I know that is where aluminum starts to melt, but are sere pistons really that soft? I would not want to see egt's like that regularly, but about a week before I blew a headgasket I got inpatient on the highway and passed somebody on a hill with my truck redlined (75 mph) anyway my pyro read 1450 for about 15 seconds. The pyro is located on the exhaust manifold 3 cylinders back on the driver side. When I toor the motor down I was afraid that there would be some damage, but the pistons look perfect and the heads checked out fine, I went ahead and had them reconditioned anyway and put 910 springs in. But how come everybody seams to say 1250 can damage your motor quickly and 1450 didn't damage mine?
1250 degrees
- Thread starter S-west
- Start date
icanfixall
Official GMM hand model
Cause it was too hot to damage anything....
Actually staying at high temps will not melt a piston as much as it softens them or burns the edges of them. This we have seen several times. Remember the oil that keeps drawing the heat away from the tops is a constant flow. Plug up an oil cooling jet and try that again. Your outcome will be different and I'm positive of that. The issue is how close to the line are you willing to get. and what faith are you putting in the pyro. Its a learning and testing phase we go thru. Kind of like running the tanks low on fuel till we just make it to the station. My good wifey had a 74 pinto with the the first all metric engine in it. That car got about 27 mpg. Her mother lived 18 miles from our home. She drove home and parked blocking me in the driveway. Next morning I started her car to move it and it fired up. Dropped into reverse and it died. Looked at the gas gauge and it was mt.. Son of a *****.. she really screwed me on that one. to this very day she tells me it ran out on me... Not her so its my fault. She still wont fuel up any car or truck. She is so lazy it hurts... Please don't try to run your engine to 1450 degrees just because someone got away with it. The possibility of something breaking is not the kind of break down you want.
Actually staying at high temps will not melt a piston as much as it softens them or burns the edges of them. This we have seen several times. Remember the oil that keeps drawing the heat away from the tops is a constant flow. Plug up an oil cooling jet and try that again. Your outcome will be different and I'm positive of that. The issue is how close to the line are you willing to get. and what faith are you putting in the pyro. Its a learning and testing phase we go thru. Kind of like running the tanks low on fuel till we just make it to the station. My good wifey had a 74 pinto with the the first all metric engine in it. That car got about 27 mpg. Her mother lived 18 miles from our home. She drove home and parked blocking me in the driveway. Next morning I started her car to move it and it fired up. Dropped into reverse and it died. Looked at the gas gauge and it was mt.. Son of a *****.. she really screwed me on that one. to this very day she tells me it ran out on me... Not her so its my fault. She still wont fuel up any car or truck. She is so lazy it hurts... Please don't try to run your engine to 1450 degrees just because someone got away with it. The possibility of something breaking is not the kind of break down you want.
redneckaggie
rebel w/o a cause
I have seen 1400 once for about 5 seconds, i have friends with cummins(12 and 24 valve) that have rode with the pyro buried(1600 deg) for about 15-30 sec. Never had my engine apart but helped them tear both of theirs down neither of them had heat damage. I have also seen engines apart that had the tops melted on trucks that were babied. Just how far do you want to test the waters....
Hi Jack. Hey Gary, that Pinto engine was built at the Lima Ohio Engine Plt. Sweet engine, lousy car, even tho I owned one myself.
FWIW this wasn't on a 6.9l/7.3l, but my first diesel was a 1980 IH Scout II with a 3.2l Nissan inline-6 IDI turbo that made 101 whole horsepower with a T-19, 3.73 gears, and stock 1/2 ton tires. Pyro probe was mounted just after the turbo in the downpipe. I climbed up a hill towing a car, and even with the pedal to the floor, I couldn't go faster than 25 mph in 2nd gear. The pyrometer got up to about 1300 degrees for two to three minutes 
I was 17 and dumb and didn't think I'd destroy anything that quickly, and I had to get over that hill. After getting home that night, I asked on a forum I was part of at the time and was told how bad of an idea that was...so, I was careful to not do anything like that again, but I didn't notice any ill effects at first, other than that the pyro would be sitting at about 800 degrees when doing 55 to 60 down the freeway (I don't recall what it did beforehand since I had owned the truck less than a week when I did that pull, but I'm pretty sure it was lower).
About a year later, I started noticing that oil consumption had gone up significantly, and I began seeing white smoke coming out from under the hood. There wasn't much at first, but over the course of a few months it got steadily worse until I got pulled over a couple of times. The smoke was coming out the factory road draft tube in puffs, and while I never did a tear-down on the engine (the truck body was so rusted out and parts for that engine were hideously expensive, it wasn't worth it financially), I'm certain that this stemmed from that incident, given how careful I was with the engine afterwards.
My example is a bit extreme, but it taught me a very valuable lesson...you may have gotten away with it this time (or, given that the head gasket let go so quickly after your incident, you may not have), but I would be VERY careful about how hot that pyro gets even for a few seconds. It just isn't worth the risk. And, IMHO even if the pistons look okay, the aluminum could have been softened enough that they're not as strong as they were, so reconditioning them was the right call IMHO.
