Dodge Nitro. Manual - part 1

2007 ENGINE

3.7L - Service Information - Nitro 

DESCRIPTION 

3.7L ENGINE DESCRIPTION 

Fig. 1: 3.7L Engine 
Courtesy of CHRYSLER LLC 

The 3.7 liter (226 CID) six-cylinder engine is an 90° single overhead camshaft engine. The cast iron cylinder 
block is made up of two different components; the first component is the cylinder bore and upper block, the 

 

2007 Dodge Nitro R/T 

2007 ENGINE 3.7L - Service Information - Nitro

  

 

2007 Dodge Nitro R/T 

2007 ENGINE 3.7L - Service Information - Nitro

  

second component is the bedplate that comprises the lower portion of the cylinder block and houses the lower 
half of the crankshaft main bearings. The cylinders are numbered from front to rear with the left bank being 
numbered 1, 3, and 5 and the right bank being numbered 2, 4, and 6. The firing order is 1-6-5-4-3-2. The engine 
serial number is located at the right front side of the engine block. See Fig. 1. 

DIAGNOSIS AND TESTING 

CYLINDER COMPRESSION PRESSURE 

The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions. 

Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise 
the indicated compression pressures may not be valid for diagnosis purposes. 

1. Clean the spark plug recesses with compressed air.  

2. Remove the spark plugs.  

3. Secure the throttle in the wide-open position.  

4. Disable the fuel system (Refer to FUEL DELIVERY - GAS ).  

5. Remove the ASD relay. Refer to REMOVAL .  

6. Insert a compression pressure gauge and rotate the engine with the engine starter motor for three 

revolutions.  

7. Record the compression pressure on the 3rd revolution. Continue the test for the remaining cylinders.  

8. See SPECIFICATIONS for the correct engine compression pressures.  

ENGINE MECHANICAL DIAGNOSTIC TABLE 

CONDITION 

POSSIBLE CAUSES 

CORRECTIONS 

NOISY VALVES

1. High or low oil level in 
crankcase.

1. Refer to SPECIFICATIONS .

2. Thin or diluted oil.

2. Change oil and filter.

3. Low oil pressure.

3. Check oil pump, if Ok, check rod 
and main bearings for excessive 
wear.

4. Dirt in lash adjusters.

4. Clean or replace as necessary.

5. Worn rocker arms.

5. Replace as necessary.

6. Worn valve guides.

6. See STANDARD 
PROCEDURE.

7. Excessive runout of valve 
seats.

7. Service valves and valve seats. 
See STANDARD PROCEDURE.

ENGINE VIBRATION

1. Counter Balance Shaft not 

timed properly

1. Refer to Engine Timing in this 
article

CONNECTING ROD NOISE

1. Insufficient oil supply.

1. Refer to SPECIFICATIONS .

2. Low oil pressure.

2. Check oil pump, if Ok, check rod 
and main bearings for excessive 

 

2007 Dodge Nitro R/T 

2007 ENGINE 3.7L - Service Information - Nitro

  

ENGINE DIAGNOSIS - INTRODUCTION 

Engine diagnosis is helpful in determining the causes of malfunctions not detected and remedied by routine 
maintenance. 

These malfunctions may be classified as either performance (e.g, engine idles rough and stalls) or mechanical 
(e.g, a strange noise). 

See ENGINE PERFORMANCE DIAGNOSTIC TABLE and ENGINE MECHANICAL DIAGNOSTIC 
TABLE for possible causes and corrections of malfunctions. Refer to DIAGNOSIS AND TESTING .  

Additional tests and diagnostic procedures may be necessary for specific engine malfunctions that can not be 
isolated with the Service Diagnosis charts. Information concerning additional tests and diagnosis is provided 
within the following diagnosis: 

Cylinder Compression Pressure Test. See DIAGNOSIS AND TESTING.  

Cylinder Combustion Pressure Leakage Test. See DIAGNOSIS AND TESTING.  

Engine Cylinder Head Gasket Failure Diagnosis. See DIAGNOSIS AND TESTING.  

