Engine Position  I
In this position the Alpina radiator is the only one that fits perfectly. This radiator is compact and quite thick.  It fits fully in the front mask of the e30 chassis.  It's the only one that does not take up any room in the engine compartment. 
 

Alpina Part Number: 17 10 122        Price: around $550

There are, however further problems with this setup.  Should the radiator ever become damaged or cease to work the engine and transmission must be raised to gain access to it.  It's possible that the radiator might slide out through the bottom of the mask with only a slight raising of the engine.  The application of this radiator is quite rare, and no known field tests of radiator replacement were available.

Some have attempted other solutions to their cooling problems.  For example: the radiator has been removed from a Volvo 360 and has been fitted into the front mask of an e30.  This radiator fits well into the allotted space, however it isn't thick enough to properly cool the M30 engine.  The picture at left depicts an unknown radiator that has been fitted into the e30 mask.  It is somewhat thicker than the aforementioned Volvo radiator.  Some minor modifications to the mask itself were required, however it appears to function well.

Engine Position II
The best radiator for this position is that from the e28 535i, or equivalent.   
 

BMW Part Number: 17 11 1 712 447       Price:  around $440, new

Interestingly enough the attachment points of the e28 radiator match up with the e30's.  On all sides the e28 radiator is a direct replacement, as seen in the pictures at left.  Radiator Dimensions: There are 73 cm between the top and bottom mounting points of the e30 and 68.5 cm between the sides.  The radiator used should be no larger.

The radiator from the e36 3-Series also fits well in the e30.  The attachment points do not line up, and custom mounts must be used.  The brass radiator of the older 635CSi also fits well in the e30.

The combination of the aforementioned Alpina radiator and an electric fan is also a conceivable option in Engine Position II.  Though no benefits would be gained over the e28 535i setup.

Engine Position III

In this position the application of the e28 radiator and a flat, yet factory, fan clutch are best.  This setup should serve to prevent future cooling issues.   Flat Fan Clutch from the 324td: BMW Part Number: 11 522 243 303 However if the Alpina radiator is used there remains enough room for a normal broad fan clutch.

Electric Fan
If there is no room for a factory fan clutch an electric fan must be used.  BMW radiators almost always have two temperature sensors.  These two sensors control a two stage electric fan.  Two fuses are present in the e30 fuse box for such controls.

This electric fan is to be installed in front of the radiator inside the front mask.  New air deflecting panels should be installed between the grill and the radiator, to promote optimal airflow.  The partially filled areas of the front grill and air dam are to be opened up in the area directly in front of the radiator.  This will provide sufficient airflow so the electric fan will not need to run constantly, and the engine will be able to be cooled during higher temperature periods, like summer.

Coolant Intake at the Back of the Cylinder Head
In the older M30 engines there is a coolant intake at the back of the cylinder head.  In the case of the e23 it points toward the passenger's side, all other models' point toward the driver's side.

Installing a Closed Cover
This intake can be closed off with a cap from the e32/e34 M30.  For proper cooling a new hose must be installed in the front of the cylinder head.  By moving this intake to the front a few cm are gained at the rear of the engine, allowing a more rearward engine position to be used.  Unfortunately higher temperatures can result, as the cylinder head will no longer have a direct supply of coolant. 
 

Cap: BMW Part Number: 11 12 1 710 771 Seal: BMW Part Number: 11 15 1 312 176 3 x Screw: BMW Part Number: 07 11 9 913 477 3 x Spring Washer: BMW Part Number: 07 11 9 332 099 Front Coolant Hose with Intake: BMW Part Number: 11 53 1 718 919

Changing the Direction of the Intake
In the case of the e23 engine, it is desirable to point the intake toward the driver's side.
 

Intake: BMW Part Number: Seal: BMW Part Number: 11 15 1 312 176 3 x Screw: BMW Part Number: 07 11 9 913 477 3 x Spring Washer: BMW Part Number: 07 11 9 332 099

Problems with Bursting Hoses

The experiences of brankoboldizar@gmx.de with the placement of the cooling system components:

From top to bottom the system should look like this:

There needs to be 1.5-2 cm height difference from the top of the thermostat to the top of the radiator.  Put another way, the output hose of the of the overflow tank must be higher than the thermostat.

For proper flow the overflow tank must be mounted as high as possible, or air will remain in the system.

I had a lot of problems with air in the system, even though I bled the system properly.  Again after a week there would be air in the system and the bubble would go to the thermostat.  This posed a great problem as the thermostat would read the engine as hot, but not open and thus not use the radiator.  Finally I came to understand the importance of the height of these components and got it under control.

Ever since these were remedied I have had no problems with bursting hoses or overheating!

Questions, Comments?