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Caterpillar 3512C ATAAC Engine

Name: Caterpillar 3512C ATAAC Engine
Brand: Caterpillar

The Caterpillar 3512C ATAAC is a 51.8 L 12-cylinder ta engine rated at 1800 rpm. It powers generator sets from Caterpillar, including the SR4B.

Also known as: CAT 3512C ATAAC

Part of the Caterpillar 3512C engine family — 4 variants share parts & fitment.

51.8 L

Displacement

Cylinders

1800 rpm

Rated speed

On this pageSpecs Generator sets FAQ Service intervals Torque & specs Fluids Procedures Wiring

Engine specifications

Displacement	51.8 L
Cylinders	12
Aspiration	TA
Rated speed	1800 rpm

Generator sets powered by this engine

Caterpillar SR4B

How to read your Caterpillar engine serial & model number →

Common problems

When the engine oil pressure is increased beyond the low oil pressure setpoint, the GSC will inform the governor that the engine speed should be increased from IDLE to RATED rpm. 2301A Control
The GSC+ detects an alarm fault
Fix: Fault alarm indicator (26) is accompanied by an alarm fault code that is shown on the upper display (29) when the alarm codes key (30) is pressed.
The GSC+ detects a shutdown fault
Fix: The engine will shut down if the engine is running. The engine will not be allowed to start.
The fault alarm indicator (3) flashes when the GSC detects an alarm fault. g00604607
Overcrank
Cause: Engine does not start within the setpoint for overcrank.
Low oil pressure indicator flashes, and the engine is shut down.
Cause: The engine oil pressure drops below the setpoints for low oil pressure shutdown that are programmed into the GSC. There are two low oil pressure setpoints. One setpoint is used when the engine is at idle speed. The other setpoint is used when the engine is at rated speed.
Low oil pressure
Cause: Engine oil pressure drops below the setpoints for low oil pressure shutdown that are programmed into the GSC+.
Fix: The tow oil pressure indicator FLASHES, and the engine is shut down. The engine is not allowed to start until the fault is corrected.
High water temperature indicator flashes, and the engine is shut down.
Cause: The engine coolant temperature rises above the setpoint for high water temperature shutdown that is programmed into the GSC.
High water temperature
Cause: Engine coolant temperature rises above the setpoint for high water temperature shutdown that is programmed into the GSC+.
Fix: The engine is shutdown and the engine is not allowed to start until the fault is corrected.
Generator parameters are not matched to the bus
Fix: If the generator and bus voltages, frequencies and phases are in sync, the lamps will light continuously. If not, the associated lamp will flash.
Fault shutdown 21
Fault alarm 22
Engine overspeed indicator flashes, and the engine is shut down.
Cause: The engine speed exceeds a certain threshold set in the GSC+.
Fix: Correct the condition by addressing any issues that caused the engine to overspeed.
Engine overspeed
Cause: Engine speed exceeds the setpoint for engine overspeed that is programmed into the GSC+.
Fix: The engine is shutdown and the engine is not allowed to start until the fault is corrected.
Engine overcrank indicator flashes, and the engine is shut down.
Cause: The engine has been cranked for an extended period without starting.
Fix: Correct the condition by ensuring proper start-up procedures are followed.

Compiled from service & troubleshooting documentation across every generator set that uses the Caterpillar 3512C ATAAC.

Service intervals

Item	Action	Hours	Months	Notes
Insulation	Test	7500 hr	12 mo	Every 7500 Service Hours or 1 Year (Standard and Standby schedule)
Rotating Rectifier	Check	7500 hr	12 mo	Every 7500 Service Hours or 1 Year (Standard and Standby schedule)
Bearing (Ball)	Lubricate	2000 hr	12 mo	Every Year (Standby schedule)
Bearing (Spherical Roller)	Lubricate	1000 hr	12 mo	Every Year (Standby schedule)
Generator Set Vibration	Inspect	2000 hr	12 mo	Every Year (Standby schedule)
Stator Lead	Check	2000 hr	6 mo	Every 6 Months (Standby schedule)

