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Just had my coolant flushed and rear axle fluid changed. Drove around yesterday for ~45mins mix of highway and local driving. Engine temp hovered around 180-200 F max, trans fluid did not get above 125 F. Oil and coolant seemed fine.
Strangely - put the heat on and it would blow warm for 5-10 mins and then just start blowing cool. Problem would go away when i turned temp up for a few minutes and then cool again.
What year? Coupe or Convertible? Top Up/On or Off/Down?
I have a '14 Coupe and when the top is off I can have it set to 78 or 80 and it will start off warm but then cools off after a couple minutes. If I turn the heat all the way up to max it will start blowing hot again. I don't have this issue if the top is on. When the top is on everything works fine. No clue why it does that so hopefully someone else knows.
180 - 200 F coolant is normal with the 2015+ thermostat . On a hot day in traffic it can be higher. Transmission temp seems OK.
You just had the coolant flushed and now your heat is intermittent - so how can that affect heat? Check the level in your coolant tank - your car may still be clearing air pockets. Correct coolant mix is 40% Dexcool / 60% water.
Cool air from the heater with the top down / off could be solar heating on the temp sensors making the car "think" heat is not required. The fact that the heater works OK with the top up / on tells you that the controls and sensors are working OK.
180 - 200 F coolant is normal with the 2015+ thermostat . On a hot day in traffic it can be higher. Transmission temp seems OK.
You just had the coolant flushed and now your heat is intermittent - so how can that affect heat? Check the level in your coolant tank - your car may still be clearing air pockets. Correct coolant mix is 40% Dexcool / 60% water.
Cool air from the heater with the top down / off could be solar heating on the temp sensors making the car "think" heat is not required. The fact that the heater works OK with the top up / on tells you that the controls and sensors are working OK.
Ron
Could you elaborate on the solar heating? I've done this when it's 45-55 degrees outside so I'd think that the cool air throughout the open cabin would prevent excess heating of the sensors?
I'm just speculating that sunlight could warm the sensors. What other differences can be caused by roof off / down? I don't think the HVAC really "knows." Warm air on a temperature setting number and HOT air at HI setting is what causes the speculation - what can make the car "think" the car is warmer than it is?
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The interior HVAC system is not intelligent. Don't use it to determine if your coolant system is working. Look at the temps for coolant and oil (obviously if coolant can't shed heat oil temp will go up too as the coolant isn't cooling the oil).
My car at the same temp (72) sometimes blows hot, sometimes blows cold. Depends on a number of factors, including where the car was parked, are the windows open, is the roof off, is it sunny, is it cloudy, what is the outside air temp, etc...
Use the Tour Mode gauge setting, which gives you a digital readout providing much better resolution. With the cruise set at 75 mph with ambient temps in the mid 80s my Z06 M7 will run coolant temps that vary between 188-192, with the oil temp varying between 188 and 190. 2015-2019 C7 Transmissions have a separate cooling system (transmission cooler behind left rear quarter panel for A8s/M7s and an added front cooler for the A8. 2014s just have the rear cooler.
I'm thinking air in the system for it to be intermittent like that. Using the digital temp display readout, my engine temps vary from 190° at lowest (coasting down long hill with ambient temps around 70°), up to 204° highest observed, at traffic lights, etc. But most prevalent temp is ~200°
This may sound dumb, but I had an issue when the driver’s seat was back too far and tripped the limit switch, the heat did not work when the top went down. As soon as the top closed the heat would blast out. So move your seat forward an inch or two and see if that fixes it.
Interesting Bill, I did not know that. My Z51 2014 temp runs a bit hotter than your temps, maybe that is why. I run ~200 on the digital numerical temp readout screen (needle gauge is always at 220).
This may sound dumb, but I had an issue when the driver’s seat was back too far and tripped the limit switch, the heat did not work when the top went down. As soon as the top closed the heat would blast out. So move your seat forward an inch or two and see if that fixes it.
There is a limit switch on the drivers seat that stop the seat when it’s fully back. I’m guessing it’s to stop the motor from running when it can’t go back any further. I have no idea why it effected the heat when the top was opened, but it did.
There is a limit switch on the bulkhead behind each seat. It feels like a tube under the carpet. When the switch is pressed (made) the seat motor will not operate rearward / potentially burn out the motor. Seat memory is also disabled so the seat will not move forward when called for. The fix is to manually bump the seat forward a bit and reset the exit memory position.
When I had my C7 Grand Sport, I didn't like the Heat/AC control.
The problem I found was when the system shut off the heat, when at temp, you get the fresh cool outside air sent.
I found the system worked best when you enable "Recirculate". This uses inside air which is at the temp you want.
So when calling for heat and the cabin air is satisfied, the heat is shut off and you can the heated air from the cabin.
When calling for AC and the cabin air is satisfied, the AC is shut off and you can the cooled air from the cabin. (Not hot outside air)
Seems to me the system is not programmed to blend outside air well with heated/cooled system air.
My 2-cents.
The interior HVAC system is not intelligent. Don't use it to determine if your coolant system is working. Look at the temps for coolant and oil (obviously if coolant can't shed heat oil temp will go up too as the coolant isn't cooling the oil).
My car at the same temp (72) sometimes blows hot, sometimes blows cold. Depends on a number of factors, including where the car was parked, are the windows open, is the roof off, is it sunny, is it cloudy, what is the outside air temp, etc...
agreed that the hvac system in this car is pretty bad.
There have been times in winter when it was in the 20's outside and it would get too hot if I turned the dial past 63
But then 62 would be cold.
There was basically a 20 degree inside temp shift when the dial was moved one degree. It's basically horrible.
I wish it was just an old school dial that went from blue to red as you turned like back in the 90's that physically controlled a valve. Simple and effective, no worthless digital crap relying on a computer to decide how to move the valve.
Operating temps
