RPM gauge and Coolant temp. gauge are not correct

[aki334]

hello to all again,

 

while driving around with OBD2 scanner connected and monitoring live data I have noticed that the RPM gauge on the instrument cluster reads between 75-100 rpm lower than it is. So when you see the RPM needle go to 500 rpm line, it is actually 600 rpm.

 

Also your engines run as high as 221F and your coolant gauge will stay at normal operating temperature starting at 190F - this is so it does not scare people that their car is overheating.

[ammcinnis]

... I have noticed that the RPM gauge on the instrument cluster reads between 75-100 rpm lower than it is.

...

Also your engines run as high as 221F and your coolant gauge will stay at normal operating temperature starting at 190F ...

I have not observed this in either our 2015 Legacy 2.5 or our 2016 Outback 2.5. The analog speedometer and tachometer are generally within one needle width of the digital reading.

 

There does appear to be some low-pass filtering (i.e. long-term averaging) applied to the coolant temperature gauge, which is typical automotive practice. Coolant temperature in my two vehicles generally stabilizes at around 200 degrees (F) +/-5 degrees. I think the highest coolant temperature I've ever observed was ~215 degrees ... in mountainous terrain on an unusually hot day.

 

... this is so it does not scare people that their car is overheating.

And you know this ... how? Edited June 13, 2021 by ammcinnis

[aki334]

I have not observed this in either our 2015 Legacy 2.5 or our 2016 Outback 2.5. The analog speedometer and tachometer are generally within one needle width of the digital reading.

 

There does appear to be some low-pass filtering (i.e. long-term averaging) applied to the coolant temperature gauge, which is typical automotive practice. Coolant temperature in my two vehicles generally stabilizes at around 200 degrees (F) +/-5 degrees. I think the highest coolant temperature I've ever observed was ~215 degrees ... in mountainous terrain on an unusually hot day.

 

And you know this ... how?

 

Yes Sir. thank you for confirming what I said exactly they are within one needle width from each other (analog vs digital) and that difference is 100rpm.

Everywhere in the world, if you see a gauge and lets say it is a pressure gauge and if the needle is on the 100 psi that means it is 100 psi we do not have to calculate any offsets +/- certain amounts. So also in every automotive school and class I have been, if the rpm needle shows 500 I read it as 500 unless there is something wrong with gauge calibration. Guys that have scan tools will know what I am talking about. Why everything with you has to be so complicated Sir in life?

 

If I go to ATM machine and say I need $500 I type in 500 to get $500, I do not expect to type 550 or 600 to get $500.

Edited June 13, 2021 by aki334

[Grnlantern1]

100 rpm difference isn't much.. My coolant temp hardly ever goes above 200° normal driving conditions sits around 197°.

 

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[ammcinnis]

Everywhere in the world, if you see a gauge and lets say it is a pressure gauge and if the needle is on the 100 psi that means it is 100 psi ...

The accuracy of purely analog gauges is typically expressed as some percentage of full scale, often 5%, 10%, or even 20%. For example, say you have an analog gauge with a maximum scale reading of 100 and a stated accuracy of +/-5% FS. That means for a true value of 100 it could read anywhere from 95 to 105; at a true value of 10 it could read anywhere from 5 to 15 and still be within specs.

 

On the other hand, the accuracy of digital gauges is often expressed as a percentage of reading, plus or minus one least significant digit.

 

As a special case, there are usually regulatory requirements for the accuracy of speedometers, analog or digital, at typical road speeds, regardless of the full scale range. 30 mph and 60 mph are common calibration points.

Edited June 13, 2021 by ammcinnis

[aki334]

100 rpm difference isn't much.. My coolant temp hardly ever goes above 200° normal driving conditions sits around 197°.

 

Sent from my SM-G988U using Tapatalk

 

It is ok to thank the above poster that joined you, but both of you need to know the differences in the cooling system between h6 and h4 to comment correctly. And from what I have read you guys have no idea how your fans operate.

 

 

Yes Sir, very nice I agree that is the temperature that is should be. However, your h6 fans are PWM controlled which means they start turning on at 30% speed at lets say 180F then slowly increase to 50% at 190F then 70% at 210F and etc.... H4 engines only turn the fan at low speed around 215F and high speed at 221F if I remember correctly .

 

Now you know... you have nice setup be happy.. - thank you for your input -Al

Edited June 13, 2021 by aki334