Coolant flush water left over in engine block

I know this question has probably been asked a good amount of times but I wan to do a coolant flush on my 2005 Acura mdx. after I flush and drain everything out of the radiator, I want to drain the remaining water in the block. after I drain the block and fill the radiator, will the thermostat have to open for coolant to get in the block? is it ok for the engine block to have no coolant in it until that happens? thanks

After you fill the cooling system, start the engine with the pressure (radiator) cap off.

Allow the engine to idle until the coolant level in the radiator drops, (that’s when the thermostat opens) and finish filling the radiator with coolant.



i trust your answer but, does the thermostat open sooner because im assuming the engine gets more hot quicker? are u sure the block having nothing in it is ok?

When you let the engine idle, the coolant reaches a temperature that causes the thermostat to open.

When you first fill the radiator, it also fills the engine block.



Suggest to hire a shop to loosen the block’s drain plugs if they’ve never been removed since the car was new. Drain plugs can rust in place & be very difficult to remove. A diy’er could damage the block trying to remove one, something best avoided. I’ve done the coolant flush and replacement job numerous times over the years on my Toyota & VW cars and Ford truck (no Acuras) and never removed the drain plugs on any of them. I drain the radiator, refill, and let the water pump do the flush for me.

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Let me be the wet blanket. If you have not serviced the timing belt I suggest you just have that done at a dealer to preserve the engine. The kit comes with the belt, water pump, and tensioners. The service includes a coolant flush. I tried to just have the coolant serviced and was properly advised to just do the belt kit. You risk ruining the engine if it breaks. Never mind if you already did it.

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My question is Why do you want to flush it? Is there a problem? Is your current coolant a muddy brown? Is it very cloudy?

I get a lot of grief here about this but in my experience, flushing a cooling system without good cause is asking for trouble, especially if you use a chemical flush.

If the coolant is clear (it is colored) and not cloudy, just drain and refill. If you are due for a timing belt, then I’d follow @bing’s advice.


the current coolant looks muddy brown and i want to add different coolant than whats already in there. I know its bad to mix coolant.

i want to do this but wouldnt this leave water in the block? I was gonna re fill it with 50/50 which would be diluted by the left over water im assuming. I’ve thought about just buying concrete coolant and doing the math on how much comes out and how much i need to add for 50/50

I don’t know about anyone else. but when a customer brings their vehicle in for a coolant service, they expect me to replace all the coolant.

Not just some of it.

Same with oil changes, transmission fluid service, etc…


i’m not sure what coolant is in there atm but would it be ok to just add coolant to the reservoir even if its not the same stuff? im assuming oem coolant is in there and i want to use prestone. prestone is 1/3 of the price per gallon lol

I’ve always refilled w/100% coolant (concentrated) then let the water pump mix it all together back to 50/50, idling engine w/radiator cap removed and front end raised. On some cooling system designs this might not be 100% effective, but it seems to work ok on my vehicles. Make sure all coolant paths including heater are circulating coolant during the re-mix process of course. Common sense says if you want this job done correctly, best hire a trained pro to do it for you.

Needs to end up with a 50/50 mix by doing this (assuming that’s the spec).

Prestone is a manufacturer of many different types of coolant. You need a coolant that meets the specifications for your vehicle. While certain types of coolants shouldn’t be mixed, you should be able to find a budget manufacturer of the same type of coolant that’s already in your system. Are you trying to switch from Dexcool by any chance?

The long life factory Acura stuff is blue. Maybe someone put the orange dex
Cool stuff in it. Bad to mix. You don’t know what’s in it. I’ve used nothing but the blue in my acuras but suit yourself. I have all my service done at the dealer but do my own oil and filter changes. The new mdx has a sticker of $71,000.

Deathcool was only used in GM vehicles.

OP has an Acura.


Ooops! Thanks. Saw the muddy brown- want to switch, mind immediately went to Dexcool…

He said he doesn’t know what is in there, just looks muddy. It came with blue so someone may have put something else in over the past 18 years. Who knows what’s in there.

Then the cooling system should be flushed.


Yeah I wonder what that water pump looks like? Be a shame to flush the system and have the pump freeze up and/or snap the timing belt and bend the valves.