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How hot is "too hot"? - 3/4/2005 2:06:22 PM   
yard-dart



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Status: offline 		I've spoken with several people on this subject, even some pros, but everyone has their own opinions as to how hot an engine can operate until the temps start to damage the engine. My thinking is that as long as it's not lean, it really doesn't matter. Many I've talked to disagree. These people say that there has got to be a point to where the temps are so high that parts of the engine will probably start to distort.

Reading through this forum, I've read where people have recorded their engines temping at over 375, even 400 degrees, without any signs that the engine is about to fail. What do you think? How hot is too hot? What temp does an engine have to get to before the internals actually start to melt down/fail.

These engines, and their components, are made up of different kinds of metals. They can withstand very high temps, but what is the breaking point?
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RE: How hot is "too hot"? - 3/4/2005 4:13:07 PM   
enjoymentboy


 

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Status: offline 		I've had an engine run over 400°F and not suffer any damage. As you state as long as it's not lean or starved for lubrication then it should be fine. That's my experience anyway. Some engines just run hot no matter how they are tuned. I honestly believe that many of the temp readings are not accurate anyway. If a heat sink is better able to shed heat than it may give a lower reading than the engine is running at and if it can't shed the heat as fast as others but it has more mass then it can technically hold more heat and still provide adequate cooling. Tune for performance and then back it off just a bit.

Enjoymentboy

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RE: How hot is "too hot"? - 3/4/2005 4:37:54 PM   
gubbs3



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Status: offline 		I think there is definitely a point at which the engine is just too hot. The most critical part of the engine that is severly affected by high temps is the upper end of the rod. Should the engine get too hot, the metal softens enough to let the piston part company. What temp this is depends on the materials the parts are made of. An engine with a steel rod probably wouldn't even be able to reach that point, but other parts would suffer anyway.

I think, with proper lubrication, an engine could be consistently run in the 300-400 range without damage. However, at this temp, should the fuel run short, a lean setting for even just a few seconds could do in the engine. On the other hand, if an engine is running at 220 and it runs lean, it still has a buffer to somewhat protect itself.

So I say, when in doubt, open the needle a little more.

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RE: How hot is "too hot"? - 3/5/2005 4:04:00 PM   
yard-dart



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Status: offline 		One thing I put into consideration is the glow plug. We all know how sensative they are. If it's not too hot for the glow plug, it shouldn't be too hot for anything else. If an engine is constantly blowing plugs, it could very well be because the engine is running to hot.

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RE: How hot is "too hot"? - 3/5/2005 4:25:43 PM   
gubbs3



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Status: offline 		I don't think the actual temp of the glow plug would do it in. I'm not sure what temp they can reach but that white-hot glowing element must be way hotter than what the engine internal temps reach. I'm sure that the platinum element can withstand more heat than an aluminum piston.

It would be nice if there was a certain known temp that the internals started to distort due to the high temp. Then the only issue would be finding what the head temp or exhaust temp would be to gauge that temp by.

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RE: How hot is "too hot"? - 3/12/2005 2:49:08 PM   
yard-dart



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Status: offline 		Could it be that the engine manufacturers don't want us knowing that magic "destruction" temprature? It could definately be figured out, although there would probably be quite a few engines to meet their demise in the testing process.

I honestly think that these engines can withstand much higher temps than what we're being told, withstanding them safely. Enjoymentboy stated that he had temped his engine at over 400 degrees. That is pretty extreme, but he does state that it suffered no apparent damage. I've read numerous threads where people find their engines running best around the 350 degree mark, and sometimes higher, without one hint of a problem.

Are we supposed to trust the "don't exceed 280-300 degrees" tale? Is it just hogwash? Why are so many other people having better performance from their engines at higher temps? Why aren't they frying their engines? Is the manufacturer telling us to keep the temps down so that we'll "wear out" our engines faster? Are the lower temps worse on our engines than the higher temps? Are we being mislead?

I've talked to some pretty competent people, people who've been in this hobby for quite some time. Some of them are in the fuel business, and some are mechanics/engine repairmen. All of them have told me that the performance heat doesn't harm an engine. They say that heat that's caused from a "lean run" is what is harmful.

I would love to know what the breaking point is, the temp which is high enough to start damaging an engine's internals.

