Cooling system upgrade - e12 to e28

Written by Michael Randell (Michael R from Melbourne) December 2004.

Big thanks to Troy Rudolph and Peter Florance for providing this truly excellent forum. KNOWLEDGE IS EVERYTHING

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Removing the existing Radiator    Getting the right Radiator    Mounting the e28 radiator    The hoses & the thermostat cover
The temperature switch/s for the auxiliary fan    Auto transmission cooling hoses    Finally - a parts list summary

Many e12 owners report overheating problems and whilst these are often due to the cooling system not functioning 100% an upgrade to e28 is quite easy for those who want something better. The standard system, if maintained properly will work fine even in hot climates. (See Cooling system maintenance FAQ) In my case the existing e12 radiator required either repair or replacement so I decided to go all the way and replace it with an e28. Had it not been leaking I would not have replaced it. “If it aint broke, why fix it”

This conversion and FAQ was done on my Australian (Euro) 1980 528i auto right hand drive. If you have a different model / year etc further investigation is recommended as models do vary. Estimated time for non mechanic is about 2 - 3 hrs once you have everything. Degree of difficulty is easy. Hardest part was rotating the lower auto trans cooling hose 180°.

The parts catalogue used here was from which is a fantastic help.  The illustrations used relate to either my 1980 528iA Euro or an 86 535iA Euro where e28 parts are referred to.

Removing the existing radiator
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The Haynes manual describes this which is pretty obvious and easy.

Drain the coolant.
Disconnect the upper and lower hoses from both the radiator and the engine.
Disconnect the overflow to the clear plastic tank
Disconnect the wires to the temperature switche/s (Bottom right hand corner)
Disconnect the 2 auto trans cooling hoses from the right hand side of the radiator (auto models only). Note that you will lose some trans fluid as you do so. Cover the ends of the hoses to keep out dust etc.
Put a note on your dash NOW reminding you to top up the fluid.
Remove the plastic fan shroud. It has 2 screws in the top and just slots into the radiator in the bottom. Either drop it out the bottom or rotate it 180° and lift out the top. (Bit of a Rubik's cube this one)
Unbolt the mount on the right hand side (2 bolts) and remove it. Move the radiator slightly to the right and wiggle it out.  

Getting the right radiator
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E28 535i     RADIATOR/FRAME Home => Select another car => RADIATOR => RADIATOR


My semi retired mechanic (and e12 owner) says never bother with second hand radiators unless they are obviously new. In particular with e28 because the tanks on the side are plastic and prone to break when brittle with age.

Finding which new radiator to get started out really hard because none of the parts catalogues showed where the temp switches for the aux air fan went. (More about them later) It was only when I actually took one out of the box that I knew it had them.

Note - the illustration does not show the location or existence of the holes for the temp switches for the aux air fan but they are located in the top right hand end.

Note also - the way an e28 is attached to the car body is different to the e12. (parts 2 - 6 in the illustration)  

The one piece fan shroud from your e12 (part 9 in this illustration) is not a direct fit but you may be able to make it fit somehow. I suggest you get the e28 one from a wrecking yard. Any e28 528i or 535i should fit. The upper shroud (part #7) is not needed as our bonnets are front hinged unlike e28 where you access the engine bay from the front and hence the additional shroud.       


I understand that all e28 528i and 535i auto's use the same radiator but I have not searched on all variants to check that. According to the box mine came in this appears to be the case and a 6 series e24 is also the same.


Part # 17 11 1 712 448

If you have a manual I believe you need
Part # 17 11 1 712 447
I have not seen one so I cant be 100% sure
it's the right choice.

For the benefit of Australian readers it cost approx $400 with GST in Dec 2004 from Hanvic South Yarra Autoparts. Phone 03 8416 8416 (Kim) 

Mounting the e28 radiator
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The mount on the left side is welded to the car and I left it in case I could not complete the install for some reason and also because I hate butchering things unless you have to.


Firstly I cut about 1cm off the lower section of the radiator e28 mount (used a hacksaw) because the radiator needed to move slightly to the left. Sit the radiator in and you will see that the bottom hose on the RHS is too close to the bodywork.

Then I cut a notch out of the e12 rubber mounting block with a sharp knife so that it held the new radiator securely in place. The first one didn't work but you have 2 and wont need the other one anyway. 

This worked fine and I did not need any bolts or to drill any holes in the car.

The e12 mount on the right hand side bolts in and I removed it all together. You need to remove this to get the existing radiator out anyway. The bolts are 10mm. 



In it's place I used a self drilling bolt and some rubber bushes either side of the plastic mount on the e28 radiator.

You could get the proper mounting hardware as shown in an earlier illustration but at the time I was keen to keep my project moving along. 

