Chrysler minivan cooling system pressure

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Just browsing around some discussions here, it seem that some members have some in depth understanding of automotive cooling systems.

Here's what I got. I'll get to the problem first and than fill in more detail.
It's a 2005 Chrysler Town & Country minivan with the 3.3l motor.
I believe the cooling system pressure is low. When the engine is at operating temperature, I think the upper radiator hose is too soft. It's under pressure but my non professional experience is suggesting to me that a hose on a 15psi cooling system feels harder. It's not seemed to be a problem here in flatland, but when we took it on a road trip, we stopped at a scenic overlook at 7000 ft, we shut it off, for about a half hour, and when we came back to the vehicle, there was a trail of coolant running away from it.

We bought it almost 5 years ago. It was a one family owned car with maintenance records since new, was in a southern state till 2015, so 99% rust free, 100k miles. It had a leaking radiator and had a Bars Leak like sealer in it. I flushed out the cooling system and installed a cheap new radiator, filled it with new antifreeze & distilled water. Now, I think when you take off the radiator cap there should be coolant right up the the bottom of the cap. But I keep checking it and it keeps needing just a little bit of coolant added. There's no apparent leaks. I rented test kit shows no exhaust gasses in the coolant. We went on our 5000 mile road trip. I took extra coolant along. Replaced the radiator cap once or twice. It's been 2 years, I think there was a little bit of coolant under the car a few times on the trip. I think the cheap replacement radiator plus removing the cap to check it too many times has caused the cap to be not seating tight enough to fully pressurize the system. I'm not checking the coolant level at the radiator cap frequently any more. The last time I did check it, it was full like I expected it should be. I can drive it like nothing's wrong but It can't be a good thing if the cooling system pressure is not where it should be. The only way I can think of to test the pressure is sacrifice a radiator hose by installing a pressure test fitting on it. On a hard fast highway drive or at high altitude, I suspect the engine is not being cooled as well as it should be. I wanna do another road trip.

Anyway it's supposed to be my road trip car but I'm driving it now cus my daily driver has a emissions problem and the license has expired, and fixing the emissions means pulling the gas tank, and there are other projects in line ahead of it.
March 2022 will be 5 years I've owned the minivan. We've put 10k miles on it 5k of which was one 28 day trip.
 
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Fill the rad to the brim and replace the pressure cap with an OE only part, then overfill the expansion reservoir by a couple of inches and recheck after a few drive cycles.
 
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You're overthinking this. It doesn't overheat or lose coolant, right?
 
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You're overthinking this. It doesn't overheat or lose coolant, right?
A little unclear but he said "when we took it on a road trip, we stopped at a scenic overlook at 7000 ft, we shut it off, for about a half hour, and when we came back to the vehicle, there was a trail of coolant running away from it."
 
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When you take the van on a trip, do you heard the cooling fans running at some point???

Are you sure the trail of what you describe as coolant is not the moisture from the AC.
 

johnd393

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It's not A/C condensate or the radiator fan not working. I just wondered if anybody ever had to actually measure cooling system pressure.
It's just something I'd like to fix before taking the van on another road trip. My daily driving is not severe enough for any of this coolant loss to happen.
 
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I remember a slow coolant loss on our 05 T&C 3.8. Finally found that it was leaking from the upper radiator hose where it connected to the thermostat housing. It would drip onto the exhaust and burn off, plus you couldn’t see it from the top, so it took me a while to find.
 
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Lots of guesswork here. If it’s leaking coolant, there’s where to start. Get under it and see where it’s coming from.

also, why are you topping off the radiator and not the expansion tank?

water pump is on passenger side of vehicle. They are generally long lasting pumps on these, to about 150k miles. However, it’s also 16 years old, so it may be time. Both heater hoses should be checked as well.
 

johnd393

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Water pump has been replaced by the prevoius owner. I got records & recepts for everything that's been done to it. A lot of stuff was done at the dealer. I'd have to look up when the pump was replaced. It's at 110k miles now
 
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The radiator was replaced with a cheap unit? I've seen these with a problem around the rad cap and where the tube goes to the over flow tank. The nipple on top of the rad for the small over flow tube may be too small so the hose does not fit tightly creating an occasional leak.

