Posted by Patrick Muschamp on 01 13 2015 11:35 AM

Model number: MMTS-F2D-03


SKUs affected: MMTS-F2D-03H; MMTS-F2D-03L


Common Installation Questions:

1. Thermostat pin hole in housing is too short for Mishimoto thermostat pin. After the thermostat is installed, the unit will not be able to fully close.

2. Thermostat pin is too long and preventing the customer from completing installation with the Mishimoto approved thermostat housing.

3. Customer is missing the Mishimoto supplied rubber o-ring.

4. Thermostat (High) is not reaching proper temprature(s) -or- (Low) is overheating the engine.



1. This is happening with some OEM and aftermarket thermostat housings. The Mishimoto thermostat is designed to function with the Motorcraft RT-1169 C91 thermostat housing specifically. If a different housing (C92 or aftermarket) was equipped on the customer's vehicle, this issue may arise causing the thermostat to not function properly. Please see attachments 1 (C91) and 2 (C92) for housing part numbers. A few customers state installation is possible if a pin-hole is drilled into the thermostat. However, Mishimoto highly suggests using the correct housing.

*The incorrect housing number is 1839304C92, the correct number is 1839304C91.

2. Mishimoto suggests warming the thermostat to aid with installation. Do not apply a direct heat source to the thermostat.  Mishimoto suggests using a pot of water to help administer the heat without applying direct heat to the unit. Refer to the attachment "Document 1" for additional information on this procedure.

*Note: As a general rule and to ensure a proper seal within the housing, Mishimoto recommends installing the thermostat into the housing and boiling the assembly in hot water. If the customer does not choose to take this step, the truck may need to go through a few heat cycles before the full benefits of the thermostat are seen.

3. While the OEM gasket be re-used, the themrostat should include a rubber o-ring. Please contact our Customer Service team at with a copy of your receipt, and your shipping information to request a replacement.

4. If the customer is experiencing this issue, please contact our Customer Service team direct at with a copy of the receipt.



1. C91 thermostat housing

2. C92 themrostat housing

3. Document 1 (see Solution 2)

 1.jpg (79.49 KB)
 2.jpg (69.01 KB)
 document 1.docx (358.17 KB)
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