"Service Engine Soon" with P0128 code

[NJExplorerFan]

Hey Guys,

I got a P0128 code from a "check engine" light that popped on Xmas night. Any idea what it could be? From what I have seen, a possible thermostat replacement? This is on a 2003 Explorer V8.

 

[Exproblems]

Hey Guys,

I got a P0128 code from a "check engine" light that popped on Xmas night. Any idea what it could be? From what I have seen, a possible thermostat replacement? This is on a 2003 Explorer V8.

The Haynes Manual lists code #PO128 as > "Coolant Thermostat" (Coolant temperature is below thermostat regulating temperature). <

Sounds to me from the code description that your coolant is not heating up to the operating range of your current t-stat. What is the coolant to water mix in your cooling system now. A 50/50 or 60/40 mix is all your need for most average climates, cold or hot. If anything, I would install a new t-stat (2003 V-8 temp range is 194 degrees to 210 degrees) and drain out the old coolant and refill with a new 50/50 mix of coolant/distilled water. The V-8 t-stat housing bolt torque is 18 ft lbs. The cooling system for the 2003 V-8 "without" rear heat holds 18.6 quarts and the cooling system "with" rear heat holds 20.1 quarts.

 

[NJExplorerFan]

Picked up a new thermostat today. Now I gotta figure out where it is. I'm told on the driver's side near the radiator. Two 10mm bolts need to be removed? Anybody have a diagram?

 

[Exproblems]

Picked up a new thermostat today. Now I gotta figure out where it is. I'm told on the driver's side near the radiator. Two 10mm bolts need to be removed? Anybody have a diagram?

I have the V-6 engine and from what I was told the V-8 t-stat setup is different than mine. You can find the t-stat housing by following the "upper" radiator hose to where it connects into the top of the engine. Where the hose ends is the t-stat housing. The Haynes manual shows an up close picture of the V-8 t-stat housing and upper hose I told you to follow to the engine, and also the 2 mounting bolts you speak of. From this photo, it looks like an easy job to replace the t-stat. There is another photo in the Haynes manual showing the t-stat housing cover as being a small cover plate (w/2 bolt holes) with the hose tubing as one piece and it appears to be made of metal, not plastic like on mine the V-6. Note, when you lift off the t-stat housing, take note of the position of the old t-stat itself, plus the O-ring and install the new one in the exact same position and remember to install the new rubber O-ring on the bottom side of the t-stat body. Wet the O-ring with fresh coolant using your finger prior to placement. When done, torque the 2 bolts to specs, re-connect the upper hose and clamp and refill the cooling system with new coolant.

 

[swshawaii]

Please copy pdf if needed ASAP. Thanks.

Thermostat and Thermostat Housing — 4.6L (2V)
http://www.mysporttrac.com/~library...ing-8212-4-6l-2v-removal-and-installation.pdf

 

[NJExplorerFan]

Thank you for posting everything guys! I will get working on it most likely on Sunday. Hopefully that will cure the problem.

 

[NJExplorerFan]

Okay, I popped in the new thermostat today and added some coolant. Immediately after I started the truck and the code was still there. I guess it needs to complete a drive cycle? Should it disappear right away? Either way, to expedite the process, I cleared the code. Hopefully it won't come back.

 

[stahrman]

Keep us posted!

 

[NJExplorerFan]

I rescanned tonight and it looks like the drive cycle is almost complete - just the EVAP has to set. No SES light yet. Should I assume all is okay or can the light still come back?

 

[stahrman]

I rescanned tonight and it looks like the drive cycle is almost complete - just the EVAP has to set. No SES light yet. Should I assume all is okay or can the light still come back?

Keep fingers crossed...lol.

 

[lkreykes]

It took about a week or so for the SES light on my Explorer to clear after replacing the thermo, it has been about a month now and it hasn't come back on since.