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Bearing bracket step minimum	less than 0.0762	mm
Other	High idle speed for droop governors	approximately 2% to 5%	above full load speed	governors equipped with droop
Other	Speed droop values commonly used	3% and 0%	%
Other	Voltage droop for 0.8 power factor load	approximately 5	%	loads with a power factor of 0.8
Pressure	Engine oil pressure at low idle	186 to 344	kPa	low idle speed
Pressure	Normal operating engine oil pressure	275 to 600	kPa	engine running at rated engine speed, SAE 10W30 oil, operating oil temperature 104 C (219.2 F), normal engine water temperature
Resistance	Exciter Armature (Rotor) (L2) resistance	less than 0.1	ohm	room temperature
Resistance	Exciter Armature (Rotor) (L2) winding resistance	less than 0.1	ohm	room temperature
Resistance	Exciter Field (Stator) (L1) resistance	3.0 to 6.0	ohms	room temperature
Resistance	Exciter Field (Stator) (L1) winding resistance	3.0 to 6.0	ohm	room temperature
Resistance	Main Armature (Stator) (L4) resistance	less than 0.1	ohm	room temperature
Resistance	Main Field (Rotor) (L3) resistance	0.75 to 2.0	ohms	room temperature
Resistance	Main Field (Rotor) (L3) winding resistance	0.75 to 2.0	ohm	room temperature
Resistance	Main armature (Stator) (L4) winding resistance	less than 0.1	ohm	room temperature
Resistance	Pilot Exciter Armature (L5) resistance	less than 0.1	ohm	room temperature
Resistance	Pilot Exciter Armature (L5) winding resistance	less than 0.1	ohm	room temperature
Resistance	Resistor (R5) resistance	27000	ohm	nominal ± 2700 ohms
Resistance	Varistor (CR7) resistance	15000	ohm	minimum
Resistance	Varistor (CR7) resistance	minimum 15000	ohms
Speed	Frequency vs RPM - four-pole generator	divide the RPM by 30	Hz
Speed	Frequency vs RPM - six pole generator	divide the RPM by 20	Hz
Speed	Low idle (50 Hz units)	approximately 80	% of full load speed	50 Hz units
Speed	Low idle (60 Hz units)	approximately 66	% of full load speed	60 Hz units
Temperature	Bearing installation heating	149	C	for press fit installation
Temperature	Bearing reinstall heating	107	C	heat for ten minutes
Temperature	Coupling installation heating	315	C	for press fit installation
Temperature	Engine water temperature operating range	88 to 100	C	88 C (190.4 F) to 100 C (212.0 F)
Temperature	Generator drying temperature (oven method)	65	C	forced air oven for 4 hours
Temperature	Generator drying winding temperature rise rate	10	C per hour up to 85 C (185 F)	do not apply heat too rapidly
Temperature	Hub reinstall heating	400	C	heat for three hours
Temperature	Oven drying method temperature	65	C	forced air drying oven for four hours
Temperature	Winding temperature limit during drying	85	C	maximum to prevent insulation damage
Torque	Exciter armature bolt (3/8 inch)	55.8	N·m	with thread lock 9S-3263
Torque	Exciter armature bolt (5/16 inch)	35.4	N·m	with thread lock 9S-3263
Voltage	Generator set functional test minimum phase voltage	minimum 85	VAC	generator set operated at half the rated speed with 12 VDC battery on F1+/F2-
Voltage	Insulation test voltage for units 600 volts or less	500	Volts	600 volts or less
Voltage	Insulation test voltage for units more than 600 volts	1000	Volts	more than 600 volts

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Ambient	Notes
Coolant	Cat DEAC		Diesel; 3,000 Service Hours or Three Years; annual S·O·SSM Level 2 coolant sampling and analysis
Coolant	Cat ELC		Diesel; 12,000 Service Hours or Six Years; add Cat ELC Extender at 6,000 service hours or one half of service life; annual S·O·SSM Level 2 coolant sampling and analysis
Coolant	Cat NGEC		Natural Gas; 16,000 Service Hours or Three Years; use interval that occurs first
Engine oil	Cat NGEO		Natural Gas
Engine oil	SAE 10W30		Referenced as the oil used when normal operating engine oil pressure is specified
Engine oil	Cat Arctic DEO SYN SAE 0W-30	-40°C to 30°C	Engine Crankcase; Industrial Engines
Engine oil	Cat DEO SYN SAE 5W-40	-30°C to 50°C	Engine Crankcase; Industrial Engines
Engine oil	Cat DEO SAE 10W-30	-18°C to 40°C	Engine Crankcase; Industrial Engines
Engine oil	Cat DEO SAE 15W-40	-9°C to 50°C	Engine Crankcase; Industrial Engines
Grease	Cat Generator Set Grease		Part Number 108-8611
Grease	NLGI No. 1.5 Grade		Caterpillar 108-8611 Grease Cartridge for spherical roller bearings; contains Clay thickener; no molybdenum disulfide; viscosity 32 cSt at 40 C, 5 cSt at 100 C
Grease	NLGI No. 2 Grade	-29°C to 177°C	Caterpillar 2S-3230 Bearing Lubricant for ball bearings; contains Polyurea thickener; for extremely low temperatures use NLGI No. 1 Grade or NLGI No. 0 Grade

