: wide engine temp swing



stoveguyy
02-24-09, 10:47 PM
i have a 96STS and I did the HG last year but the car never overheated before or now but i get a funny temp swing. i have the DIC set to display temp. it almost always stays at 205 on the highway. i drive 20 miles and than poke along in traffic for a bit and the temp will climb to 220. than i get back up to speed and it will drop down to 190 and than climb back up to 205. the fans do work and i am not really worried about running hot but why does it dive down to 190? it did this about 4 months ago and i thought it was a fluke but it did it today again. my kid goes to a local collage and i sometimes make a run down there to drop off stuff. thats where the 20 mile stint comes in. than i motor around the school looking for a parking spot and that when the temp climbs. it never does this around my neighborhood or on the highway. its only on this school run. coolant level is fine.

Ranger
02-24-09, 11:14 PM
Tensioner working properly?

JimD
02-24-09, 11:56 PM
i have a 96STS and I did the HG last year but the car never overheated before or now but i get a funny temp swing. i have the DIC set to display temp. it almost always stays at 205 on the highway. i drive 20 miles and than poke along in traffic for a bit and the temp will climb to 220. than i get back up to speed and it will drop down to 190 and than climb back up to 205. the fans do work and i am not really worried about running hot but why does it dive down to 190?....

Understand my comments are based on experience with '98 and '04 engine models (eleven+ years and 200,000+ miles).

But I don't see any cause for concern. The coolant temperature excursions you are seeing are consistent with my experience when driving with air conditioning OFF.

As to why the coolant temperature drops as low as 190 degrees at highway speeds, I suggest that the increased air flow over the condenser/radiator causes the thermostat to "hunt" for the calibrated temperature for a short period of time.

The thermostat cannot anticipate the coolant temperature changes, it can only respond/react.

Submariner409
02-25-09, 04:06 PM
I agree with JimD. Between highway and off-the-ramp in town my 2002 reacts just about the same way with the HVAC system off. If the system is on and set to any a/c run function then the temp and gauge never move from 200.

STSj90
02-25-09, 07:58 PM
i have a 96STS and I did the HG last year but the car never overheated before or now but i get a funny temp swing. i have the DIC set to display temp. it almost always stays at 205 on the highway. i drive 20 miles and than poke along in traffic for a bit and the temp will climb to 220. than i get back up to speed and it will drop down to 190 and than climb back up to 205. the fans do work and i am not really worried about running hot but why does it dive down to 190? it did this about 4 months ago and i thought it was a fluke but it did it today again. my kid goes to a local collage and i sometimes make a run down there to drop off stuff. thats where the 20 mile stint comes in. than i motor around the school looking for a parking spot and that when the temp climbs. it never does this around my neighborhood or on the highway. its only on this school run. coolant level is fine.


You say it almost always stays at 205 during cruising? I dont think thats right...Unless my car is weird or somthing. My STS runs at 187-190 during cruising. (even gets down to 185) My temp never gets to 200+ during cruising even when im romping on it. I never seen my temp go above 192 when cruising at a steady speed.

I think i understood his post right. He's saying he will speed up from slowing down or from a stop and the temp will go down to 190 for alittle bit of cruising then while still cruising it'll go back up to 205??

With my experiance with my car, If its at 205 while cruising at a steady speed. Somthings not right.

stoveguyy
02-25-09, 08:20 PM
my normal temp is 205. i put in a used a/c compressor last summer and i was fiddling around with freon charge levels a lot so i had lots of extended idling while i charged the a/c. the fans do work with a/c. i can drive 100 miles on the interstate and it will constantly read 205. my kids school is literally 2 blocks off the freeway. i get off the ramp, 205. drive 2 blocks and idle for 5 min while i wait for the kid to come down from the dorm and it hits 215. takeoff and get on the onramp and viola, 190 for about 1 minute than it will climb up to 205 and stay there. i go to the store 1 mile away, 205. come home and its 205 or 206. ok, it flucuates 1 or 2 degrees. i think some cars just have slightly different thermostats or even temp gauges. i bet if i put in a different temp sensor the reading would change

Ranger
02-25-09, 09:03 PM
205 - 215 is normal operating temperature. Stoveguyy, your temps don't sound like anything to be concerned about. STSj90, if yours never gets above 200 you DO have a weird one.

