Flushing the Cooling System

E28 technical advice asked and given! Troubleshooting, modifications and more.
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dragonbar
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Flushing the Cooling System

Post by dragonbar »

My new radiator will be here today so the swap will start tonight (and hopefully end before cars and coffee in the morning). I figure, while I have the cooling system open, I may as well flush everything too. So my question is this; is there a preferred method to flush the system? Can I just put a hose up to a water passage and blast it, or is there something else a little more refined?

Also just off the top of someones head, what is the total coolant capacity? I need to know how much coolant to buy today.
Coldswede
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Post by Coldswede »

12 quarts
Blue Shadow
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Post by Blue Shadow »

When I did the E23, I put 12 quarts into the car after a complete flush. The system was EMPTY.

When I did the E28, I put over 11½ quarts into the system. I was very happy with getting all the old stuff out of the systems.

Here is what I did
Drain radiator
Drain motor
Pull a hose or two from the thermostat housing and flush
Continue to flush
Flush the radiator through the hose (not necessary with your new radiator)
Flush out the coolant overflow, pull it and wash it out
Have the heat on/open, this can be operated by voltage to the control valve
When everything is clear, use air to blow out the entire system to remove all the remaining water.

Close up the system install the radiator and pour in the amount the of antifreeze you want in the system and finish it off with distilled water. Being in Houston, you can do with less than a 50% mixture. Water is a better heat transfer fluid than antifreeze.
bojangles
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Post by bojangles »

Blue Shadow wrote: Water is a better heat transfer fluid than antifreeze.
Not so sure about this.

Also the coolant raises the boiling point above 100C (212F) You really need to have the right amount of coolant for all kinds of reasons. Corrosion etc...
1st 5er
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Post by 1st 5er »

Don't forget to use the block drain plug.
tsmall07
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Post by tsmall07 »

bojangles wrote:
Blue Shadow wrote: Water is a better heat transfer fluid than antifreeze.
Not so sure about this.
It's true. The pressure in the cooling system raises the boiling point of water enough to be adequate on it's own.

Whenever I replace my coolant (every 2 years) I just open up the block drain and drain the radiator. That gets pretty much all of it out. No need to really "Flush" the system unless yours is extraordinarily dirty. I'm not one to spend extra dough on OEM fluids, but I always use blue BMW coolant. It's designed to run in aluminum core rads and I can always tell if coolant on the ground is mine or not. You can get the right coolant for an aluminum rad elsewhere, but the BMW stuff isn't much of a premium over the other stuff. Also, I always fill with distilled water. You'll extend the life of your rad if you don't pump it full of the impurities that can be found in tap water. Put the minimum amount of coolant (anti-freeze) to keep your system from freezing in the winter. It'll stay cooler with more water in the system. Calling anti-freeze "coolant" is a misnomer. If you want it to stay really cool, fill with distilled water and Water Wetter, but you'd have to change it every winter (or maybe not since you live in Houston. I don't know how cold it gets there).
1st 5er
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Post by 1st 5er »

tsmall07 wrote: fill with distilled water and Water Wetter, but you'd have to change it every winter (or maybe not since you live in Houston. I don't know how cold it gets there).
Somewhere around 18 F this past winter was our low.
Mike W.
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Post by Mike W. »

bojangles wrote:
Blue Shadow wrote: Water is a better heat transfer fluid than antifreeze.
Not so sure about this.

Also the coolant raises the boiling point above 100C (212F) You really need to have the right amount of coolant for all kinds of reasons. Corrosion etc...
As Tyler mentioned water is better at transferring heat than anything else commonly used. That doesn't mean it is wise to run straight water for an assortment of reasons including boiling point and corrosion.
Coldswede
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Post by Coldswede »

33% antifreeze/water mixture is considered optimum for corrosion protection and cooling IF there are no freeze protection considerations.
bradwood
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Post by bradwood »

So can a normal hose and tap water be used to flush?

Assuming it should then have a final flush with distilled or demineralised water before the water/collant refill?
1st 5er
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Post by 1st 5er »

Yes.
bojangles
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Post by bojangles »

tsmall07 wrote:
bojangles wrote:
Blue Shadow wrote: Water is a better heat transfer fluid than antifreeze.
Not so sure about this.
It's true. The pressure in the cooling system raises the boiling point of water enough to be adequate on it's own.
xxxxxx Put the minimum amount of coolant (anti-freeze) to keep your system from freezing in the winter. It'll stay cooler with more water in the system. Calling anti-freeze "coolant" is a misnomer. If you want it to stay really cool, fill with distilled water and Water Wetter, .
Well I suppose it depends on what you call better.
Coolant (mixture) transfers heat marginally less that plain water, but water alone does damage to the engine.
Water wetter is meant to be added to coolant mixtures, not just water.

When you have a concern with engine cooling, it is when the liquid boils that you are f*cked. every degree of protection when you are nearing that point is equally important.
Pressure alone is good for 20-30 degrees of protection above plain water, and using coolant instead of water can give you an extra 5-10 degrees.
the difference in heat transfer is much less, the mixture is about 95% as good as plain water and to compensate, the solution is to increase the flow through the system.

From an engineering standpoint, the car's cooling system is designed with the flow needed to give maximum protection from boiling with pressure and coolant mixture.

there is no question that if you run straight water, you will boil over sooner, under the same conditions.
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