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2005 4.6L STS
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Discussion Starter · #1 ·
Hello all,
New problem with the sts. On a real hot day it boiled out the overflow. The temp gauge never showed it hot the gauge is always between the center mark and the one below it. I did notice the fan stayed running after shutting off the car for a few minutes then it puked out the overflow.
I replaced the expansion tank cap and hooked up the OBDII reader and drove around, the temp went between 190 and 208 with the ac on. What is the normal operating temp of these cars? Any thoughts on what may be going on?
Oh and the radiator, t stat, and belts have been changed a few months a go. Unrelated problem.
 

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2002 F55 STS, 2014 Explorer XLT, F-150s
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The Northstar thermostat is set to begin opening at 188 and fully open at 206. Most of the (FWD) Northstars run around at about 190 - 205 day in and day out. The cooling fan sequencing is different for your engine compared to mine so you'll need to get into a GM/Cadillac service manual to find that info. In the FWD cars fans don't go to SLOW until 224 degrees and that's not even remotely close to overheat conditions (267).

The proper cold coolant level in the surge tank should be about half full - the airspace is the "spring" against which the warming, expanding coolant works to create system pressure, probably 18 psi for your engine. That pressure is what raises the boiling point of 50/50 coolant from about 225 degrees to 276 as well as insuring "solid" coolant flow to the centrifugal water pump. Not enough airspace, the engine heats to operating temps, coolant expands and blows out the overflow.

A/C condenser - in front of the radiator - clean and bug-free?
 

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2005 4.6L STS
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Discussion Starter · #4 ·
Yes it is clean and bug free I will make sure it 9s filled half full when cold and take it out this weekend for a romp and see what happens. I hope it was the cap.
 

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2005 4.6L STS
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Discussion Starter · #5 ·
Update.
Ran some errands freeway and streets 100 deg. Day ac on the temp gauge ran just below the middle mark I assume this is normal?
At every stop I made no problems everything was fine. When I got home I looked at the temp gauge and it was in the same spot so I shut off the car and when I got out I heard the radiator fan running so I ran into the garage and grabbed the OBDII reader and plugged it in when I turned on the car the temp gauge was just below 3/4 but dropped to normal almost instantly. The OBDII reader showed the coolant temp was 226 and after a couple minutes it studied at 220 ac still on. So is this normal? It didn't boil over but it could of been because I started it back up, I will be running the same errand later today and this time I will have the OBDII reader already connected and I will not restart it and see what it does.
 

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2015 SRX LUX 2014 CTS LUX Phantom Grey (previously 2008 STS)
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Do you see any bubbling in the overflow tank? If so that's a sure sign of a blown headgasket
 

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2005 4.6L STS
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Discussion Starter · #7 ·
Bubbling when? I will have to look and see.
On other cars I have owned in the past when a head gasket was blown you had water and oil mix and you could open the radiator cap cold and their would be pressure in it.
With this car no smoke oil is clean and no pressure when its cooled down.
With the 4.6 blown head gasket a intermittent issue? Meaning I can drive it same distance same temperature and have it boil over 1 out of 5 trips?
 

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2002 F55 STS, 2014 Explorer XLT, F-150s
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Northstars do not normally mix oil and coolant or coolant and oil if a head gasket is failing due to cylinder block head bolt hole thread failure(s).

The engine cooling system uses a purge line that runs from a high point on the water crossover to the top side of the surge tank. This is a constant bleed for air and gases to find their way into the normal airspace over the coolant in the surge tank. To test for bubbles - possible airlock in the system - you remove the line from the side of the surge tank, engine cold, remove the surge tank cap, and hold the end of the line in the open filler neck. Have an assistant start the engine normally. You shoud see a small steady stream of coolant flowing.

IF a head gasket is failing it's possible that the amount of exhaust gas blown past a fire ring and into the cooling passages is small - that would allow several run cycles without overheat. The overheat occurs when enough air/gas is present to airlock the water pump, causing cavitation and no coolant flow, thus overheating the engine.

You also need to check the water pump drive system, but for your longitudinally mounted engine that's out of my knowledge base.
 

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Discussion Starter · #9 ·
Thanks for the info. If you are talking about the top small hose on the expansion tank that runs to the top of the radiator I can see through the expansion tank (its clear) while the car is running and I wouldn't call it a 100% constant flow as it looks more like it sputters every second or so.
 

