Overview
The GMC Jimmy (K5) and Chevrolet Suburban models of the Square Body era (1973-1987) present unique cooling system challenges due to their larger size, heavier weight, and often more demanding duty cycles compared to their pickup truck counterparts. These vehicles frequently require cooling system modifications to maintain optimal operating temperatures, especially when equipped with larger engines, air conditioning, or when used for towing applications.
This article covers essential cooling system upgrades and modifications specific to Jimmy and Suburban models, addressing the increased cooling demands of these larger Square Body vehicles. Proper cooling system modifications can prevent overheating, extend engine life, and improve overall reliability under heavy-duty conditions.
Common Issues
Heat-Related Problems Specific to Jimmy/Suburban Models
Inadequate Cooling Capacity
- Factory radiators often undersized for heavy-duty use
- Single-row radiators insufficient for V8 engines with A/C
- Poor airflow due to larger frontal area and body design
Air Conditioning Load
- A/C condenser blocks significant airflow to radiator
- Increased engine load from A/C compressor generates additional heat
- Factory cooling systems marginal when A/C is engaged
Weight and Duty Cycle Issues
- Heavier curb weight increases engine load
- Frequent stop-and-go driving reduces airflow
- Towing applications exceed factory cooling capacity
Airflow Restrictions
- Factory fan shrouds often inadequate
- Missing or damaged air dams reduce cooling efficiency
- Debris accumulation between A/C condenser and radiator
Parts & Materials Needed
Essential Cooling System Components
Radiators
- Griffin Radiator 1-25222-X: 3-row aluminum radiator for 1973-1987 Suburban/Jimmy
- Champion Cooling CC52: 4-row copper/brass radiator, direct fit
- Cold Case Radiators CHC542A: High-performance aluminum, 1.25" tubes
- Part Number GM 14096221: Factory 3-row heavy-duty radiator (discontinued, used market)
Electric Cooling Fans
- Flex-A-Lite 180: 16" reversible electric fan, 2400 CFM
- SPAL 30102120: 16" puller fan, 2400 CFM, curved blade design
- Derale 16925: Dual 11" fan setup for maximum airflow
Fan Shrouds and Mounting
- Part Number GM 15056644: Factory heavy-duty fan shroud (1981-1987)
- Cold Case FSC542: Custom aluminum shroud for electric fan conversion
- Speedway Motors 910-25140: Universal adjustable fan mounting kit
Water Pumps and Components
- Edelbrock 8851: High-flow water pump for small block Chevy
- Stewart Components 13401: Stage 1 high-flow water pump, SBC
- Flowkooler 1543: High-performance water pump with improved impeller
Thermostats and Housing
- Robert Shaw 333-180: 180°F high-flow thermostat
- Stant 45359: SuperStat 160°F performance thermostat
- Mr. Gasket 2670: Chrome thermostat housing with temperature gauge port
Tools Required
- Socket set (10mm-19mm, 3/8"-3/4")
- Torque wrench (10-150 ft-lbs)
- Drain pan (minimum 4-gallon capacity)
- Coolant pressure tester
- Multimeter for electrical connections
- Drill and bits for mounting modifications
- Hose clamp pliers
Step-by-Step Guide
Phase 1: Radiator Upgrade
Preparation
1. Allow engine to cool completely (minimum 4 hours)
2. Disconnect negative battery terminal
3. Remove front grille and headlight bezels for access
4. Drain cooling system at radiator petcock and engine block drain plugs
Radiator Removal
1. Remove upper and lower radiator hoses
2. Disconnect transmission cooler lines (automatic transmission models)
3. Remove fan shroud mounting bolts (4x 10mm bolts)
4. Lift out mechanical fan and shroud assembly
5. Remove radiator mounting bolts (2x upper, 2x lower brackets)
6. Carefully lift radiator from vehicle, noting A/C condenser clearance
Installation of Upgraded Radiator
1. Install new radiator using factory mounting points
2. Torque specifications: Upper brackets 15 ft-lbs, lower brackets 20 ft-lbs
3. Connect transmission cooler lines with new O-rings
4. Install new radiator hoses with spring-type clamps
5. Fill cooling system with 50/50 coolant mixture (capacity: 18-20 quarts)
Phase 2: Electric Fan Conversion
Mechanical Fan Removal
1. Remove fan clutch using Part Number OTC 6673 fan clutch wrench
2. Note: Fan clutch has reverse threads (turn clockwise to remove)
3. Remove water pump pulley if clearance is needed
Electric Fan Installation
1. Mount electric fan to radiator using supplied brackets
2. Position fan as puller configuration (pulling air through radiator)
3. Maintain 1" minimum clearance between fan and radiator core
4. Secure all mounting hardware with thread locker
Electrical Connections
1. Install relay kit with temperature switch
2. Connect power wire to alternator output terminal
3. Ground wire to engine block or radiator support
4. Temperature switch installation in thermostat housing
5. Switch activation: 185°F on, 175°F off for most applications
Phase 3: Airflow Improvements
