: cooling fans come on at what temp?

11-20-09, 08:02 PM
I have a 99 Deville with the Northstar and I just replaced the motor. Im getting worried because the cooling fans arent coming on and the temp is getting up over 215. Does anyone know what temp the fans should come on, and what temp is considered HOT for a northstar?

11-20-09, 08:17 PM
205-215 is normal operating temperature. Fans come on low at 224 and high at around 230.

11-21-09, 12:11 AM
Holy Cow! Thanks for the info! Out of curiosity...what is considered "overheatiing"?

11-21-09, 02:30 AM
Personally I consider anything over 240 overheating... although the idiot warnings don't come on till around 255ish

11-21-09, 10:44 AM
The thermostat is set to begin opening at 188 and fully open at 206. Unless the HVAC system is in AUTO, when fans run in slow all the time (A/C function commanded ON) the fans are controlled by the engine coolant temperature sensor and come on in SLOW at 224 and FAST at 236. The car should run, on the highway, at about 196-204. With the HVAC OFF, the temp will go to 224 in traffic, fans come on, and the temp goes down to 213 when fans turn 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. Fans do not run above 45 mph. (They're not needed then.) About 255 is the Northstar "overheat" warning point. Camel mode engages at around 270.

11-21-09, 11:17 AM
Sub and I have some different "normal" temps. Mine are from several years of watching the digidash coolant temperature on my '97 Deville. 205-215 was normal on that car. My current '03 has the analog gauge so no telling what it is actually running at. Maybe I'll get a reading tonight when I get home and in the garage from my IR thermometer just for the hell of it.

11-21-09, 03:52 PM
I'm using the ScanGauge instrument which plugs into the OBD-II port and reads a slew of stuff in real time. Coolant temp is monitored every degree.
Been watching temps for over a year now at everything from DC traffic jams to 132 mph. Pretty damn consistent. Nice instrument.

Several years ago JimD did a photoshopped gauge pic by idling the car and putting cardboard in front of the radiator and using an IR thermometer to read temp at each gauge tick. I updated it last year with the Scan Gauge readings under road conditions. To get the 245 and 260 marks I pulled the fan fuses and idled up and down our .5 mile gravel road. Still, it never boiled over.

11-26-09, 12:54 AM
this may be a bit off topic but i was thinking about investing in a digital IR temp. gun and was just wondering what model you gents stand by

11-26-09, 08:54 AM
Most IR guns are pretty accurate. Where the expense occurs is in the effective range (in inches from the heat source) and the size of the heat source "patch" read by the instrument. You'll pay around $75 - $125 for a good gun with 10-12" range and about a 1" patch. It will have quick respnse times and a temperature save feature. Mine's a "Thermo", which looks like a generic gun made in China. $50.

11-26-09, 12:05 PM
Here's mine. I'm quite happy with it.
Here is the listing. http://www.thetoolwarehouse.net/p-1159-electronic-specialties-est65.aspx
They do have some cheaper ones. http://www.thetoolwarehouse.net/nsearch.aspx?keywords=thermometer

11-26-09, 10:06 PM
thanks for the info!!

11-30-09, 11:51 PM
I understand that running 50/50 mixture is the general specification. Running less concentrated (more water than anti freeze/coolant) keep the engine cool off a bit. I always thought that more concentrated was better but it purpose was more of a corrosive inhibitor and ant freeze. Since we all live in different region and climate, we can get away with more or less than the 50/50 mixture. For me I can run less since the maximum temperature in SoCal is less than 95* and hardly does it dip below 45*.
Its time to replace my cooling system and what percentage do you think I should have the mixture. Also my engine operating temperature is 217* */- 5, hottest I seen was 228* during emission test with no fan on. According to Sub my engine is running a little hot and according to Ranger I'm in normal operating temperature. I'm so paranoid that I have my coolant temperature display on my DIC at all time.

12-01-09, 08:33 AM
I live in Nor Cal, Bay Area, and my car when highway driving is right at the 12 o'clock position. Slow down for a stop light or in traffic and it creeps up to about 217 and sometimes 225, as soon as I start driving again it drops down. Perfectly normal.

12-01-09, 12:09 PM
its time to replace my cooling system and what percentage do you think i should have the mixture.

12-01-09, 01:58 PM
Anything less than a 50/50 concentration of distilled water/coolant is not recommended by any manufacturer, does not provide the necessary concentration of corrosion inhibitors, and actually lowers the boiling point of pressurized coolant.

The thermostat determines the operating temperature of the engine by regulating coolant flow rates. All the coolant does is to transfer heat from here to there.

A mixture of less than 50/50 does not cool the engine any better than 50/50 or 70/30. Water wetters do not cool any better (the thermostat thing). So-called "high flow" water pumps do not cool an engine any better; the faster a liquid flows past a heat source, the less time it has to absorb heat from that source............

GM recommends 50/50 for general use and up to 70/30 - coolant/water - for heavy duty use. Anything over 70/30 begins to lower the boiling point again.

03-09-16, 10:59 AM
Mine was running at 196 to 201, the I had to add some sealant(head gaskets) Now it's 201-205, sometimes as high as 220. I was really worried about this and you set my mind at ease. Thanks to all of you.

03-09-16, 11:41 AM
There are many, many more recent threads on fans and cooling systems for the Northstar than this one, dead for 7 years. Please look at the dates of the most recent posts in a thread of question - that way you always see the latest and greatest.

Study the several cooling/fan/gauge sticky threads at the top of this forum main threads page - updated, recent timeless info.

Pray that the sealant goop has not ruied the engine.
......... and Welcome Aboard !!! :highfive:

03-12-16, 05:56 PM
Mine was running at 196 to 201, the I had to add some sealant(head gaskets) Now it's 201-205, sometimes as high as 220. I was really worried about this and you set my mind at ease. Thanks to all of you.

That sealant you added is going to come back to haunt you ...

03-12-16, 07:46 PM
Oh boy, you'll be back.