Modern vehicles, their thermostats, and P0128

[emmett442]

Howdy!

New member, long time lurker.

Recently (last night) dealt with this issue on my Crown Vic last night. This is one of many other vehicles that I've addressed this problem on - It seems to me that this is relatively common, or at least more common than it was maybe 15-20 years ago.

Is it just me? For a while, I thought failing thermostats were a thing of the past. Especially when considering today's use long life coolants, and improved gasket technology (translating to less use of stop leaks and such). Or perhaps, it's just that coolant temp is monitored nowadays, making it seem like it's a more frequent problem?

Anyway, I know you guys are big advocates of pictures, so here's a few from last night. 2011 Crown Vic, 75k miles, religiously maintained by myself. I'm pleased with it's condition:

 

[sasilverbullet]

Yep, that is VERY clean! Congrats!

 

[NateDN10]

I had to replace the thermostat on my '05 Chevy Cobalt after 10 years with the P0128 code. I did a few radiator drain and refills during the time I had it. Thermostats still wear out!

 

[bullwinkle]

Interesting-I thought an '11 Crown Vic would use Premium Gold (like my '03 MGM, which also got a new thermostat recently due to the old one being weak, despite spotless Gold coolant).

 

[emmett442]

It came with Gold, but shortly after I got it (3-4 years and 40k miles ago) I switched it to Dexcool to keep both the Malibu's and Vic's maintenance schedule and materials coordinated. I prefer stocking one coolant, and changing them at the same time - when one is due, so is the other!

I've been mostly a 'GM man' (owned many a Cadillac in the past), and I've accumulated lots of positive experience with Dex, so it's become my go-to for all of my vehicles.

Nothing scientific about it - just became comfortable with it over the years.


Haven't had time to feel this place out yet... do I have to go get my flame suit on for putting Dex in a Ford???

 

[bullwinkle]

At least it didn't seem to hurt anything, I've switched a couple vehicles from green to PG-but I wasn't brave enough to switch them to Dex.

 

[emmett442]

:

:

I've used Dex in everything - I can't remember having a problem that I could attribute to the type coolant used...

 

[DoubleWasp]

Thermostats are a wearable component. Wax pellet weakens over time, and eventually fails.

 

[emmett442]

^^^That would explain a 'stuck closed' problem, but the 'stuck open' failures seem to be more common. Again, with such clean systems in modern vehicles, I'm surprised at the number of stuck open failures.

 

[Merkava_4]

Was your thermostat stuck open or closed ?

 

[emmett442]

Open, as the P0128 states (Coolant Temperature Below Thermostat Regulating Temperature)

It mustn't have been stuck wide open because I had good heat and the engine warmed up most of the way, according to the dashboard. It just doesn't seal correctly when closed.

This seems to be the common theme.

 

[bullwinkle]

Originally Posted By: Merkava_4
Was your thermostat stuck open or closed ?
Mine wasn't stuck open, & it didn't throw a code, but it would take a long time to build up heat, & barely make it into the normal range. Put in a new lifetime warranty Stant Superstat (195F), back to normal.

 

[cb_13]

Ford uses the fail safe thermostats. So they SHOULD be stuck open if they fail. The computer will pick up on one that isn't fully closing long before I'd personally realize it is taking longer to put out good heat.

 

[carviewsonic]

I replaced two thermostats in the last two years, one on a high mileage Buick, the other on a very low mileage Buick (that one surprised me). Both were opening too soon and set off the PO 128 code.

 

[Merkava_4]

Originally Posted By: bullwinkle
Mine wasn't stuck open, & it didn't throw a code, but it would take a long time to build up heat, & barely make it into the normal range. Put in a new lifetime warranty Stant Superstat (195F), back to normal.


Can you tell if the thermostat on the left side in the picture is stuck open ?

 

[George7941]

A ScanGauge will let you monitor thermostat performance and you will notice any abnormalities long before P0128 is set.

The thermostat (Stant Superstat) in my truck doesn't have the crisp performance it had when it was new. It has developed a bit of laziness and the coolant temperature cycles between 89C and 91C, whereas when new it would maintain a rock steady 90C.

 

[SHOZ]

I can't remember the last time I had to change t-stat. I drive the cars till the rust takes them over, at least 150k miles/10 years.

 

[circuitsmith]

Back when my cars used the green 2 year coolant I changed the thermostat and radiator cap every other coolant change (4 years).
Working the 'stat plunger by hand the new one always felt smoother than the old one.
With my current car I did the first coolant change at 5 years (even though the manual said 7 years) and recently changed the 'stat, rad cap and coolant at 10 years.
My first car, a '76 Chevy Nova, had the thermostat stick closed on the highway: bad scene.
That prompted me to take a proactive approach.

 

[SteveSRT8]

PO128 is a code set when your vehicle does not reach operating temp in a prescribed period of time for 3 trips. About ten minutes IIRC.

3 good trips will shut it off by itself, no intervention needed. It's not something that requires a lot of worrying...

 

[MNgopher]

Your thermostat will often get lazy long before setting any codes. I've had this happen multiple times on Fords, particularly on the modular V8's. Using any kind of scanguage, torque, etc... you can see it. And when it finally actually gets cold, like it did this week, it reveals itself even more...

Also had a thermostat fail closed on my '97 Explorer. The thermostat on that one was literally in two pieces when it failed, so not sure I believe the idea they are all fail safe...