Troubleshoot overheating coolant--air bubble?
11-04-2014, 08:23 AM
#1
AudiWorld Member
Thread Starter
Troubleshoot overheating coolant--air bubble?
When the car is started and allowed to idle for a couple minutes, the coolant temperature gauge rises as normal to the center line, and remains stable.
After driving for several minutes, the needle rises to one line right of center. If I don't turn the heat on high and the blower all the way up, it will continue rising. Turning on the cabin heat seems to maintain it around one line right of center.
VCDS shows no codes related to engine temperature or coolant sensors. The only code I am seeing is from a failing EGT probe, which afaik is unrelated (new sensors ordered, btw).
Both auxiliary fans turn on some time after the needle has risen to at least one line right of center.
When I put my hand on the upper radiator hose, it is warm, but not hot. This is after about fifteen minutes of combined idling and slow, low-rpm driving. The lower radiator hose feels cool. If I remember right, flow is in through the top (from the water pump & block), out through the bottom (to the coolant manifold and thermostat).
At this point I feel like it's safe to assume the thermostat is operating correctly, since coolant temp remains generally stable and doesn't just bury the needle after a couple minutes of warmup.
I also suspect the fan switch and fan controllers are operating correctly.
Only thing left I can think of is an air bubble.
When I changed the TB/WP and associated parts back in April, I was unable to remove the hose leading to the heater core (the one near the brake fluid reservoir), so I just filled the coolant reservoir, worked bubbles out as I could, turned the heat up, and let it idle while maintaining fluid level. I'm thinking now that it's cold (eg, this is the first time I've turned on heat in the car since April) maybe I dislodged an air bubble, so it's time to fight with that bleed hose after all.
Thoughts, anyone? Tips on freeing stuck hoses from their pipes?
Thanks,
Sean
After driving for several minutes, the needle rises to one line right of center. If I don't turn the heat on high and the blower all the way up, it will continue rising. Turning on the cabin heat seems to maintain it around one line right of center.
VCDS shows no codes related to engine temperature or coolant sensors. The only code I am seeing is from a failing EGT probe, which afaik is unrelated (new sensors ordered, btw).
Both auxiliary fans turn on some time after the needle has risen to at least one line right of center.
When I put my hand on the upper radiator hose, it is warm, but not hot. This is after about fifteen minutes of combined idling and slow, low-rpm driving. The lower radiator hose feels cool. If I remember right, flow is in through the top (from the water pump & block), out through the bottom (to the coolant manifold and thermostat).
At this point I feel like it's safe to assume the thermostat is operating correctly, since coolant temp remains generally stable and doesn't just bury the needle after a couple minutes of warmup.
I also suspect the fan switch and fan controllers are operating correctly.
Only thing left I can think of is an air bubble.
When I changed the TB/WP and associated parts back in April, I was unable to remove the hose leading to the heater core (the one near the brake fluid reservoir), so I just filled the coolant reservoir, worked bubbles out as I could, turned the heat up, and let it idle while maintaining fluid level. I'm thinking now that it's cold (eg, this is the first time I've turned on heat in the car since April) maybe I dislodged an air bubble, so it's time to fight with that bleed hose after all.
Thoughts, anyone? Tips on freeing stuck hoses from their pipes?
Thanks,
Sean
11-04-2014, 02:01 PM
#2
AudiWorld Super User
Overheating engine with top hose not hot generally is coolant not moving through radiator. What's your oil temp?
11-04-2014, 08:39 PM
#3
11-05-2014, 03:25 AM
#4
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Sounds like you are on the right track with all your diagnoses. Suggest you try bleeding - or at a minimum, raising the front end of the car (as if on ramps) and running the engine from cold (with heater running) to try to eliminate any air pockets.
11-05-2014, 07:32 PM
#5
AudiWorld Member
Thread Starter
More testing this evening. Maybe I misremembered some details, in my original post...here's what I noticed and found.
When I start the car, the coolant temp gauge flips straight up to center. It hasn't been started in about 24 hours, and it's pushing freezing outside...no way the coolant is at operating temperature, so what gives? Is this normal behavior? I don't remember. If someone could check their vehicle and let me know, I'd really appreciate it. I would be amazed if the block held heat for 24 hours in the mid 30s, and if that needle position (straight up at start) isn't normal, maybe I have a sensor or gauge issue rather than a water pump or thermostat problem.
