Leaking radiator - (Bonnet, Header Tank, Viscous coupling, Radiator removal)

Here is a picture showing the top of a Silver Shadow 1 radiator. You may notice burnt cooling liquid on the radiator ridge which certainly indicates from a leak.

The radiator thus needs to be removed for a test and consider a resolder.
It also brings an occasion to remove and check the header tank by inspecting both cooling sensor and pressure valve, performing a pressure test and even maybe have it opened checked from the inside, clean and resoldered too.

Removing the radiator

0- Car sits on a ramp, battery off. (pic 1)

1 - Removing the bonnet / hood (not mandatory)
According to WM section L12, the radiator removal can be done without taking off the bonnet.
But for more comfortable access to the radiator, the removal of the bonnet / hood can be performed as described in WM S51 :

• lift up the bonnet
• Bonnet lamp leads
• note position of the bonnet lamp leads for correct assembly (pic 2)
• disconnect the bonnet lamp heads at the snap connectors adjacent to the switch on the right-hand hinge bracket
  
• for older cars it is also necessary to disconnect the two leads from the termination block at the front of the engine compartment
• detach the clips securing the leads to the right-hand hinge brackets (pic 3); on early cars also remove the screws and detach the two clips securing the lead to the front of the engine compartment;
• bonnet removal (this aluminium part of the body only weights 8kg)
• detach bonding strip (or earthing strap) situated at the front of the bonnet (pic 4)
  
• careful : refit NOW the bolt securing the earthing strap because it also holds the grille in place
• using a soft pencil, scribe correlation marks round the washers of the set screws securing the bonnet to the hinges (pic 5)
  
• with two assistants supporting the bonnet remove the eight 1/2 AF set screws securing the bonnet to the hinges
• it is preferred to proceed in two steps : removing 3 screws on each side and the last one with the two assistants the bonnet steady
• remove the bonnet (pic 6) note that its weight is only about 8 kg
  
• bonnet can be stored of the car's roof laid on a thick blanket
• Fitting back the bonnet
• reverse procedure but note : the height 1/2 AF set screws should not be fully tightened until the bonnet clearances are not 9/64 in / 3,571mm (for a 4-door saloon car)

2 - Draining the cooling liquid

• fit a rubber hose to the radiator tap and direct into a clean container (pic 7)
  
• drain radiator liquid into a big container using the bottom drain tap until it is completely empty (pic 8)
  
• cover container to prevent the liquid from contamination

3 - Removing the grille (not mandatory)
A grille inspection / cleaning can be performed easily once the bonnet is unmounted.

• remove 2 (3 on SRH25085) bolts securing the bottom grille to the front bumper (pic 9)
  
• 4 bolts are remaining securing the top of the grill to the skirting (plinthe/ rebord) (pic 10)  : unscrew the 2 inner ones first
• then remove the 2 outer ones (pic 11)
• the last bolt remaining (also securing the earthing strap) holds the grille in place
• if fitted disconnect the mascot alarm leads (pic 12)
  
• ease the grille forward and put it aside for further examination (pic 13)
  

4 - Removing the header tank

• remove the set of hoses connecting the header tank to the radiator : Header tank to radiator and Pump to header tank (pic 14 - 15)
  
• remove the three bolts (boulons) anchoring the header tank (pic 16)
• remove coolant probe (pic 17) and drain pipe (pic 17b)
  
• see here for detailed explanation and pictures on the process

• release the lower radiator hose from its spout (bec) (pic 18)
• release the top radiator hose (pic 19)
  
• disconnect with a crows foot wrench the two automatic transmission fluid lines (called "heat exchange pipes" in WM) (pic 20)
  
• transmission fluid will drain from these connections : blank the left side tube with  a plug (5/8 in. UNF) because the transmission will drain entirely
  
• fit blanking plugs to prevent the ingress of dirt and moisture

6 - removing the reflector (not mandatory but gives access to the steering cooler in order to inspect)

• this part is a piece of metal covering the front of the radiator block (AC condenser and steering cooler)
  
• remove the four 1/18 in. - 11mm screws (pic 21)
• detach the reflector
  

7 - Removing part of the radiator shroud / cowl (enveloppe)

• deeper into the engine bay, remove the two upper shrouds (retaining nuts are two sets of 2BA located on the side (pic 22)
  
• (remove only the upper left cowl in Waples)
• be careful these nuts tend to rust and become extremely fragile. Use a lot of penetrating oil and unscrew gently or you will break them
  
• gently release the shroud

8 - Removing the viscous coupling unit

• remove the 4 nuts (écrous) holding the fan and viscous coupling to the water pump pulley extension cone (pic 23 to 25)
  
• the rear face of the clutch tends to rust itself to the front of the face of the water pump pulley : use penetrating oil
  
• remove fan and clutch assembly and set if on a clean surface with front face down
• Take care not to damage the radiator matrix.

• Position a bottle jack the support he radiator center (pic 26)
  
• spread old towels all over the top of the engine and secure the fenders also
  
• the radiator is held in place with four sets of 1/2 in. screws and washers -  two on  each side - all accessible from the engine compartment (pic 27)
  
• remove all but one of the upper screws and locate an assistant
• as you remove the last screw have your assistant hold the radiator in place so it remains balanced on the bottle jack
• Carefully withdraw the radiator (pic 28 - 29)
  

From the forums

Here is one position : The SY1 radiator can be removed without taking off the bonnet.
The header tank and viscous coupling/fan unit need to be removed first, but when done so there is plenty of room to pull out the radiator.
The header tank is held in place by 3 bolts (with nuts), the one nearest the front of the car is a little difficult to access however I found using a 1/4" extension on the socket through the bonnet gap was the best way to undo it.
The viscous coupling is fastened to the water pump by 4 nuts. They are easy to remove and the whole unit can be (carefully) lifted out.
Make sure they are torqued up tight when replaced - I used thread locker to make sure they do not come loose.

Sources :
WM section L2; Waples pp90-91; Tee One Review 6 p 48; Forums advisers
Read also here

Related pictures

picture 1 : front wheels of the car sit on a wooden ramp