: Temp gauge position, what is the basis for this?



TryMe96Z
07-05-10, 02:37 PM
I am curios how the temp gauge in the dashboard determines its position. Based off what has been mentioned previously on CF (http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/201600-customer-paranoia-temp-guage-need-input.html) it sound like it is a sliding scale. On a 200 mile trip this weekend I though my 96' was very close to overheating as the gauge in the car was at the 6th mark from the left. This was at 70mph, with outside temp of 85*-90*. After seeing the guage/temp picture posted here (http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/201600-customer-paranoia-temp-guage-need-input.html#post2263677) I was convinced there is something wrong with my cooling system. After doing some diagnostics with an OBD2 scan tool I found my gauge to read like so:
http://www.porteighty.biz/uploads/TempGaugeExplanation-Mine.jpg



My fans are kicking on in SLOW when the AC is on.
When the AC is OFF, the fans kick on SLOW at about 219*
This is in 80* weather.
Engine is not getting hot enough, 236* I believe, to trigger the FAST fan speed.

So is my gauge, temp sensor, or obd2 computer messed up or do they just measure on a sliding scale as to avoid upset customers as indicated by the thread above?

Useful specs from other threads:


188* Thermostat begins to open.
206* Thermostat fully open. AlldataDYI claims it is at 195*
196*-204* Highway.
205*-215* Normal operating temperature
224* In traffic with HVAC OFF. Fans should turn on, and temp should go to 213*.
224* Fans come on at SLOW.
236* Fans increase to FAST. May also come on with a transmission temp of 302*.
255* "overheat" warning point.
270* Camel mode engages


Fun facts about N* cooling system (fyi for those who are digging for information):


Fans do not run above 45 mph, as they are not needed.
Fans run anytime the A/C is on.
Temp will cycle from about 185 to 225 during highway and town driving with the A/C OFF.
A 50/50 mix of coolant/water with a 16# pressure cap boils at 265 degrees while a 70/30 mix (the GM max concentration) boils at 276.

Submariner409
07-05-10, 04:58 PM
If you read between the lines and look at the other gauge pics with numbers superimposed you'll slowly come to the conclusion that the gauge pointer position is determined solely by the ECT, a temperature-variable resistor which drives the gauge. The ECT sensor is manufactured with tolerances, the electrical connectors are subject to variations, and the whole mess is dependent on the vehicle's electrical syatem voltage at any given second: the gauge is merely a moving coil voltmeter, controlled by the ECT sensor resistance to ground !

Here's MY gauge, annotated with a ScanGauge, (www.scangauge.com), and it is a modification of the original work done by JimD. After two years of "why ??" I added the disclaimer in the gauge field.

All of YOUR work is, to quote an old Navy disclaimer, WNL: "within normal limits"

Ranger
07-05-10, 10:32 PM
That does not look right to me. If your gauge numbers are correct we would all be running right around the first tick mark.

tateos
07-06-10, 07:55 PM
Is the temp gauge really hard wired to the ECT sensor. I never looked into it, but I always thought the ECT sensor fed info to the PCM, and the PCM then used that info in many different ways, including displaying the temp on the info center (if so equipped) and also controlling the display on the temp gauge. In other words, if the temp gauge is actually a voltage gauge with 5 volts as the top of the range, I assumed that the PCM (or BCM or whatever it is) varies the voltage supplied to the temp gauge between zero and five volts, but in a linear manner.

Submariner409
07-06-10, 09:18 PM
OK, insert a "PCM" somewhere between ground, "ECT", vehicle voltage, and "gauge".

Yes, the ECT is a variable resistor. Yes, the PCM uses this changing voltage info for several purposes. Yes, the ECT drives the dash gauge. If we wanted it to, the ECT could open the glove box at some preset temperature. It is used to "tell" the PCM to set the camel mode, does it not ?

tateos
07-07-10, 12:55 PM
OK Sub - thanks. BTW, what I meant to write was that the PCM varies the voltage sent to the temp gauge, but NOT in a linear manner.

