Thermostat Question

[gearz]

I've noticed that my thermostat is opening at a higher temperature than it used to ( I can tell because I have a Scan Gauge mounted in the X which monitors multiple engine parameters via the OBD II port). I was opening at 200*, then 204*, later 206* and lately 207*. Once it opens it always drops to normal at 190*. I guess I'm worried at some point it might not open at all which wouldn't be good. The thermostat was replaced about 4 years and 30,000 miles ago.
Should I replace it now before it fails to open or am I worried about nothing?
TIA
gearz

 

[Fifty150]

Your ScanGauge number has nothing to do with your thermostat. What you are seeing is the temperature of your fluid inside your engine. Don't just go by what the ScanGauge II says while you are driving. The ScanGauge II has no way of monitoring whether your thermostat is open or closed, or when it actually opens.

When your thermostat opens, you will hear a click and be able to feel the fluid in the upper radiator hose. Start your truck cold, open the hood, let the truck idle, and wait. Then physically check to see when your thermostat is actually openning. Once the thermostat is actually open, then you can watch the ScanGauge to see what temperature you are at, and high much hotter the fluid gets before you begin to cool down.

Your thermostat is suppose to open at 190, and is fully open at or about 205. So for you to see fluid temperatures climb up to 210+ before the radiator and fan brings the coolant back down to 190 is absolutely normal depending on driving conditions and ambient temperature. While you are checking with the hood open, the heat is being released so you will not see the temperature climb as high as you would with the hood closed and idling in traffic.

 

[SoNic67]

NO, it's not normal. A thermostat is not opening suddenly, it is progressive. There should be no "noise" or "jump" in temperature. It starts to open at 190F, but is continous opening to 218F. The temperature should slowly go towards the 200-205F mark and stay there (+/- few degrees) with the t-stat half-open at medium engine load.
The sensor that is read by scangauge is right next to the thermostat, it senses practically the same temperature. The only difference in reading (from the t-stat setting) should be due to the accuracy of that sensor.
I think that the actual t-stat that you have "hangs" mechanically (friction) - going both ways (opening and closing).

 

[2TimingTom]

It's a cheap and easy (fairly) thing to replace. If you suspect it, change it.

 

[gearz]

Thanks guys for the responses. I think I'll replace it as a preventative measure.
Question: Is the Motorcraft thermostat worth the extra bucks?

 

[Fifty150]

Question: Is the Motorcraft thermostat worth the extra bucks?

Motorcraft is your best choice for maintaining OEM operating conditions. Thermostats are cheap enough that you aren't saving any money by going with an aftermarket part to save money. If you aren't doing the work yourself, the labor alone will be too expensive if you have to pay a technician twice to replace a failed thermostat that you saved a couple of dollars on.

However, you can opt for an aftermarket thermostat that opens a little earlier if you're worried about overheating. For my model year & engine, I have seen 160 degree and 180 degree thermostats.

 

[SoNic67]

I did go with a aftermarket one because I wanted a lower temperature - 180F. The Motorcraft 192F had extra air-bleed - a hole with a small ball to let the air go out before the tstat opens. It looked better done, but they don't have the 180F one.

 

[waskly]

I've noticed that my thermostat is opening at a higher temperature than it used to ( I can tell because I have a Scan Gauge mounted in the X which monitors multiple engine parameters via the OBD II port). I was opening at 200*, then 204*, later 206* and lately 207*. Once it opens it always drops to normal at 190*. I guess I'm worried at some point it might not open at all which wouldn't be good. The thermostat was replaced about 4 years and 30,000 miles ago.
Should I replace it now before it fails to open or am I worried about nothing?
TIA
gearz

this is why gauges are padded.

i woudnt worry over anything till it hit over 230*

and cant cool down.

 

[Fifty150]

I did go with a aftermarket one because I wanted a lower temperature - 180F.

Which make? Hypertech?