[fristim]

98 concours, I just replaced the radiator about 4 days ago. Drove the car on a 200 mile trip and now I'm getting coolant being pushed out the resiviour. Weirdest thing happens I'm pulling in my aunts garage and I notice that there is a trail of coolant I look and its coming out the resiviour. So I refilled today and everything is fine until the temp gets to about 220 right before the cooling fans come on. At that temp it, with the resivour cap off you can slowly see the coolant level rise and if I leave it running it will start pushing the coolant out the resivour. I noticed one time that the temp got up to 232 and the cooling fans were on high. I pulled the return line off and its fine. It flows a steady stream until the coolant starts being pushed out of the tank. At that point it starts steaming. I've also noticed that my temp seems a lil wierd, I can drive the car just fine and its not using any coolant but my temp does fluctuate, now my temp actually drops like if the coolant temp is 177 if I park and idle the motor then the temp will drop down to 170. I've blown back on the return line and there seems to be no blockages. Any help would be greatly appreciated. THank you.

 

[C170B]

I am sorting through a similar senario with overheading mystery on N* 94 Concours.

Thankful for all info avail this web site. It doen't have to be the dreaded N* gasket so I offer hope and empathy.

I am becoming suspicous of "sick" thermostats being culpable.

I wanted to share a piece of new info that I was unaware of regarding thermostat on 4.6 N* . GM is wanting to advise all that a replacement thermostat HOUSING is available. Original is black plastic and replacement is cast aluminum; comes complete w thermostat already installed cost is 47.00 the original part number is 89017649

I asked hard questions as to why they created the new part in alum instead of plastic. Parts guy was vague.

You may have replaced the thermostat at same time you did radiator however I would remove and install the best replacement available (OEM?)

 

[Ranger]

Is the surge tank cap on properly? Holding pressure? Water pump belt tensioner ok? Thermostat operating properly?

 

[Eldyfig]

So I refilled today and everything is fine until the temp gets to about 220 right before the cooling fans come on. At that temp it, with the resivour cap off you can slowly see the coolant level rise and if I leave it running it will start pushing the coolant out the resivour.

This is all normal. With the cap off, there is no pressure being maintained on the system. It will "boil" over. As far as the original overflow while driving, what was the coolant temp? It may be possible that you overfilled it. Or, like Ranger said, your might need a new cap. The old one might not be maintaining its pressure setting.

 

[fristim]

The coolant temp during the original overflow was 212 but like you said I may have over filled it. The water pump has about 15000 miles on it and the belt and tensioner have about 10000 they all seem to be fine. I think my best bet is to change the thermostat and also the coolant cap. So this behavior is not indicative of head gasket problems?

 

[Eldyfig]

212 is within the normal operating range.

This is not a reason to worry about the headgasket. Change out the cap first and drive it for a while. See if any problems still exist.

When refilling the north* cooling system, only fill to about 2 inches below the opening. This allows room for expansion.

 

[zonie77]

This behavior could be indicative of head gasket problems but could be indicative of anything that causes overheating.

I highly recommend using only a GM thermostat.

Everyone elase made good suggestions. The only thing I'd add is flushing the radiator if possible. It's a royal pain when this happens away from home.

 

[powerglide]

Yeah that sucks that youre away from home, thats a nightmare.
When I did the coolant change my manual specifically said I should clean out the inside of the reservoir and if its not cleaning out, then replace it.
When I checked it out it was full of this black gummy crap. Luckily/unluckily the tank was cracked and I was replacing it anyways.

I guess I'm trying to say, maybe the flush will help it out if its not the cap.
Hopefully its not the head gasket, folks tend to jump to that scenario....especially if you;ve been here long and read all these posts over the years.

Good luck!

 

[Eldyfig]

On your trip did you ever see the coolant temp get too hot. If you have the digital readout of the temp, did it ever get above 230?

If you really need to flush, try to get out as much of that tap water as you can when your done. Blow it out with some shop air by putting the air hose into the cap opening and letting it blow out the bottom of the system.

 

[Ranger]

Blow it out with some shop air by putting the air hose into the cap opening and letting it blow out the bottom of the system.

A shop vac with the hose on the exhaust port (high volume, low pressure) works even better.

 

[CadillacSTS42005]

check your coolant system for air bubbles

 

[Eldyfig]

That's right, Ranger. That was what I was picturing in my head.

 

[zonie77]

I just reread and the radiator was just replaced...so...why was it replaced? Were you having overheating problems? (a good assumption but I did learn something in the Navy!)

If it was overheating and you've rpld rad, water pump, and tensioner you don't have a lot left. Did you replace the thermostat? If not that's next. Use a GM stat. We had trouble with a good aftermarket one sticking. Replace the pressure cap if you havn't already done so. If you replace the stat make sure it has a small air hole through it. This will minimize the chance of an air lock. Some new ones are coming with this already in...If not I recommend putting one in the face of the moving section, just 1/8th" to 1/4" at the most.

If those don't fix it you need a cyl pressure test to check for bad head gaskets.

And just to get it out of the way...N*'s don't put oil in the water and they run great even with leaking head gaskets. The normal symptom when first having problems is loosing coolant after going up hills, rapid accelleration, and/or high speed cruise. Gradually it gets worse and you loose coolant constantly.

 

[fristim]

I changed the rad. because of a hole in the hot side of the plastic tank. I did change the thermo and the coolant cap and all is well. Cruising temps at 205-197 with it generally being about 201 most of the time. No coolant loss yet. I will keep an eye on it and thanks for everything guys!!!!!

 

[Freddy Oberding]

Where do you find the digital read-out of the temperature? I have had my 97 for a short time with an overheating problem and would like to see the temperature that mine is running at.

 

[Eldyfig]

Try this link...

http://www.cadillacforums.com/forums/showthread.php?t=55326