EGT and engine shutoff

[Peteandsharon]

OK, so I've got the Edge Insight hooked up to my '08 F250. And as I stated in a previous thread, the primary reason I got it was to measure the exhaust gas temperature (EGT). I have always believed that the EGT will tell you (among other things) when it's alright to turn your diesel engine off. The rule of thumb was always to shut down when the EGT got down to about 300 degrees.

What I'm finding with my current diesel is that sometimes that's unreasonable. Sometimes the EGT comes down relatively quickly and I shut down after a minute or so. Sometimes I have to let it idle for 5 minutes or so before it gets there. I just sit there twiddling my thumbs and wasting diesel fuel.

The Edge Insight has several EGT pids. I am using the hottest one which I assume has the sensor closest to the exhaust manifold.

Anyway, I'd like to know if any of you use the EGT for this reason or do you use any other rule of thumb for shutting down a diesel. I had an EGT guage installed on my previous 7.3L diesel and used the same rule of thumb but it didn't seem to take as long to get to the 300 degree level.

I'm assuming in this discussion that we agree that it's not a good idea to shut a turbo diesel down hot so I guess the question is how are you judging that it's OK to do so.

 

[bighorn3370]

on my 7.3 I always wait untill it as lest 300 or blow. i am not sure on the new 6.4 but on the 6.0 with the new turbos on them you could not get the egts down that low.

 

[Peteandsharon]

Yeah, on the 6.4 it WILL get there but it just takes longer to do so. Not sure if a different target temperature makes more sense. I know for a fact that if I did not have the guage, I wouldn't know to idle it for so long.

 

[truknutt]

You guys got me thinking and I never recalled reading or seeing a target EGT for Turbo Cool down with the 6.4L. On the 6.0L (way back in the 2003 dark ages) 300-350 was the target EGT at turbo cool down.

From what I've found on the Powerstroke.org forum and in my 6.4L Owner's Guide Supplement, the issue isn't so much the temps at shut down, it is that the hot bearings get oil run over them for 3-5 minutes so as to prevent "coking" or carbon deposit build-up.

Excessive idling in order to reach the 300 degree EGT is damaging also.

From Detroit Diesel: "Even a warm/hot engine is damaged by idling. One minute at idle is as bad on most engines as two miles of driving at 60 mph on the interstate, whether gasoline- or diesel-powered.

Diesels pull a full gulp of air on every intake stroke. They have no throttle butterfly like gas engines to restrict air flow for idling. They just change the amount of fuel being fed into the injectors to control speed/torque. If the engine isn’t working hard, it gets a smidgen of fuel, not enough to maintain block temperature, and the intake air is like a big blast of refrigerating (cool) air, especially if the turbo isn’t spinning at full compression. Thus the engine cools to below its design operating temperature and you get the high wear factors again."

Guess when we pull into a rest area or such, I'll just start doing a walk-around check of the truck and coach while the turbos are cooling down...3-5 mins worth...that's if my old guy bladder can take the extra 3-5 minutes!

 

[Peteandsharon]

If I recall correctly, there is "something" in the diesel supplement to the owners manual but it is very vague. It doesn't give specific directions and doesn't really state a reason. Simply that shutting down a hot diesel immediately is not healthy.

That's an interesting point you make about idling being bad for a diesel. That kinda runs counter to logic since you always see the big rigs idling away at truck stops.

I've always known that the real issue is the coking of oil in the turbo but since the EGT measure that I am taking is pre-turbo, that temperature has a direct influence on how hot the turbo is and consequently how liable it was to "coke up".

Regardless, it would be nice to know if Ford has any specific recommendation on this. I'm starting to cheat a bit because I get impatient. Now 320 degrees is getting to look good enough. I don't want to do anything harmful but it's a little silly to take a group of people to Walmart and have everyone already be inside the store while I'm still out there waiting to be able to turn my truck off.

 

[dieselengineer]

This is a very good question. The other part of the question is where do you measure the EGT. I have a sensor before the turbo like most and one after the turbo. So I have pre and post turbo. The sensor in the post position does not cool down as fast as the pre position. So if your sensor is in the post turbo position, 300* F may not be the correct number. I have found that the A/C effects the cool down time also (the intercooler gains heat from the condensor). After a long run or hard pull and I am going to stop, I shutdown the A/C, set the idle to high idle speed (cruse control on, I really like this feature on the dodge) and get out of the truck. Like Dave says, go check the tires and bearings, etc. By the time I get back to the truck the temp is way below 300^ F.

 

[beardedone]

In response to dieselengineer's comments, there was a recent consumer type letter from Cummins about the engine temps and they reminded everyone that the new diesels like the 2007 & up are designed to run at higher temperatures then ever before. Also the idle factor is high up on the "beware of" list. So now a lot of people are just taking it easy, slowing down before they stop moving, only let it idle briefly and then shut it down. It sure pays to have gauges and know your temps though.

 

[porthole]

Who wants to sit in a truck and watch a gauge so you can shut it off?

Since doing some mods to my truck and the fact that we have a Cyclone ordered I decide EGT's are now important.

But watching the temp gauge is not the answer I was looking for.

I found several different shut down timers available. One (BD I think) uses an EGT probe reading to shut the truck down at a predetermined temp.

Another (the one I purchased) is set everytime you shut down manually.

If my EGT is over 300 I will usually set it to shut down after 1 or 2 minutes.

If I was just running the truck hard I will sit it for 3-4 minutes.

The real purpose is to keep the oil circulating while it cools down a bit.

The coking comes from high temps and the lack of lube oil circulating, and gets much worse if you have just spooled up the turbo before shutting down.

So for me the idle down is really a chance for the oil to keep circulating a bit while the turbo spins down to it's idle speed.

 

[Peteandsharon]

I guess there is a related question and that has to do with the regen process. When I purchased the truck, I was told not to turn off the engine if it is in the middle of regen. Let it sit and idle until the regen process is done. Recently I have heard other opinions. The contradictory opinion is that you should not let it idle. Either keep driving normally unitl regen is done OR shut it down and let the regen start up the next time you drive. The argument is that regen doesn't work under idle conditions. Given the fact that the regen drastically hikes the EGT I can't imagine that you would want to shut it off in the middle of a regen. On the flip side, you might have to idle it for 15 minutes if a regen just started. Hmmmmmm!! I guess I have to ask this question then. What are you guys doing if you arrive home in the middle or start of regen?

 

[beardedone]

If you idle through a Cummins re-gen then they advise to keep your rpms' well up, like 1000 - 1200

 

[dieselengineer]

Does anyone use the high idle feature on the cummins? I am talking about cruse control / set button jumps the idle speed to 1200rpm

 

[beardedone]

I use my high idle in the winter, in the summer not so much. With these new engines being sensitive to more than a couple of minutes idle time I don't even start the engine until I have my seatbelt and sunglasses on. With the garage door open I flash it up and am on my way. If I have to idle then I either use the high idle and run it at about 1100 or I shut it down, depending on circumstances. The 6.7 and all late model diesels are similar. Too much soot too quickly.