Ever notice how the temp gauge goes from 100 to 220 to 260?

Does anybody know if the gauge really has 120 degree span over the first half and only 40 over the second half?

Or, is the 100 mark really 180, (as I suspect) and the gauge is really linear?

Has anyone ever checked it with a scan tool to know for sure? I'm trying to figure out what temp my car is running at but that 100 mark is really confusing.

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1988 Fiero - It's like an Actual Miniature Car

the gauge is not really accurate, anyways.

I checked mine out when I got my Auto X-Ray. With the needle at 220*, my actual engine temp was around 205*.

You have two choices for acurate coolant temp.

ECM scanner as indicated above or Pyrometer on, or aimed at, the thermostat neck. You can get IR pyrometers for about $100 now. An AutoXray will run you $150-200 but is very usefull when you know how.

Never trust a dash gauge. There are many things that can screw them over. Always confirm what they say before altering anything.

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11-Sept-01, The day the world as we knew it ended.

Autometer ProComp water temp gauge: 65bux.

Not having to guess wether your custom $30,000 automobile is in danger or not? Priceless...

PS: A pyrometer for a hundred bux? Show me! I want to check my tyre temps!

Best!
Ben

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Ben Cannon
88 Formula, T-top, Metalic Red. (2:13.138 at Sears Point) "Every Man Dies, not every man really Lives"
88 Formula, Northstar, Silver, In-Progreess. -Mel Gibson, "Braveheart"

My ALDL scanner showed my temp gauge to be pretty accurate. Now if only my fuel gauge was as accurate....

quote Originally posted by Formula88: My ALDL scanner showed my temp gauge to be pretty accurate. Now if only my fuel gauge was as accurate....

But is it linear or logarithmic??

Ben, dig around... Motor Magazine ( www.motor.com ) I think recently listed an IR unit for about $100. You can also get contact units that plug into standard DVOMs for about the same.

Even a Fluke thermo adapter and a contact probe isn't a whole huge amount differant $ now. Fluke and Simpson are about the two most known names in profesional meters. They are on the same level as Textronics is for high end electronics measurment tools. (Very high up the food chain...)

the sad thing is that GM has some of the most accurate gauges out all of the automakers...

ps: never have any trouble with my gauges' accuracy, in any of my GM vehicles. of course, the most common problems are senders and poor connections.

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1987 Pontiac Fiero Coupe #18,838
3800 Series II SFI
4T60-E Trans
3.33 Final Drive

1987 Pontiac GTA
5.7L SuperRam MPFI
4L60-E Trans
3.73 SRD

1988 Pontiac Grand Am
3300 V6 MFI
4T60 Trans
3.33 Final Drive

http://dtcc.cz28.com

Factory gauges were meant for a basis for comparison.....not necessarily an accurate reading. That goes for oil and temp especially. They rely on pressure or temp to be converted to an electrical signal which is not always accurate.

Phil

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GTDude
25 years GM experience

The temperature gauge reads a temp, its actually that temp. so if it reads 100 in your car, then its really 100, not as you though 180. Its what it says.

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The gauge is linear, the sender is not. The resistance varies ALOT more at high temps then at low temps. so the reading is correct... well as correct as a gauge gets.

Cheers!
Eric

I did a lot of calibration work on the gauges and came up with this:

Oil Pressure. Amazingly good. Most GM's are.

Fuel Level. Yes, there is fuel or no, there isn't any fuel. Many times correct at half scale. Drive for 100 miles until it hits ful, drops normally until 1/2 tank, drops like it's been shot until the last 1/8. Stays there forever until you get out and walk. Function of the sender. Not linear in any sense of the word.

Voltmeter. Amazingly good.

Water Temperature. Artic or steam generator. I added 12 ohms in series with the gauge to make it read 220 when then ECM read 220 (they are different locations in the water jackets). The ECM sender is really no better either. Other than that, the only thing you know is that it's less than or greater than 220. The sensor has a very nice transfer function that can't be easily duplicated in the meter (read: the gauge is always wrong but good enough to put your mind at rest or cause you to suck the upholstery up your a$$ trying to get home before the needle disappears on the right). 100 is closer to 100F than it is 1M degrees Kelvin. 260F is closer to 260F than absolute zero. 260F is really more like 240F-280F. The ECM doesn't go beyond 304F so why should the gauge? Won't be any coolant in there anyway. Starting to get the drift?

For you Canadian folks, do the math in your head like I have to when I drive rental cars in Toronto. Wait, I just start walking when the car stops.

Hope that helps......I know, not usable information.

[This message has been edited by terryk (edited 06-16-2002).]

So if the oil pressure gauge is good, when my car is warmed up and the pressure drops to 20 does that mean something is actually wrong with my car?

quote Originally posted by carpetviper: if it reads 100 in your car, then its really 100, not as you though 180. Its what it says.

Thanks, I finally got the answer to my question, (and a lot more) Now that I know it's not linear, I'll not bother to figure out what temperature it is reading.

Now I know why most cars just have a "C" and "H" and don't bother with numbers.

By the way, I don't rely on the gas gauge at all anymore. The 88 Fiero gas gauge has to be the worst. I keep track of the mileage and keep a container of "Mr Rescue" in the trunk for emergencies.

The quarter way mark is where all my 180 deg t/stat cars run at so I would venture that it is 180-185.

20 PSI hot idle is fine. Sure, a new engine will idle up around 30-40 (assuming the spring in the bypass hasn't been mucked with), but 20 is fine on a normal engine.

GM assumes 10 PSI/1000 RPM is good. I think spec for the HVHP pump in the HO and L44 engines is something like 55 PSI at 1200 RPM, but as long as you meet the 10 PSI/1000 RPM, assume it's fine.

quote Originally posted by Standard: the gauge is not really accurate, anyways. I checked mine out when I got my Auto X-Ray. With the needle at 220*, my actual engine temp was around 205*.

I concur, the gages read high up around 220 to 240; I was checking my new fan switch which is supposed to turn the fan on at 204 degrees. I put on the brake, put the car in gear to help heat it up, and waited for at least 15 minutes for the fan to come on. My infrared non contact gage showed 207 degrees when the fan came on. At that point the gage showed about 235 to 240.