And by the way, I happened to check my gauge yesterday while I was driving and thinking of this thread, and the needle was where it usually is when warmed up and cruising, just a blond c-hair to the right of 12:00. I checked the DIC and the coolant temp readout there said 201 or 203 (it was 105 here in Phoenix at that time). TryMe's temp gauge definitely reads higher at a given temp than mine does. I think with the needle at the first hash mark after 12:00, I would be at 220+ coolant temp. Like you wrote, there are variable that cause gauges to read differently in different cars

Submariner409
07-07-10, 01:18 PM
Sorry for the snit - hot temps and booze last PM............

I wonder if anyone - Stewart Warner ? - makes an electric thermocouple similar to an old aircraft cylinder head temperature unit: you placed the washer-like thermocouple on the spark plug, exactly replacing the washer, and hooked the leads to a gauge/voltage source. BINGO ! temperature. I'll bet something similar would work on a water pump housing bolt..........Hmmmmmm.

Looking at TryMe96Z's gauge photoshop, his numbers do seem a bit high, but if they're repeatable and he knows that, not to worry.

The temp is supposed to hit 100 here again today - at 6 PM we're headed out 50 miles for dinner at a to-die-for seafood restaurant, so I'll try to blow something up and keep track of the temps while doing it.........Later.

tateos
07-07-10, 08:19 PM
OK Sub - Mmmm, seafood - sounds really good. I spent my first 45 years in the Boston area - took good seafood for granted. Now I'm in the desert, where by the way, it over 100 degrees EVERY DAY lately, and will be for a long time, and I love it here, but good, fresh seafood is hard to find. I was always a "Fried Fisherman's Platter" kind of guy. Enjoy!

Anyway, I've seen mention of the temp gauge being damped, to lessen the fluctuations observed by the driver, and I was always intrigued by the fact that, assuming the PCM merely sends a voltage to a "dumb" gauge, it's the algorithm in the PCM that's "damped". In other words, if the gauge is a 5V gauge at full scale, and 12:00 is 2.5V, then the algorithm goes something like: 180 degrees = 2.2V to the gauge, 185 degrees = 2.4V, 190 degrees = 2.5V 195 degrees = 2.5V 200 degrees = 2.5V 205 degrees = 2.55V 210 degrees = 2.6V 215 degrees = 2.8V, etc. etc.

Submariner409
07-08-10, 08:52 AM
Yeah, the ECT sender has a weird resistance vs. temperature scale. Look up some senders in the Stewart Warner catalogs - they used to give resistance ranges for various temperature and pressure senders.

"Sender" is really a misnomer: the sensor itself is a variable resistor, so it controls electrical voltage TO (FROM ?) GROUND, (depending on which notation of DC electron flow direction you adhere to).

tateos
07-09-10, 05:16 PM
OK, this has piqued my interest enough for me to observe the position of my gauge, and I can report that the needle on my gauge remains in exactly the same position, just barely to the right of 12:00, from 190 degrees to 217 degrees, per the DIC. At 219, it is noticeably moved to the right, at least the width of the needle. Midway between 12:00 and the next hash mark is 223 or 225 degrees.

Robertsong
07-12-10, 04:25 PM
I would like to get some advice regarding Temp Gauges, and lack thereof! I have a 94 Concours, a great car, with all the goodies. Problem is only idiot lights available. Meaning unless there is a problem I have no idea of how the car is operating especially with regards temperature. Question is can a gauge be installed, after market, since GM did not find it necessary to install one on the dash. For that matter there is no tach either. So what would be the opinion of you experts out there, is it worth installing temp gauges and a tach? I can't remember which of the moderators uses the phrase, "if it aint broke, don't fix it", but for peace of mind, does it make sense? And if so, do you have a recommendation as to which gauges to install, and approximate cost? As always I value your wisdom and advice.
Thanks
Robertsong

Submariner409
07-12-10, 06:27 PM
Which engine does this car have - I dunno......

Aftermarket coolant temp gauges in a Northstar can be a problem - there just aren't any extra block holes to open/drill/tap in order to install a sending unit, either mechanical or electrical.

