Overheating in traffic...

[Robsa6]

So I've had my A6 for 3 years and the whole duration I've fought an overheating issue in traffic. It started out as a stock 2.7t and overheated in traffic when it was above 80 degrees out. Dumped the mech. fan for an electric fan and it didn't get better and nursed it thru the rest of the summer and spring the next year I put an aluminum rad. off of ebay on it thinking it would solve my issues and yet again no change. Did timing belt, water pump and a low temp thermostat thinking the earlier start temp for circulation may help it out. No go... Found the elec fan inside the rad support not working and replaced it with another used one I had laying around. Got better but not good. Installed a FMIC after I went stage 3 and while knowing it may be a bad idea I bought two 7" elec fans for the condenser above the FMIC and a dual fan controller for the inward fans to combat the issue. Now I'm getting somewhere right? Nope... Still hot and seems like it's getting worse. So I thought about the fan i replaced the mech. fan with and it was only rated for 1400 CFM hmmm ok went to summit racing and got the Zigo 14" fan rated for 2800CFM and was thinking I finally got the fix for the problem and again was let down. I know it's not just my gauge showing wrong as it will boil out the coolant at the tank after too much in traffic with it. (I just gave myself second degree burns on my left arm because the threads were stripped out of my old cap and it blew off while I was trying to let some pressure off. ) New expansion tank, new radiator, new fans, new, new, new! Still hot after twenty minutes in traffic.

I've pressure tested the system and it's held 15 PSI for an hour so I feel the system is holding pressure, It's got hot heat so I feel like the coolant is circulating, I'm running straight distilled water right now because it cools better than Antifreeze mixed.

So a little about how the fans operate and while this is backyard as hell and I wouldn't have done this if I wasn't forced to by POs "repairs" is this:
A/C pump is on a relayed switch to activate the inner fans when the pump is running (Always cool A/C even when the car is hot) and the 2 7" fans are on the controller set to cycle the fans on low speed at 185 and high speed at 197 and they run most of the time when the car is running in slow speed traffic. I mentioned this to say that the car will cool itself right off to normal temps with the A/C pump unplugged and the 4 fans running. I'm getting ready to rewire the pump with the low pressure/high pressure switch in line to cycle the compressor as I know it's no good for the pump to run with no oil but I'm doubtful it's gonna make a big difference in the temp of the car. Or is the pump running unswitched like I've got it causing lots of extra heat?

Oh and the low temp thermostat is long gone as is the Aluminum radiator in favor for a replacement from AutoZone which was the larger of the two cores offered. Please anyone who's got any ideas or have been thru the FMIC thing and conquered the high temp thing let me know what you did.
Thanks in advance
Burning up in Georgia!

Also notable is the car has 240k on it and in the middle of this the engine was swapped for a lower mileage one with 90k on it. No change

[Royal769sr]

In for results

Sent from my SM-G930T using Tapatalk

[brokenwrench]

PURE WATER HAS A LOWER THERMAL TRANSFER COEFFICIENT THAN PURE ANTIFREEZE!!!!! Sorry, but everyone needs to know that. If you're trying to transfer as much heat as possible, use straight antifreeze.

While I don't have this issue with my current car, when I've seen it before it's usually either a bubble in the coolant, restricted coolant flow (i.e. crud buildup in the coolant lines or bad thermostat), a problem with the AC system, or a bad radiator fan. A bad head gasket can cause it, but you said you changed the engine out. Are you sure all your fans are working properly? Have you tried driving in the same ambient temp without your AC on (miserable to try, I know, but important to determine the cause)? If the only thing that triggers the condition is your AC being on/off, then that should be your only focus. How clean is your AC condenser? If you haven't tried it yet, you might find someone who can pressure wash the front of your car to clear out any crud clogging the air flow through your condenser.

Also, I'm not sure what the coolant bleeding procedure is for this engine yet, but do you hear any gurgling in the coolant when the engine rpm changes?

[glennda5id]

PURE WATER HAS A LOWER THERMAL TRANSFER COEFFICIENT THAN PURE ANTIFREEZE!!!!! Sorry, but everyone needs to know that. If you're trying to transfer as much heat as possible, use straight antifreeze.

I believe you have that backwards.

[brokenwrench]

I believe you have that backwards.

Nope. That statement, while difficult to prove with scholarly papers, is based partly on 20 years of experience designing and building engines and partly from personal experience. While the heat capacity of water is higher, the thermal transfer rates are slightly better with antifreeze. Running pure antifreeze in the winter keeps the engine from fully warming up, whereas adding percentages of water allows the engine to run warmer.

The best I can tell, it has to do with the slightly higher boiling point of antifreeze vs water. For the same volume of coolant, the radiator inlet will run at a slightly higher temperature, allowing improved thermal transfer rates through the radiator.

