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  #1  
Old 02-01-2025, 12:34 PM
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Question Coolant flush questions, N62

It's time to flush the coolant. Last time it was done professionally and I no longer have my good friend and mechanic to help me, RIP.

I've watched several YT videos and read through this water pump replacement guide by @Hayaku: (concentrating on step 41 and forward)

https://www.xoutpost.com/e5344waterpump.htm

I intend to flush the radiator several times with distilled water before doing a final fill with undiluted coolant. Time is not an issue. I got a new cap, brass bleed screw for the expansion tank and blue screw for the bottom. And the undiluted BMW blue coolant.

My questions are:

1. What is the total amount of coolant in an N62 4.4i? Google says 2.2 US gallons.

2. How much coolant drains from the radiator when you open it, the expansion tank and tank's bleeding screw? (need to calculate how much pure coolant to put in at the last step)

3. It sounds like I should wait until the coolant temperature drops to 50-60C before starting a new drain and fill cycle, correct? (I have a Foxwell or could use the hidden menu to monitor)

4. I saw a post where somebody said it's good to run the A/C as well as the heat after each fill. Is that a good idea? I don't see that in Hayaku's instructions.

I figure I will do three or four distilled water flush cycles.

Thanks!
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Old 02-01-2025, 02:58 PM
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The guide you a w referencing is for an M62, N62 is a slightly different procedure so I would advise looking up instructions for an N62

What you are describing is also not a full coolant flush. A full flush requires removing the block drains. Otherwise you will get out maybe half of the coolant volume. TIS has coolant volume listed in it, I am quite sure it's more than 2.2 gallons if you do a full proper flush.

Brass bleed screw is also imo a bad idea. The plastic bleed screws are rarely an issue, only a problem if you overtighten them. If you overtighten a brass bleed screw it strips the $80 expansion tank instead of the $6 plastic bleed screw.
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Old 02-01-2025, 06:21 PM
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Thanks for the feedback, BimmerBreaker.

You're right that Hayaku's is an M62. The version of TIS I have doesn't have a separate entry for the N62 (I think it's a TIS version from 2005). Maybe they are the same. I'll search again and see if I can find anything. I didn't see anything in my Bentley manual that listed the N62 capacity.

Edit: It looks like capacity is 3.75 gallons and about 1.5 comes out of the radiator. Lots of horror stories about access to the plugs on the engine block here, though the e53 may be easier:

https://www.bimmerfest.com/threads/e...-v8-n62.657484

I realize it's not a full flush. Even optimistically assuming you get a full mix, I'd still be at around 1:16 old coolant mix : distilled water after four radiator flushes.

I'll take my chances with the brass screw. A lot of people are happy with them. I understand your point about not tightening it too much.

Last edited by haigha; 02-01-2025 at 06:50 PM.
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Old 02-02-2025, 12:15 PM
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I’ve got an M62, so take it with a grain of salt, but I think it’s the same radiator and aux heater pump setup on the N62 e53s. If so, I’ve read about lots of guys getting trapped air. I’ve always had the best luck draining via the large hose on the bottom right of the radiator…outlet I think, and it empties a lot faster. Then I fill as much as I can via the radiator inlet hose on the top left, next to the tank. Just dump it in the radiator with a funnel, and right into the pump, via the hose fitting, taking care to squeeze the hoses often, then continue filling. Then fill the tank as the last step.

The M62 aux heater pump bleed method has always been a 100% solution for me.

I’ve got to replace the coolant tank sensor, on the bottom of the tank and would rather not drain the coolant too much. I’m wondering if I can get enough out of the tank with a pump or turkey baster, etc. so I don’t make a huge mess.
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Old 02-02-2025, 12:40 PM
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AFAIK The coolant sensor is magnetic and not exposed to coolant directly so no need to drain anything
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Old 02-02-2025, 01:31 PM
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Quote:
Originally Posted by haigha View Post
Thanks for the feedback, BimmerBreaker.

You're right that Hayaku's is an M62. The version of TIS I have doesn't have a separate entry for the N62 (I think it's a TIS version from 2005). Maybe they are the same. I'll search again and see if I can find anything. I didn't see anything in my Bentley manual that listed the N62 capacity.

Edit: It looks like capacity is 3.75 gallons and about 1.5 comes out of the radiator. Lots of horror stories about access to the plugs on the engine block here, though the e53 may be easier:

https://www.bimmerfest.com/threads/e...-v8-n62.657484

I realize it's not a full flush. Even optimistically assuming you get a full mix, I'd still be at around 1:16 old coolant mix : distilled water after four radiator flushes.

I'll take my chances with the brass screw. A lot of people are happy with them. I understand your point about not tightening it too much.
They are not the same. You need to find TIS procedure "Repair Instructions (REP) Removing and installing/replacing water pump (N62/N62TU)"

N62 water pump replacement requires removal of the vibration damper. It is a slightly more involved job than on an M62. You'll also want to replace the small coolant pipe from water pump to the valley pan.
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Old 02-02-2025, 02:11 PM
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Quote:
Originally Posted by 80stech View Post
AFAIK The coolant sensor is magnetic and not exposed to coolant directly so no need to drain anything
That’s great news, thanks! Why would BMW choose to have a less complex and leak prone part, in a fluid system!?
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Old 02-02-2025, 04:13 PM
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Quote:
Originally Posted by BimmerBreaker View Post
They are not the same. You need to find TIS procedure "Repair Instructions (REP) Removing and installing/replacing water pump (N62/N62TU)"..
Thanks for the pointer. I'm only doing flush, not replacing the water pump. I referenced Hayaku's procedure at step 41 onwards. I'll look to see if my TIS has the N62 procedure to see if it's any different.

The coolant is more than a decade old (but fewer than 20k miles on it). Tests out to 10 F which it never gets here, but still!

Last edited by haigha; 02-02-2025 at 04:21 PM.
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Old 02-02-2025, 04:20 PM
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Quote:
Originally Posted by Henn28 View Post
...Then fill the tank as the last step.

The M62 aux heater pump bleed method has always been a 100% solution for me.
Thanks for the tips. I'm probably going to use the radiator flush method with the expansion tank. Not in a hurry.

I wonder if a two-person operation with one monitoring the drain and the other keeping the sealed funnel, with shut off valve, on the expansion tank topped off with distilled water would avoid the introduction of air... wouldn't any air escape through the bleeding hole if done that way?

I guess the last fill with pure coolant would have to be done the standard way?
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Old 02-02-2025, 09:01 PM
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You should really consider getting the vacuum fill tool. It's great I would never do again without it.
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