Temp gauge and. Vent temp

Son in laws 07 focus. Not my kid. Cel for low coolant temp. P0128? Gauge is normal position. Needle is vertical. Vents feel “ok”.
-15f last week. Said ok.
Is 30f today. Still feels ok.
Scan tool says it’s 153f. I believe my eyes
So, it’s his temp sensing skills? He cannot tell warm air from hot air?

Normal operating temperature is around 200F so that’s definitely low. I am not a mechanic but I suspect a stuck thermostat.


In most cars a p0128 code is always going to be a thermostat . Replace it and clear the code or eventually it will clear on its own after the replacement . 153 degrees is way too low for any car . Most run between 195 and 205 . I suspect what you think is normal on the guage is low and will run a little higher on the guage once replaced .

“Scan tool says it’s 153f.” – Ignorant question: You mean an OBD scan tool, and not a scanning (no-touch sensing) thermometer, right?

“So, it’s his temp sensing skills?” I’m not sure what this means, but I think it hints at my thought: Are you SURE that the 153f measurement is right?

I’d try to find a way to verify that measurement before I changed any parts. (OTOH, changing the thermostat might be simpler than verifying the measurement. If the temp come up to normal, fine. If it stays at 153f, then you have to either find a way to verify or learn to live with a suspect bogus measurement.)

I had a similar code on my Lesabre a few years ago. I really couldn’t tell there was any issue other than the check engine light. Heat worked fine, etc. I took the thermostat out and the rubber gasket around it had failed, allowing coolant to bypass the thermostat. So, in winter, on the highway, the engine couldn’t stay at a high enough temp, basically.

I’d go ahead and replace the thermostat if it’s pretty accessible. $5 part, so I’d take that gamble.

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You won’t have to clear a code for that. It won’t take more than two days to clear by itself after the problem is fixed.

07 focus has a thermostat/plastic housing assy. It’s under p/s pump. Not real hard to reach. I’ll start there. Aftermarket units are $20-25. Ford ones are much more. But, ford buys them from supplier?

I’d feel comfortable buying aftermarket, depending on the brand. Gates or Stant would be good. Looks like Rockauto lists one with a sensor and one without. The one with the sensor is 3-4 times as much as the one without. Not sure if yours has the sensor in the housing or not. Motorcraft “without sensor” is about 30 bucks on RA. With sensor is $100 more.

When you’re done stick a thermometer in the dash vent with the temp turned all the way hot. A good vent temp should be 160 degrees or more.