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Discussion Starter #1 (Edited)
I am somewhat familiar with bleeding the cooling system of air in a 1996 Chrysler Concorde with a 3.5L engine, but here of late, I can't seem to get all of the air removed from the system.

If you have been reading some of my previous posts, I replaced the water pump about 2 months ago, bled the system of air, and all has been well (with the cooling system) since then.

Yesterday, I drove 100 miles to Winston-Salem, and when I parked the car, I lifted the hood to check the overflow tank, and it appeared empty to me. I placed my hand on the radiator cap, and it did not feel hot, so I gently broke the seal, and all of a sudden, coolant began bubbling out.

I immediately tightened the cap, and all seemed well until we began our trip home about 2 hours later, and I noticed the engine temp was elevated somewhat, so I pulled over to check things out. Nothing was leaking, and since the engine temp was not badly elevated, I hit the interstate highway, and the engine temp stayed close to normal at highway speeds.

However, after arriving in our hometown, I noticed the engine temps rising again a bit, but not too bad (about the 10:00 - 10:30 O'clock position), so I assume air must be in trapped in the coolant.

This morning, thinking the air had worked it's way back to the overflow bottle, we started driving around town, and I noticed the temp rising to the 11:00 O'clock position, so I turned around and went home to manually bleed the system of air.

I hooked up some clear tubing to the check valve on the thermostat housing, run the other end of the tube into an empty coolant jug, and cracked the valve to let any air escape (engine running). Some air came out moments later, and then it seemed like the air in the tubing began to bubble like foam. This went on for what seemed like minutes, although I only collected about a quart of coolant in the bottle.

I have never seen air escape this way. Is this normal, or is it a sign of a blown head gasket? Should I try bleeding the system again tomorrow with a cold engine and loose radiator cap?

The engine seems to be running well, and I don’t recall seeing steam from a hot tailpipe just yet.
 

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I am somewhat familiar with bleeding the cooling system of air in a 1996 Chrysler Concorde with a 3.5L engine,...
Be sure to follow the procedure in the FSM.

Does the 1st gen. have an actual radiator cap, and the overflow bottle is vented to ambient air (i.e., is not pressurized)? I assume that the check valve you refer to is a bleeder valve, and that the FSM procedure involves making sure there is plenty of coolant in the overflow bottle to ensure that the system can pull make-up coolant into the radiator as it cools down and you need to check the level in the bottle and add coolant as needed between the first couple of warmup cycles after refilling and bleeding the system.

But in any case, I’d make sure you follow the FSM procedure exactly thru a couple of warm-up/cool-down cycle before coming to any conclusions.
 

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Also, 2nd geners have found that bleeding with the car on an incline with front end higher than rear end helps ensure air rises to the bleeder when bleeding seems to be a problem. Could be the case with 1st gens. too. But really, making sure there is adequate coolant in the reservoir thru a couple of warm-up/cool-down cycles should be the key to burping out the last bit of air.
 

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i hope you are putting coolant back in as you bleed.
you should never try removing the cap on a hot engine.
it's under pressure.
 

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i hope you are putting coolant back in as you bleed...
= follow FSM procedure.

...you should never try removing the cap on a hot engine.
it's under pressure.
It’s actually worse than that. The pressure raises the boiling point, so with it under pressure, the coolant could be well above the boiling point that would apply at ambient pressure.

So - boiling point of 50/50 coolant at ambient pressure is 223°F. Let’s say it’s under around 14 psi, so it’s boiling point is now about 250°F. Let’s say it’s temperature is 240°F. So it’s not boiling because of the pressure. But - if you open the cap, suddenly, the pressure drops to ambient, which drops the boiling point back to 223°F - but it’s at 240°F, which is 17°F above it’s boiling point. So what you get is what’s called flash steam, which is a violent expansion of the liquid into a mix of boiling hot liquid and steam coming at you - dangerous - feel the burn!
 

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Discussion Starter #6 (Edited)
Much agreed about the danger of cracking the coolant cap with hot coolant inside the system, and it was a boo-boo on my part, but I have cracked and removed the cap on many warm engines (with the engine running) with little to no issues. It's after the engine has been cut off when things become dangerous (speaking of my own experience here).

With that said, the coolant systems of these cab-forward designed Chryslers are unlike anything I have encountered before - including two Dodge Caravans I have owned.

I was talking to a radiator mechanic about my problem yesterday, and he said these cars have a tapered front end which causes the radiator to sit lower than the top of the engine, so Chrysler had to move the coolant cap to higher location. Thanks for the incline tip, Peva. That makes a lot of sense.

