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Discussion Starter #1
My 2016 is at 93,000 miles and I had ironically just got the 180 degree thermostat delivered. When I drove to work one morning (10 minute drive) I parked and saw that my engine temp still was just under a quarter of the way on the gauge. Usually it reaches normal quick.

Got the engine up to temp on the way home then turned my heat on and watched as the needle slowly started to drop.

I automatically had a hinkering that my Tstat is going bad and sure enough research indicates it's stuck open.

I know things go bad but I don't see much on here about stuck open tstats. Anyone had to replace one? I'm starting to wonder about that Prestone coolant I used. It has the Ford spec but I don't know if topping up with it is great.

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Im not a MK3 guy but I know that low/poor heat heat due to the thermostat being stuck open on all 2005+ Duratec engines is very common. I had to the replace the thermostat in my 2005 for just that reason. BTW my car went 193K miles on its original thermostat. Its a bit of a PITA job so buy a quality replacement - I used Motorcraft.

Good luck
Paul
 

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I for one change any stat at 100K or so, it's stupid to lose an engine over such a cheap part. Probably explains why I have never overheated ever too. One car overcooled when I ignored my own rule once.

To me a stat change is normal maintenance, you don't wait for it to mess up..
 

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Discussion Starter #4
Well I'm pissed. I changed to the 180 thermostat and it's still acting up. Was 41 F out this morning. Turned the heat on after a couple of minutes and car wouldn't heat up to operating temperature. Then turned the heat off and it got there. Turned it back on and it dropped to a quarter again. Bullshit.


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A lot of things can cause poor heating system performance: low coolant temp, failed thermostat, low temp thermostat, poor coolant circulation, cooling system blockage, failing water pump, failed plenum air dist/blend system.

What is ECT reading? What are interior vent temps? What brand thermostat did you install?

Paul
 

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Discussion Starter #6
A lot of things can cause poor heating system performance: low coolant temp, failed thermostat, low temp thermostat, poor coolant circulation, cooling system blockage, failing water pump, failed plenum air dist/blend system.

What is ECT reading? What are interior vent temps? What brand thermostat did you install?

Paul
Low temp thermostat doesn't make any sense. Plenty of people here do the 180 stat and have no issues. Plus this started before I replaced the thermostat. It's a stant just like others here use.

I would think a blockage would cause overheating not underheating. Here's some text I sent to Tom the other day:


"So it's running about 176 degrees F at highway speed with the heat on full blast and up to about 204 F without the heat. At idle when I turn the heat on all the way it drops to about 154 F or lower. It maxed out at about 204 F again at idle without the heat.


Common denominator seems to be that turning the heat all the way up drops the engine temperature. "






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In real-world life, how long do you idle your car with the heat on full-blast? Honestly those numbers don't look bad at all except for the idle w/ heat on full blast. And I wouldn't think you're blasting max heat for very long before it gets super toasty in that car. I'm running similar numbers here on 60 degree mornings. Temp is hanging out btwn 175-205 depending on speed and traffic. Obviously I'm not blasting my heater but even if I were, I wouldn't be idling long enough to worry about the temp dropping for too long.
Cranking up the heater IS a way to drop coolant temp, or slow overheating. I used to do it in the middle of our West Texas summers to keep my old worn-out El Camino from overheating while driving up a mountain. Sweated my ass off but got over the mountain.
Could be what you're seeing in coolant temp drop is perfectly normal for this specific example: cold weather + idle + cooler t-stat + max heat. But take any one of those variables out and it's all good.
 

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Discussion Starter #8
Except it was doing this even with the old stock 192 thermostat. I've never seen the heat cause a problem before this. Let me put it this way. If I use the 3 or 4 speed before the car is up to operating temperature it will never reach it. It just hangs out near a quarter the entire time. Literally won't let the car reach operating temp. What car do you know that you can't just get in it and turn the heat on without limiting the engine temperature? This is isn't right. I understand also that using defrost turns the fan on but the car should not be dropping down to 154 F like I just started it up. Trust me this is the only car I drive so I know when something is amiss.

My brother said either the thermostat or the fan but both thermostats do it and the fan turns on and off with the defrost like it should. I'm heavily leaning coolant temperature sensor on this.

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I would think a blockage would cause overheating not underheating. Here's some text I sent to Tom the other day:
It depends on where the blockage is which could affect the performance of your heating system. And poor coolant flow - due to blockage or failing water pump - can cause hot/cold spots. The ECT only samples in one spot.

You never answered: What are your vent outlet temps?

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Discussion Starter #10
It depends on where the blockage is which could affect the performance of your heating system. And poor coolant flow - due to blockage or failing water pump - can cause hot/cold spots. The ECT only samples in one spot.

You never answered: What are your vent outlet temps?

Paul
Not sure about vent outlet Temps. What's the best way to test those?


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Not sure about vent outlet Temps. What's the best way to test those?


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Using a high quality automotive/commercial HVAC thermometer:

(Yes you can buy a thermometer at HF/Autozone for $4.99 but they are so inaccurate they are less than useless)

Paul
 

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Discussion Starter #14
Have you tried hooking up an OBD2 reader to see what the computer is telling the cluster?


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I've used test mode and I've data logged the car. The actual temperature of the engine goes down.

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Discussion Starter #16
Bad coolant temp sensor then?


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That's what I'm thinking. Even though everything online says a bad coolant temp sensor leads to overheating. The radiator fan kicks on and off with the defrost and higher engine temp so I don't think it's malfunctioning either. This car has always had a small coolant seep that I could never find so I don't think it has anything to do with a leak.

That sensor is above the thermostat right? Looks like you need a wrench to get it out.

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Discussion Starter #18

Number 19 is the sensor retainer. The sensor itself wasn’t listed.


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Hmm. Gotta be something out there more definitive. I'm not sure if it's the coolant sensor or cylinder head sensor above the stat.

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