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

VR3 Regulator Adjustment Procedure adjustment

⚠ The VR3 regulator is protected by a fuse(s) and a solid-state overcurrent protection. If a fuse becomes open, contact a Caterpillar dealer.

Remove the access panel of the generator.
Loosen the locknut on the voltage droop potentiometer (1).
Remove the protective screw from the voltage level potentiometer (2) and from the voltage gain potentiometer (3).
Turn the voltage droop potentiometer (1) counterclockwise to zero droop. Tighten the locknut.
Turn the voltage gain potentiometer (3) counterclockwise to zero, then to about 1/4 of full range of clockwise travel.
Perform required maintenance on the engine before you start the engine.
Start the engine and allow the engine to warm up.
Increase engine speed to full governed rated speed (high idle).
Set the no-load voltage with the voltage level potentiometer (2) or the voltage adjust rheostat.
Close the load circuit breaker and apply full load gradually. Adjust governor control to nameplate frequency or rated speed.
If the voltmeter reading increases above no-load voltage, turn the voltage gain potentiometer counterclockwise. If it decreases, turn it clockwise.
Remove the load. If necessary, adjust the voltage level potentiometer (2) to obtain desired voltage.
Apply the load. Repeat Steps 10 through 12 until the voltage at no load equals the voltage at full load.
Tighten the locknuts. Install the protective screws and the access panel of the generator.

Generator Set Functional Test diagnostic

⚠ Do not exceed half rated speed

⚠ Do not allow output to exceed nameplate rating

Tools: Digital Multimeter, 12 VDC Battery

Disconnect wires F1 and F2 from voltage regulator
Disconnect generator load
Connect 12 VDC battery to wires F1+ and F2-
Operate generator at half rated speed
Measure AC voltage across terminals T1-T2, T1-T3, T2-T3
Record voltages at half speed, then at ±10% speed variations
Verify minimum 85 VAC output at half speed
Verify speed changes produce proportional voltage changes

Rotating Rectifier - Test diagnostic

Tools: 6V-7070 Digital Multimeter, 146-4080 Digital Multimeter (RS-232)

Touch the red ohmmeter lead to the rectifier terminal marked '+'.
Touch the black ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate an open circuit or high resistance.
Touch the black ohmmeter lead to the rectifier terminal marked '+'.
Touch the red ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate a good diode or low resistance.
Touch the black ohmmeter lead to the rectifier terminal marked '-'.
Touch the red ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate an open circuit or high resistance.
Touch the red ohmmeter lead to the rectifier terminal marked '-'.
Touch the black ohmmeter lead to terminals AC1, AC2, and AC3; the meter should indicate a good diode or low resistance.
If the meter does not indicate the expected result, the rectifier is bad. Replace the rectifier.

Rotating Rectifier Block Diode Test diagnostic

⚠ Shorted diode can damage exciter rotor

Tools: Digital Multimeter 6V-7070

Set digital multimeter to diode range and remove all leads
Test forward bias on each diode (black to positive, red to AC terminals)
Verify readings between 0.4 and 1.0
Test reverse bias (red to positive, black to AC terminals)
Verify overload (OL) readings on reverse bias
Replace rectifier block if any reading is outside specifications

Varistor - Test diagnostic

Tools: Ohmmeter, Test Light

Using an ohmmeter, place the ohmmeter across the varistor. The resistance should be a minimum of 15000 ohms.
Disconnect either lead of the varistor (CR7).
Place the test light across the varistor.
Observe the results. The lamp should not light.
Reverse the test light.
Observe the results. The lamp should not light.
If the test light illuminates in either direction, there is a short in the varistor. Replace any faulty varistors with comparable operating characteristics.

