Thermostat break-in period???

[zephram22]

When you replace a thermostat, does it have a break-in period that it goes through? A couple days ago, I wrote the the new thermostat I had install when I was taking care of some problems (overheating, AC Clutch failure) had failed. It was still overheating. I've learned some new things by observing the engine, both visually, and by sound.

1. Before I had the thermostat replaced, I tried to bleed the collant system. Well, when I put the cap back on, I put it on the wrong way. The arrow was facing away from the overflow tube. But, it this configuration the engine did not overheat.

2. After I started having the new problems with the new thermostat (actually the same problems as with the old one), I decided to bleed the system again. I ran the engine for about 1 hour with the radiator cap off. With the cap off and the egine idleing I looked at the coolant tank. The fluid level was rising and falling about an inch at a steady rate. Took about 4 seconds for one cycle. For about five minutes during this hour, I held kept the RPMs of the engine at about 3500. No sign of overheating whatsoever. OK, that I had fixed it. But, as soon as I got on the thruway to come home, it overheated. So, I now know that no matter what my engine speed is, the car will only overheat when it is in drive.

I decided to buy a new surge tank cap. Got the 18PSI one from Napa and installed it. No change..Damn thing still overheated. So, decided to put the other cap back on. Before I did that I noticed that the coolant level looked low. So, I added some coolant. Did that early today. No more overheating as of yet. The entire problem seems to have gone away...for the time being anyway.

4. I said that I had a gurgle in my coolant lines. I've come to the conclusion, after listening very closly, that I have air in the heater core. I noticed that when I have the air temp set all the way down at 60F, there is no gurgle. As soon as I set the temperature to a higher temp, the gurgling begins almost instantly. I really don't know how I'm going to get that air out. I've been trying for a couple of days already. I do know that besides the coolant cap there is some sort of vacuum bleeder valve. Just got to find it.

PS. Filled the car up with a combination of gas, octane boosters, and injector cleaner. Total cost to fill the tank with premium and the additives. Around 75 dollars. I should have done it yesterday. Gas prices went up forty cents overnight here. I think some of the stations around here have passed 3.50 -3.60 for 93. Eh, the cheapest stuff I can get is still 3.30 per gallon.

[protek22]

Zephram,

If you changed the thermostat and still have the same issue, it probably wasn't your problem. The gurgling is an indication of either air or combustion gases in the system. Since this is a closed system, there should be no gurgling in the heater core, unless the system is breached somewhere. An external breach would be accompanied by an external coolant leak of some type. A faulty surge tank cap might also introduce air, but yours appears to be OK. Purging usually gets the air out, so this indicates an ongoing breach of some type in your system. I'd suggest trying to narrow this gurgling down to either an internal leak, or a plain air pocket. Air pockets don't add much to system pressure but internal leaks do. An air pocket would cause random overheating and coolant loss, until purged. Overpressure from an internal leak will cause cyclical loss of coolant out the overflow, and overheating until fixed. Look for a stream of bubbles coming up in the resevoir when you open the throttle. This is a clear sign of an internal leak, and the source of your gurgle. If you don't see a stream of bubbles when throttling, then you may just have a trapped air pocket. Purging should eventually remove the all air.

[zephram22]

I finally figured out the problem. The car came from the dealership with a faulty pressure cap. Go a new one and now everything works perfect. I cannot believe that when I took the car to the shop a few days ago they did not check for that.

[zephram22]

Forget it.. I must be an idiot...and I guess the mechanic is too. Thought it was the cap...Nope...Car overheated about 8 times in a 30 mile trip tonight. Lost a good amount of coolant through the surge tank. There is air in the system, that I know. But I can't get a real response from anyone as to whether or not there is a bleed screw on the damn 2002 3.5.

I knew this car was a mistake. I should has bought one that was still in production. At least then I would not keep getting blank stares from mechanics who have never heard of the 3.5 engine.

[protek22]

There is no bleed screw on the Aurora. My previous post covered the scenario you're dealing with pretty thoroughly. It would have been better if you could have located a real Cadillac Northstar mechanic but I guess you have to go with what's available. If you are actually losing coolant that is a sign of overpressure. Plain air in the system wouldn't do that and wouldn't continue to occur. It doesn't look good at this point, but it looks like there could be an internal combustion leak most likely due to the headgasket. I would get a real expert opinion on this.

[zephram22]

Originally Posted by protek22

There is no bleed screw on the Aurora. My previous post covered the scenario you're dealing with pretty thoroughly. It would have been better if you could have located a real Cadillac Northstar mechanic but I guess you have to go with what's available. If you are actually losing coolant that is a sign of overpressure. Plain air in the system wouldn't do that and wouldn't continue to occur. It doesn't look good at this point, but it looks like there could be an internal combustion leak most likely due to the headgasket. I would get a real expert opinion on this.

Well, I know there are no internal leaks. The mechanioc did a combustion gas test a few days ago. No problems. I flushed the system out last night. It should be interesting to see what happens when I drive it today.

[zephram22]

Originally Posted by protek22

There is no bleed screw on the Aurora. My previous post covered the scenario you're dealing with pretty thoroughly. It would have been better if you could have located a real Cadillac Northstar mechanic but I guess you have to go with what's available. If you are actually losing coolant that is a sign of overpressure. Plain air in the system wouldn't do that and wouldn't continue to occur. It doesn't look good at this point, but it looks like there could be an internal combustion leak most likely due to the headgasket. I would get a real expert opinion on this.

I also was pretty sure on the bleed screw. I didn't think there was one. I'm just trying to explore all posibilties since I can't get the cooling system to repressurize itself.

[protek22]

Do you see a stream of bubbles come up in the resevoir, if you open the throttle a bit? Do you still hear the gurgling in the heater core? Exactly what kind of a combustion test did the mechanic do, chemical or with a probe?