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Old 11-16-2017, 10:43 PM   #1
rgrafton
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Default Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Car warms up fast, Heat works really well and car seems to run just fine. I was thinking of leaving the thermostat alone as to keep the car running a bit cooler. I know during the summer months it will probably edge closer to the 1/2 mark anyway. I just hated how when i replace the thermostat in my '94 SL, it seemed to run much hotter (always went up to 3/4 mark and fan would kick on and bring it back down)... it just seems to do that way too often and the oil is pretty much toast at 3k miles

So, my questions are:
Roughly what temperature is the 1/4 mark on our cars (SOHC, specifically '02 SC1 in case it matters)?

Also would it be bad to run with the temperature a bit lower than normal for a long period of time? Or would it actually be OK or potentially beneficial?? For instance, Would running the engine cooler keep the oil from breaking down as fast?

...
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Old 11-16-2017, 11:35 PM   #2
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Those temp gauge systems are hardly precision instruments. Use live-data to check temperature if it is a concern. If the engine runs normally and fuel economy is reasonable, don't worry about the temp. All the BS about "half a needle above 1/4" and such is meaningless, akin to determining cylinder wear with a tape measure.

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Old 11-17-2017, 12:09 AM   #3
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Live data lies so stick a thermometer into the reservoir and see what the temperature reads. Get back into the right rear corner for the best indication.

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Old 11-17-2017, 04:52 AM   #4
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

As suggested, use a reader to display live temperature information. Despite one naysayer here, if temperature sensors weren't reliable (excluding the infamous OEM ones used from '91-'01), every coolant sensor is relied on for the engine computer to determine correct fuel mixtures (among other sensors). The same sensors used world wide allows every technician to display actual coolant temps as part of diagnostics during repairs requiring temperature info. If these sensors lied then the entire world of EFI systems and electronics are all lies. Fortunately, electronics and sensors like the ones used to monitor coolant temps are fine and reliable enough for engine computers to use in controlling emissions. Don't let misinformation misguide you. You always have the choice to use a thermometer (infrared, dial type, whatever) while readers are perfectly capable for this purpose while displaying other info.

Using a reader ti display actual coolant temps should show between 180F-200F. If below this range, its your choice to leave the t-stat as is or replace it. The downside to lower coolant temps is lower fuel mileage and loss of heater function in winter in extreme cases. Extreme cases are shown below with melted seals not allowing correct operating temps. The ones shown are from the faulty coolant sensors that never sent correct temperature info, overheating the engine and melting the seal. The temperature gauge needle never went above the 1/4 mark. A reader will display whatever temps are and its presumed your '02 uses the brass sensor (all Saturns after '01 were upgraded with the brass sensor).
Attached Images
File Type: jpg plastic-brass cts.jpg (82.8 KB, 3 views)
File Type: jpg t-stat 1.jpg (119.5 KB, 5 views)
File Type: jpg t-stat 2.jpg (60.8 KB, 5 views)

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Old 11-17-2017, 08:31 AM   #5
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Quote:
Originally Posted by rgrafton View Post
Car warms up fast, Heat works really well and car seems to run just fine.
this highly suggests your thermostat is fine. When my tstat seal cracked (looked like the first tstat pic fdryer posted), I could never develop good heat in my '98 SL2, even after a 25 minute drive in 50F weather

I will say that since everything else was working fine in the car (all sensors, etc), I never noticed that the thermostat died by monitoring my MPG. Only after I confirmed the bad tstat, and looking back at my records, I saw a 1~2 mpg drop from fill to fill from when the tstat was known good; within a normal variation for driving patterns and traffic

Quote:
I know during the summer months it will probably edge closer to the 1/2 mark anyway.
That also suggests a good thermostat.
Quote:
I just hated how when i replace the thermostat in my '94 SL, it seemed to run much hotter (always went up to 3/4 mark and fan would kick on and bring it back down)...
Some searching will show that the 3/4 mark on your '94 was roughly 220F, and that 1/2 on your current '02 car is also roughly 220F.

Up through 1995, the cars were designed to show 1/2 as "normal" range, with the fan turning on at 3/4 or 220F. Drivers who were used to seeing a gauge in the middle panicked and brought their cars back to dealers. Dealers found no problems but complained at how much time they spent, so Saturn recalibrated the gauge to show roughly 3/8* as "normal" range with fan turning on at 1/2 or 220F

*As mentioned, the gauge is not a precision instrument. Some folks have a confirmed "normal" reading at the 1/4 mark . . . that is, in the 205~220 "normal" range, as demonstrated by a thermometer in the return stream and/or OBDII reading, their gauge was at 1/4.