Winding Resistance Measurement diagnostic

⚠ Temperature affects resistance; test at room temperature only

⚠ Winding damage if outside specifications

Tools: Digital Multimeter, Milliohmmeter (Wheatstone Bridge)

Disconnect winding from other components before measuring
Measure armature windings with milliohmmeter (L2, L4, L5)
Measure field windings with multimeter (L1, L3)
Test at room temperature only
Compare measurements to specification values
Verify no continuity between windings or between winding and ground

Lead to Lead Connection installation

Tools: Varnished cambric tape 5N-4685, Vinyl plastic tape 5N-4686, Cable straps

Fasten leads using flat plated washer under bolt and nut
Apply two layers of varnished cambric high voltage tape
Overlap tape 50% of width while wrapping
Extend tape 25 mm onto wire insulation on each side
Apply two layers of vinyl plastic tape over cambric tape
Extend vinyl tape 51 mm onto wire insulation on each side
Group all phase leads and secure with cable straps

Leads to Terminal Strip Connection installation

Tools: Flat plated washers, Cable straps

When multiple leads attach to bus bar, place on alternate sides
Use flat plated washers under bolt head and nut
Group all generator phase leads together after connection
Tie phase leads together with cable straps
Maintain minimum 25 mm clearance between phase-to-phase connections

Bearing (Ball) - Lubricating Process maintenance

Tools: Grease fitting, 8F-9866 Grease gun

Remove either the louver assembly or the rear plate from the rear of the generator housing.
Remove the top grease pipe plug and remove the lower grease pipe plug.
Install a grease fitting in the grease pipe.
Grease the shielded ball bearings with 2S-3230 Bearing Lubricant (53.28 mL (1.8 ounces) to 59.20 mL (2.0 ounces)).
Wipe off the excess grease. Remove the top grease fitting. Install the plug.
Operate the generator for one hour to allow the grease to expand and force excess grease from the cavity.
Stop the engine. Install the plug in the bottom grease pipe and wipe off the excess grease.
Install the louver assembly or install the rear plate.

Generator - Dry (Controlled Current Method) maintenance

Tools: 8T-0900 Clamp on ammeter (1200 amperes), External Power Source, Rheostat

Make an external power source.
Disconnect F1+ and F2- from the voltage regulator. Disconnect the generator load. Connect generator output leads T0, T1, T2, and T3. Install the clamp-on ammeter on output lead T1.
Connect the rheostat at maximum resistance value. Connect the external power source to wires F1+ and F2-.
Start the generator set and run at idle speed.
Monitor the phase current. Gradually increase engine RPM until rated phase current or full generator set speed is obtained.
If more phase current is necessary, slowly turn the rheostat until the rated phase current is reached.
On an hourly basis, stop the drying procedure and check the insulation resistance. Repeat until the insulation resistance is acceptable.

Generator Isolating for Maintenance maintenance

⚠ Personal injury or death can result from high voltage.

Tools: Audio/visual proximity tester, Ground straps, DO NOT OPERATE warning tags

Stop the engine.
Attach a DO NOT OPERATE or similar warning tag to the engine prime mover starting circuit. Disconnect the engine starting circuit.
Disconnect the generator from the distribution system.
Lock out the circuit breaker. Attach a DO NOT OPERATE or similar warning tag to the circuit breaker. Verify all points of possible reverse power flow are locked out.
For power, sensing, and control circuitry, remove the transformer's fuses.
Attach a DO NOT OPERATE or similar warning tag to the generator excitation controls.
Remove the cover of the generator's terminal box.
Use an audio/visual proximity tester insulated for the proper voltage rating to verify the generator is de-energized.
Add ground straps to the conductors or terminals. During the entire work period, these ground straps must remain connected.

Recommended Periodic Insulation Test Procedure maintenance

⚠ Personal injury or death can result from electrocution. The megohmmeter applies a high voltage; discharge the leads before touching.

