Does engine performance diminish while overheating?

[Awass]

Besides the obvious threat of explosion, if an engine is in the overheating zone does it produce less thrust? Are there any adverse effects?

[LameLefty]

I've wondered that too. Shouldn't there be some adverse impact like a reduction in ISP?

[rkman]

No. They just explode when overheating gets to 100%.

[SRV Ron]

If you are pushing an engine above its 100% rating, it should be threatened with overheating.

For some, like the Mainsail, it seems to be a function of what fuel tanks it connects to or if it is in the center of a cluster. For the LV-N, it is the design that threatens overheating if run at full power for an extended period. Then, I have had some launches where overheat shows up and others with the same design where it doesn't.

I could see having an engine, if pushed beyond 100%, produce more thrust at the expense of efficiency. Not sure how it happens with the Space Shuttle where they routinely go to 110% during the early phase of its launch and throttle back during the period of maximum aerodynamic resistance.

Currently, I don't think that a change of efficiency in relation to overheating has been programmed in to a flight. Perhaps, in the future when you have the ability to push 110% throttle to get a heavy rocket up to speed until some of the fuel has been used up.

Edited August 20, 2013 by SRV Ron

[Spica]

Theoretically, if an engine heats up to a higher temperature than it's rated heat is set to, its Isp would still increase because the gas will be under higher pressure than it would be at in normal flight. However, I doubt that this actually happens because all materials get softer and weaker if heat is applied to them. So, eventually, the rocket engine would melt, and explode. Taking all attached fuel tanks with it.

Spica

[GoDores]

I could see having an engine, if pushed beyond 100%, produce more thrust at the expense of efficiency. Not sure how it happens with the Space Shuttle where they routinely go to 110% during the early phase of its launch and throttle back during the period of maximum aerodynamic resistance.

Currently, I don't think that a change of efficiency in relation to overheating has been programmed in to a flight. Perhaps, in the future when you have the ability to push 110% throttle to get a heavy rocket up to speed until some of the fuel has been used up.

The Shuttle Main Engines didn't do anything special. They were initially designed to a certain maximum thrust spec, which was designated as 100% thrust. Later, in testing, it was found that they could safely produce more thrust than originally designed. Rather than redoing all the documentation, programming, etc. to set the new max safe thrust at 100%, they just kept the original max thrust value defined as 100% and designated new higher thrust values at over 100%.

That wouldn't really carry over to KSP where engine thrust ratings are defined in-game and no one's writing procedures for anything. If an engine were changed or modded to produce more thrust, its new higher thrust would still be 100%.