Temperature gauge not working properly

Tiny
CALEBS0615
  • MEMBER
  • 2012 FORD FUSION
  • 3.0L
  • V6
  • 4WD
  • AUTOMATIC
  • 192,000 MILES
As I'm driving the car, if I'm under a heavier load the cars coolant temperature gauge will rise. If I stay in the throttle long enough it will rise to around 3/4 staying under the red, but not actually overheat. If I lift off the throttle it almost immediately returns to just under half on the gauge in less than 10 seconds. The coolant pipes aren't any extra hot. The heat stays warm. The fans are on high during the instance. It won't happen until the car has actually gotten to operating temperature. The gauge doesn't rise while it sits, and it doesn't rise quickly while warming up. There's white marker in engine bay says "hg 178642" The water pump and belt looks recently replaced. Thermostat has been replaced. It doesn't use any coolant or bubble when the gauge rises.
Saturday, December 4th, 2021 AT 10:06 AM

11 Replies

Tiny
KASEKENNY
  • MECHANIC
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I think you are on the right track with some of the things you have checked.

This is normally one of two causes. Clearly, we could have other things going on but the most common causes of this are a head gasket that is starting to fail, or you have an air pocket.

So, let's start with checking the head gasket just to be sure. So that means we need to start with using the chemical test that is shown in this guide:

https://www.2carpros.com/articles/head-gasket-blown-test

I doubt you will find the other signs if this only causes an issue when you are accelerating so we need to get the engine hot and then rev the engine while using this blue chemical to see if you are getting any change in the color to show there are combustion chamber gases.

If there are not any then we need to bleed the system and make sure there are no air pockets.

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

I would go ahead and flush it just to be sure the coolant is good and clean because it sounds like this is a new vehicle to you.

Please run through this info and let's cross these two off the list for sure and then dig deeper if needed. Thanks
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Saturday, December 4th, 2021 AT 4:31 PM
Tiny
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The coolant looks very clean, I've drained quite a bit doing the thermostat once and the gasket again a separate time. But a flush can't hurt. I bought the blue chemical and the block tester and tried that for a few minutes with the chemical staying blue. Then I had an idea to get the bubbles out. I used the big yellow spill free funnel and filled it about halfway with coolant and gave the car some revs with the heat all the way on. Some bubbles came out at first, but the coolant gauge still acts the same.
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Sunday, December 5th, 2021 AT 11:15 AM
Tiny
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Okay. That is great info and a great result.

Now we need to turn to finding out if the gauge is accurate.

Are you able to get the temperature to rise and fall like this while sitting still? Meaning can you get the engine warmed up and then just rev the engine in park and get the gauge to rise and fall of the gauge?

If so, we need to use a laser temperature gauge and see if the coolant passage that the temperature sensor is in is actually getting hot and falling like this or do, we have a temperature gauge that is overly sensitive?

When you rev the engine, the temperature is going to go up, but your vehicle appears to be going way too much so the temperature gauge may be jumping when it reaches these temperatures. Basically, it is just a resistor in the tip of the sensor that changes the voltage as the temperature changes, and it may be the issue.

https://www.2carpros.com/articles/how-to-use-an-infrared-temperature-meter

So, we need to see if the temperature is just going up a couple of degrees or 10s of degrees which means the sensor is accurate.

At which point that means we most likely have a restriction in the system somewhere.
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Sunday, December 5th, 2021 AT 12:43 PM
Tiny
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I can't get the temperature gauge to rise while it's in park or neutral. Only during a driving instance. If the temperature shows, it's high, I can take my foot off the pedal, and it drops to normal temperature in about four jumps.

I was thinking the next step would be the temperature sensor as well. I located it while doing the thermostat and gasket yesterday. I also noticed there's a couple different temperature thermostats. 180,188,190,192. I don't know if any of those would make a big difference, but I got the 180 degree one because that's what the car calls for from factory.
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Sunday, December 5th, 2021 AT 1:20 PM
Tiny
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Yeah. They offer different temperature opening based on if you live in a cold area or not.

Basically, I would go with the 180 as well because the others are meant for specific situations and are not common.

Can you get a recording of this gauge when this is happening? It should not be jumping. The gauge should be moving smooth and steady as the temperature is always being monitored and temperature changes don't jump. Temperature changes gradually so your gauge should be moving smoothly so based on that, I think the sensor is the issue.
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Sunday, December 5th, 2021 AT 3:45 PM
Tiny
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I started the video when I put my foot down. I kept it in fifth on the standard shift and went up a short hill. Roughly 5 seconds after I let off the gas pedal, you'll notice the quick downward movement of the needle. I guess it doesn't really jump around but just goes down rather quickly almost in 4 or 5 steps.
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Monday, December 6th, 2021 AT 3:30 PM
Tiny
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That is a great video. Has it ever actually overheated? Doesn't look like it ever overheated so that is very strange operation which tells me it may just be a sensor issue.

Even when it is going up, it jumps in levels and is not a steady sweep up and down.

So, if there are no air pockets, no blown head gasket, doesn't overheat, then I have to think we have an issue with the sensor.
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Tuesday, December 7th, 2021 AT 11:05 AM
Tiny
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That's what I was leaning towards. You are correct saying it has never over heated. I can stay in the throttle say to be driving on the interstate and it'll stay high and never overheat.
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Tuesday, December 7th, 2021 AT 3:35 PM
Tiny
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Yeah. That points to an air pocket most likely but could be a head gasket but the head gasket would normally cause the overheat.

However, it seems like you have eliminated those options all together so the last thing that makes sense is a sensor/gauge issue because it doesn't seem like it is actually getting that hot.
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Tuesday, December 7th, 2021 AT 5:20 PM
Tiny
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Thank you very much for the help. Using the spill free funnel as the highest point in the system seemed to have made a huge difference. It will still get hot on the gauge, but it takes a lot more. I'll try that method again and get a coolant temperature sensor. I'll get at that this weekend, and I'll be sure to let you know what happens.
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Thursday, December 9th, 2021 AT 4:52 AM
Tiny
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Okay. That is great. The air pocket would be the most likely cause so that makes sense. You can even jack the corner of the vehicle up closest to the funnel as well to help force the air to the highest point and it will escape.

Keep us posted. Thanks for the update.
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Thursday, December 9th, 2021 AT 12:01 PM

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