Click here to go back to that illustration

On the bottom there are two rubber mounts that sit in metal retainers. I retained these but had to cut them a bit as the e28 is narrower on the bottom.

On the left hand one there is a small metal tab on the bottom of the radiator. Bend it flat so the radiator sits down on the rubber mount. 

No pictures worth showing unfortunately but its pretty obvious what to do. 

It is shown as part #17 in the final illustration of this FAQ. Click here to go to that illustration.


The hoses and the thermostat cover
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Hoses – The e28 radiator is different and
you WILL NEED both the top and bottom hoses to suit. The short U shaped hose however does not need to be changed but I did anyway. 

Top hose (e28)         11 53 1 276 647  (#15)
Bottom hose (e28)    11 53 1 289 859
U shaped hose         11 53 1 266 459  (#16)
#16 is the same part # for both e12 and e28

You DO NOT NEED the thermostat housing (part #1 in the illustration) nor do you need to remove it. Just leave it alone. 

You may also want to replace the hoses going to the additional air valve (for cold starting) located under the intake manifolds if you’re really keen. The link below takes you to the parts catalogue for those parts. e12 Additional air valve





Thermostat and cover - Some owners said they needed the e28 thermostat cover 11 53 1 268 650 (part #5 in the illustration) I bought one but it was basically the same as the e12 part.I then got one off an e28 from the wreckers and it to was the same. So maybe there is a difference with USA spec to Euro?

If you do need it a new one is surprisingly expensive so try your local wrecking yard for this one.

Get a new thermostat, gasket and O ring (parts 7, 8 &  9 in the illustration) while you’re at it. They’re cheap and important and prone to occasional failure. They are usually supplied as a kit.  

e12 and e28 part numbers are different and are

e28 Thermostat          11 53 1 713 040 
e12 Thermostat          11 53 1 254 065
e12 Gasket                11 53 1 250 357    
e12 Rubber O ring      11 53 1 250 399
e28 thermostat cover  11 53 1 268 650

I stayed with the e12 thermostat.


The temperature switch/s for the auxiliary fan
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This car is an '86 euro e28 535iA showing the two temp switches. All e28 528 & 535's have this setup as far as I know. One switch activates the auxiliary cooling fan at 91° C and the other increases the fan speed if the temperature reaches 99°C

Note also just below them how the radiator mounts to the body using the factory fittings.

By comparison not all e12’s are the same. I have two 528iA’s and they are different. One has provision for one 91°C switch in the bottom and the other doesn’t (because it has no A/C and no auxiliary fan).

My good car has just one switch but has the wiring for both. That may have been because it originally had both but a different radiator was later fitted. After 25+ years anything could happen. By fitting the e28 radiator I now had a dual speed fan again.

To test which wires are which simply bridge them (which is what happens when the switch closes) and listen to how fast the fan spins.  

If for some reason you don't need both switches just block off the spare one. (Maybe with old switches from the wreckers that are not connected)

Auto transmission cooling hoses
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E12 528i     TRANSMISSION OIL COOLING Home => Select another car => ENGINE => COOLING


If you have an auto there will be two hoses connected to the right hand side of the radiator to cool the trans fluid. The connections are the same as e28 and screw straight on.

The top hose is a direct fit but the bottom hose connection is much closer to the bottom radiator hose which prevents it bolting straight on. Its not shown in the illustration here but mine has a 15° connector on the end of the hose and to make it fit you need to rotate the hose 180°.

Easiest way to do this is to loosen the hose at the other end (hard to get at), rotate it 180° and re-tighten. It may also be secured to the car half way along its length (parts 5 & 14 in the illustration). Disconnect it because you will need all the length on it you can get. You should now be able to attach it quite easily to the radiator.

CAUTION Having detached the hose from the car MAKE SURE it is not going to contact the hot exhaust by re-attaching it somehow. I used big cable ties.

Hot exhaust + rubber hose + trans fluid = fire. 

Top up your trans fluid. I used about 500ml. 

Finally - a parts list summary
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New parts Part number
e28 radiator for 528i or 535i auto 17 11 1 712 448
e28 radiator for 528i or 535i manual (check this to be sure) 17 11 1 712 447
e28 Bottom hose 11 53 1 266 462
e28 Upper hose 11 53 1 266 467
e12 Intermediate hose (same as e28) 11 53 1 266 459
e12 Thermostat (most likely supplied with the gasket & O ring. 11 53 1 254 065
e12 Gasket 11 53 1 250 357
e12 O ring 11 53 1 250 399
Gasket sealant if replacing the thermostat
New hose clamps if yours are not 100%
Used parts from the wreckers
e28 528i or 535i fan shroud
e28 Thermostat cover (mine was the same as e12 but others say they are different? 11 53 1 714 861
Mounting hardware for e28 radiator or a self drilling bolt and some rubber bushings

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