< Message edited by yard-dart -- 3/12/2005 2:51:32 PM >

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RE: How hot is "too hot"? - 3/19/2005 3:00:51 PM   
Fuelman


 

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Status: online 		Meltdown temp? I have no idea, but my educated guess is that cast aluminum will start disfiguring rapidly around 700 degrees. Keep in mind that this is well beyond the capability of the lubricants (even castor) to protect the moving parts. One thing to consider is that the brass sleeve will expand at the top faster than the piston will so at some point in the elevated temps, it will loose compression rapidly as the sleeve gets too big for the piston. Once cooler, it will run just fine. if your lubes hold up, and it was not lean, there should be little if any additional wear caused by this happening. Problem is; most folks that experience this condition are running too lean, starving the engine of oil.
Most car folks ruin engines from running them too cool rather than too hot. The magic temp to reach in order to minimize wear (regardless of the instructions, and measured at the base of the glowplug) is 230 to 240 degrees F. The upper range is basically untill the sleeve out expands the piston, and the design fit is out of tolerance causing compression loss.

Does this help John?

Fuelman


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RE: How hot is "too hot"? - 3/26/2005 3:57:32 PM   
yard-dart



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Status: offline 		Brian,

That's some very interesting info. Yes, you've definately helped to shed more light on the subject.

Thanks,

John


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RE: How hot is "too hot"? - 3/27/2005 12:15:25 AM   
Polar_Bus


 

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quote:

ORIGINAL: yard-dart

I've spoken with several people on this subject, even some pros, but everyone has their own opinions as to how hot an engine can operate until the temps start to damage the engine. My thinking is that as long as it's not lean, it really doesn't matter. Many I've talked to disagree. These people say that there has got to be a point to where the temps are so high that parts of the engine will probably start to distort.

Reading through this forum, I've read where people have recorded their engines temping at over 375, even 400 degrees, without any signs that the engine is about to fail. What do you think? How hot is too hot? What temp does an engine have to get to before the internals actually start to melt down/fail.

These engines, and their components, are made up of different kinds of metals. They can withstand very high temps, but what is the breaking point?


The actual melting point of aluminum is 1220F. But dont let this high number fool you. If you are measuring 400 degrees at the heatsink, the internal piston crown temp is probably closer to 500 degrees. A side effect of an overheating engine is detonation. Detonation will burn a hole righ through a piston. An overheated engine will break down the lubrication between the piston and the sleeve causing it to jam and destroy themselves. I have accidentally pushed my engines to about 340F, without even knowing it. Running in grass on a hot summer day is when it will happen. A heavily loaded 1/8 MT engine will overheat much quicker than say a 1/10 on road. I always check my temps a few times just as a precaution even when I think the engine is in perfect tune.
Rich


< Message edited by Polar_Bus -- 3/27/2005 12:16:26 AM >

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RE: How hot is "too hot"? - 3/27/2005 12:55:06 AM   
Fuelman


 

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quote:

A side effect of an overheating engine is detonation. Detonation will burn a hole righ through a piston. An overheated engine will break down the lubrication between the piston and the sleeve causing it to jam and destroy themselves.


Actually, you got them reversed. A side effect of detonation is overheating. Yes, detonation will pop a hole through the piston top very quickly on some engines, a little more difficult on others but possible on any of them. If it is being run too lean, yes, detonation will occur even if you do not hear it (frying egg sound). Yes, an overheated engine will overstress the lubricants quite rapidly, if the extremely high temps are caused by it being too lean. If elevated temps are from a lack of cooling, and the engine is running just fine (not sagging or fading at full throttle) and is NOT TOO LEAN, your lubricnats will probably hold up.

Heat is nothing to be afraid of in a car engine, running them too lean is.

Fuelman


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RE: How hot is "too hot"? - 3/30/2005 2:37:32 PM   
Cummins


 

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Status: offline 		this is a really useful post. Why does running an engine too cool damage it?


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RE: How hot is "too hot"? - 3/30/2005 4:52:37 PM   
yard-dart



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Status: offline 		Cummins,

Hear is what I've learned. An engine has to run at, or above, 240 degrees in order to keep from prematurely wearing its piston. The piston sleeve is slightly tapered toward top dead center. If the engine does not reach the 240 degree mark, the temperature that has to be met in order for the sleeve to expand, the piston is being "pressed" into a tighter space. Therefore the piston is going to wear. From that point on, as long as the engine is ran at that needle setting, you may never notice a performance change. But, if the engine is ever leaned in order to reach optimal performance, the sleeve will heat up, expand, and there will not be a good fit because of the smaller piston diameter. At that point, the engine will loose compression and performance is going to drop quickly, maybe even to the point of not running at all.

This is the info that I have been given. It makes complete sense to me.

I hope this helps shed more light on the subject, and as always, I'm open to any arguments.

John

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RE: How hot is "too hot"? - 3/30/2005 5:13:03 PM   
Cummins


 

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Status: offline 		Thanks, that cleared up some stuff for me.


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