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TSB 07-01-91

Overheating Or No Heat Condition.

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Models: 1989 - 1990 (AD) Ram Pickup/Ram Cab & Chassis (RWD/4WD) With Cummins 5.9L Diesel Engine

Symptom/Condition:

Some vehicles may exhibit an overheating or no heat condition. Interference between the thermostat and cylinder head coolant passage opening on engines built before engine serial number 44465181 may result in the thermostat sticking in the opened or closed position.

The circumference of the cylinder head coolant passage opening was enlarged, April 1990, beginning with engine serial number 44465181. In addition, a new thermostat package PN 83506401 was released and is the only one available for service.

When installing the new thermostat package PN 83506401 on these engines, the following procedure MUST be followed. Failure to follow the procedure may result in an overheating or no heat condition.

Parts Required:

1 - Thermostat Package     PN 83506401

Package Contents I
1 - Thermostat I
1 - Seal I
1 - Template I
1 - Instruction Sheet

Installation Procedure:

This procedure involves positioning a template over the thermostat opening in the cylinder head coolant passage, checking the size of the opening circumference and removing excessive material.

1. Verify engine serial number is before 44465181 Figure 1.

NOTE-. IF THE LETTERS "G OR M" ARE STAMPED ON THE CYLINDER HEAD, THIS PROCEDURE IS NOT REQUIRED, FIGURE 1.

3. Position the template supplied with the new thermostat on the cylinder head as shown in Figure 2.

4. If the cylinder head coolant passage inside circumference is smaller than the inside circumference of the template, mark the area with a scribe, Figure 3.

NOTE: IF THE CYLINDER HEAD COOLANT PASSAGE IS THE SAME CIRCUMFERENCE AS THE TEMPLATE, PROCEED TO STEP 9.

5. Remove the template, use a shop towel to cover the coolant bypass passage. Figure 4.

6. Using a cutting tool, such as a rotary file, remove the excess material from the scribed area. Figure 4.

7. Remove the shop towel from the coolant bypass passage.

8. Use a shop vac or magnet to remove the machined shavings from the cylinder head coolant passage.

9. Install the thermostat as outlined on page 7-19 In your 1991 Rear Wheel Drive Truck Service Manual, Publication #81-370-1108.

10. Using a metal stamp, mark the cylinder in the area shown in Figure 1 as follows:

• Stamp the letter "G" for cylinder head that was inspected and did not need to be machined.
• Stamp the letter "M" for cylinder head that was inspected and did require machining.

Notes:

POLICY: Reimbursable within the provisions of the warranty.

TIME ALLOWANCE
Labor Operation No. 07-40-05-90 . . . . . . . . . 0.8 Hrs.

FAILURE CODE:    07 - Binds, sticks or seized