Today, I tried to bleed the system of air, but the system had little or no air to bleed. The cooling fans are working, and I am wondering if the thermostat is suspect after seeing the temps go above normal again. I replaced the thermostat in 2013 (engine was running cooler than normal), so I may replace it again since it is so easy to get to.
 

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Discussion Starter #7
Could the temp sending unit be faulty? In all my years of driving, I have never seen one go bad, but there is always the first time.
 

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just being sure peva. of all steps above, he doesn't say level in bottle or if he's adding.

but like in the first post, if it's hot and nothing in the bottle, it's low.
 

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just being sure peva. of all steps above, he doesn't say level in bottle or if he's adding.

but like in the first post, if it's hot and nothing in the bottle, it's low.
No problem. I was reinforcing what you were saying on both adding coolant and not relieving pressure on a warmed up or hot system.
 

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Could the temp sending unit be faulty? In all my years of driving, I have never seen one go bad, but there is always the first time.
Possible, but I’d be surprised.

If you replace it, I always recommend going only with OEM from the dealer on sensors because calibration tolerances and quality are generally a lot looser in aftermarket than for OEM parts.

(I worked for an OEM manufacturer, and I know for a fact that production quality fallout often gets sold into the aftermarket. When we had a run of parts that were out of OEM specs., our sales department had a special phone number for one of, at the time, the “big three” to call to sell off those parts into the aftermarket at a bargain price. Also, on a given part, there are generally two acceptance specs. - one for OEM, and a much looser spec. for aftermarket. We see examples of this on this forum on the oil pressure sensors for our cars - people often replace a leaking or “low pressure light” sensor with aftermarket on a car with good oil pressure, and still get the low pressure light at idle - replace with OEM sensor, problem gone.)
 
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Discussion Starter #11 (Edited)
Thanks for the info, Peva. I'll keep it in mind if I change a sensor.

As for the overheating problem, I replaced the old thermostat today, but the engine temp is still running slightly above normal for such a cool day, although I don't think there is much (if any) air in the system after doing a bleed off. (I made sure to top off the coolant level from previous bleed offs this week too.)

Even so, I am glad I changed the thermostat since the new one (Stant OE 195°) has a tiny jiggly valve to help bleed off trapped air.

My next step is to check the temp sensor. I have a multi-meter, but I am not an expert in this area. Is there any other sensor that can cause a 1996 Concorde (3.5L engine) to run hot? PCM maybe? If a sensor is bad, wouldn't that make the fans run full time, or not at all?
 

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How old is the radiator? Have you ruled out it being clogged?
 

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Discussion Starter #14
What's a normal reading look like on a given 1st generation Chrysler temperature gauge anyway?

Will the needle position vary from thermostat to thermostat? (speaking of quality brands here)

So far, the needle position on the new thermostat sits a bit higher than the previous t'stat did (both rated at 195°), although I haven't seen the new one read much past the 10:30 mark yet - however, the ambient temps have been below normal of late, but the high should reach near 70 tomorrow.
 

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rusty said:
...Will the needle position vary from thermostat to thermostat? (speaking of quality brands here)...
Very possible.

On 2nd gen, the brand of thermostat can make a noticeable difference in how fast the engine heats up and what temperature it settles out at - I would think that would be true with 1st gen as well. This is due to big differences in the designs of the thermostats from one manufacturer to another even though the nominal temperature ratings are the same, as well as unit to unit variations of the same manufacturer’s part due to poor quality control and looser tolerance specs. on parts diverted to aftermarket. It can even make a difference with the OEM brand purchased in aftermarket vs. the same part purchased from a dealer (because the production tolerance specs. are generally a bit tighter for the OEM part).

On my 3.2 2nd gen, I put in the Gates (OEM brand) from aftermarket, and the engine was very slow warming up, and it settled out at a noticeably lower reading on the gage. People here suggested replacing it again with a dealer part (the same Gates part), so I did, and the engine temperature behaved normally after that. Other people had experienced the same thing.

Is it possible to install the thermostat backwards on 1st gen? I ask because on 2nd gen 3.2/3.5, it was possible in many brands of t-stat, and you’d get overheating if that was done.

You may already know this, but it is a good idea to check for opening of a new thermostat at the correct temperature, and that it opens and closes fully, in a pan of water on the stove using an accurate thermometer. It’s not unheard of to get a bad one out of the box, even with an OEM part from the dealer.
 

