EGT Question

[GM Smitty]

300 miles towing today, 18000# GCW, crappy PA roads. tongue.gif Alot of hills, Hot Juice Level 1, this truck impresses me every time I hook up the trailer.

Anyway, EGT's spent alot of time above 1000 due to the hills (highway and two lane roads), never exceeded 1200, but spent significant time right at 1200. Sometimes 2-3 minutes straight at 1200. Is this a bad thing to do? You guys who are towing every day, does this sound normal?

Thanks - Josh smile.gif

[sdaver]

1300 or less is what I have heard... :D dave

[mackin]

Not recommended but the Max exceeded 1400 "sustained " during initial testing ...... This motor is NO light weight ......


Mac :eek:

[GM Smitty]

Thanks fellas... :D :D

Josh

[a64pilot]

Keep it below 1300-1400 sustained and you won't hurt it IMHO. Just be sure to idle it for quite some time to let the turbo cool before shutdown ;)

[jesshd]

Letting the turbo cool is no longer neccesary. Back in the days of oil only cooled turbos, if you shut it off too soon, it would "cook" the oil in the turbo and cause coking. Coking bad, failed bearings. The newer IHI, Garrett and others are water cooled as well as oil cooled. They don't need an idle cool down. Synthetic oil will not coke. If you are concerned about it (I do this on my other mucho modified turbo "rice burner" and on the truck) is just take it easy and stay out of the boost for about the last mile or two before shutdown.

Jess

[a64pilot]

Jess,
I realize that the center section of the newer turbos are water cooled and coking may be a thing of the past (hopefully) I still think it is a good idea to allow the hot end of the turbo to cool a little slower when hot.
I'm one of those people that don't work an engine until it's up to operating temp and try to cool one slowly prior to shutdown.
Aviation recip engines that are allowed to cool quickly are refered to as having been shock cooled, bad things happen. More and more turbine engine operaters are going to a two min. idle before shutdown to allow gradual cooling of the engine. I am comparing apples to oranges here, but I believe there is a correlation.
IMHO if you are working the snot out of an engine, 1300-1400 sustained is working the snot out of it, I think it would be beneficial to allow the turbo, and other components, temps to cool some prior to shutdown.
It can't hurt and my intuition says it would be benificial. FWIW

[hoot]

I have a highway run every day that ends in both directions with a few miles of residential backroads. For me, that's plenty of cooldown in itself. It runs with almost no boost for a few miles.

I don't think it's a good idea to heat the turbo up under load and immediately shut it down, water cooled or not.

[Burner]

What happens to metal when it cools? Heating metal and sustained temps is not a bad thing, as long as they are not "way over" the limmit. However, cooling the metal too fast is quite destructive. Metal will warp more when it is cooled than heated. ;) Think about that when you shut down your Turbo. ---- The design allows for stock "shut down" temps, say 900 at most. I don't think that our system will handle more than than 1,200 degree shutdown. If you knew how much water was in the turbo and how much heat you had, your "cokeing" question would be ansered. A mole (measure of heat) is the ammount of energy it takes to heat one gram of water one degree... I think. Find your temp, know the ammount of "leftover" water in the system, the evap point of your oil, the cumbustion point oil your oil and work the numbers. You may find out that 30 seconds will do.... but you'll never know until you work the numbers. ;)


Burner-------> :D

[jesshd]

I do not disagree with this at all. I am also not advocating getting into boost right after you start the truck or shutting it off right away after working it hard. All I am saying is that turbo timers and idling for 2 minutes before shut off are not needed. I have a water cooled turbo on the fun (race) car that has been subjected to what race cars are subjected to for 4 years and just letting the car run normally out of boost for the last few minutes has been fine. I expect (rather know) that this turbo is much more robust. Just give the engine time to come up to operating temps before running it hard and stay out of boost for the last couple of miles before shutting it off and it will last as long if not longer than the truck.

Jess

[mdadgar]

You can water-cool your turbo all you want, but if the water ain't circulating, the turbo ain't cooling.

Guess what happens when you shut off your motor?

After a hard tow, idle your motor down for a minute or two before shutting it off. Doing some slow driving through a residential zone is fine, too.

- Mark

[huntindog]

StrangeEngine
Actually, that's not true.
In the beginnning of the automobile there was no such thing as a water pump. The water circulated, by means of convection???(not sure if that's the right term). Of course it wasn't very efficient but it did work. So long as the turbo water jacket is connected to the rest of the system, then it will work as the turbo temp will go into the entire cooling system.This won't be efficent enough to cool with the engine running, but with the engine off and no additional heat being generated, it works fine.

[jesshd]

You should do whatever you are the most confortable with. Having talked to engineers at Garrett and IHI and Aerodyne, I have had a lot experience with this same subject and am follwing their recommendations as well as over 4 years experience with building engines for water cooled turbos on high performance gas applications. Staying out of boost and running normal for the last mile or two is plenty of cooling for the turbo. You don't need to sit and idle the engine for minutes before shut off. If you feel you need to, then get a turbo timer. That is just one more way cool toy to add :D

Jess

[huntindog]

This subject is concerning temps in the 1300-1400 "sustained" range. I find this rather humerous as I can only envision two scenarios where this would be a problem.
#1 A long uphill tow while juiced, followed by imediatly shutting the engine off.
Not a very likely scenario.
#2 Driving at "go to jail speeds" for a long time, also while juiced.
This scenario is more likely, as the nice police officer will probably ask that the motor be turned off.
LOL.

[MaxACL]

Consider an up-hill pull w/heavy trailer on a hot summer day and the fuel pickup tube going dry on your new 115 gal tank (because of the up hill incline). All of a sudden... no RPM. :eek:

[a64pilot]

Guy's didn't mean to start anything. Yes 1300 or so sustained would be very hard to do, but if you find a way to do it I don't think it would hurt to idle for two min. or so. Other componets will benefit from being allowed to come off of a high heat soak other than the turbo. I wasn't talking about driving home from the supermarket or anything, I was referring to "working the snot out of it". For me a turbo timer would be a waste of money.
BTW the old car's did use a "thermal syphon" effect to circulate water, convection would be the right term. Water would be first fed to the block and convection would cause it to rise in the head and then to the radiator. Later a pump was added to boost this effect. On my 93 LT1 and on My 95 6.5 they had "reverse flow" cooling in that the heads are fed the water first, from there the water is pumped down through the block. Pretty sure the Dmax is the same. Anyway the head in a modern overhead valve engine is where most of the heat is released and this is the reason for the "reverse flow". Would there be any water flow through the turbo after shutdown? I doubt it, because of this reverse flow thing.
Bottom line if you work the snot out of it what could idleing for a short time, or running easy for a couple of miles hurt?