Tools: 142-5055 Insulation Testing Gp, 9U-6003 Insulation Testing Gp

Take the generator out of service.
Visually inspect the generator for moisture. If moisture exists, do not perform this insulation test. Dry the unit first.
Inspect the installation. Determine the equipment that will be tested by the insulation tester.
Discharge the capacitance of the windings.
Disconnect T0 from ground.
Disconnect the regulator sensing lead wires: 20, 22, and 24.
Connect the insulation tester's RED lead to ground.
Connect the insulation tester's BLACK lead to T0.
For units 600 volts or less set the voltage to 500 Volts. For units more than 600 volts set the voltage to 1000 Volts.
Use the 30/60 Time Resistance Method: apply voltage and observe readings at 30 seconds and 60 seconds.
Record the 60 second reading corrected for temperature. Record temperature and humidity. Remove voltage.
Evaluate the readings by comparing the 60 second resistance reading with previous readings taken under similar conditions.
Switch the insulation tester to OFF to discharge the leads, then disconnect the insulation tester's leads.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
	3	Delta - 6 lead	6	Winding pitch must be two-thirds or the generator must be derated.
	3	Wye - 10 lead (high voltage)	10	Illustration 13. Only used on 3306B generator sets and 3406C generator sets. Terminal T0 is the neutral lead.
	3	Wye - 10 lead (low voltage)	10	Only used on 3306B and 3406C generator sets. Terminal T0 is the neutral lead.
	3	Wye - 12 lead (high voltage)	12	Terminals T10, T11, and T12 become neutral connections when tied together.
	3	Wye - 12 lead (low voltage)	12	Terminals T10, T11, and T12 become neutral connections when tied together.
	3	Wye - 4 lead	4	Only used on 3306B generator sets and 3406C generator sets. Terminal T0 is the neutral lead.
	3	Wye - 6 lead	6	Terminals T4, T5, and T6 become neutral connections when the terminals are tied together.
240	3	Delta - 12 lead	12	Terminals T6 and T9 become the neutral connections when tied together and grounded. T2 and T10 connection is the high phase. 240 V, 60 Hz, three-phase: 208 Volts between the high phase and neutral; 240 Volts between either of the low phases and neutral.
Four Lead Wye	Three-phase	T1/T2/T3 to loads, T0 to neutral	T1, T2, T3, T0	Regulator leads 22, 24, 20 from T1, T2, T3 respectively
Six Lead Delta	Three-phase	T1/T6, T2/T4, T3/T5 series loop connections	T1, T2, T3, T4, T5, T6	Delta configuration
Six Lead Wye	Three-phase	T1/T2/T3 to loads, T4/T5/T6 to neutral	T1, T2, T3, T4, T5, T6	Regulator sensing from T1, T2, T3
Ten Lead Wye High Voltage	Three-phase	T1/T2/T3 to loads with T4/T7, T5/T8, T6/T9 series connections	T1, T2, T3, T4, T5, T6, T7, T8, T9, T0	High voltage configuration
Ten Lead Wye Low Voltage	Three-phase	T1/T7, T2/T8, T3/T9 parallel connections	T1, T2, T3, T4, T5, T6, T7, T8, T9, T0	Low voltage configuration
Twelve Lead Delta	Three-phase	T1/T12, T2/T10, T3/T11 series loops with jumpers	T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12	Delta configuration with 12 leads
Twelve Lead Wye High Voltage	Three-phase	T1/T2/T3 to loads with series connections	T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12	High voltage configuration with 12 leads
Twelve Lead Wye Low Voltage	Three-phase	T1/T7, T2/T8, T3/T9 parallel connections	T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12	Low voltage configuration with 12 leads

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Also used in

Caterpillar 784B — Dump Truck
Caterpillar 785B — Dump Truck
Caterpillar 785D — Haul Truck

Other equipment known to use this engine, via filter-application cross-reference — useful for sourcing parts even when your exact machine isn't listed elsewhere on this page.

Common questions

What is the displacement of the Caterpillar 3512C ATAAC?

The Caterpillar 3512C ATAAC has a displacement of 51.8 liters with 12 cylinders.

Which generators use the Caterpillar 3512C ATAAC engine?

The Caterpillar 3512C ATAAC powers 1 generator set(s), including Caterpillar SR4B.

What is a common problem with the Caterpillar 3512C ATAAC engine?

A commonly reported issue on generators using the Caterpillar 3512C ATAAC is: When the engine oil pressure is increased beyond the low oil pressure setpoint, the GSC will inform the governor that the engine speed should be increased from IDLE to RATED rpm..