STSj90
02-25-09, 09:21 PM
205 - 215 is normal operating temperature. Stoveguyy, your temps don't sound like anything to be concerned about. STSj90, if yours never gets above 200 you DO have a weird one.

Damn, that make's me feel good as hell. :thumbsup:

It gets above 200 at idle and stop and go traffic. But AT cruising speeds, My temps are as i stated above ALWAYS.

Thats just wierd. I thought my temps were normal. Anyone else have temps like myne? No lie, My temps are what i posted above. Thats acually making me wonder if my thermostat is the wrong one. But my car has always ran at these temps. Even before the coolant change and thermostat change.

Ranger
02-25-09, 09:58 PM
Wrong stat is a possibility.

JimD
02-25-09, 10:20 PM
This thread illustrates one of the reasons why car makers are reluctant to display actual coolant temperatures.

Consider several mass production realities here. If you have a cooling system thermostat that is designed to be 'wide open' at 185 degrees F with an acceptable manufacturing tolerance of 5%, that thermostat could be 'wide open' at a temperature anywhere between 176 degrees and 194 degrees F.

Then you should consider the same 5% manufacturing tolerance for coolant temperature sensors. And do not overlook the fact that the Northstar coolant temperature sensor is not mounted on the thermostat housing.

Kind of puts a 10 degree temperature variation from car to car in perspective.

A practically impossible to achieve 3% manufacturing tolerance would account for a 10 degree F difference from car to car.

Maintain the cooling system as GM recommends and keep the needle out of the RED

Submariner409
02-26-09, 11:16 AM
........BINGO !!!! from JimD. Also, the Seville/Deville cars fitted with "gauges" have a dead spot at 12:00 on the temp gauge......that spot goes from 190-something to 200-something.

The pic was done by a member years ago and is darn close to the real thing. Tolerances. The thermostat is supposed to start at 188 and be fully open by 206.

JimD
02-27-09, 01:55 PM
The pic was done by a member years ago and is darn close to the real thing.

That would be me....

Blocked air flow, torque converter stalled, coolant temperature information taken from OBD port with an interface box and displayed on a laptop.

The primary reason for all that was to learn the ON <--> OFF and low speed - high speed switching temperatures for the fans (1998 Seville).

The only printed specifications I have been able to locate for the thermostat is in the 2004 Deville Service Manual, pg 6-14; Full Open temperature = 185 degrees F.

Submariner409
02-27-09, 05:37 PM
2002 FSM, p6-547, specs to begin opening at 188 and be fully open at 206, checked with two Tempilsticks.

Interesting to start a thermostat comparison thread for the entire FWD Northstar run. There's more to this than meets the eye..........

dkozloski
02-27-09, 06:24 PM
As a practical matter, anything under 240 is fine. Dex raises the boiling point and the pressure cap raises it some more. You have plenty of margin before it boils.

tateos
03-05-09, 06:59 PM
My 97 ETC, post HG project, always is at 197 degrees when cruising with the AC off - I see that on the DIC readout - it never seems to vary more than 1 degree max, from 197. Stop and go, with the AC off, it goes up to as high as 228.

Cadillacon22s
03-11-09, 02:41 AM
My temp at a stand still would get up to 228 on a hot day, and return to about 200 as i got the car moving. When the car over heats a message will tell you to stop the car "engine hot" to give you a chance to save you car from potential engine damage.

Cadillacon22s
03-11-09, 02:48 AM
Cadillacs are great

Destroyer
03-12-09, 12:32 AM
Cadillacs are greatYeah! Nothing like overheating....................in style. :thumbsup:

ryannel2003
03-12-09, 12:37 AM
^Lol. Can't get that stupid Cadillac Style jingle outta my head though.