Fan Shroud Modification
1. Install custom shroud sized for electric fan diameter
2. Seal all gaps between shroud and radiator
3. Ensure shroud extends minimum 1" beyond fan blade tips
Air Dam Installation
1. Install or repair factory air dam under front bumper
2. Part Number GM 15056789: Factory air dam for 1981-1987 models
3. Seal gaps around radiator support with foam weather stripping
Year/Model Differences
Early Models (1973-1980)
Radiator Specifications
- Single-row radiators standard on most applications
- 22" x 19" core size typical for small block engines
- Side-mount transmission cooler connections
Fan Configuration
- 18" or 20" mechanical fan with thermal clutch
- Fixed-pitch fan blades
- Basic stamped steel shroud
Cooling Capacity
- Marginal cooling with A/C and V8 engines
- Frequent overheating in stop-and-go traffic
- Limited factory heavy-duty cooling options
Later Models (1981-1987)
Improved Factory Systems
- Two-row radiators more common
- Heavy-duty cooling package available (RPO V01)
- Better fan shroud design and airflow management
A/C Integration
- Improved condenser mounting and airflow design
- Factory electric cooling fans on some models
- Better integration of A/C and cooling systems
Model-Specific Differences
K5 Blazer vs. Suburban Cooling
- Blazer: Shorter wheelbase creates different airflow patterns
- Suburban: Longer body provides better heat dissipation
- Both require similar cooling modifications for optimal performance
2WD vs. 4WD Considerations
- 4WD models have different radiator mounting due to front differential
- Transfer case adds heat load requiring additional cooling capacity
- Ground clearance affects air dam effectiveness
Tips & Best Practices
Performance Optimization
Coolant Selection
- Use high-quality ethylene glycol coolant with corrosion inhibitors
- Recommended: Prestone DEX-COOL for 1995+ compatibility
- Add Water Wetter for improved heat transfer (1 bottle per system)
System Pressure
- Install 16 PSI radiator cap for improved boiling point
- Higher pressure caps (18-20 PSI) for extreme duty applications
- Ensure all hoses rated for increased pressure
Thermostat Strategy
- 180°F thermostat optimal for most applications
- 160°F thermostat for racing or extreme performance use
- Never run without thermostat - causes poor circulation
Installation Best Practices
Electrical Fan Wiring
- Use minimum 12 AWG wire for fan power connections
- Install 30-amp fuse or circuit breaker for protection
- Route wiring away from exhaust components and moving parts
Radiator Mounting
- Use new rubber mounting cushions to prevent vibration damage
- Ensure radiator sits level and properly aligned
- Check clearance to A/C condenser and other components
Cooling System Bleeding
- Fill system slowly to prevent air pockets
- Run engine with radiator cap off until thermostat opens
- Top off coolant level after initial heat cycle
Common Mistakes to Avoid
- Installing pusher fans instead of puller configuration
- Oversizing electric fans leading to excessive current draw
- Neglecting to seal air gaps around radiator and shroud
- Using incorrect thermostat temperature range
- Failing to upgrade hoses and clamps with system modifications
Troubleshooting
Overheating Diagnosis
Temperature Gauge Reading High
1. Verify gauge accuracy with infrared thermometer
2. Check coolant level and condition
3. Test radiator cap pressure rating
4. Inspect for external coolant leaks
Electric Fan Not Operating
1. Check fuse and relay operation
2. Test fan motor with direct 12V connection
3. Verify temperature switch operation
4. Inspect wiring for damage or corrosion
Poor Cooling Performance
1. Check for restricted airflow through radiator
2. Verify proper fan direction (should pull air through radiator)
3. Inspect water pump operation and belt tension
4. Test thermostat operation in hot water
System Pressure Testing
Pressure Test Procedure
1. Allow system to cool completely
2. Remove radiator cap and install pressure tester
3. Pump to system pressure rating (typically 15-16 PSI)
4. System should hold pressure for 15 minutes
5. Pressure loss indicates leak requiring repair
Common Leak Points
- Radiator end tanks and core tubes
- Water pump weep hole
- Intake manifold gaskets
- Heater core connections
- Transmission cooler lines
Performance Verification
Temperature Monitoring
- Normal operating temperature: 180-195°F
- Maximum acceptable: 210°F under severe conditions
- Install aftermarket temperature gauge for accurate monitoring
Cooling System Flow
- Upper radiator hose should be hot after thermostat opens
- Lower hose should be cooler, indicating heat transfer
- Heater should produce hot air when system reaches operating temperature
Airflow Testing
- Electric fan should move noticeable air volume
- Check for proper shroud sealing and air direction
- Verify A/C condenser not blocking excessive airflow to radiator