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1998 Deville
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Discussion Starter #1
98 DeVille with 4.6L Northstar. Normal operating temp used to be about 205 deg F as I recall. Lately during warm days (95 deg) it is running hotter. I flushed engine & radiator, replaced with DEX-Cool and supplement pellets, new 185 deg thermostat, and new radiator cap (thanks post from vitovent!), but doesn't seem to have made much difference. Runs at 222 deg while idling at traffic lights with A/C on, then down to about 196 while driving at speed with airflow through radiator. Both cooling fans are running when hot at idle. What is proper/normal high end temp range for this engine?

- Jon
 

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2003 deville
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604 Posts
The supplement tablets from the manual, I believe they stopped advising using them quite a few years ago. The head gaskets if they leak will be from the bolts pulling loose not from anything a pill or pour in can fix. Usually you actually end up clogging up the cooling system reducing its ability to cool as efficiently. Also just to be sure is the coolant/water mix about 50/50? I saw an older post from ranger said his 97 ran 206 conistantly summer, 213 winter.
 

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White Diamond '03 DHS (with DTS floor shift)
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Yeah, that's pretty normal. As Purlux said, my '97 (digidash) ran around 205 in the summer and up to 2105 in the winter. 222 might be a tad high, but considering it is in 95 degree heat and idling in traffic, I'd cut it a little slack, but keep a close watch on it. If it starts going higher, it may be time for concern.

Did you check for flow from the purge line? Those tabs tend to clog it up.
 

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1999 SLS w/F45
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Mines run between 190-196 all day long in 90+ degree weather idling, the only way i would see it get to 222ish, is if im moving at 10-20 mph than stop, move again at 10 mph and than stop, a cycle like that(and still 222 is rare with AC on), but as soon as i come to a complete stop, its instantly goes back to 190-196 temp.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Yeah, that ^^^^ Check the purge line. The supplement tablets went away in 2006 or so and the service manuals and radiator stickers were never updated. There IS a GM/Cadillac TSB (Technical Service Bulletin) on the discontinuance of the tablets. it basically states that the tablets are not to be used for routine cooling system maintenance but will only be used after specific finding for special problems by a GM field representative.

"Normal" Northstar cooling system temps run from 190 to about 215. Depending on traffic, ambient temperature, A/C and fan usage you might see 224 once in a blue moon.

grandma, If your 1998 has a coolant heated throttlebody, do the purge line bypass. It most certainly improves purge flow.

Northstars use the same temp sender for coolant, so the marks on this gauge correspond to relative positions on other sizes/types.
 

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1997 Cadillac Deville D'Elegance
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Mine has had the headgaskets replaced using Norms inserts. With a 100 degree heat index, meaning humid as h**l, it will run between 201 and 217 with the a/c on in mixed driving. Every now and then, it will get up to 222, then cool back down after a couple minutes. Never goes over that. Basically, if 222 is as hot as it gets, and you are not losing coolant, then don't sweat it. Heck, the LOW speed fans do not even kick in until 224. Of course, the masses will cry 195-205 is the norm.
 

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2011 DTS Premium w/1SD | 1999 Deville Base (RIP @179K Miles)
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Lucky. I studded my engine and sometimes see 217-222 on the highway. Going up a steep grade it went up to 231.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Of course, the masses will cry 195-205 is the norm.
Yep - right on. "The masses" represent the majority, and that 190 - 205 is where most Northstars run - day in, day out, regardless of road characteristics or ambient temperatures.

Remember that both fans are supposed to run in SLOW any time an A/C compressor function is set, so that temp gauge needle should sit at 12 o'clock - plus or minus a needle's width - all day long.

Heat Index (Relative Humidity relationship) is for humans and mammals - it determines rate of evaporation of perspiration (Real Feel) and has absolutely NO effect on metals or plastic. To an engine/radiator 100 degrees air temp is 100 degrees air temp, whether it's in the Sahara or Charleston, SC.

We can argue all day, but for a Northstar cooling system in good condition 217 - 224 on the highway is too warm for "normal".

Here's the cooling fan circuit for the pre-2000 Northstar. 2000 - 2005 is in my albums.
 

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1999 SLS w/F45
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True, an Northstar should never run that warm on the highway, I recently made a 57 mile trip when the temp was 97 degrees outside. AC on full blast the entire way doing 70-80mph and the temp hand stayed flat dead at 12 o"clock the entire way
 

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1998 Deville
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Discussion Starter #12
Crap, wish I would have had that info before I put in the Bars-Leak pellets. Did some internet searches that talked a lot about which Bars-Leak stuff was same as the pellets, etc. and so that's what I got. Must have been older posts. So, should I drain and flush the system again to get that stuff out of there now?

What is the "purge line"? referred to? I'm not familiar with that. Why would you bypass it - does it get clogged? Car always ran right about 205 deg all day long until recently when it has been getting hot while at traffic lights...

My 98 does not have analog temp gauge like in the posted image - just a digital readout of the temp number.
 

