Hey there, everyone. I've looked all over the web and in this forum, but nobody seems to know the solution. My car has 62,000 miles on the odometer, and I'm not sure if the coolant has ever been drained. I would like to flush it out. So, here are my inquiries:
1. The bottom shield and the large bottom hose seem to be the only two pieces of hardware that can be used to accomplish this. I haven't been able to locate the second cooler that has been mentioned in videos on YouTube; it's supposedly located behind a wheel well. A second person offered the idea of running the engine with distilled water added to the expansion tank's return line until the water flowing out of the line into a bucket became clear. Turn off the engine and fill up. Also, I'm not a fan of using the engine for this procedure, and it seems like a waste of resources. Is it not possible to simply drain the system by running the electric coolant pump through the bleed process?
Coolant manufacturer 2. In my opinion, G48 is the best coolant for my BMW, but is it required by BMW? The reason I'm asking is because I can't seem to get my hands on BMW coolant.
3. It's possible that I have a tiny, slow leak. The possibility that it's just the cap was brought up somewhere, I believe. No other leaks have been detected. No pressure testing has been performed. As far as I can tell, an egr cooler leak is internal and hence invisible. Would it not trigger some sort of code? Is there anything else that could indicate this? Any signs or symptoms?
TIA
2018 328d xdrive Engine coolant refill
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petracolemanmu
- Posts: 14
- Joined: Mon Apr 06, 2026
Re: 2018 328d xdrive Engine coolant refill
Your last seven digits of VIN are much appreciated.
That rules out the use of a secondary cooler; instead, you'll need to manage a mechanical (i.e., belt-driven) water pump, an expansion tank, and a radiator.
I believe a cooling system drain and refill will suffice at 62,000 miles. Use a 50/50 mixture of BMW blue and Zerex G48 or another color that meets BMW specifications (such as the blue one in Walmart). Whether you prefer to purchase it already mixed or dilute it with distilled water is entirely up to you. Keep in mind that all you need to dilute the BMW coolants is the concentrate. Typically, I will purchase the concentrate and then mix it myself using grocery store distilled water. Yes, removing the front undercover is necessary.
In my opinion, there is no drain plug on your radiator. On the bottom left, you should see a smaller hose fitting with a quick disconnect, if memory serves. Just lift the spring clamp, wiggle it up and down and slightly side to side, and the hose will come right off. You run the danger of damaging the fitting or an alignment tab if you twist the hose. After disconnecting the hose, remove the expansion tank cap to facilitate the drainage of the used coolant into a basin.
I think that's pretty much it. Apply some dielectric grease to the inside o-rings of the disconnected hose, and then click it back on once the draining has ceased. When it's completely seated, you'll hear two distinct clicks. The next step is to add new coolant to the system and turn the engine on. Make sure the expansion tank's upper bleed hole isn't releasing any air bubbles. Adjust the coolant level, cap the tank, and turn off the engine once you get a stream of fluid.
After you take the cap off the next day while the engine is cold, all you have to do is adjust the fluid level to where it should be for optimal performance.
While the system is draining, you should inspect the expansion tank's top seam for white stains around the entire perimeter. Apparently, that's where the cooling system wants to start leaking first. In such case, you'll need to swap out the expansion tank for one that's BMW-compatible, such as a Behr/Mahle model. Avoid using Dorman, cheap imitations, and similar products.
Keep in mind that if you must drive the vehicle, you will empty the expansion tank of any new coolant. If you still can't locate the leak in that tank, you might want to investigate further by purchasing a coolant system pressure tester.
Even though intercooler leaks are conceivable, the only ones I'm aware of have affected N57 engines, while yours is an N47.
That rules out the use of a secondary cooler; instead, you'll need to manage a mechanical (i.e., belt-driven) water pump, an expansion tank, and a radiator.
I believe a cooling system drain and refill will suffice at 62,000 miles. Use a 50/50 mixture of BMW blue and Zerex G48 or another color that meets BMW specifications (such as the blue one in Walmart). Whether you prefer to purchase it already mixed or dilute it with distilled water is entirely up to you. Keep in mind that all you need to dilute the BMW coolants is the concentrate. Typically, I will purchase the concentrate and then mix it myself using grocery store distilled water. Yes, removing the front undercover is necessary.
In my opinion, there is no drain plug on your radiator. On the bottom left, you should see a smaller hose fitting with a quick disconnect, if memory serves. Just lift the spring clamp, wiggle it up and down and slightly side to side, and the hose will come right off. You run the danger of damaging the fitting or an alignment tab if you twist the hose. After disconnecting the hose, remove the expansion tank cap to facilitate the drainage of the used coolant into a basin.