FWIW...
with a T-19, 3.73 gears, and stock 1/2 ton tires. Pyro probe was mounted just after the turbo in the downpipe. I climbed up a hill towing a car, and even with the pedal to the floor, I couldn't go faster than 25 mph in 2nd gear. The pyrometer got up to about 1300 degrees for two to three minutes I was 17 and dumb and didn't think I'd destroy anything that quickly, and I had to get over that hill. After getting home that night, I asked on a forum I was part of at the time and was told how bad of an idea that was...so, I was careful to not do anything like that again, but I didn't notice any ill effects at first, other than that the pyro would be sitting at about 800 degrees when doing 55 to 60 down the freeway (I don't recall what it did beforehand since I had owned the truck less than a week when I did that pull, but I'm pretty sure it was lower).About a year later, I started noticing that oil consumption had gone up significantly, and I began seeing white smoke coming out from under the hood. There wasn't much at first, but over the course of a few months it got steadily worse until I got pulled over a couple of times. The smoke was coming out the factory road draft tube in puffs, and while I never did a tear-down on the engine (the truck body was so rusted out and parts for that engine were hideously expensive, it wasn't worth it financially), I'm certain that this stemmed from that incident, given how careful I was with the engine afterwards.
My example is a bit extreme, but it taught me a very valuable lesson...you may have gotten away with it this time (or, given that the head gasket let go so quickly after your incident, you may not have), but I would be VERY careful about how hot that pyro gets even for a few seconds. It just isn't worth the risk. And, IMHO even if the pistons look okay, the aluminum could have been softened enough that they're not as strong as they were, so reconditioning them was the right call IMHO.
FWIW...
Knuckledragger
blowing chunks and grabbing porcelain
1450 for 15 seconds is not enough time to melt through the tops of the pistons, but may have been enough to soften the ring lands. Run the EGTs at 1250 for a few minutes and you will definitely have holes. The amount of time required will vary from engine to engine, but as Gary said, plug one piston cooler and you are going to notice in a hurry. The piston tops are about 5/8" thick, it takes time for all that mass to get hot enough to melt through.
The way a diesel engine works tends to keep the interior pretty clean compared to a gasser. Mostly soot in the oil rather than baked on deposits.
The way a diesel engine works tends to keep the interior pretty clean compared to a gasser. Mostly soot in the oil rather than baked on deposits.
icanfixall
Official GMM hand model
Ever see the cooling system in a top fuel dragster engine.. Well they don't have a cooling system around the cylinders or the heads. Its the volume of fuel being pushed and sucked into the engines that cools them... Kind of shocking to think the very stuff used to make fire and power is what cools an engine. I recall they run something like 12 gallons per 1/4 mile. All thats done in less than 4 seconds.. Really impressive. And we have issues with keeping our 7.3 cool. Mel figured it out for me once while we were talking. He mentioned that the 6.9 heads and blocks have coolant passages open in the lower corners of the engines where our 7.3 has the opening but the gaskets don't and the heads and the blocks are plugged. We need to fix that by running the 6.9 head gaskets and punching holes in the plugs so we have coolant flowing thru ALL of the heads and block. Not just part of it for better emissions.
Kind of shocking to think the very stuff used to make fire and power is what cools an engine. I recall they run something like 12 gallons per 1/4 mile. All thats done in less than 4 seconds.. Really impressive. And we have issues with keeping our 7.3 cool. Mel figured it out for me once while we were talking. He mentioned that the 6.9 heads and blocks have coolant passages open in the lower corners of the engines where our 7.3 has the opening but the gaskets don't and the heads and the blocks are plugged. We need to fix that by running the 6.9 head gaskets and punching holes in the plugs so we have coolant flowing thru ALL of the heads and block. Not just part of it for better emissions.So my 6.9 is all set with that then? No having plugs to punch holes in? My 6.9 never ran hot at all, sure my egt's got up there if I wasn't carefull but the water temp stayed low, Or at least the guage says so. And with the turbo and intercooler I'm thinking it will run even cooler. Because I was way over fueled for naturally aspirated
jaluhn83
Full Access Member
The EGT does not at all equal the temp of the pistons. You have a heat flux through the pistons and cylinders and heads - heat flows in from the combustion gases but then out to the coolant, oil or air. The pistons typically are the weakest link due to them taking a large amount of heat but having no contact with the coolant to reject heat directly. Instead the heat flows out through into the cylinders and to the oil being sprayed on the bottom of the piston.
The fact that the max safe EGT and the melting temp of aluminum is similar is a coincidence. If the pistons get much over about 300* you're going to have problems both due to expansion and scuffing and the material softening.
It's not so much the instantaneous high EGT that is bad as continual high temps - 30 seconds at 1500 is unlikely to cause much damage while 5 minutes at 1350 would be much more worrisome to me.
The fact that the max safe EGT and the melting temp of aluminum is similar is a coincidence. If the pistons get much over about 300* you're going to have problems both due to expansion and scuffing and the material softening.
It's not so much the instantaneous high EGT that is bad as continual high temps - 30 seconds at 1500 is unlikely to cause much damage while 5 minutes at 1350 would be much more worrisome to me.
icanfixall
Official GMM hand model
Even at truck or tractor pulls you normally don't see molten aluminum poring out the stacks but you will see blocks blowing apart. Look at the temps and pressures in the top fuel engine with no coolant going thru the heads or the block because they are cut from solid aluminum blocks. Its the volume of fuel going thru them that cools them. I'm sure I can run some very high pyro temps with my engine build and the ceramic coating piston tops but why test this to failure. I'm not one to push the safe limits.
82F100SWB
Full Access Member
Most big rigs run post turbo pyros. Steady egt's of 1200-1500 are not uncommon with modern emissions engines. Melted exhaust housings on turbos are not uncommon, but melted pistons are.
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Sent from my Galaxy Nexus using Tapatalk 4
coming home from the 2012 rally, I hit 1500 passing the group I was with climbing a hill in western pa.. was there for 15 seconds or so. I will hold mine around 1150-1200 for a long time climbing hills around me with trailer and truck behind me. no ill affects yet
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