You could get creative with a cobbled together brass pipe T in a coolant line - the heater supply side is generally the best because it is always at current system temp - but that's a hokey looking mod. (and if you do install a T in a coolant line, you need to properly ground the T for an electrical gauge unit.......)

Ranger
07-12-10, 10:11 PM
I can't remember which of the moderators uses the phrase, "if it aint broke, don't fix it"
That would be me.


but for peace of mind, does it make sense?
Personally, I don't think so, but it's your peace of mind. All depends on just how concerned or worried you are. The tach is more aesthetic than useful, though I have to admit, I do like it in my DHS. The factory temp gauge is little more than an idiot light anyway. A REAL temp gauge will fluctuate so much that it will most likely drive you to drink.


Which engine does this car have - I dunno......
I think it has a Northstar, Sub.

tateos
07-13-10, 06:45 PM
I thought the DIC displayed engine temp, or at least can be programmed to do that, no?

Ranger
07-13-10, 09:46 PM
I think if you have an analog gauge, you have no digital readout, but I think it can be added to the pre-2000's.

Necrosan
07-13-10, 11:53 PM
It should always have the option on 93-95 M.Y. cars to see the temperature in the DIC on the bottom.
I average anywhere from 196-235 depending on outside temperature and load. (usually closer to ~200)
Thing doesn't really read the "real" temperature, as it never cycles past all digits in the DIC (IE, will go from 196-203, etc.)
Dumbed down gauge for sure.

tateos
07-14-10, 09:28 PM
Right - that's what I thought - it's part of the DIC, or worst case, can be added with simple programming

Pete1996
08-17-10, 09:15 AM
1996 STS:
I have been watching the water temp over the last few years more carefully
since coming here and reading about all the issues. Mostly, I see the temp
gauge at 12:00 if ambient is below 80 degrees. I see it go to one needle
thickness over 12:00 when ambient is around 85 degrees. This has been
a very hot summer here in the NE and highway cruising with 95+ ambient AC
on we are seeing mostly 225 degrees sometimes 245 degrees. It goes
slowly back to 215 deg if we turn off the AC.

It also runs completely normally around town with the AC on in 85 degree
heat with a temp of about 210-215, but again when it is 95+ I have seen as
high as 245 degrees when stopped in traffic.

Another thing I notice in 90 degree weather is that when I stop for say
fast food, with the car off for 10 to 15 minutes, the temp is 245 on startup
then comes down as we get moving along.

I think that Sub's gauge markings are correct based on this, and that the
cooling system is operating fairly normally since it is probably sized to work
hardest (245 deg fans full on) in 95 to 105 degree ambient temp.

We are loosing coolant needing to top up once after the long winter, and
maybe twice in the hot summer. I expect that this is an early sign of head
gasket failure; the car has made it to 145K miles without replacement. The
car is basically in excellent shape but has the high oil consumption issue and
coolant loss. Unfortunate that they did not get this motor right from the
start.

Mark C
08-17-10, 12:21 PM
The ECT raw data is sent to the PCM/ECM for engine control stuff. The PCM sends the data to the IPC over the serial communications bus that all modules hang off of, which inturn displays it up on the gauge. The IPC has a regulated power supply that is supposed to take the voltage variance caused by the alternator charging the battery out of the circuit, so that the guages on the dash will always display the same output for any given input info regardless of wether the alternator is puting out 15V or 12.5 V.

You can reprogram 97s and earlier to display engine temperature thru the DIC if you want, I don't beleve its possible on 98s and up.

Pete1996
11-08-10, 11:37 AM
So much for my theory below, it was 51 degrees out yesterday and the temp
hit 245 while in stop and go traffic for about 5-10 minutes. Cooled back down
after going about 30 MPH for 5 min or so.

Purge line is not clogged.

Both fans are coming on (at least when the AC is on) and the AC was not on.
Perhaps I need to check the fans with the AC off, not sure how to do that.

Is this likely just the thermostat?

The car is loosing coolant and it seems to be getting worse - is this most
likely the head gaskets? About 1/2 gal per 2000 miles used to be
about 1/2 gal per 5 to 10K miles.

