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Discussion Starter · #1 ·
Good Sirs, need some help.

'08 F450, 6.4 with 138k. Bought truck in July and had no problems until December. Check engine light came on, had codes read by dealer resulting in P0128 Coolant Thermostat Malfunction. Symptoms matched code, no heat indicated on gauge and no heat from heater. Bought Motorcraft replacement thermostat kit and went to work. After much cursing and two trips to buy extensions and wobble attachments to get the bolts out I found the old therms didn't look that bad and were not stuck open but the rubber coating on one of the flanges was torn. Installed new therms and buttoned everything back up. Engine built heat but seemed to do so more slowly than it should and seemed to get close but didn't quite get as hot as it should. Ran this way with no codes and going into regen as it should for 3 weeks. Check engine light came back and P0128 code is back... I've never experienced getting a bad thermostat out of the box but I guess it could happen. Before I tear this thing apart again, is there anything else that could be preventing this thing from building heat or, is there anything anyone knows of that would cause thermostats to go bad that fast in succession?

ANY help anyone can give would be greatly appreciated!

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