Damped coolant temperature gauges

[rationull]

My normal route home was crawling today due to an accident so just for fun I decided to ruin my average mpg for this tank by taking the more scenic route. Driving relatively hard and uphill for a while (nice curvy ridge climb) I noticed my temperature climbing a little higher than usual on my scangauge, but of course my dash gauge, being damped, stayed at its normal level.

So I got to wondering about how these [stupid] damped temperature gauges read when they're on the hot side. In my 07 civic the gauge climbs fairly linearly from the low end of the scale to its normal operating position, as if to act like an undamped gauge (although I think there's a time component to it too), but I've never seen it climb above the middle. I think the highest I've ever seen the temperature on my scangauge is about 211 degrees or so, with a normal operating temperature of 182-186 degrees for easy freeway cruising. I don't know how hot would be "too hot" on this particular car but presumably it would be well above 211 degrees since the I don't think the gauge moved at all at that temperature. I also know the gauge doesn't start to drop below the middle until about 170 degrees or so.

Just out of curiosity, how do these things tend to work? Do they just shoot up directly to the red when it's just about too late, or do they tend to start behaving like a real gauge again once the temperature starts to approach dangerously hot? I guess I can understand the purpose of the damped gauges but for those of us who pay attention to our cars a real gauge would sure be nice. I guess they don't want them moving during normal operating cycles but 40 degrees is a little too big a range for my taste.

 

[XS650]

On many VWs the instrument cluster reads the temperature sensor and uses a lookup table to tell the needle where to point.

On my Jetta, the middle mark on the gauge is 190F. As long as the temperature is within several degrees of 190F the needle points to the center. I think it's about +/- 10 degrees to get it to move off the center mark. Outside the artificially widened center reading, it acts normally. I suspect your car takes the same approach.

 

[rationull]

That approach seems to make sense. I'm sure the civic (maybe it's the same for all Hondas, I don't know) takes a similar approach but it seems like the center range is larger. I could be wrong though. With the weather warming up maybe I'll have a chance to pay more attention to it in traffic and find out soon enough. What's considered a "normal" temperature range on modern aluminum gas 4 bangers anyway? I'm assuming it's a smaller range than on older engines with iron blocks, right?

 

[Quattro Pete]

In my car, the dead range of the coolant guage is pretty wide - from 75C to 113C (167F to 235F), according to technical literature. Before and after that, the needle is supposed to move normally, although if your coolant temps are above 235F, you probably already have a pretty serious problem on your hand.

 

[meep]

accord = same. Very wide range I suspect.

M

 

[blackcherry06]

I think this is just a mechanism to keep everybody from showing up at the dealership wanting their car looked at because it's running warm. If it appears to run at the same temperature every time they drive it under any condition, it instills confidence and keeps unnecessary work from swamping the service departments.

 

[The_Jeff]

Having had a head gasket problem on a dodge I can confirm that above "normal" the gauge practically rockets to "H" when overheating, with only ~20'F more temperature. Which is good for scaring people into shutting down before cracking something.

If you feel like wasting gas idle the car until the electric fan comes on and take note of that temp. On my saturn it's 221'F. That will give an indicator of design specs.

 

[rationull]

Originally Posted By: eljefino

If you feel like wasting gas idle the car until the electric fan comes on and take note of that temp. On my saturn it's 221'F. That will give an indicator of design specs.


Yeah I guess that's one way to do it. Maybe next time I have to do the idle learn procedure I'll do that.

So seems like this is a pretty common design. Fair point that by the time the temp is up that high you've got a problem anyway, but hopefully the gauge starts to move up before the temperature's gotten dangerously high for the engine.

 

[Whimsey]

The water temp gauge in my 2002 F-150 is an idiot gauge. It stays dead center no matter the outside temp or driving conditions. My 1996 Ford Contour Zetec has a gauge that actually goes up and down depending on the outside temp and driving conditions. Though sadly it has no numbers just the word "NORMAL". But at least I can see whether it's getting hotter or cooling down. In stop and go traffic when the electric fan comes on I can see the temp gauge "go down" so I at least know the cooling fan is working.

Whimsey

 

[meep]

My Jeep has an unbuffered gauge. I probably see about a +/- 15F swing (30F total) during normal driving. I see +20F during shutdown / heat soak. Have never seen that swing indicated in newer cars.

M

 

[brianl703]

I have a Scanguage in my 2006 Saab 93. During highway driving in colder temperatures the coolant temp is as low as 184F, in stop and go traffic in the summer it may go up to 210F, between 184F and 210F the temp gauge never moves.

 

[Shaman]

I think most are designed to keep the sheeple from freaking out about their cars. There was someone on a Toyota Surf forum who found a way to make it read “right”. If there is interest I can try to find the thread.

Found it

http://www.toyotasurf.asn.au/forum/viewtopic.php?t=14717