The car has never overheated into the red as far as I know.



1996 STS:
I have been watching the water temp over the last few years more carefully
since coming here and reading about all the issues. Mostly, I see the temp
gauge at 12:00 if ambient is below 80 degrees. I see it go to one needle
thickness over 12:00 when ambient is around 85 degrees. This has been
a very hot summer here in the NE and highway cruising with 95+ ambient AC
on we are seeing mostly 225 degrees sometimes 245 degrees. It goes
slowly back to 215 deg if we turn off the AC.

It also runs completely normally around town with the AC on in 85 degree
heat with a temp of about 210-215, but again when it is 95+ I have seen as
high as 245 degrees when stopped in traffic.

Another thing I notice in 90 degree weather is that when I stop for say
fast food, with the car off for 10 to 15 minutes, the temp is 245 on startup
then comes down as we get moving along.

I think that Sub's gauge markings are correct based on this, and that the
cooling system is operating fairly normally since it is probably sized to work
hardest (245 deg fans full on) in 95 to 105 degree ambient temp.

We are loosing coolant needing to top up once after the long winter, and
maybe twice in the hot summer. I expect that this is an early sign of head
gasket failure; the car has made it to 145K miles without replacement. The
car is basically in excellent shape but has the high oil consumption issue and
coolant loss. Unfortunate that they did not get this motor right from the
start.

Ranger
11-08-10, 11:59 AM
It's sure looking like head gaskets. Get a block test kit and test the air in the surge tank for the presence of exhaust gases. You might already be able to just smell them by sticking your nose in the tank.

tateos
11-08-10, 12:40 PM
HG gets my vote. The most common way to lose coolant on a Northstar with failed/failing HGs is when coolant is forced out of the cooling system by combustion gases blowing by the HGs

vincentm
11-08-10, 01:44 PM
My gauge shoots up to just about 11:58, ive got blown head gaskets, but dont take mine up hills or past 50mph, stay on top of oil level, and top off coolant when needed until i can get mine fixed this month. But yea to me this sounds like a HG

Submariner409
11-08-10, 01:59 PM
The car is loosing coolant and it seems to be getting worse - is this most likely the head gaskets? About 1/2 gal per 2000 miles used to be about 1/2 gal per 5 to 10K miles.

FWIW my coolant was exchanged in 11/07. To date I have not added one drop and today's level is where it was the morning after the exchange. That should provide a baseline for what is believed to be a properly operating Northstar. (Next coolant change: 04/11)

Unexplained coolant loss, especially with no drips or puddles, is worrisome. Losing 2 quarts in 2,000 miles is excessive.

Pete1996
11-09-10, 04:12 PM
Seems odd that the temp comes right down again once we get moving - actually this usually happens more when it is low on coolant, I'll have to check it. But seems that if something was seriously wrong it would not come back down to normal. I'm going to warm it up and try to test the fans.

Ranger
11-09-10, 05:21 PM
What happens in a head gasket failure is that exhaust gases get pumped into the water jacket. When that bubble reaches the ECT sensor the temperature gauge goes up, as air does very little to cool the engine. Then when you start to move, you throttle up and the water pump starts spinning fast enough to move coolant through the system and displace that air. The coolant reaches the ECT sensor and the gauge comes down.

Pete1996
11-10-10, 12:22 AM
Thanks Ranger - that makes sense.

It does smell in the surge tank, just not completely sure if it is exhaust gas. Not sure what we will do with this car if it does need HGs.

Pete1996
11-12-10, 01:57 PM
OK took it out yesterday and got it good and hot with some highway driving, left it idling in the driveway and it took about 5 min to get to 225 it is usually at about 200 deg when moving - both fans came on with this idling test. Generally when in stop and go traffic and stopped for a long time lately it has been getting to 245 on occasion as I stated above.

I didn't notice any overflow during the driveway test yesterday but today I see a 2 ft diameter puddle on the driveway where the overflow was located.

I'm going to guess that the exhaust gases are causing excessive heat and pressure - or maybe I just need a new radiator cap? Wishful thinking, LOL!

