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!

 

[eljefino]

If it makes you feel better when the thermostat opens on a cold winter day a slug of very cold antifreeze suddenly enters circulation into the block etc.

I like the way you think though; there is no such thing as too much paranoia or too little thermal shock.

 

[onion]

It won't hurt a thing to do that job with the engine hot. It'll just be kinda unpleasant to work on. Might be a good idea to let it cool down for 10 minutes or so, though.

 

[wantin150]

I wouldn't think that just doing a radiator drain and re-fill would even affect the heads. You're not introducing anything cold into the block if you're not flushing.

 

[VK56VD]

so my idea of doing a radiator drain and re-fill the second time with a thousand miles is a good one since getting the the block plug is very difficult in the maxima's. my idea behind this is to have a higher percentage of fresh coolant in the system without a flush and opening up the plug for the block.

 

[wantin150]

From what I have read, the radiator is only about 50% of the total capacity. So if you drain and re-fill twice, you would roughly have a 75/25 mix of new/old (in theory).

 

[Titan]

Quote:

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From what I have read, the radiator is only about 50% of the total capacity. So if you drain and re-fill twice, you would roughly have a 75/25 mix of new/old (in theory).

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Of course, this depends upon the application. My Subaru manual states that my cooling system has 9.8 quarts, IIRC, and when I drained/filled, it took 8 quarts...one jug of coolant, one jug of distilled water.