peanut

i never have understood what the actual circumstances are to extremely high egt's. Whats the first thing to melt, crack, blow up or whatever? what type of repairs would be required. just curious as i have never really known what would happen.

thanks,
peanut

DieselDaze

Sustained EGT's about 1250 or higher will melt down the pistons.
Ive seen cracked pistons, partially melted pistons and pistons with large sections missing on them from high EGT's.

Not pretty.

Rich

infidel

This is from a 12 valve that was operated for an hour at 1400°

DZLPWR

Aluminum melts at 1350* or around there, so running EGTs close or above that for a sustained run will melt pistons and warp exhaust parts and such. So, melting pistons are detrimental to the engine!

1320

I would bet that probe placement/qaulity is the reason here but.....why is alumnum in gas engines better, I say that cause they run 1600 all the time....well.....10 seconds at a time. I ve seen 1700 lots....even 1900 once.

I ve heard that cummins tested at 1350 for 24hrs? Is it true? I don t see how or why a gas engine with small , lighter pistons could saftly absorb mor eheat then the cummins pistons?

I attribute most of these variances to probe placement, accuracy of the equip. Ive measure 1400 at least 36 inches off the head port on a gas engine. I regularly measure 1600 on a turbo gas engine 12 inches from the exhuast port , just before the turbo. I understand that a sustained temp would /could cause the distruction, but for mometary blasts, 10-15 seconds, 1600 should be very very very safe. Pulling a hill for 15 minutes, I would guess a bit less....but if the cummins test is TRUE then 1350 should be easy also, even for 15 minutes if they tested for 24hrs.

DRD

I think part of it is that with gasoline engines you get cooling from the fresh mixture when the gas evaporates in the cylinder, pulling lots of heat out of the cylinder when this happens. Generally more fuel=less temp as opposed to diesel with more fuel=more temp

DRD

I think part of it is that with gasoline engines you get cooling from the fresh mixture when the gas evaporates in the cylinder, pulling lots of heat out of the cylinder when this happens. Generally more fuel=less temp as opposed to diesel with more fuel=more temp

infidel

One thing to consider when pushing high egts is "Is my gauge really reading right?"
I know of two guys who have had melt downs with the pyro in the safe zone only to find out later that it was reading low.

DZLPWR

Infidel, i was wondering, can you have your pyro checked for accuracy? If so by who or how? Ive always thought about the problems an inaccurate pyro could bring... .

infidel

Easiest way for most folks is to trade pyros with someone else and see if the readings are similar. We have high temp digital thermometers in the labs at work. I took a 150W light bulb, wrapped the entire bulb with aluminum foil with a probe inside and was able to get 950° out of it steadily. I have since used this method to check pyros but don't think the number would be accurate for everyone depending on your local voltage. My bet is a few volts difference could make considerable difference in temps.

Some easy ways to see if your pyro might be off-
It should read somewhat close to the outside temperature after the engine has been shutdown overnight and shouldn't run much below 250° idling after warm-up.
The above is really no guarantee as most gauges, especially pyros, are only accurate in the middle of their range.

I know folks have talked about infrared temp guns and welder's temp sticks on the outside of the manifold but I don't see how it could be very accurate since you're measuring the temp of the metal not the exhaust gases.

CrewCabCummins

On the way home from pismo last month I was having some fun with a Ford and pulled Questa grade at a little over 70...This was with my 93 and a loaded 27' Aljo TT and the back of the truck was full of crap...1200 to 1350 all the way up..since then the truck runs BETTER than EVER..Go figure???..Sure was fun leaving a new truck with a slightly smaller trailer SOOOOO far behind...Then there was the DM on 41 near lemoore...But that's another story..

BigBlue

It's a good idea to occasionally load these engines up and heat them up. It cleans the heads and everything and frees things up.