Time to get an exhaust gas test kit I suppose.

Ranger
11-12-10, 09:48 PM
Time to get an exhaust gas test kit I suppose.
Yup.

Pete1996
11-13-10, 10:50 AM
My son had the car out last night and he saw steam from under the hood and the low coolant warning.
He waited for an hour or so at work, topped it up and drove the 5 miles or so home. I asked him to
check the cap and he said it was not turned all the way clockwise - I had topped it up just recently
and was fairly sure that I turned it all the way. Does the cap "let go" under overpressure?

Looking at it today and it is very wet under the hood. The drivers side headlight is wet, the air box,
and the TB area looks to have been steam cleaned. It seems as if something burst - I have to get it
hot and look for the leak. The question is if I did not tighten the cap I would think that it would not
have gone over pressure - so again does over pressure pop the cap?

I think something near the radiator burst, anything other than the radiator or hoses that is a common
point of failure? Is there a thread with a list of things to check when loosing coolant before blaming
head gaskets?

EDIT: Filled it with water, warmed it up, and I see a stream coming from a split in the lower
radiator hose. I hope this has been the coolant loss issue all along! I'm going to change it today,
any tips will be appreciated. Thanks again for all the help!

Ranger
11-13-10, 11:54 AM
Does the cap "let go" under overpressure?
Well, yes and no. The cap does not "let go under pressure". It's job is to maintain the pressure it is rated for (usually around 16-18 psi). It has a relive valve in it and if that pressure is exceeded, it will vent the excess pressure via the overflow tube and may well expel coolant as well.

RippyPartsDept
11-13-10, 12:24 PM
get that rad hose fixed and hope for the best...

... although being pessimistic i would guess that the rad hose leak could have been caused by an overpressure situation due to HG failure

:crossedfingers:

Pete1996
11-13-10, 03:14 PM
Thanks, yes fingers crossed. The hose has a 1996 date code, LOL, so it is original.

My question about the cap is can it turn back one notch from excessive pressure?
I would think not, but .....

Submariner409
11-13-10, 04:28 PM
Thanks, yes fingers crossed. The hose has a 1996 date code, LOL, so it is original.

My question about the cap is can it turn back one notch from excessive pressure?
I would think not, but .....

Remember that unpressurized 50/50 coolant boils at about 220 degrees. The cooling fans don't go to SLOW until 224, so you would run a very real risk of constant overheating due to a non-pressurized system - that 16 psi allows the system to function normally up to 265 degrees without boiling.

Pete1996
11-13-10, 05:19 PM
OK, new hose is in and with a 15 mile run it seems to be back to normal - I hope without loosing coolant from now on.
I noticed several here mention green DEX-COOL, I have orange in there that comes in the silver Prestone container that says GM approved.
Is this the right stuff? I also have a yellow bottle of Prestone that claims to be 100% compatible with all engines and safe to mix
with all other types - can I mix this stuff? I've not used it in the STS so far.
I ran out to get more of the GM approved stuff in the silver bottle but it would be nice to know if the yellow is also safe to use in the future.

RippyPartsDept
11-13-10, 05:34 PM
dexcool is not green
antifreeze is green
dexcool is orange

Submariner409
11-13-10, 05:55 PM
I noticed several here mention green DEX-COOL, I have orange in there that comes in the silver Prestone container that says GM approved.

Rippy's correct and the silver Prestone jug/orange coolant is what you want. Mix 50/50 with distilled water from the grocery store.

One gallon of pure DEX + one gallon of distilled water = 2 gallons of 50/50.

Use a clean 2-quart kitchen pitcher. Fill it with distilled water. Pour half of the pure DEX into the half empty distilled water jug. Pour the distilled water in the pitcher into the half empty DEX jug. BINGO !!! 2 gallons of coolant and the pitcher is still clean.

