Reverse flushing the heater core?

Post your E12 technical questions and comments here. Please, no off-topic posts.

Moderators: Mike W., Pierre

Post Reply
canada karl
Posts: 1058
Joined: Tue Jan 06, 2009 3:50 pm

Reverse flushing the heater core?

Post by canada karl »

Which hose is inlet and which is outlet?
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
User avatar
Mike W.
Posts: 2782
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Reverse flushing the heater core?

Post by Mike W. »

The opposite of what I thought. Hot should be on top, and cold or return on the bottom. Wrong. I'll spare you the long story, but it is,

Hot or in on the bottom.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
canada karl
Posts: 1058
Joined: Tue Jan 06, 2009 3:50 pm

Re: Reverse flushing the heater core?

Post by canada karl »

So to reverse flush the heater core I go thru the cold on the top,correct?
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
User avatar
Mike W.
Posts: 2782
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Reverse flushing the heater core?

Post by Mike W. »

canada karl wrote: Wed Jun 22, 2022 8:38 am So to reverse flush the heater core I go thru the cold on the top,correct?
Correct. But if you're really trying to flush it with a hose I'd go back and forth a few times, alternating between top and bottom.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
canada karl
Posts: 1058
Joined: Tue Jan 06, 2009 3:50 pm

Re: Reverse flushing the heater core?

Post by canada karl »

Thanks Mike 8)
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
HB528i
Posts: 111
Joined: Mon Dec 09, 2019 7:53 pm
Location: Huntington Beach

Re: Reverse flushing the heater core?

Post by HB528i »

I don’t think it really matters. We just had this discussion on the e9 Forum. On a CS water enters on top from manifold, on a CSi it enters on bottom, same heater. Some say it enters on top from back of head on a CS, it’s not going to make a difference.
User avatar
Mike W.
Posts: 2782
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Reverse flushing the heater core?

Post by Mike W. »

HB528i wrote: Thu Jun 23, 2022 11:43 pm I don’t think it really matters. We just had this discussion on the e9 Forum. On a CS water enters on top from manifold, on a CSi it enters on bottom, same heater. Some say it enters on top from back of head on a CS, it’s not going to make a difference.
I don't think E9s had a heater valve, I know E3s did not, and that is the difference. If connected wrong the heater valve can flutter and bypass coolant in an E12.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
HB528i
Posts: 111
Joined: Mon Dec 09, 2019 7:53 pm
Location: Huntington Beach

Re: Reverse flushing the heater core?

Post by HB528i »

Thanks, I assumed no valve in the e12.
User avatar
Mike W.
Posts: 2782
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Reverse flushing the heater core?

Post by Mike W. »

HB528i wrote: Fri Jun 24, 2022 1:05 pm Thanks, I assumed no valve in the e12.
There is and replacing it has been described as the worst job on the car.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
canada karl
Posts: 1058
Joined: Tue Jan 06, 2009 3:50 pm

Re: Reverse flushing the heater core?

Post by canada karl »

Yah you need tiny fingers and a tiny wench! :lol:
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
User avatar
Mike W.
Posts: 2782
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Reverse flushing the heater core?

Post by Mike W. »

canada karl wrote: Mon Jun 27, 2022 8:16 am Yah you need tiny fingers and a tiny wench! :lol:
And to be a contortionist while laying on your back. :twisted:
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
Post Reply