Changing coolant on a hot engine bad?

[VK56VD]

Hello All!

I just bought 2 gallons of Nissan Long Life Coolant for my '99 Nissan Maxima. I want to drain the radiator and re-fill with new coolant. After driving several days, I want to repeat the same steps again to get a higher percentage of new coolant mixed in.

I read on some boards that changing out the coolant on a hot engine is bad as it can warp the heads?

I will be doing this at my mechanics shop so the engine will be hot from driving. Should I wait for the engine to cool or is it safe to drain on a hot engine w/o re-precautions.

I would think most shops do not wait for engines to cool before they do radiator service on customers cars. Are they changing the fluid in an incorrect manner than?

Also, am I doing the right thing by changing the fluid twice so that a higher percentage is mixed in as I am not connecting the radiator to a flush machine as I am strictly sticking to Nissan Coolant to keep things safe.

Thanks a bunch!

 

[VK56VD]

somebody must know something about this...

 

[The Critic]

If you drained the engine block as well, you'd get at least 80% (usually) of the old coolant out.

You're "supposed" to wait until the engine is cool, but by the time you have the system drained (I also do the block drain, and finding the plug can take some time), the engine is usually cool.

 

[Junior]

You can drain it hot but you have the typical issues with high pressure coolant, steam and burns. It won't hurt the engine but it might hurt you.

The precaution is to not put cold coolant back into a hot engine.

 

[VK56VD]

thanks for the replies. I read on maxima.org that the drain for the block is very hard to get to. That is why I wanted to drain the radiator the second time within a thousand miles to have a higher percentage of new coolant in the system.

 

[Chris142]

If the engine was overheating and you dumped in ice water you could crack the block......So goes the tale anyway.

 

[alreadygone]

Supposed to be 50/50 mix. After draining rad, stick garden hose in on low and run fresh water in while engine is running. After a few minutes system will be all water. Then drain rad again, add pure antifreeze and you'll have almost exact 50/50 mix. Genuine OEM is so much B. S.

Bob

 

[NYEngineer]

Quote:

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If the engine was overheating and you dumped in ice water you could crack the block......So goes the tale anyway.

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It's no tale. I watched a guy pour cold coolant into a hot Cat 3412 once and crack the head that I had just finished installing. I wanted to crack him.

 

[kgb007stb]

If you can't wait for the engine to cool off, preheat the coolant to 150F and you can pour it into a hot engine. This decreases the temperature difference, I have done this several times without any ill effects.

 

[porcupine73]

If you wait at least say even five minutes after running before draining you should be OK. Though yes it's hot and under pressure. If you were to shut the at operating temp engine off and immediately drain the coolant you could have an issue. Waiting at least say 5 minutes makes sure the engine parts are not hotter than the coolant. If you watch the coolant temp after shutting off a warm engine it will rise at least a few degrees.