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Very possible.

On 2nd gen, the brand of thermostat can make a noticeable difference in how fast the engine heats up and what temperature it settles out at - I would think that would be true with 1st gen as well. This is due to big differences in the designs of the thermostats from one manufacturer to another even though the nominal temperature ratings are the same, as well as unit to unit variations of the same manufacturer’s part due to poor quality control and looser tolerance specs. on parts diverted to aftermarket. It can even make a difference with the OEM brand purchased in aftermarket vs. the same part purchased from a dealer (because the production tolerance specs. are generally a bit tighter for the OEM part).

On my 3.2 2nd gen, I put in the Gates (OEM brand) from aftermarket, and the engine was very slow warming up, and it settled out at a noticeably lower reading on the gage. People here suggested replacing it again with a dealer part (the same Gates part), so I did, and the engine temperature behaved normally after that. Other people had experienced the same thing.

Is it possible to install the thermostat backwards on 1st gen? I ask because on 2nd gen 3.2/3.5, it was possible in many brands of t-stat, and you’d get overheating if that was done.

You may already know this, but it is a good idea to check for opening of a new thermostat at the correct temperature, and that it opens and closes fully, in a pan of water on the stove using an accurate thermometer. It’s not unheard of to get a bad one out of the box, even with an OEM part from the dealer.
By backwards, do you mean upside down or spun around 180 degrees? if the latter, then yes for sure. Last one I installed was a "high flow" stat from AutoZone. It had a mark to tell which way to point toward the radiator but not all have those I don't think. Honestly, I think most people just sit it in any which way as long as it's not upside down and don't even think about it.
 

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Discussion Starter #18
Very possible.

On 2nd gen, the brand of thermostat can make a noticeable difference in how fast the engine heats up and what temperature it settles out at - I would think that would be true with 1st gen as well. This is due to big differences in the designs of the thermostats from one manufacturer to another even though the nominal temperature ratings are the same, as well as unit to unit variations of the same manufacturer’s part due to poor quality control and looser tolerance specs. on parts diverted to aftermarket. It can even make a difference with the OEM brand purchased in aftermarket vs. the same part purchased from a dealer (because the production tolerance specs. are generally a bit tighter for the OEM part).

On my 3.2 2nd gen, I put in the Gates (OEM brand) from aftermarket, and the engine was very slow warming up, and it settled out at a noticeably lower reading on the gage. People here suggested replacing it again with a dealer part (the same Gates part), so I did, and the engine temperature behaved normally after that. Other people had experienced the same thing.

Is it possible to install the thermostat backwards on 1st gen? I ask because on 2nd gen 3.2/3.5, it was possible in many brands of t-stat, and you’d get overheating if that was done.

You may already know this, but it is a good idea to check for opening of a new thermostat at the correct temperature, and that it opens and closes fully, in a pan of water on the stove using an accurate thermometer. It’s not unheard of to get a bad one out of the box, even with an OEM part from the dealer.
That's a very good idea, and I did not do that.

So far, this new Stant OE seems to be holding it's own, so I guess that tells me the old unit was indeed failing. However, I'll know more if we get some temps in the 70s and 80s.
 

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I haven't had this particular car but on several of my dodges I've had great luck bleeding them by, while the engine is cold, installing a heater core backflushing kit, leaving the cap on the tee open, then holding a milk jug full of distilled water upside over the radiator cap opening and squeezing the jug to force water into the system until the bubbles stop coming out of the tee.

Then I fill the radiator with antifreeze until the color starts to show at the tee then seal the whole thing up and usually all the air is gone and the mixture and everything is perfect.
 

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Thanks for the info, Peva. I'll keep it in mind if I change a sensor.

As for the overheating problem, I replaced the old thermostat today, but the engine temp is still running slightly above normal for such a cool day, although I don't think there is much (if any) air in the system after doing a bleed off. (I made sure to top off the coolant level from previous bleed offs this week too.)

Even so, I am glad I changed the thermostat since the new one (Stant OE 195°) has a tiny jiggly valve to help bleed off trapped air.

My next step is to check the temp sensor. I have a multi-meter, but I am not an expert in this area. Is there any other sensor that can cause a 1996 Concorde (3.5L engine) to run hot? PCM maybe? If a sensor is bad, wouldn't that make the fans run full time, or not at all?
195??
maybe the 1G's call for a different part but isn't that thermostat supposed to be rated at 185?
 
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