Can I run the water pump on just distilled water?

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5,868
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Atlanta,GA
I'm planning on flushing out the coolant on my BMW sometime next week.

I don't really want to take off the water pump hose and the other hoses to let coolant out. It'll create a big mess, which I don't really want.

So, I plan on unbolting the radiator drain plug and letting all the coolant drain out the radiator. Then Adding 2 gallons of distilled water and bleed the system/ turning the water pump on without starting the car.

After I'm done bleeding the system and draining the water out, I'll add the 50/50 BMW coolant.

Can I harm the water pump or other coolant items by just bleeding the system with distilled water?

If I turn the water pump on when there's no coolant in the system, can I harm the water pump that way by running it dry?

Any other things I should be cautious of?
The radiator isn't the lowest point so you're still going to have a lot of coolant remaining. If it were then BMW shop manuals wouldn't require removal of the hose at the electric water pump.

As for running the water pump with distilled water only. There's no issue with causing damage to the pump. Constantly running the water pump will use a lot of charge from your battery. The bleed procedure runs for 12 minutes.

Finally your coolant/water mix is going to be well below the 50/50 recommendation.

I guess it's possible that if you parked the car with the nose facing downhill you could get most of the coolant out. and then just refill with 50/50 mix but that's going to be a mess as well.

IMO I would just wait to change the coolant whenever you go in the replace the water pump or just pay a shop to do it.
 

mosaud1998

Thread starter
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440
Location
Chicago, IL
The radiator isn't the lowest point so you're still going to have a lot of coolant remaining. If it were then BMW shop manuals wouldn't require removal of the hose at the electric water pump.

As for running the water pump with distilled water only. There's no issue with causing damage to the pump. Constantly running the water pump will use a lot of charge from your battery. The bleed procedure runs for 12 minutes.

Finally your coolant/water mix is going to be well below the 50/50 recommendation.

I guess it's possible that if you parked the car with the nose facing downhill you could get most of the coolant out. and then just refill with 50/50 mix but that's going to be a mess as well.

IMO I would just wait to change the coolant whenever you go in the replace the water pump or just pay a shop to do it.
Yeah, that's what some people on the BMW forums said. They said to do a drain and refill with BMW 50/50 is the best route to go. Just repeat this procedure every 2-3 years.
 

mosaud1998

Thread starter
Messages
440
Location
Chicago, IL
The radiator isn't the lowest point so you're still going to have a lot of coolant remaining. If it were then BMW shop manuals wouldn't require removal of the hose at the electric water pump.

As for running the water pump with distilled water only. There's no issue with causing damage to the pump. Constantly running the water pump will use a lot of charge from your battery. The bleed procedure runs for 12 minutes.

Finally your coolant/water mix is going to be well below the 50/50 recommendation.

I guess it's possible that if you parked the car with the nose facing downhill you could get most of the coolant out. and then just refill with 50/50 mix but that's going to be a mess as well.

IMO I would just wait to change the coolant whenever you go in the replace the water pump or just pay a shop to do it.
This is what one forum member said:

Problem is: Anytime you add LESS-Concentrated mix of Antifreeze/Coolant than 50/50, you dilute the Concentration to LESS than 50% antifreeze. Bentley says capacity of cooling system is 2.23 Gallons with Automatic Transmission. So if you "don't want to make a mess" and forego draining at the pump (which is the LOW spot in the system), you MAY get ~ 1.5 gallons (6 quarts) of coolant out of system when you simply open the radiator drain plug.

Do NOT "UNBOLT" -- the plug is a PZ4/P4 fitting in a plastic housing with 19mm Hex to hold with 19mm spanner while loosening plug. FAILURE to hold that 19mm hex to prevent it turning WILL result in breaking assembly. Then you WILL have a "mess" on your hands ;-)

So HOW's your algebra? If you drain 1.5 of 2.23 gallons of 50/50 mix (do you even KNOW what it's concentration IS, or do we just ASSume? If you live in FL or TX (at least unless it's February ;-) the freezing point is NOT important, but the corrosion factor IS. If you fill the partially-drained system ONCE with distilled H2O, run the pump to circulate the new mix, and then Radiator Drain, refill with H2O, and repeat, after draining the last time, HOW MUCH water, and how much Antifreeze (by volume) remain in the block, trans cooler, etc.???

Point is, HOW exact do you want to be? What impurities, pH, or ion exchange issues are you seeking to address by the "flush" or Drain & Refill.
 
Messages
5,868
Location
Atlanta,GA
Yeah, that's what some people on the BMW forums said. They said to do a drain and refill with BMW 50/50 is the best route to go. Just repeat this procedure every 2-3 years.
IIRC the fluid is lifetime or 100k miles and it actually performs as advertised. It's why I always suggest to change the fluid when the water pump is changed out. You can of course do it as often as you want but it's not really necessary. I think lifetime coolant has been the industry norm for over a decade.

I've yet to see any evidence of coolant degrading and causing problems in a N-series engine.
 
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1,816
Location
California
If the cooling system is maintained in good condition, all it needs is a drain & fill done properly (remove hoses, plugs, knock sensors, etc. as needed). No flushing. If the cooling system is questionable and could benefit from a flush, it's OK to run straight water through the system briefly. But it should be restored to proper coolant chemistry as soon as possible.
I have called the local authorities many times over the years regarding proper disposal of automotive coolant. They have always told me to dump it into the toilet with a couple extra flushes to help dilution and treatment.
 
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124
Location
Raleigh, NC
I wouldn't put coolant in the drain. I don't care what they say. It's much better to take it to a proper place than dump it.

Also losing 5-10% coolant isn't going to cause corrosion. Having old 50/50 is worse, in my book, than 40/60 that you replace every 3-5 years.
 
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