Operation during low engine temperatures
03-25-2002, 06:08 AM
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Operation during low engine temperatures
I have a 1997 A6 Quatro Wagon. The coolant temperature indicator is always right on bold line marking the lower acceptable temperature. This is regardless of temperature outside.
I have mentioned the issue to the Audi dealer, however they think it is OK because the computer does not send an alarm. However, being a Mechanical Engineer I understand that operating the engine at low temperatures you loose efficiency which results in loss power, torque, gas mileage etc.
(Facts/thoughts.: The thermostat is just replaced and appearantly working, the indicator may be innacurate).
Does anyone have any thoughts on this issue, or is it typical that the automobile works in the lower indicacted temperature zone.
I have mentioned the issue to the Audi dealer, however they think it is OK because the computer does not send an alarm. However, being a Mechanical Engineer I understand that operating the engine at low temperatures you loose efficiency which results in loss power, torque, gas mileage etc.
(Facts/thoughts.: The thermostat is just replaced and appearantly working, the indicator may be innacurate).
Does anyone have any thoughts on this issue, or is it typical that the automobile works in the lower indicacted temperature zone.
03-25-2002, 07:03 AM
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Maybe they used the wrong thermostat.
to get a better feel for the coolant temperature, use the climate control panel to access the coolant temperature. If it's clearly off spec, take it where you had your thermostat replaced and have them fix their mistake.<ul><li><a href="https://www.audiworld.com/tech/int5.shtml">Accessing Coolant data via climate control</a></li></ul>
03-25-2002, 08:42 AM
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Ditto. If you are concerned, dealer can read out engine temps ...
with VAG scan tool, I believe.
Interestingly, on my Vette, both digital and analog gage readings are available. They agree almost perfectly. On the Impala, I noticed the same thing you have. Dealer checked with scan tool and engine temp was 195F where it belonged, but analog gage showed low in the operating range.
Interestingly, on my Vette, both digital and analog gage readings are available. They agree almost perfectly. On the Impala, I noticed the same thing you have. Dealer checked with scan tool and engine temp was 195F where it belonged, but analog gage showed low in the operating range.
03-25-2002, 09:42 AM
#5
It's the thermostat. Just like a home thermostat, it's what regulates internal water temp...
You can get in in varying ranges, for example, 70C, 75C, 85C, 87C, 90C, 95C, 100C, 110C - although I don't know why people would buy higher than normal (water only) boiling point - maybe for very cold climates.
Depends on where you live, a lower engine temp runs slightly richer and therefore provides more power.
I plan to go lower when I replace the thermostat soon (just hit 60K, so I'm doing belts and water pump). I may even bore the bypass hole slightly bigger to lower the temps even more. Oh yeah, less friction from the water pump and slightly richer mixtures. Don't worry about smog and cruising. That's what close loop is for ;P
Depends on where you live, a lower engine temp runs slightly richer and therefore provides more power.
I plan to go lower when I replace the thermostat soon (just hit 60K, so I'm doing belts and water pump). I may even bore the bypass hole slightly bigger to lower the temps even more. Oh yeah, less friction from the water pump and slightly richer mixtures. Don't worry about smog and cruising. That's what close loop is for ;P
03-25-2002, 10:09 AM
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Re: It's the thermostat. Just like a home thermostat, it's what regulates internal water temp...
Why does your engine run richer and add power when you lower the engine temp? It does not make sense to me. My intuitive mind tells me that the higher the temperature differential, the more power. Further, how does it run more rich. Is that because it burns less portion of the fuel because of the colder temperature? This to me means that the you are not using all the energy in the fuel, and therefor screw both power and fuel consumption. Please clarify.
03-25-2002, 10:45 AM
#7
It's because when an engine is cold, some of the fuel is wasted sitting on the walls of the intake
track or just spit out in raw form. This is because fuel doesn't atomized very well on a cold enginre. The end result is more fuel is dumped to keep the car running, and also the rpm is increased until the engine reaches sufficient temps for it to idle properly with very little air and fuel.
The main indication by the ECU for engine temp is the water temp sensor (nothing new, done from day one of EFI). Therefore the one (uhrmm) cheat to add more fuel is to fool the ECU that the engine is at a cold state. Now, when the engine is warm (the intake track, cylinder head, etc), you will use that fuel. So, this is a trick for people adding forced air induction or nitrous to enrichen the fuel slightly by modifying the voltage of the temp sensor.