I bled the coolant circuit at the screw next to the throttle body and at the heater core. That hose is no picnic to get off...I used two different picks and a pair of channel locks, plus a tiny dab of grease, and it still took a good half hour to work it loose. No air trapped in the line, but I did make an amusing little fountain with compressed air...good trick, that. The heater is blowing hot air no problem, as well.
After several minutes of driving and idling, and the coolant gauge two lines right of center, the upper rad hose is still warm, the lower rad hose is still cool. Neither auxiliary fan turns on unless I turn the ECON setting off, in which case both fans turn on, but the coolant temperature gauge does not drop. When I turn ECON mode back on, both fans turn off. I have no idea if the fan switch is busted or not, but I figure that's unlikely, and the fans simply do not turn on because the coolant at the fan switch is still cold.
I'm at a loss to explain why the rear coolant temp sensor--the green one--would show any coolant temperature at all if coolant isn't flowing, also why the heater core would blow hot air without coolant flow, and why the car would maintain temperature at idle and slow driving for several minutes, then show a coolant temperature spike.
At this point, I'm stuck thinking this is either the water pump impeller spinning on the shaft, the thermostat not opening but allowing bleed (don't Audi tstats fail closed?), or the CTS is reading wrong, but the physical symptoms don't suggest it's the CTS. The oil temperature during all this is cold...if it came off the line at all, it wasn't by much, and certainly isn't getting to the point I'd consider the car "warm" and ready to lean on the throttle.
If anyone has any suggestions before I tear the whole damn front of the car apart again after six months and 10k miles on warranty replacement parts, I would love to hear them.
This damn well better not be a failed part after six months and <10k miles.
-Sean
When I start the car, the coolant temp gauge flips straight up to center. It hasn't been started in about 24 hours, and it's pushing freezing outside...no way the coolant is at operating temperature, so what gives? Is this normal behavior? I don't remember. If someone could check their vehicle and let me know, I'd really appreciate it. I would be amazed if the block held heat for 24 hours in the mid 30s, and if that needle position (straight up at start) isn't normal, maybe I have a sensor or gauge issue rather than a water pump or thermostat problem.
I bled the coolant circuit at the screw next to the throttle body and at the heater core. That hose is no picnic to get off...I used two different picks and a pair of channel locks, plus a tiny dab of grease, and it still took a good half hour to work it loose. No air trapped in the line, but I did make an amusing little fountain with compressed air...good trick, that. The heater is blowing hot air no problem, as well.
After several minutes of driving and idling, and the coolant gauge two lines right of center, the upper rad hose is still warm, the lower rad hose is still cool. Neither auxiliary fan turns on unless I turn the ECON setting off, in which case both fans turn on, but the coolant temperature gauge does not drop. When I turn ECON mode back on, both fans turn off. I have no idea if the fan switch is busted or not, but I figure that's unlikely, and the fans simply do not turn on because the coolant at the fan switch is still cold.
I'm at a loss to explain why the rear coolant temp sensor--the green one--would show any coolant temperature at all if coolant isn't flowing, also why the heater core would blow hot air without coolant flow, and why the car would maintain temperature at idle and slow driving for several minutes, then show a coolant temperature spike.
At this point, I'm stuck thinking this is either the water pump impeller spinning on the shaft, the thermostat not opening but allowing bleed (don't Audi tstats fail closed?), or the CTS is reading wrong, but the physical symptoms don't suggest it's the CTS. The oil temperature during all this is cold...if it came off the line at all, it wasn't by much, and certainly isn't getting to the point I'd consider the car "warm" and ready to lean on the throttle.
If anyone has any suggestions before I tear the whole damn front of the car apart again after six months and 10k miles on warranty replacement parts, I would love to hear them.
This damn well better not be a failed part after six months and <10k miles.
-Sean
11-06-2014, 01:47 AM
#6
AudiWorld Super User
More testing this evening. Maybe I misremembered some details, in my original post...here's what I noticed and found.
When I start the car, the coolant temp gauge flips straight up to center. It hasn't been started in about 24 hours, and it's pushing freezing outside...no way the coolant is at operating temperature, so what gives? Is this normal behavior? I don't remember. If someone could check their vehicle and let me know, I'd really appreciate it. I would be amazed if the block held heat for 24 hours in the mid 30s, and if that needle position (straight up at start) isn't normal, maybe I have a sensor or gauge issue rather than a water pump or thermostat problem.
