Change coolant hot or cold?

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6,592
Location
Suburban Washington DC
All those darn rich people, buying new cars every 3 years, never having to change the coolant. I feel if you're gonna do it, do it right. I have no problem on my Honda's to remove the block plug.

168Engine block drain plug.JPG


And even then I fill with water, drive 10 minutes, repeat 5 or 6 times until there is no trace of old coolant. Takes an hour or two but then it's done for the next 100,000 miles.
 
Messages
342
Location
Maryland
Over the years I've had two friends go to the emergency room fr55om engine coolant burns.
OTOH I know of no one going to the ER for motor oil burns.
That second friend to the ER, the incident happened after the engine had been cooling for nearly an hour.
Just as an FYI, the heat capacity of water at 77 Deg F is approximately 1 Cp. The heat capacity of motor oil at 77 Deg F is approximately 0.45 Cp Therefore a water antifreeze solution holds more heat than motor oil at a given temperature. It's the amount of heat and not the temperature that determines how bad a burn is.
 
Messages
6,592
Location
Suburban Washington DC
Just as an FYI, the heat capacity of water at 77 Deg F is approximately 1 Cp. The heat capacity of motor oil at 77 Deg F is approximately 0.45 Cp Therefore a water antifreeze solution holds more heat than motor oil at a given temperature. It's the amount of heat and not the temperature that determines how bad a burn is.
What about the difference in adhesion between the two? Spill some hot coolant on your arm and you can wipe it off in less than a second on your shirt before it does much damage. Oil will stick to your skin much more.
 
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342
Location
Maryland
I would think that by the time one gets the oil wiped off relative to the time it takes to get hot coolant off, the oil will have lost more heat than the coolant solution and therefor make for a less severe encounter. Remember, the amount of oil left behind on skin will weigh less than a similar amount of coolant on skin, and therefore have less heat to transfer.
 
Messages
342
Location
Maryland
No. Motor oil density is less than water. I'm not sure what the density of a 50:50 water:coolant is, but it's closer to that of water than motor oil.
 
Messages
342
Location
Maryland
FYI, at 77 Deg F, density of 100% ethylene glycol is 1.11 g/mL, the density of water is 1.00 g/mL, and the density of motor oil ranges from 0.78 to 0.84 g/mL. Hence a 50:50 solution of water:ethylene glycol coolant equals approximately 1.05 g/mL.
 
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1,665
Location
California
I change coolant after the engine's been run at full temp for a while, then shut it down for about 1 hour before draining.
I want particles to be in suspension as much as possible so they drain out, but at the same time I don't want to get burned.
 
Messages
17,931
Location
NH
I drain cold, try to do every 2 or 3 years. Just a drain and fill. So many vehicles go 10+ years without issue for me to think it’s somehow critical—ok, maybe there’s some models for which it is, but I’m not sure about it matters for most.

I know in ye olden days there were valves in the heater core to steer coolant, so on a flush one would need to fiddle with the heat setting. Not sure if anything modern uses that.

To me, if I drain half and refill, but do so when the coolant is say “half worn”, then the coolant is now mostly new (75% good) once again. Sure I could drain the block and do a flush, but to what gain? If I changed the coolant before it was worn out, then just what is getting flushed out?

I’ve heard of coolant filters, so I don’t want to discredit the notion that the system can make particles over the years. Just that this service is just not one to lose sleep over.
 
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6,592
Location
Suburban Washington DC
To me, if I drain half and refill, but do so when the coolant is say “half worn”, then the coolant is now mostly new (75% good) once again. Sure I could drain the block and do a flush, but to what gain?
That's kinda like changing the oil filter only every OTHER oil change. Why would you drain and refill the coolant when it's "half worn" at say 50,000 miles instead of changing it all at 100K? "Half worn" still protects as well as new.
 
Messages
17,931
Location
NH
That's kinda like changing the oil filter only every OTHER oil change. Why would you drain and refill the coolant when it's "half worn" at say 50,000 miles instead of changing it all at 100K? "Half worn" still protects as well as new.
Less work than messing with a block drain. I pay a bit more but do less work. Even trade in my eyes.
 
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5,512
Location
down in the park
Umm no. Motor oil temperatures can reach over 300 degrees. Coolant maybe 250 and just when under pressure, maybe 230 outside the cooling system. Of course you, wait 10 or 20 minutes if the engine is hot before changing it. And wear gloves. Do you change your oil cold too?....Wait, better not answer that.
Coolant could turn to steam when pressure releases. Also, there's much more energy in 200F coolant than in 200F oil. About 50% more.

But of course, only an idiot would change fluids at operating temp. The smart guys wait until the danger of burns has passed, especially since exhaust parts are even hotter and very close to human body parts when working under the vehicle.
 
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