Similar effect is achieved when you lower the water temp by changing the thermostat opening temp. The engine will be in a colder state but efficient enough to use all that fuel properly. And you are only talking about a few degrees celsius as I pointed in my early post. I haven't opened up the Audi yet, but I bet it has a 90 if not 95C thermostat in there. The dealer probably put an 85 one or lower.
Thermostats are usually found in cars of colder climates. Go south of the border, Asia, etc, there are no thermostats. The temperature is controlled by the cooling fan, and they operate on a very wide range of engine temps. However, in modern cars with automated climate controls, thermostats are needed for regulation - for the comfort of the passengers that use that heat.
In racing, thermostats add friction and load to the engine, and reduce efficiency in cooling.
BTW, cooler engines have a lesser chance of pinging. Meaning the ECU can delay retarding the standard timing till later.
MPG may suffer slightly but that depends on driving. On cruising, the 02 sensor will tell the ECU to maintain stoich, so MPG on the highway should be as good.
The main indication by the ECU for engine temp is the water temp sensor (nothing new, done from day one of EFI). Therefore the one (uhrmm) cheat to add more fuel is to fool the ECU that the engine is at a cold state. Now, when the engine is warm (the intake track, cylinder head, etc), you will use that fuel. So, this is a trick for people adding forced air induction or nitrous to enrichen the fuel slightly by modifying the voltage of the temp sensor.
Similar effect is achieved when you lower the water temp by changing the thermostat opening temp. The engine will be in a colder state but efficient enough to use all that fuel properly. And you are only talking about a few degrees celsius as I pointed in my early post. I haven't opened up the Audi yet, but I bet it has a 90 if not 95C thermostat in there. The dealer probably put an 85 one or lower.
Thermostats are usually found in cars of colder climates. Go south of the border, Asia, etc, there are no thermostats. The temperature is controlled by the cooling fan, and they operate on a very wide range of engine temps. However, in modern cars with automated climate controls, thermostats are needed for regulation - for the comfort of the passengers that use that heat.
In racing, thermostats add friction and load to the engine, and reduce efficiency in cooling.
BTW, cooler engines have a lesser chance of pinging. Meaning the ECU can delay retarding the standard timing till later.
MPG may suffer slightly but that depends on driving. On cruising, the 02 sensor will tell the ECU to maintain stoich, so MPG on the highway should be as good.
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03-25-2002, 10:56 AM
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Good questions. Your intuition is more correct ...
than the post you are answering, IMO.
Additionallly, IMO, not all information posted on this forum is correct...unfortunately. Sometimes it's because some concepts are difficult to explain without higher math (non-calculus physics, for example), and other times it's because folks don't always realize that what they believe to be truth is not.
Engines are designed to run at a certain internal temperature range. Some of it is power related, but lots is emmisions and economy related, and therefore mandated. Arbitrarily changing thermostats can be counter-productive. True, there are some aftermarket ECM programs which want 160F thermostats vs 195F, but this is a backdoor way to get a little more power in certain situations.
A computer controlled engine runs "rich" or "lean" depending on what has been programmed into it, or if a sensor fails or is altered or disconnected. To run "rich" more fuel is injected. This could legitimately be done by the computer for drivability, especially when the engine is warming up, or to limit combustion temps at high power settings to preclude engine damage. Failure of a component in the engine control system usually puts it in a backup mode where rich is almost always safer than lean.
My $.02
Additionallly, IMO, not all information posted on this forum is correct...unfortunately. Sometimes it's because some concepts are difficult to explain without higher math (non-calculus physics, for example), and other times it's because folks don't always realize that what they believe to be truth is not.
Engines are designed to run at a certain internal temperature range. Some of it is power related, but lots is emmisions and economy related, and therefore mandated. Arbitrarily changing thermostats can be counter-productive. True, there are some aftermarket ECM programs which want 160F thermostats vs 195F, but this is a backdoor way to get a little more power in certain situations.
A computer controlled engine runs "rich" or "lean" depending on what has been programmed into it, or if a sensor fails or is altered or disconnected. To run "rich" more fuel is injected. This could legitimately be done by the computer for drivability, especially when the engine is warming up, or to limit combustion temps at high power settings to preclude engine damage. Failure of a component in the engine control system usually puts it in a backup mode where rich is almost always safer than lean.
My $.02
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