I bled the coolant circuit at the screw next to the throttle body and at the heater core. That hose is no picnic to get off...I used two different picks and a pair of channel locks, plus a tiny dab of grease, and it still took a good half hour to work it loose. No air trapped in the line, but I did make an amusing little fountain with compressed air...good trick, that. The heater is blowing hot air no problem, as well.
After several minutes of driving and idling, and the coolant gauge two lines right of center, the upper rad hose is still warm, the lower rad hose is still cool. Neither auxiliary fan turns on unless I turn the ECON setting off, in which case both fans turn on, but the coolant temperature gauge does not drop. When I turn ECON mode back on, both fans turn off. I have no idea if the fan switch is busted or not, but I figure that's unlikely, and the fans simply do not turn on because the coolant at the fan switch is still cold.
I'm at a loss to explain why the rear coolant temp sensor--the green one--would show any coolant temperature at all if coolant isn't flowing, also why the heater core would blow hot air without coolant flow, and why the car would maintain temperature at idle and slow driving for several minutes, then show a coolant temperature spike.
At this point, I'm stuck thinking this is either the water pump impeller spinning on the shaft, the thermostat not opening but allowing bleed (don't Audi tstats fail closed?), or the CTS is reading wrong, but the physical symptoms don't suggest it's the CTS. The oil temperature during all this is cold...if it came off the line at all, it wasn't by much, and certainly isn't getting to the point I'd consider the car "warm" and ready to lean on the throttle.
If anyone has any suggestions before I tear the whole damn front of the car apart again after six months and 10k miles on warranty replacement parts, I would love to hear them.
This damn well better not be a failed part after six months and <10k miles.
-Sean
When I start the car, the coolant temp gauge flips straight up to center. It hasn't been started in about 24 hours, and it's pushing freezing outside...no way the coolant is at operating temperature, so what gives? Is this normal behavior? I don't remember. If someone could check their vehicle and let me know, I'd really appreciate it. I would be amazed if the block held heat for 24 hours in the mid 30s, and if that needle position (straight up at start) isn't normal, maybe I have a sensor or gauge issue rather than a water pump or thermostat problem.
I bled the coolant circuit at the screw next to the throttle body and at the heater core. That hose is no picnic to get off...I used two different picks and a pair of channel locks, plus a tiny dab of grease, and it still took a good half hour to work it loose. No air trapped in the line, but I did make an amusing little fountain with compressed air...good trick, that. The heater is blowing hot air no problem, as well.
After several minutes of driving and idling, and the coolant gauge two lines right of center, the upper rad hose is still warm, the lower rad hose is still cool. Neither auxiliary fan turns on unless I turn the ECON setting off, in which case both fans turn on, but the coolant temperature gauge does not drop. When I turn ECON mode back on, both fans turn off. I have no idea if the fan switch is busted or not, but I figure that's unlikely, and the fans simply do not turn on because the coolant at the fan switch is still cold.
I'm at a loss to explain why the rear coolant temp sensor--the green one--would show any coolant temperature at all if coolant isn't flowing, also why the heater core would blow hot air without coolant flow, and why the car would maintain temperature at idle and slow driving for several minutes, then show a coolant temperature spike.
At this point, I'm stuck thinking this is either the water pump impeller spinning on the shaft, the thermostat not opening but allowing bleed (don't Audi tstats fail closed?), or the CTS is reading wrong, but the physical symptoms don't suggest it's the CTS. The oil temperature during all this is cold...if it came off the line at all, it wasn't by much, and certainly isn't getting to the point I'd consider the car "warm" and ready to lean on the throttle.
If anyone has any suggestions before I tear the whole damn front of the car apart again after six months and 10k miles on warranty replacement parts, I would love to hear them.
This damn well better not be a failed part after six months and <10k miles.
-Sean
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11-07-2014, 11:44 AM
#8
AudiWorld Member
Thread Starter
It was the CTS. "Bad" doesn't begin to describe it...I'll post a photo later. 65K miles on this sensor, and personally as inexpensive and easy as they are to replace when they're not in pieces, and as much trouble as this was to track down and correct, I'm going to call it part of regular maintenance every couple oil changes.
Just happy at this point I didn't have to tear apart the engine looking for debris.
Just happy at this point I didn't have to tear apart the engine looking for debris.
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