In your code, the image_url gives the directory of the image where it stored on the hosting service. You need to append the domain name to the image_url variable and use the requests library to download it.
Use the following code and it will work.
import bs4
import requests
url = "https://parts.bmwmonterey.com/a/BMW_2004_330i-Sedan/_52014_5798240/Cooling-System-Water-Hoses/17_0215.html"
resp = requests.get(url)
soup = bs4.BeautifulSoup(resp.text, "html.parser")
img = soup.find('img')
image = img["src"]
img_url = "https://parts.bmwmonterey.com" + str(image)
r = requests.get(img_url)
with open("image.jpg","wb") as f:
f.write(r.content)
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solved How to scrape simple image from webpage