Quote:
it just seems to do that way too often and the oil is pretty much toast at 3k miles
You can't tell anything definite by the color of the oil. Have you ever had a test done on your oil at 3k?

edit: there is a "used oil analysis" sticky thread at the top of this forum, if you get bored and want to read If you are replacing your oil every 3k, it might be worth it ($20 or so?) to get it tested at 3k. If your driving is fairly consistent and you use the same oil/filter all the time, if the lab suggests you can drive on the oil to 7k miles, you can change the oil at 5k~6k miles, have a cushion, and still save money/oil

Quote:
Roughly what temperature is the 1/4 mark on our cars (SOHC, specifically '02 SC1 in case it matters)?
The variation between cars is too wide. No answer will be valuable to you - you have to check; either OBDII or thermometer, whichever is easier and provides you with a sense of comfort

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Last edited by alordofchaos; 11-17-2017 at 08:37 AM..

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Old 11-17-2017, 09:08 AM   #6
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Quote:
Originally Posted by rgrafton View Post
Also would it be bad to run with the temperature a bit lower than normal for a long period of time? Or would it actually be OK or potentially beneficial?? For instance, Would running the engine cooler keep the oil from breaking down as fast?
The down side of running the car cooler then originally designed is that the temperature readings sent to the PCM affect fuel management.

At the gauge reading at 1/4 your car is likely running rich and that will eventually that will affect your exhaust manifold, air injection system (emissions), pre-cat and catalytic converter. These components will get clogged up with carbon deposits and then your into some cash outlay to repair/replace. It also negatively affects your MPG.

To determine if your thermostat is faulty, start your engine from cold and put your hand on the hose coming from the thermostat to the radiator. If it gets warm before the engine is at operating temperature then your thermostat is leaking. It should be closed until ~188 degrees when it begins to crack open.

If the thermostat test is favourable then look at your ECTS and the ECTS connector. These will both send false readings to the PCM if they fail. If the connector has been replaced before make sure that the wires are soldered and not crimp connected. Crimp connectors are a failure point too.

As alordofchaos mentioned the 94 gauge reading is different than the 2002. The Gen3 gauge reading should be a touch higher than 1/3. The general consensus for a replacement thermostat for these cars is a Stant 14279.

...
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Old 11-17-2017, 11:43 AM   #7
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

If the car is (or even thinks) its running a 1/4 its going to run richer. Your mileage will suffer.

-Robert

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Old 11-17-2017, 12:00 PM   #8
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Not only mileage but the cool temps cause the oil to sludge badly and moisture to collect causing acids to build up not to mention the excess fuel washing down the cylinders will cause excessive wear and tear to not having good film on the cylinders
On my 99 SL2 I tested my gauge readings with a thermometer and found that at just a needle width over the 1/4 mark temp was between 190 to 200F My fan would turn on at just under 1/2.
The 96 I had was at 190 to 200 when it was at just about half on the gauge and the 2001 I had was at the same 190-200 at about 3/8 on the gauge.
As for reading the temps with a scan gauge well all bets are off if the sensor is not good or something is wrong in that circuitry. So scan gauge is not always the best indicator.
Bottom line it's always best to have the engine up to PROPER normal operating temps (but then MBR may think that's BS too LOL)

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Old 11-17-2017, 12:53 PM   #9
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Quote:
Originally Posted by underthehood View Post
On my 99 SL2 I tested my gauge readings with a thermometer and found that at just a needle width over the 1/4 mark temp was between 190 to 200F My fan would turn on at just under 1/2.

The 96 I had was at 190 to 200 when it was at just about half on the gauge and the 2001 I had was at the same 190-200 at about 3/8 on the gauge.
The 99 and 01 gauge readings you've stated corresponds with what I'm seeing on my 99 and 01. When I got the 99 up and running last year I though it had a bad thermostat because of the compared difference. I replaced it with a new Stant and it only changed marginally. The 99 reads notably lower than the 01. I didn't know this was normal until your post.

...
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Old 11-17-2017, 09:46 PM   #10
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

sounds like my thermostat is fine then. Thanks!

...
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Old 11-18-2017, 09:50 AM   #11
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Default Re: Driving long term on "bad" thermostat - temp sitting around 1/4 mark

Quote:
Originally Posted by trottida View Post
The 99 and 01 gauge readings you've stated corresponds with what I'm seeing on my 99 and 01. When I got the 99 up and running last year I though it had a bad thermostat because of the compared difference. I replaced it with a new Stant and it only changed marginally. The 99 reads notably lower than the 01. I didn't know this was normal until your post.
Have you been verified that is also the temp the computer reads? You can be at the right temp but if the computer thinks itís colder itís going to run rich. Just need to hook a scanner.
-Robert

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