Intake Manifold Leakage Diagnosis. See DIAGNOSIS AND TESTING.  

CYLINDER COMBUSTION PRESSURE LEAKAGE 

The combustion pressure leakage test provides an accurate means for determining engine condition. 

Combustion pressure leakage testing will detect: 

Exhaust and intake valve leaks (improper seating). 

wear.

3. Thin or diluted oil.

3. Change oil and filter.

4. Excessive bearing clearance.

4. Replace as necessary.

5. Connecting rod journal out-of-
round.

5. Service or replace crankshaft.

6. Misaligned connecting rods.

6. Replace bent connecting rods.

MAIN BEARING NOISE

1. Insufficient oil supply.

1. Refer to SPECIFICATIONS .

2. Low oil pressure.

2. Check oil pump, if Ok, check rod 
and main bearings for excessive 
wear.

3. Thin or diluted oil.

3. Change oil and filter.

4. Excessive bearing clearance.

4. Replace as necessary.

5. Excessive end play.

5. Check thrust washers for wear.

6. Crankshaft journal out-of 
round.

6. Service or replace crankshaft.

7. Loose flywheel or torque 
converter.

7. Tighten to correct torque

 

2007 Dodge Nitro R/T 

2007 ENGINE 3.7L - Service Information - Nitro

  

Leaks between adjacent cylinders or into water jacket.  

Any causes for combustion/compression pressure loss.  

1. Check the coolant level and fill as required. DO NOT install the radiator cap.  

2. Start and operate the engine until it attains normal operating temperature, then turn the engine OFF.  

3. Remove the spark plugs.  

4. Remove the oil filler cap.  

5. Remove the air cleaner.  

6. Calibrate the tester according to the manufacturer's instructions. The shop air source for testing should 

maintain 483 kPa (70 psi) minimum, 1,379 kPa (200 psi) maximum and 552 kPa (80 psi) recommended.  

7. Perform the test procedures on each cylinder according to the tester manufacturer's instructions. Set 

piston of cylinder to be tested at TDC compression. While testing, listen for pressurized air escaping 
through the throttle body, tailpipe and oil filler cap opening. Check for bubbles in the radiator coolant.  

All gauge pressure indications should be equal, with no more than 25% leakage. 

FOR EXAMPLE: At 552 kPa (80 psi) input pressure, a minimum of 414 kPa (60 psi) should be maintained in 
the cylinder. 

Refer to step CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART. 

CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART 

ENGINE LUBRICATION DIAGNOSTIC TABLE 

CONDITION 

POSSIBLE CAUSE 

CORRECTION 

AIR ESCAPES THROUGH 
THROTTLE BODY

Intake valve bent, burnt, or not 
seated properly

Inspect valve and valve seat. 
Reface or replace, as necessary. 
Inspect valve springs. Replace as 
necessary.

AIR ESCAPES THROUGH 
TAILPIPE

Exhaust valve bent, burnt, or not 
seated properly

Inspect valve and valve seat. 
Reface or replace, as necessary. 
Inspect valve springs. Replace as 
necessary.

AIR ESCAPES THROUGH 
RADIATOR

Head gasket leaking or cracked 
cylinder head or block

Remove cylinder head and 
inspect. Replace defective part

MORE THAN 50% LEAKAGE 
FROM ADJACENT 
CYLINDERS

Head gasket leaking or crack in 
cylinder head or block between 
adjacent cylinders

Remove cylinder head and 
inspect. Replace gasket, head, or 
block as necessary

MORE THAN 25% LEAKAGE 
AND AIR ESCAPES THROUGH 
OIL FILLER CAP OPENING 
ONLY

Stuck or broken piston rings; 
cracked piston; worn rings and/or 
cylinder wall

Inspect for broken rings or piston. 
Measure ring gap and cylinder 
diameter, taper and out-of-round. 
Replace defective part as 
necessary

 

2007 Dodge Nitro R/T 

2007 ENGINE 3.7L - Service Information - Nitro