EDIT: half empty

RippyPartsDept
11-13-10, 06:41 PM
[edit: reading comprehension ftw]

maeng9981
11-17-10, 02:54 AM
Pete, I'd say a block test would not hurt anything. I am not trying to scare you or something, but your situation pretty much sounds like my 00 SLS journey. I have a long thread on Seville/Eldorado forum, it is titled "What are the steps after ruling out HGs?" which turned out to be the HGs. If you are smelling something other than Dex-cool from your surge tank, also try to open the coolant cap in the morning (engine completely cold) and see if the system is still under pressure.

Mine started from an intermittent temp spike to 1:00 that never happened before. It got worse over time (touching the "Engine Hot - A/C Off" limit - which is around 250 degrees I guess.) but the whole situation made me think it is not the HGs - block test gave me negative results and I had no symptoms, not even coolant loss (or it was leaking too slowly to notice). Tried troubleshooting by replacing numerous numbers of caps, water pump belt, coolant drain & refill, purge line cleaning, radiator & condensor fins cleaning, and things I don't remember......

I slowly realized that I was working on the wrong thing for months -- all of the sudden the engine started to shake bad upon cold start. Noticable coolant loss came out of nowhere. Threw away that autozone block test fluid and bought the fluid from NAPA which was more blue in color. Tested and yellow. Now I see white smoke from the exhaust.

I am either letting a shop to stud my engine, or putting it for my project of 2011. I am not in hurry.

Anyway, if you do decide to block test it, get a good fluid which has distictive blue color, like this blue, NOT like this.

Pete1996
11-17-10, 02:02 PM
Thanks maeng, our car is dead, I'm sure it is HGs.
Drove about 20 min on the HW started to overheat into the red, pulled off and eventually got the stop engine warning.
Let it cool for the rest of the day, filled it up again, drove home at 50 to 55 and made it without another overheat.
It is good enough for around town below 50 mph but that is about it.
I've put so much DEX-Cool (and oil) into this rediculous car that I am sick of it, LOL!
I've owned a lot of cars over the years, don't like Fords at all, GM is better, but Honda
has been reliable for me in an almost unbelieveable way. I like to work on classic
sports cars but not everyday drivers - they should just run and be reliable, we have
the technology. I've owned and restored several Alfa Romeos which have had aluminum
blocks since I'm sure the 1950s maybe even 1940s without problems.

When I stick my finger in the surge tank and wipe some of the crap off the
sides it is black like exhaust and smells like the stench from a bus passing by -
guess I don't need a test kit.
I consider this car to be at end of life since I'm sure it will need a lot more
work - struts, bushings, O2 sensors, whatever ....
Unfortunate that the exterior and interior are fairly nice and clean - for this
reason I'd just like to get another 10-20K miles out of it.

maeng9981
11-17-10, 05:44 PM
If you stud your engine, it will definitely last longer than 10-20k. Jake gives 5 year / 100,000 mile warranty to his shop's customers. There are a lot of studded Northstar out there and 0 failure so far. The only weak link on Northstar is the head gasket/bolts.

Call me crazy but after I get my engine studded, I will ride it until it falls apart on it's own. I will fix whatever goes out until the parts are unavailable anymore.

RippyPartsDept
11-17-10, 05:51 PM
:yeah:
i feel exactly the same way... i just hope that the HG never blows

Pete1996
11-17-10, 08:47 PM
maeng - yes I am aware that a studed engine should last a very long time,
but I don't want to replace everything else that is going to go in another
100K miles. So, I wish I could buy 20K more miles for 20% of the price
of a stud job. Then there is the oil leak and consumption issue.

If you enjoy these cars then your view is fine. I just like having a car that
goes forever with just basic and scheduled maintenance.

I like the good things about the Northstar motor but actually it seems to
me that it belongs in more of a sports car - the Vette for example, perhaps
a twin turbo version. The 500 HP supercharged motor seems to belong in
the STS since it just seems odd to be winding out a sedan to 7K RPM.
What was GM thinking? I suppose they wanted to compete with BMW and
MB with advanced technology.

I like this, LOL:
http://www.youtube.com/watch?v=8As1zshWxn0

maeng9981
11-18-10, 03:48 AM
I understand your point. Actually Northstar was intended to minimize the scheduled maintenance. Unfortunately everything other than the scheduled maintenance costs an arm and a leg.