I think that's pretty much it. Apply some dielectric grease to the inside o-rings of the disconnected hose, and then click it back on once the draining has ceased. When it's completely seated, you'll hear two distinct clicks. The next step is to add new coolant to the system and turn the engine on. Make sure the expansion tank's upper bleed hole isn't releasing any air bubbles. Adjust the coolant level, cap the tank, and turn off the engine once you get a stream of fluid.
After you take the cap off the next day while the engine is cold, all you have to do is adjust the fluid level to where it should be for optimal performance.
While the system is draining, you should inspect the expansion tank's top seam for white stains around the entire perimeter. Apparently, that's where the cooling system wants to start leaking first. In such case, you'll need to swap out the expansion tank for one that's BMW-compatible, such as a Behr/Mahle model. Avoid using Dorman, cheap imitations, and similar products.
Keep in mind that if you must drive the vehicle, you will empty the expansion tank of any new coolant. If you still can't locate the leak in that tank, you might want to investigate further by purchasing a coolant system pressure tester.
Even though intercooler leaks are conceivable, the only ones I'm aware of have affected N57 engines, while yours is an N47.
Re: 2018 328d xdrive Engine coolant refill
Your lengthy and prompt response is much appreciated. I had a feeling this was the way to go, but I was hoping for a less tedious and chaotic procedure. (What does "IIRC there..." mean? I'm not great with TLA.) I take it you mean hose 8?
Is it important to "flush" with distilled water to remove any remaining coolant, or is it safe to leave it alone?
I will make sure to check the tank once I drain the system. If my understanding is correct, the expansion tank is connected to the pump or pressure device in order to conduct a pressure test of the system. How can I verify the cap if that's the case?
ps. Because I saw it in one of your posts, I thought it would be helpful to include the vin.
Is it important to "flush" with distilled water to remove any remaining coolant, or is it safe to leave it alone?
I will make sure to check the tank once I drain the system. If my understanding is correct, the expansion tank is connected to the pump or pressure device in order to conduct a pressure test of the system. How can I verify the cap if that's the case?
ps. Because I saw it in one of your posts, I thought it would be helpful to include the vin.
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petracolemanmu
- Posts: 14
- Joined: Mon Apr 06, 2026
Re: 2018 328d xdrive Engine coolant refill
I believe I remember correctly 
You should only need to drain and refill the coolant if the color of the fluid in your vehicle remains similar to blue coolant. The recommended interval is every six months, but if you're behind, there's no harm in getting ahead of schedule.
Indeed, a clear water flush would be appropriate if you were attempting to flush out anything undesirable. Another option would be to access the engine block drain plugs, which can be quite challenging to reach.
In order to achieve a clear water flush, you should use tap water until you achieve the desired effect. This may necessitate multiple starts with the car's thermostat on high and the fan speed set to low, but not off. After that, you can remove the tap water by adding a few gallons of distilled water. Afterwards, it's necessary to do some calculations in order to estimate how much water is still in the engine and then add the appropriate amount of concentrate. Then, to finish it all off, there's the 50/50 mix.
Make sure the heater controls are set to the way I described above before you refill.
A pressure tester with an adapter that fits the expansion tank is necessary because it is attached to the threaded portion of the tank. You can also find adapters with the threads that match the cap. Another option is to remove the cap and check the o-rings. If they are flat on both sides, you can simply replace the cap. The price isn't exorbitant.
Alright then. It is very helpful to have the VIN7.
You should only need to drain and refill the coolant if the color of the fluid in your vehicle remains similar to blue coolant. The recommended interval is every six months, but if you're behind, there's no harm in getting ahead of schedule.
Indeed, a clear water flush would be appropriate if you were attempting to flush out anything undesirable. Another option would be to access the engine block drain plugs, which can be quite challenging to reach.
In order to achieve a clear water flush, you should use tap water until you achieve the desired effect. This may necessitate multiple starts with the car's thermostat on high and the fan speed set to low, but not off. After that, you can remove the tap water by adding a few gallons of distilled water. Afterwards, it's necessary to do some calculations in order to estimate how much water is still in the engine and then add the appropriate amount of concentrate. Then, to finish it all off, there's the 50/50 mix.
Make sure the heater controls are set to the way I described above before you refill.
A pressure tester with an adapter that fits the expansion tank is necessary because it is attached to the threaded portion of the tank. You can also find adapters with the threads that match the cap. Another option is to remove the cap and check the o-rings. If they are flat on both sides, you can simply replace the cap. The price isn't exorbitant.
Alright then. It is very helpful to have the VIN7.
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petracolemanmu
- Posts: 14
- Joined: Mon Apr 06, 2026
Re: 2018 328d xdrive Engine coolant refill
As you can see in the right-hand column, the eight in a circle actually represents hardware. I was referring to the hose in item 7.