Engine temp question

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I don't understand engine temps. Ok, My thermostat opens at 170deg F, coolant boilover protection works to 270deg F, engine oil flashpoint is like 380deg F. But I'm sure the engine runs even hotter than that because if a put a few drops of water on my exhaust manifold it evaporates instantaneously in a burst of steam. It must be over 500deg F right? How hot does it get in an engine?
 
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Also your cooling system is under pressure and uses coolant, this helps with the cooling process and prevents boil over at lower temperatures that normal water would boil over at. ;\)
 
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 Originally Posted By: kevinf
I don't understand engine temps. Ok, My thermostat opens at 170deg F, coolant boilover protection works to 270deg F, engine oil flashpoint is like 380deg F. But I'm sure the engine runs even hotter than that because if a put a few drops of water on my exhaust manifold it evaporates instantaneously in a burst of steam. It must be over 500deg F right? How hot does it get in an engine?
Exhaust gas temperatures can be over 1000 degrees F
 
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 Originally Posted By: Junior
 Originally Posted By: kevinf
I don't understand engine temps. Ok, My thermostat opens at 170deg F, coolant boilover protection works to 270deg F, engine oil flashpoint is like 380deg F. But I'm sure the engine runs even hotter than that because if a put a few drops of water on my exhaust manifold it evaporates instantaneously in a burst of steam. It must be over 500deg F right? How hot does it get in an engine?
Exhaust gas temperatures can be over 1000 degrees F
Well over. 1600F+ isn't unusual at full power.
 
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Engine coolant needs to not exceed 240F or so. Any hotter than that your risking headgasket damage. Some imports with all aluminum engines will blow a head gasket around 220F.
 
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 Quote:
I don't understand engine temps.
You probably haven't been exposed to principles of steam or fundamental principles of heat exchange. Without such exposure, there's a great deal of magic involved.
 
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Kevin: I have a couple tools I use to help me in my quest to accumulate information that I don't really need. . . A couple weeks ago, I found this at Home Depot: Basically, you point it at what you want to measure (something other than, we hope, your retina...) and presto, temp reading. Hmmmm, 92 on the seat -- perhaps I should eat less Mexican. . . So far, I've seen temps in the 180s when the beam is pointed into the oil filler after shut down. I've seen 350 to 550 on the exhaust manifold and front cat (have not measured after a real hot run yet). I also use this, a Scan Gauge II for precise coolant readings. Typical coolant temps in the hybrid cycle between about 180 and 195. On three or four occasions, I've seen it peak over 200. No scientific precision here -- just some food for thought.
 
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 Originally Posted By: XS650
 Originally Posted By: Junior
 Originally Posted By: kevinf
I don't understand engine temps. Ok, My thermostat opens at 170deg F, coolant boilover protection works to 270deg F, engine oil flashpoint is like 380deg F. But I'm sure the engine runs even hotter than that because if a put a few drops of water on my exhaust manifold it evaporates instantaneously in a burst of steam. It must be over 500deg F right? How hot does it get in an engine?
Exhaust gas temperatures can be over 1000 degrees F
Well over. 1600F+ isn't unusual at full power.
A typical engine can not handle those temperatures. Aluminum melts at a little over 1200F. Anything much over 1100-1200 on a continuous basis is an equation for trouble. Typical cruising are much lower. At idle temps would be in the 3-400F range.
 
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The aluminum never reaches that temp. If it's a piston, it's been cooled by the intake charge and the oil from below. If it's the head, it's sitting in a bath of fluid that can't get anywhere near the melting point. There's an insulating layer of unburned fuel on the piston and combustion chamber. I will tell you one thing though, you run an aluminum head engine out of water and continue to drive it, you will find a melted head when you go to change the head gasket. I thought the temp for aluminum was around 1600f. Maybe that's the molten pouring temp.
 
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 Originally Posted By: Gary Allan
I thought the temp for aluminum was around 1600f. Maybe that's the molten pouring temp.
Sounds like a pour temp. It melts around 1200f, falls apart at lower temperatures.
 
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I should have thought of it, but if I get out today, I'll shoot the Al immediately adjacent to the exhaust ports to see how hot the area is. We can assume, I suppose that the exterior surface temps will be somewhat below what's actually being exposed to hot exhaust gasses.
 
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Well, I've been out on a multi-stop 17.5 mile trip, in hot, clear conditions. Immediately upon pulling in the garage, I used the laser-IR temp gun on multi points around the engine room. See this thread which I just started. As you can see, the temps for the aluminum, at least on the surface, but immediately adjacent to the exhaust ports, are far, far below any temp at which the aluminum would be structurally compromised.
 
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 Originally Posted By: XS650
Most any gasoline engine can handle 1600F exhaust gas temperatures.
I know this is apples to oranges, but in the offroad diesel engines we use, the continuous EGT limit is usually somewhere between 1200F and 1300F at the turbine inlet. 1400F for something like 5 minutes max. 1600F on a continuous basis sounds high to me, But, I am not as familar with gasoline engines. I suppose you do get the cooling from the vaporization of the fuel and diesels have a higher compression ratio so the EGT is going to be cooler due to more expanision (ideal gas law) Maybe that 1600 EGT relates to similar combustion temps between the two. Hmmm, I don't know, typing out loud now.....
 
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Diesel run excess air through them at full power. That helps keep temperatures down. Instead of running at stoiciometric which is about 15:1` for diesel, they run 17:1 and leaner at full power. I believe 20:1 isn't unusual at full power. For a crude approximation consider air temperature increase directly proportional to the air:fuel ratio. Crunch the numbers and the extra air mass largely explains the temperature difference.
 
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Yeah, I think you are correct. I failed to remember that 20 some percent of the charge air mass is washed through the combustion chamber during exhaust. I guess I know just enough to be dangerous. :)
 
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Some aspects to keep in mind, particulary with piston crown temperatures. The piston is exposed alternately to burning air/fuel, exhaust, intake air, and compressing air...all in rapid succession. Therefore, you will have a wave of heating and cooling processes taking place. 1600F exhaust is followed by a similarly timed 100F intake temperature, surface temp approximating the average of the two, the bulk metal temp being lower through heat transfer to the oil beneath the piston. Also, there's a tiny boundary layer on top of the piston which (should) insulate the piston crown..part of the reason that detonation is so bad...it removes this thin layer
 
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