What year of caddy this goes on waterpump housing crossover GM part#12553133

check with GM spares shops as the regulator may have been upgraded to what you had
AS long as it fits , with the right fittings and the right pressure settings , the shape of it will make no difference to the operation

If you have the 3100 v6 engine, the thermostat is located behind an aluminum housing behind the exhaust crossover tube almost directly below the throttle body. If you have the 2.4 dohc engine, it is under a steel housing on top of the waterpump which is underneath the exhaust manifold on the back side of the engine.

Thermostat Removal & Installation To Remove:

1. Before servicing the vehicle refer to the precautions at the beginning of this section.
2. Partially drain the coolant, (until the level is below the thermostat).
3. Remove or disconnect the following:
   • The air cleaner and duct assembly
   • The crossover exhaust pipe
   • The radiator hose from the thermostat housing
   • The thermostat housing bolts
   • Any remaining sealer from the bolt threads
     
     
   • The thermostat housing
   • The gasket
   • The thermostat

To Install:

1. Install or connect the following:
   • The thermostat
   • The thermostat housing
   • The gasket NOTE: Apply RTV sealer, GM P/N 1052366 or the equivalent, to the thermostat housing bolt threads.
     
   • The thermostat housing bolts
     1. Torque to: 18 ft. lbs. (25 Nm)
   • The radiator hose to the thermostat housing
   • The crossover exhaust pipe
   • The air cleaner and duct assembly
   • The coolant
2. Thoroughly inspect the cooling system for leaks.

Thermostat Removal & Installation To Remove:

1. Before servicing the vehicle refer to the precautions at the beginning of this section.
2. Partially drain the coolant, (until the level is below the thermostat).
3. Remove or disconnect the following:
   • The air cleaner and duct assembly
   • The crossover exhaust pipe
   • The radiator hose from the thermostat housing
   • The thermostat housing bolts
   • Any remaining sealer from the bolt threads
     
     
   • The thermostat housing
   • The gasket
   • The thermostat

To Install:

1. Install or connect the following:
   • The thermostat
   • The thermostat housing
   • The gasket NOTE: Apply RTV sealer, GM P/N 1052366 or the equivalent, to the thermostat housing bolt threads.
     
   • The thermostat housing bolts
     1. Torque to: 18 ft. lbs. (25 Nm)
   • The radiator hose to the thermostat housing
   • The crossover exhaust pipe
   • The air cleaner and duct assembly
   • The coolant
2. Thoroughly inspect the cooling system for leaks.

the thermostant is behind the exhaust crossover pipe, this is the pipe that connects the front exhaust manifold to the rear, the housing is behind that, its a tight fit,also if you follow the upper radiator hose from the radiator to engine the housing that the hose goes to is where the thermostant goes,heres a diagram, hope this helps,

This is the thermostat housing:



The thermostat sits inside of it...which looks like this:



These are the steps to remove and replace the thermostat:

3.4L Engine

1. Drain the cooling system.
   
2. Remove the air cleaner.
   
3. Remove exhaust crossover pipe.
   
4. Disconnect the surge tank line fitting from the coolant outlet.
   
5. Remove the thermostat housing to intake manifold bolts.
   
6. Remove the thermostat housing outlet and thermostat
   
7. Clean the mating surfaces.
   

To install:

1. Install the thermostat and housing outlet.
   
2. Install the thermostat housing bolts. Tighten the thermostat housing bolts to 18 ft. lbs. (25 Nm).
   
3. Install exhaust crossover pipe.
   
4. Connect the surge tank line fitting to the coolant outlet. Tighten the fittings to 15 ft. lbs. (21 Nm).
   
5. Install the air cleaner.
   
6. Fill the cooling system.
   
7. Inspect the system for leaks.
   

your thermostat is bad

heres how to fix it

1. Drain the cooling system.
2. Remove the air cleaner.
3. Remove exhaust crossover pipe.
4. Disconnect the surge tank line fitting from the coolant outlet.
5. Remove the thermostat housing to intake manifold bolts.
6. Remove the thermostat housing outlet and thermostat
7. Clean the mating surfaces.

To install:

1. Install the thermostat and housing outlet.
2. Install the thermostat housing bolts. Tighten the thermostat housing bolts to 18 ft. lbs. (25 Nm).
3. Install exhaust crossover pipe.
4. Connect the surge tank line fitting to the coolant outlet. Tighten the fittings to 15 ft. lbs. (21 Nm).
5. Install the air cleaner.
6. Fill the cooling system.
7. Inspect the system for leaks.

3.4L Engine

1. Drain the cooling system.
2. Remove the air cleaner.
3. Remove exhaust crossover pipe.
4. Disconnect the surge tank line fitting from the coolant outlet.
5. Remove the thermostat housing to intake manifold bolts.
6. Remove the thermostat housing outlet and thermostat
7. Clean the mating surfaces.

To install:

1. Install the thermostat and housing outlet.
2. Install the thermostat housing bolts. Tighten the thermostat housing bolts to 18 ft. lbs. (25 Nm).
3. Install exhaust crossover pipe.
4. Connect the surge tank line fitting to the coolant outlet. Tighten the fittings to 15 ft. lbs. (21 Nm).
5. Install the air cleaner.
6. Fill the cooling system.
7. Inspect the system for leaks.

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Water Pump
This pump fits a 6.5 n/a civilian and millitary HMMWV. Ref 94 Suburban AC Delco 251-589 (Needs Heater 5/8" Nipple 12339396) $120.00
GM part number for 1995 6.5 N/a is 88894044. The AMG part number is 5743241
Pump for a 6.2 n/a is 12534418

Water Pump Backing Plate - AMG 5743232 $96.00
1998 Stud-type water pump pulley amg# 6006809 37.72, gm #12556143.
8 blade fan 6009790 222.81, stud mounted fan clutch for this fan 6009791 153.78
Try these: 96-98 Fan clutch GMC G30 6.5 TD
ACDelco#15-4680
GM#15028400
1999 and up
big-nut fan clutch 6009991, big nut water pump amg#5745093, ac delco# 251-603.
The 6.2 and the 6.5 waterpump do share the same basic casting. However, the pump rotors inside the pump are reversed between the two. This due to reversed direction of rotation from V belt to serpentine belt. DO NOT fit a 6.5 pump on a 6.2 or vice versa. If you do, it will not pump water!!!
Thank you , Quinn

Remove the radiator and have it boiled out to clean it. All those years of GM sealing tabs used for coolant repairs have taken a toll. Hope this helps