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1998 Deville
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Discussion Starter #13
I'm going to let my daughter take the DeVille to school with her for her first car so I'm worried about making sure there are no problems that will strand her. The car runs at about 196 deg while driving down the highway with air flowing through the radiator - Only now it gets up around the 222 mark while sitting at traffic light idling where it didn't seem to do that before. That's why I thought at first the electric fans might not be running, but they are. So don't know what changed. Flushing and changing coolant and new thermostat & radiator cap didn't make a difference. Still trying to know if I even have a problem or not.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Our cooling systems use a totally sealed setup - the surge tank is at system pressure at all times. Proper fill level is half full, cold - see the FULL COLD and arrow molded into the tank top. The arrow goes over and down to the midseam.

The purge line comes from the system high point, through the throttlebody in some models and over to the surge tank. Its function is to pass off air bubbles in the system to the surge tank airspace. The water pump is a centrifugal unit: Any air bubbles and it cavitates and flow slows or stops = high temps and/or overheat. If that purge line clogs you get higher running temps and oddball overheats from system bubbles.

Engine cold - open the surge tank. Remove the purge line from the upper side of the surge tank and hold it in the open filler neck. Have an assistant start the engine normally. The line should spit and flow a steady stream into the filler neck.

The heated throttlebody circuit was found to be a clog point and not needed anyway, so it was deleted for 2000. Easy to see in those that have it.

Simply run a single length of proper sized reinforced fuel line directly from the hollow bolt/nipple over to the surge tank nipple. No need to cap off the TB nipples.

Your second post - recent - remember that the fans only run all the time when some A/C compressor function is set. Otherwise they go to SLOW at 224 degrees, the engine cools to 213, fans shut off, the cycle repeats. Fans WILL cycle in town and probably never run at speeds over 30 mph - they're then not needed.
 

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1998 Deville
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Discussion Starter #15
Thanks for he good info! I did run the bypass for the Throttle Body -didn't seem to make a difference and the lines I took off were not clogged, but good preventative maintenance I guess if the heating of the intake through the Throttle Body is not really effective anyway. Drained the cooling system (again) and currently have radiator flush in now to clean it out again and get the "supplemental pellets" out. Both electric fans seem to be working as they are supposed to: Both come on at low speed when A/C is on and then kick to high speed at somewhere above 225. Will see how it goes.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The throttlebody, on these and other engines with similar induction, was done to prevent possible throttlebody bore icing during warmup on cool, humid mornings. The extremely high velocity of the tiny amount of air entering the intake manifold at fast idle and slow speeds caused a venturi effect - rapid pressure drop - on the intake side of the throttle blade and that causes ice to form. The theory was to heat the TB bore. Wasn't needed because the TB is bolted to the water crossover - it heats right along with the crossover metal.

Tiny amount of air entering the engine ???? Yep - even at 65 - 70 on the highway the throttle blade is open only 7% - 10% and the manifold is in high vacuum. The only time any appreciable amount of air enters the engine is during wide open throttle power runs.
 

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98 DeVille with 4.6L Northstar. Normal operating temp used to be about 205 deg F as I recall. Lately during warm days (95 deg) it is running hotter. I flushed engine & radiator, replaced with DEX-Cool and supplement pellets, new 185 deg thermostat, and new radiator cap (thanks post from vitovent!), but doesn't seem to have made much difference. Runs at 222 deg while idling at traffic lights with A/C on, then down to about 196 while driving at speed with airflow through radiator. Both cooling fans are running when hot at idle. What is proper/normal high end temp range for this engine?

- Jon
 

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  1. All northstars run at 12 o clock when the a.c. is on it does not matter if its hot outside if ur going up a hill it stop and go traffic it will always stay at 12 o clock. But with a.c. off in stop and go traffic it will climb to 230 then the fans will turn on and cool it back tob12 o clock does it over and over in stop and go traffic but if u drive on highway with a.c. off it will stay at 12 oclock. I know this cause my daily is s 2000 DHS I INSTALLED A 180 degree thermostat and bought a 80 amp relay and wired up the fans using the 80 amp relay so when the key is on the on position both fans turn on daily is a pearl white DHS I love it even tho I have to be fixing little things that go out and 1 thing it does not leak a drop of oil i use amsoil signature series 5w30 and All ways use shell gas
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Bad idea to bypass the built-in fan controls, and your blanket statement "all Northstars" is grossly incorrect. Several different sets of fan controls and operating temps were used from 1993 to the end of the FWD Northstar installations, with the 2006 and later being quite different from your (our) setups.

Your (our) fans are set to go to SLOW at 224, FAST at 236, and run in SLOW any time any A/C function is set. Fans don't run at over 30 - 35 mph - not needed.

The normal Northstar thermostat is set to begin opening at 188 and fully open at 206. Most Northstars, with cooling systems in good condition, run at between 190 - 205 all day 24/7/365.

Tricking the fans to run all the time only lessens the fan motor replacement intervals.

See Posts 5, 10, and 14 for what is correct.

Always check/replace the water pump drive belt tensioner pulley at between 50 - 75,000 miles. That little $24 pulley will put you on the side of the road for big bucks if it ever seizes.

Pulley and tensioner (Notes).JPG
 
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