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2002 F55 STS, 2014 Explorer XLT, F-150s
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Yes, the purge line is the small one that runs from the top of the surge tank over to the cooling system high point. That surge tank is pressurized and sits on top of a T-fitting in the heater return line, so there is a constant exchange of coolant in the tank as well as level changes due to coolant temperatures. The purge is a constant gas/air bleed to the airspace over the coolant in the surge tank and, under normal conditions, should be a smooth, steady flow with few or no bubbles or spits.

The older Northstar took the purge from the top section of the water crossover; my Explorer uses an engine jacket high point, the F-150s use a nipple on the top of the driver's side radiator tank. All "high points" where air/gas would tend to collect.

In any event, a perfect system would have no - none - air or gas in it.
 

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Discussion Starter · #11 ·
Just got back from a short drive and opened the hood to look and see if I could see any water flow into the expansion tank. I couldn't. I did find a coolant leak at the upper radiator hose I will fix that and retest this weekend and see what happens. So what is the normal operating temp?
 

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The Northstar uses a thermostat set to begin opening at 188 and fully open at 206. Most of these engines run, day in and day out, at between 190 - 210, depending on ambient temps, traffic conditions, HVAC compressor use, fan sequencing. Anything up to 220 or so is completely normal - actual overheat occurs at over 270 - but you need the GM/Helm service manual for YOUR car/year to get the straight skinny. There are many differences between your Northstar and mine, so get the best info from the source: The service manuals.

Unpressurized 50/50 coolant boils at about 224 degrees - easily attainable with long idling periods. Is your surge tank pressure cap in perfect condition? How about the seal lip on the surge tank filler neck?

Older coolant recovery systems had an expansion (overflow) tank, unpressurized, vented to atmosphere. Our surge tank (expansion tank) is fully pressurized, sealed, and is an integral flowing part of the cooling system. The surge tank and its airspace replaces the top tank of older downflow radiators; our radiators are crossflow, so there's no easy way to have a tank/airspace above the core.

.................. note that the 50/50 coolant concentration line is out of sequence.
 

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Discussion Starter · #13 ·
Yesterday when I found the coolant leak the car was running and at normal temp I could squeeze the upper hose about a 1/4 of the way together. If a true closed system is important then I must fix this leak before any further diagnosis as this could be the cause I HOPE of the issue.
 

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Discussion Starter · #14 ·
Update.
Sofar no leaks and no more boiling over, I don't know if it was the leak causing it or if the weather cooling down a little but for now all is good.
Btw the leak was the upper radiator hose at the engine was leaking, tightened the clamp to stop the leak.
 

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2002 F55 STS, 2014 Explorer XLT, F-150s
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I don't know if it was the leak causing it or if the weather cooling down a little
That has absolutely no bearing on whether an engine will overheat or not; only on the period of time between engine start and (with problems) overheat.

You can drive the car at 45 below in Fairbanks, AK (ask DKOZ) or at 120 degrees in AbuDhabi and it will do just fine with a clean, tight, maintained cooling system.
 

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2006 STS V8 AWD, '95 Ford Ranger
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I don't know if it was the leak causing it or if the weather cooling down a little
I drove my '04 CTS in -55F weather in Fairbanks, Ak and the same car in Needles, Ca at +116 with no problems.
 

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Northstars do not normally mix oil and coolant or coolant and oil if a head gasket is failing due to cylinder block head bolt hole thread failure(s).

The engine cooling system uses a purge line that runs from a high point on the water crossover to the top side of the surge tank. This is a constant bleed for air and gases to find their way into the normal airspace over the coolant in the surge tank. To test for bubbles - possible airlock in the system - you remove the line from the side of the surge tank, engine cold, remove the surge tank cap, and hold the end of the line in the open filler neck. Have an assistant start the engine normally. You should see a small steady stream of coolant flowing.

IF a head gasket is failing it's possible that the amount of exhaust gas blown past a fire ring and into the cooling passages is small - that would allow several run cycles without overheat. The overheat occurs when enough air/gas is present to airlock the water pump, causing cavitation and no coolant flow, thus overheating the engine.

You also need to check the water pump drive system, but for your longitudinally mounted engine that's out of my knowledge base.

So well explained. This post answered my question before I even asked. I definitely have a blown head gasket on my 02 DeVille. Thanks to everyone especially Submariner409
 
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