-cup. Above this area is where the cylinder head also super heats and cracks.

So my conclusion: 1200F might be okay on normally aspirated IDI, but on turbo IDI running high pressures, it's not okay.

 

[Dougal]

Possibly, but it would have been like that from new, because I've never noticed a change. Here's the story:

My Stock 2LTE: Easily hit 1200F on hills even in the city. Totally pathetic. I believe now it's the emissions equipment which kill these motors; specifically the throttle plate which limits air (design to draw in EGR gas). As others have noted, the Euro version 2LT-II without emissions is a much more reliable motor with fewer head issues.

My Tuned 2LTE: With each of these changes, I saw progressively a drop in EGT. Removed throttle plate, highflow dump/exhaust, efficient intercooler, as much air as possible (waste gate disabled), more fuel (but limited by 10mm pump). Now very hard to hit 1000F under the most extreme conditions (fuel limited because only 10mm pump). It's been like that for 12 years now.

My theory on the piston damage:
- fuel mix coming out of the pre-cup is hotter than the average cylinder temps that I measure in exhaust stream. It's easy to see on these pistons this is the case. I believe this is why 2LT pistons have a cooling gallery in piston crown while 2L/3L NA engines don't. Localized heating caused piston failure in my case, because I was pushing my IDI well beyond it's design intent.

All 2LTE pistons look like this with a mushroom showing where hot fuel mix comes out of pre-cup. Above this area is where the cylinder head also super heats and cracks.

So my conclusion: 1200F might be okay on normally aspirated IDI, but on turbo IDI running high pressures, it's not okay.

View attachment 3872269

Yeah I'd suspect the probe. Can you post up stock fuelling/boost and power/torque figures (metric preferred)? With those I can calculate stock AFR ratios to a decent accuracy.
Those early IDI japanese diesels tended to run filthy rich and hot.

 

[lacalvette]

Just to add my grain of salt, the EGT being at turbo inlet , the prob read an hotter temperature that individual cylinder would shows. At full load it could be 100C more. If the turbo inlet is at 600C, each cylinder could be at 500C.

If the EGT probe is at the turbo outlet, that's a different story because the more the engine is loaded, lower temperature will be read. Ex: engine half loaded, the turbo outlet temp will show about the same temp as individual cylinder exhaust. Lets says 400C. At full load, each cylinder will be around 500C and turbo outlet could be at 440C.

 

[jayp2]

Isnt the best place to put EGT probe at the junction of all exhaust manifold runners which is a little higher than turbo inlet?

Should show more accurate EGT's no?

 

[AirheadNut]

Yeah I'd suspect the probe. Can you post up stock fuelling/boost and power/torque figures (metric preferred)? With those I can calculate stock AFR ratios to a decent accuracy.
Those early IDI japanese diesels tended to run filthy rich and hot.

I don't know what the stock fueling is on a 2L-TE, I believe boost was 82.7kPa, power was 71.3kW 2 3800rpm and torque 240Nm @ 2400rpm. Compression ratio 21.0:1 according to the 1992 JDM sales brochure.

 

[lacalvette]

Isnt the best place to put EGT probe at the junction of all exhaust manifold runners which is a little higher than turbo inlet?

Should show more accurate EGT's no?

For simplicity and conveniance I guess. On these engine, we use EGT as a reference only. As to know if it is the best place or safe temp? We don't have specification from the manufacturer so it is general. Toyota must design their engine to work on the safe side. If someone install a pyro on a stock turbo direct injection 13BT, 12HT... and indirect turbo 2LT and share datas, I guess we could use these as reference to run a turboed 3B, 1HZ, 14B etc (on safe side)

If we had a way to measure peak pressure through a glow plug and report that with the position of the piston making a graph, knowing engine material limit, we could probably determine what would be safe and not.

Those engine are getting old and many were neglected so there is many factor to consider.
Side note: if coolant was not regularly change, depot can form everywhere inside the bloc and head, reducing cooling. Hard to remove, I said to a welder (cast iron fusion weling process) last time, heating the head to 800C is a good way to get rids of deposit! He said well not all the time, even then some still remain !!!

In marine industrie, engines come with all spec, pyro at each cyl head outlet, turbo inlet and outlet, regular maintenance, then you know exactly when exhaust temp is not safe...

 

[Dougal]

I don't know what the stock fueling is on a 2L-TE, I believe boost was 82.7kPa, power was 71.3kW 2 3800rpm and torque 240Nm @ 2400rpm. Compression ratio 21.0:1 according to the 1992 JDM sales brochure.

Workshop manuals often list injection pump cc/1000 shots.

 

[AirheadNut]

Workshop manuals often list injection pump cc/1000 shots.

