87 Accord-Engine Overheated

About 2 weeks ago, my 87 DX Accord engine (240,000 mi) severely overheated (temp gauge red-lined) and the engine stopped. Car sat at the curb over night. Had the
car towed to a local garage the next morning. When they went to look at it they noted: 1. The car started right up (and even called me to ask why did I bring the car into their shop) 2. Added 1 gallon on water to the radiator. 3. Did a pressure check on the cooling system and saw no indication of leaks.
They said due to the overheating, the compression on the engine is probably worse, so gas mileage will be less.
I've changed the oil and filter.
But, in the intervening 2 weeks, here's what I noticed: 1. Gas mileage seems to have gone from about 25 to 34 mpg. 2. The values (which previously rattled because they were loose), now are totally silent. 3. The engine runs smoothly and quietly, even uphill, under load.
So, is the surprising improvement only temporary and the engine will totally die in the not-too-distant future, or have I someone managed to overheat the engine enough to compensate for 240,000 miles of wear but not damage it, as it nor seems to run almost as new????
I love the car and thought I had destroyed it, but now I wonder and ask you for your sage advice / opinions.
Thanks! Ken
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KenA wrote:

How bout driving it till something falls off or quits working. bob
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information?" But that's not our call; here's my 2 cents' worth.
The risk is that the head may have warped. Aluminum has twice the thermal coefficient of expansion compared to iron, so when the engine overheats badly the head is often forced to bow up. So, keep an eye open for any of the typical signs of head gasket leaks: *unstable temperature, with spikes of overheating *the coolant level drops although there are no puddles under the car *sweet, white smoke from the exhaust *milky appearance of the oil on the dipstick or oil floating on the coolant in the reservoir The classic shade-tree test for head gasket leakage is to start with a cold engine, remove the radiator cap and start the engine. Pinch off the hose going to the reservoir and put the palm of your hand on the radiator cap opening. If you feel a steady pressure rise in the next few seconds or (worse) pulsations, that's bad news for the head/gasket.
Either way, I wouldn't trust the engine to any long road trips for a few weeks, until it earns your confidence. Having to deal with head gasket problems hundreds of miles from home would be a hassle.
Mike
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wrote:

The good news is they still had iron liners at that time.
If it was a quick/brief overheat, and the actual temperature never really went that high, you should be OK. Though just why things would get *better* afterwards, must remain a mystery! Maybe a sticky valve unstuck. Was it running hot beforehand, or was this all sudden?
J.
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KenA wrote:

sure, you now have coolant and the temp sensor is now telling the ecu to inject the correct amount of gas.

that needs to be fixed asap. there should be some lash. see the sticker under the hood for specs.

isn't it amazing how the acoustic damping of a little coolant makes an engine quieter?

try and figure out how you lost the coolant in the first place. you may get lucky and have this engine continue to run. more likely however, the head gasket will start to leak, if it's not already the cause of your coolant loss. continue to operate the vehicle and pay close attention to any symptoms. look for bubbles in the coolant and monitor coolant level [*inside the radiator* and the expansion bottle] every day when cold in the morning. and cross your fingers.
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