[Robsa6]

Thanks for the reply brokenwrench. I've always heard that water is better at cooling than antifreeze too. (Several years hanging around nascar shops and a lifetime of surfing hotrod shit on the internet) I do know racecars all use water exclusively and that's evidence enough for me but I will likely try the antifreeze thing since I've been thru a plethora of changes trying to chase this issue. I do know my fans are working as the two on the front working off the controller will cycle with the car off and several times with it running I've had the hood up and they are spinning. I even did the paper test to make sure the fans were wired correctly as pushers on front and pullers on back. I also know the rear fans are working when I turn on the A/C because the rocker switch goes to a relay that runs both and the pump. If I get out and manually disconnect the A/C the car runs perfectly cool no problems it'll even bring it down from a tick or even two ticks past center on the gauge fairly quickly while idling. I don't hear any gurgling and know the burp procedure for this car. I also have hot heat so I'm fairly certain I've got the air out as the heater core is the highest place in the system.

To touch back on the antifreeze thing it may very well cool better if it's got any "wetting" agents allowing the liquid to coat the inside surfaces better than aerated water might. Same theory as redline water wetter and purple ice which I've read that the antifreeze used now is usually pre mixed with these ingredients making us both right is suppose unless you have a different theory as to why antifreeze seems to cool better. Thanks again and I look forward to any more insight, questions, or suggestions any of you all might have!

[glennda5id]

Do these fans have a high and a low? Maybe the fans are coming on, but not in high mode?

[AudiTuner1187]

Seems to me that your getting too much heat from your ac. As prevoisly said, check your condenser fins. Possibly too much freon in the system? This overworks your compressor which creates more heat on top of higher pressures which means higher temperatures. Your compressor could be on its way out but, I would think you would hear some noises from it.

Sent from my SM-J320P using Audizine mobile app

[Robsa6]

Seems to me that your getting too much heat from your ac. As prevoisly said, check your condenser fins. Possibly too much freon in the system? This overworks your compressor which creates more heat on top of higher pressures which means higher temperatures. Your compressor could be on its way out but, I would think you would hear some noises from it.

Sent from my SM-J320P using Audizine mobile app

Thanks for the reply! The compressor is newish and the fans will def. go low and high I've heard the difference in them. The Freon level is what is supposed to be in there based on temp at the time of checking the pressures. The A/C is either on or off is the only thing that I keep coming to as far as an issue rather than cycling when the pressure is too low or too high. I'd think the problem might be the pressure gets too high in taffic because of lack of airflow being as I've only got 2 7" fans on the upper portion of the condenser?

[Robsa6]

Condenser was cleaned and "brushed" when I last reinstalled the FMIC to straighten up the fins on it and I think it's "clear" as the fns on the inside of the rad will suck paper to the condenser and the FMIC when testing

[AudiTuner1187]

So, after re reading a bit more thorough, you not having pressure switches hooked up is your problem. Your compressor is supposed to run till it hits high pressure (condenser cant remove all that heat as fast as freon is absorbing) compressor shuts off till low pressure switch is activated (lets pressures equalize) and kicks back on.
If your ac never shuts down, you will never keep up.

Sent from my SM-J320P using Audizine mobile app

[Robsa6]

That's what I have been going back to too. I guess I wanted to hear "yeah dumbass the a/c will cause ungodly heat hooked up like that" Thanks

[AMcoCR]

I don't know if this is a close scenario but with my 4.2 I had a similar issue that was resolved once I turned the heat all the way up until the engine temp dropped. (It was like an oven in the car.) Then went back to Auto and never had the problem again. This tip came from an independent Audi workshop near me.

[Robsa6]

I don't know if this is a close scenario but with my 4.2 I had a similar issue that was resolved once I turned the heat all the way up until the engine temp dropped. (It was like an oven in the car.) Then went back to Auto and never had the problem again. This tip came from an independent Audi workshop near me.

I've done the whole heat to drop temps thing and while it works I'm not lucky enough to have had it solve my problem. Thinking that would help burp some air out of the system and cool the car better if it did have air in it. The belly pan is also a very likely culprit but it doesn't really make sense to me that it would help in traffic or idling .

[CAL4.2]

I don't know if this is a close scenario but with my 4.2 I had a similar issue that was resolved once I turned the heat all the way up until the engine temp dropped. (It was like an oven in the car.) Then went back to Auto and never had the problem again. This tip came from an independent Audi workshop near me.

Yes, that trick helps in a pinch to get the heat down. The underlying problem is still there, which is likely a dying/dead electric fan, fan clutch, or both (assuming thermostat is fine).

[Robsa6]

So I'm parting the car out and building an S4... Got a sweet deal on an 01.5 automatic and it needs a transmission and seeing as the A6 is a 6speed it makes sense to pull the transmission and rebuild the 1-2 shift collar and synchros and swap the car over. It's already a stage 3 car and doesn't have any cooling issues as of now LOL. Thanks for the help guys I do believe the problem was is the combination of the pressure switch being jumped and the fmic overwhelming the cooling system.