The 2L-T manual lists 13.94-14.26 cc/200 shots at 1200 pump rpm, the manual supplement I have for the 2L-TE is all in Japanese but as far as I can tell it shows 10.0-10.4cc/200 shots at 1200 pump rpm and 450mmHg positive boost.

 

[Dougal]

Workshop manuals often list injection pump cc/1000 shots.

The 2L-T manual lists 13.94-14.26 cc/200 shots at 1200 pump rpm, the manual supplement I have for the 2L-TE is all in Japanese but as far as I can tell it shows 10.0-10.4cc/200 shots at 1200 pump rpm and 450mmHg positive boost.
View attachment 3874030

Alrighty. Putting these numbers together.
What everything means:
VE is volumetric efficiency. 1.0 would mean the engine gets fills each cylinder 100%, VE 0.5 means it would only get 50% air into each cylinder.
BSFC is Brake Specific Fuel Consumption. Basically efficiency, lower number is better.

2400rpm (max torque). To get 240Nm at 50cc/1000 shots (10cc per 200) means BSFC of 200g/kwh. Which is only acheived by VW TDI and other super efficient tdi's. So it's definitely not that.

Using 70cc/1000 shots (14cc/200 shots) for max torque I get:
VE 0.9
BSFC 284g/kwh (that's what I expected).
Using 12psi boost, and 10% intercooling (incidental heat loss) I get an
A/F ratio of 14.7:1.

This is of course silly high. But I think it's real. These engines were hot and smokey, being IDI the measured EGT is low even though it's hot and smokey inside.

Checking max power at the same 70cc fuelling doesn't work. There's not enough air to burn that fuel.
Fuelling at 50cc for max power. I think this is too optimistic. The engine would need to be more efficient at 3800rpm than 2400pm which it never is:
VE 0.8, that's okay.
Boost 12psi. that's okay.
BSFC 272g/kwh which is unlikely because it's better than max torque.
A/F 17.9. This is too lean for an old IDI at max power.

Fuelling at max power works at 60cc
VE 0.8
Boost 12psi
BSFC of 326 g/kwh (high fuel use, low efficiency, but believable).
A/F ratio of 14.9 Which is hot and smokey.


How do these numbers look?

 

[TheBussman]

Alrighty. Putting these numbers together.
What everything means:
VE is volumetric efficiency. 1.0 would mean the engine gets fills each cylinder 100%, VE 0.5 means it would only get 50% air into each cylinder.
BSFC is Brake Specific Fuel Consumption. Basically efficiency, lower number is better.

2400rpm (max torque). To get 240Nm at 50cc/1000 shots (10cc per 200) means BSFC of 200g/kwh. Which is only acheived by VW TDI and other super efficient tdi's. So it's definitely not that.

Using 70cc/1000 shots (14cc/200 shots) for max torque I get:
VE 0.9
BSFC 284g/kwh (that's what I expected).
Using 12psi boost, and 10% intercooling (incidental heat loss) I get an
A/F ratio of 14.7:1.

This is of course silly high. But I think it's real. These engines were hot and smokey, being IDI the measured EGT is low even though it's hot and smokey inside.

Checking max power at the same 70cc fuelling doesn't work. There's not enough air to burn that fuel.
Fuelling at 50cc for max power. I think this is too optimistic. The engine would need to be more efficient at 3800rpm than 2400pm which it never is:
VE 0.8, that's okay.
Boost 12psi. that's okay.
BSFC 272g/kwh which is unlikely because it's better than max torque.
A/F 17.9. This is too lean for an old IDI at max power.

Fuelling at max power works at 60cc
VE 0.8
Boost 12psi
BSFC of 326 g/kwh (high fuel use, low efficiency, but believable).
A/F ratio of 14.9 Which is hot and smokey.


How do these numbers look?

Wouldn't we be seeing thick black smoke at that air fuel ratio? i have a 2lt-e the shop that's believed to be stock, Unmodified and is very clean, can't see anything in the mirror.

 

[Dougal]

Wouldn't we be seeing thick black smoke at that air fuel ratio? i have a 2lt-e the shop that's believed to be stock, Unmodified and is very clean, can't see anything in the mirror.

In a direct injection yes you would. I have a spring that's too soft in my 4BD1T boost compensator and it dips to about 15:1 through transition. I get a small visible puff of black when I accelerate through that. When tuning in my old (direct injection) work car it had visible black exhaust smoke but was down to 12:1. Once tuned in around 17:1 it was visibly clean and much smoother.

IDI though gives a grey haze at that A/F level which is hard to see at the drivers seat but easy to see at the exhaust. You'd have to dyno that one to see if it's still putting out rated fuel/power. At this age it's normal for most of the horses to be lame.