The rad cap is pulled down against a seal by ramps as you twist it when installing. These ramps my be too small. Bending/squeezing the tangs or tabs on the cap, that engage the ramps, might help the cap to fit tighter and seal better.

The cap has two seals, the center/smaller seal mounts on a spring loaded plunger and mates with a circular seat in the top of the rad. This regulates system pressure. Look very closely at both of these surfaces, seal and seat, for nicks or other imperfections.

The quality of the plastic tanks on aftermarket radiators can be very poor and not made to exact dimensions where the rad cap installs.
 

johnd393

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The radiator was replaced with a cheap unit? I've seen these with a problem around the rad cap and where the tube goes to the over flow tank. The nipple on top of the rad for the small over flow tube may be too small so the hose does not fit tightly creating an occasional leak.

The rad cap is pulled down against a seal by ramps as you twist it when installing. These ramps my be too small. Bending/squeezing the tangs or tabs on the cap, that engage the ramps, might help the cap to fit tighter and seal better.

The cap has two seals, the center/smaller seal mounts on a spring loaded plunger and mates with a circular seat in the top of the rad. This regulates system pressure. Look very closely at both of these surfaces, seal and seat, for nicks or other imperfections.

The quality of the plastic tanks on aftermarket radiators can be very poor and not made to exact dimensions where the rad cap installs.
Exactly.
 
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Most auto parts stores in my area have a coolant system pressure tester. It has a PSI gauge. You can hook it to the radiator or reservoir, crank the car up and monitor the pressure.
 

johnd393

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I didn't think those testers could do that. I'll have to look into it. I know you can pump pressure into a system, when cold with the engine off, to check for leaks. I improvised a way to do that. It held pressure. It lost a little over hours, maybe a day, I don't remember, but I couldn't be sure my improvised apparatus was a perfect seal.
Took it for a ride while watching temperature as reported by a scan tool. While the dash gauge pointer was steady just a needle width below the center mark, the scanner reported from 194 to 209. Maybe the dash gauge is just slow to respond. It was too short a stop & go trip to draw any conclusions.
 
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The gauge on your dash will not move at all if the temp is in the normal acceptable [to the computer] range. They are made like this so customers will not worry and return to the dealer claiming their car is not running at a steady temp.
 

johnd393

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Went on some highway drives with the scanner displaying coolant temp. I'm seeing too much 200 to 210 degrees for the mild weather and a 195 degree thermostat. I'm thinking either a there's a a temperature sensor that's a little off or maybe a new thermostat is a good idea. It might not be enough temperature difference to matter, but I used to be a Measurement & Control technician in a previous millennium.
I also thought the temperature was varying too suddenly, like I think I've seen when a cooling system is low on coolant.

Now here's sum weird chit. Sometimes at a stop light, if I ease the brake just a little so that it can try to creep forward, sometimes there is a pulsation in that creep that is in time with the lights flickering. And than at a stop when the lights were not flickering, the creep was steady. I have not repeated this enough times to know if it's a real thing or just random worn brake thing. If the brake is fully released the pulsation is not felt.
 
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If you're wanting to replace the thermostat, use an oem only part. They tend to be more consistent than aftermarket.
 
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I put a pressure gauge on my Gen Coupe 2L turbo once. I have a manual fan controller. The pressure is normally around 10 psi but when it gets up to 210F then it gets near 16 psi the cap pressure setting. Set the fan at 205F and watch the pressure and fan do a cycle dance.
 

johnd393

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I have a 1984 Corvette, on which, the radiator fan is controlled by a simple temperature switch that switches on at 238 degrees. That's how it works. It turns out that the boiling point of the coolant mix under pressure is like 268.
 

johnd393

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The dealer wanted $25 for the thermostat and they didn't stock it. Their price for the gasket was $40. Even the guy behind the counter thought it was a unusual price. Picked up a thermostat & gasket at Autozone. Got the cheaper $10 one with one year guaranty. It looks right.
 
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