Thanks Larry, seems reasonable and just makes good sense.

Just a follow up if I may. Is the currently available (less than $100) cooldown timer working well with the 04.5?

jr

 

I do understand what happens when oil 'cokes' the turbo bearings. The only thing is, it doesn't seem to happen with today's oils.

So Larry, how many turbo failures, due to oil coking, have you seen? I have had none in over thirty years of owning and driving diesels. Not one. If fact I have had shops suggest that the turbo could be reused at overhaul time. I know of no one who has had this type of turbo failure, either. I don't dispute that it can happen, but it must be rare.

Apparently it isn't just DC who wants to 'make it through the warranty period, either. AFAIK, no other manufacturer puts on a turbo timer from the factory.

UPS's drivers drive their trucks the way they're told to. You can bet that if there was a penny to be saved by idling before shut down, they'd do it.

 

CP's response is the real acid test for effect, but jarmar's question about the relationship between Pyrometer reading and engine temperature is important.

If the pyro is reading 1800*, does that necessarily mean the engine temperature is high? It may just be high enough at the #3 cylinder to melt the piston.

Or, is the real relationship of importance the pyro because it reflects the temp of air going through the turbo; air that would cause the coking effect?

 

I really know very little about this technically, but reason seems to suggest that the hot gases flowing through the exhaust pipe could cool significantly ahead of the surrounding parts. The mass of the iron parts would hold the heat at least a little longer. Is this notion too far out?

jr

 

Sounds right, but I would like to hear a technical explanation. Much of what takes place in an engine is counterintuitive and defies common sense logic.

 

It is interesting that no one has answered what appears to be a very important question for anyone towing or tricking out their truck.

What is the relationship between EGTs and engine temperature?

If there is no correlations between the two, then anyone who suscribes to the notion of "coking" will have to time their shutdown or buy an automatic timer...the pyrometer is no longer useful in calculating shutdown time.

This is only an important topic if one believes that they need to be fairly accurate about shutdown temperature.

 

I emailed Cummins on this issue over a week ago and have received no response.

jr

 

I am by no means an engine expert nor did I stay at a Holiday Inn last night, but here is what I think:

EGT is a reflection of how hard the engine is working, i.e., how much fuel it is consuming per hour, i.e., how much waste energy is going out the exhaust.

Engine temp (a misnomer, since we really measure coolant temp) is a function of the thermostat setting and, at its upper limit, the amount of heat the radiator can dissipate to the surrounding air.

EGT is not going to have an effect on coolant temp until the amount of heat coming to the radiator is greater than the amount of heat the radiator can dissipate to the air. Localized areas such as exhaust valves, seats, and guides bear the brunt of this heat transfer, but that is true of any engine, turbo'd or not.

 

CP,

So if I understand the implications of your explanation, I can finish a long tow, let my Pyro get to 290* and shut it down without fearing that the core temperature of the engine is going to influence the coking effect. All of this is assuming that the cooling system is doing its job and my temp guage shows normal (which it always does).

The Dodge Owner manual says that after a long tow, you should let the engine idle about 5 minutes. The engineers are really just dummying-down the instructions for everyone who does not own a Pyro and putting in their usual - protect warranty exposure - overkill.

 

I have an 03 and i let it cool down for 2 minutes after hard pulling but when just driving the cooldown time up my road is plenty........i also run heavy equipment and i let that stuff cool down to......because 3 minutes is cheaper than a turbo....

 

Once you turn off the engine - oil no longer circulates through the engine (nor the turbo). The oil in the turbo just sits there. If the turbo is cool enough this is not a problem. However, if the turbo is too hot for the oil - the oil will coke up. A pyrometer will tell you how hot the exhaust gases are (and also - how hot the material is surrounding where the sensor is installed - therefore in a way - how hot the turbo is). If you let the engine idle for cooldown - you let fresh oil continue to circulate through the turbo while the turbo cools down. The turbo cools down in two basic ways - the fresh oil takes heat away - and the cooler exhaust travelling through the turbo soaks up the heat and takes it out the tailpipe.

 

I think it depends a lot on WHERE you install the pyro.
I installed mine in the outlet neck of the manafold (very close to the turbo)
A cummins service manager told me this was the best place to put it.
It cools down to 400 real quick (at idle) but then cools very slowly.
I have a cooldown timer, and I use it unless the gauge reads BELOW 400.
I have a friend who has had a 98 sense it was new, he tows, and he never lets it cool. He has not had any problems yet. Don't know how many miles he has on it.

 

Bartonkj is exactly right!
We are not worried about engine temp, we are concerned with the temp of the turbo bearings. By letting it idle, you are letting cooler engine oil (~200*) circulate through the turbo bearings. This coupled with the exhuast gas taking heat out of the 1800* turbo housing and pipes will cool the turbo down. Once the EGT or Pyro gauge shows you are 300 or 400 degrees, the temp in the turbo is low enough that when you turn the engine off, it will not heat the remaining oil in the turbo and turbo bearing to "coking" temp. Engine temp has nothing to do with the cool down period, ( or at least VERY little.)

 

Yup, Im a driver for Fed ex, and I drive a freightliner chassied truck with a CTD in it every day, and I cant afford to sit for a minute to "let the turbo cool" between stops.. so I shut it off, jump out, deliver and start back up again... the truck Im currently driving has over 300k on it and its still driving strong.
IDEA! Wodner if they woudl notice if I chipped mytruck??
Scott

 

I know years ago when I was a Heavy equipment operator Dozers,Trackhoes, ETC. we were drilled to allow at least a 5 min. cool down on the turbo powered tractors. Used to run the motors 4 or 5 hours at a time, eat lunch and, run another 6 hrs. digging and pushing heavy loads never once had a motor problem while allowing a little cool down on the motors.

take it for what its worth

Sittenbull