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I am in a phase of constant curiosity now.:rolleyes: Guess I didn't get enough of it when I was three.

Anyway I was wondering what actually happens to a motor when it overheats. I am especially curious about the newer motors. Does it expand the head gasket an warp it? Make the block expand and crush the piston? What really happens?
 

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Simple answer (from the old days) Your screwed:D I'm going to let the experts chime in on this one:yes:
 

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Headgasket can blow, piston can sieze in the bore, oil can break down and lose lubricity? Result, engine fubared if ran too long.
 

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Things warp and move. Aluminum expands faster than iron so the pistons grow in the bores and can scuff or sieze, If ring gaps are tight the rings can sieze. Valves can sieze in thier guides. Oil looses viscosity and failes to lubricate causing friction and localized heat, scuffing or melting bearings. Basically any sealing surface is prone to leak due to warping or twisting, and any parts which move against one annother are subject to galling, melting or siezing.
generally the newer (less hours of operation) the motor is the bigger the problem, due to tighter tollerances.
 

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My 5.0 Mustang threw a belt on a very late night ride home from the girlfriends back in the day. I pegged the temp gauge and kept driving. When I finally got home and turned the motor off it clanged, banged, groaned for a minute or two, like it was alive. Never heard anything like that before. Got a new belt and the next day it started right up no problem, no leaks or weird noises at all. Problem was hot restarts. It would not crank when hot. Even a brand new starter, heat shield and battery did nothing for this condition. Did what any normal person would. Traded it in.
 

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I once got called to help instrument a GM 4 cylinder. They were having head gasket warranty problems and needed to find out the root cause.
I internally strain gauged the head bolts (tiny hole in the middle, ship in a bottle style), calibrated them and after they were installed went to the GM tech center in Milford, Michigan. They had the engine installed in a fully instrumented (thermocouples, pressure sensors, the works) FWD GM car and strapped on the computerized chassis dyno.

The test plan was to run the car through a test cycle, drain a liter of coolant, re run the test and drain another liter. We repeated the test until the engine overheated and the gasket failed.

Processing the data took awhile, but it was very interesting. The bolt strain can give you the amount of stretch. We could take the CAD math data with the test data and computer animate a 3d model of the engine to show what was happening.
You could see what was distorting and how the longer bolts stretched, lost tension then the head gasket would blow out in a certain area.
Every engine design is different and this one had "cost savings" that made it less robust if the coolant was low.
Many modern engines have low coolant limp home protection modes that cut power to save the engine.
 

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Friend of mine sister threw the fan belt off a car on the interstate and kept driving even after the temp light came on. She drove at least 60 miles at highway speed. She got to the top of the exit ramp before it died. It was a lates 70's Mercury with a 400M. The car would still turn with starter but would not start. It must have welded the rings to the pistons because it didn't have any measurable compression.
I also know someone that fell asleep in their car on a really cold night. They started the car but didn't know the water in the engine and radiator had frozen solid. The car sat and idled and got so hot it melted the electrodes out of the spark plugs before it died. It was a Lincoln Continental with a 462 engine. As bad a some of those old Fords spark knocked with low octane fuel I bet this one was dieseling after it should have died.
 

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How much heat can a typical SBC take before there's gonna be problems? Personaly I get uncomfortable at anything over 200 in the Nova, but my Silverado runs at 210 all day. I had the original 350 hit 230 once when I lost a fan belt and it was fine. I know there is no simple answer to this question as every engine is different, but as a rules of thumb what is too hot?
 

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Overheating is a complex problem.

Your engine has materials that grow at different rates under heat. Cast Iron, steel, aluminum, and various alloys of the same materials all have different thermal expansion rates. If in the design temperature range, no problems, once you get out of the range problems occur. Seizing or even loosening of parts. (Wrist pins can loosen up)

Cast iron or cast aluminum growth and twisting stabilizes after cycling through temperature. 50 cycles gets most of it. That is why new engines make lots of noise cooling. Old race car builders wanted blocks with 50,000 miles on them to start from. Nice and stable. When you go into a new temperature range there is all new growth and twisting.

Head gaskets often go. Faster when block and heads are different. Caused by loosening of the gasket by stretching bolts or complex twisting forces. In some cases burned or blown out from the engine pre-ignition or knocking when hot.

Bolts can come loose. Spark plugs often. I often removed spark plugs with my fingers from engines that had been overheated. (when cold!)

Old oil sludge is melted off the outside and inside of the engine. The stuff inside can plug filters or oil passages.

Oil viscosity drops, oil pressure drops and lubrication capability drops as the need for it has sky rocketed.

With low coolant or when you start blowing steam, parts of the engine can be much hotter than what the temp gauge shows. We had a race car showing 210 from the steam on the gauge, but the heads were glowing red near the exhaust.

Depending on the engine, lights come on from 245 or up.

When an engine has been run for any extended period of time overheated (light on) it is usually a loss for anything below the intake.

What is the temp that causes problems? It all depends on engine, time and temp.
 

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What actually happens when a motor overheats?
...um, it gets hot?

I lost a belt in the waterbox and didn't know until I crossed the finish line at Pomona a little over 260°--didn't seem to have any effect whatsoever, but that's about 100° higher than my normal race temp.
 
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