Overheating with AC on

[Wolfsbora]

Hi all, I’m having an issue with overheating that just started. My FiST is a 2019 with 47K miles and I’m the original owner. Quite a few parts related to airflow have been upgraded including a Whoosh V3 intercooler (this will be important a bit later in the post). Yesterday was easily in the 90s during the day in Pittsburgh. Obviously, the AC comes in handy for situations like this. Unfortunately when I run it the coolant temp, according to my Cobb AP, ramps up 50 degrees and the overheating light comes on. The Cobb has the car tuned with the Dizzy 93 tune. Sometimes I run the E30 but E85 is tough to come by here (not that this is relevant). My partner drove the car on a 900 mile round trip over the weekend without issue but she barely used the AC, let alone it wasn’t as hot as yesterday.

Coincidentally I just installed a Velossa Tech Big Mouth last week. That is the only mod I’ve done in quite some time.

I’ve researched this and have found people saying it’s the large intercooler blocking the radiator - I’ve had my intercooler on the car for over 3 years through countless hot days and this was never a problem. I don’t believe the fan is the issue since the car stays sub-200 degrees when the AC is off.

Should I upgrade the radiator? Whoosh has the Koyo 36mm Hyper Core NFLO Triple Pass Radiator for over $100 off, making it cheaper than the Mountune. If so, should I upgrade the coolant hoses, too? Anything I else I should do?

I’ve included the list of mods I’ve done to the car over the years for reference. Most can be ignored regarding this issue.

 

[LostInTransit]

Have you had the car actually serviced or a coolant flush? if anything above deals with the coolant system, you could have a failed or failing thermostat or an air bubble in the system. You may need to burp the system and use a more aggressive coolant. make sure that you're actually using the correct coolant for your car and as a last resort if at some point coolants have bene mixed, you could be getting a coolant mix reaction which when mixed the coolant can crystalize and harden causing flow blockage in the system. just to add when burping the system always turn you heater on to low as to allow the coolant to flow through the system

 

[SteveS]

It might be the fan not turning on or stepping up when you turn the AC on.

 

[akiraproject24]

Funny I also have a 2019 with lower miles. Yesterday it was reading 93 degrees out and on my way home from work (fine on highway portion). I noticed my accessport coolant temp had peaked at 216 which Ive never seen that high.

My car has same intercooler as yours but with a whoosh hybrid turbo and tune obviously. My car did have the coolant changed last summer when I did the hybrid turbo install. I also have a highflow cat and manifold and both plus the heat sheild have thermal coating. Anyhow, I'm over in the eastern part of the state near philly and my temps were running high yesterday too.

 

[SteveS]

Funny I also have a 2019 with lower miles. Yesterday it was reading 93 degrees out and on my way home from work (fine on highway portion). I noticed my accessport coolant temp had peaked at 216 which Ive never seen that high.

My car has same intercooler as yours but with a whoosh hybrid turbo and tune obviously. My car did have the coolant changed last summer when I did the hybrid turbo install. I also have a highflow cat and manifold and both plus the heat sheild have thermal coating. Anyhow, I'm over in the eastern part of the state near philly and my temps were running high yesterday too.

216 degrees wouldn't be considered overheating.

We routinely get mid and upper 90s temperatures here and on our FiST we routinely use the AC, and the digital temp graph on the dash always stays right in the middle. Never overheats. It's completely stock.

Obviously running a tune is making the engine work harder, which generates more heat.

But to the OP, check the function of the fan to be sure it's running when the AC is turned on. And also make sure you haven't got low coolant or any air in the cooling system. If the car is truly staying in the 190s running in 90+ weather and just turning on the AC makes it overheat, something is wrong with the systems that compensate for the AC being on. If you were working in the area of the air intake you may have inadvertently unplugged something.

 

[M-Sport fan]

Yeah, as stated previously on my car, I have to switch the AC ON in order to bring the temps down when the temps start climbing fast due to stop and go traffic idling (it also helps drop the temps rapidly when moving after idling in traffic as well).

If I leave the AC off (and therefore the fan, of any speed), the temps will skyrocket in stop and go traffic, whereas once moving at any decent speed, the temps will even sometimes dip into the upper 170s, even on a 95*F day in bright sunshine.

I know that the (non AC turn on temp of the) fan is set to activate at ridiculously high coolant temps in order to help fuel economy/efficiency (and like Intuit claims in order to preclude/prevent carbon 'load up' of the plugs and whole upper cylinder/pistons/valves).

But given how easy it seems to destroy the factory head gaskets with escalating coolant temps, and then crack/warp the head, or 'ovalize' the sleeves, block, deck areas on these engines, I wish that the programming engineers would have erred on the side of preventing that instead.

 

[scooter123]

I have a Mountune 3 pass in my 2019 ST and the day it was installed I saw a 3.5 mpg improvement on the drive home. There is a 3 mile or so 7% grade on I-64 coming out of Virginia into WV and in mid August temps the indicator was at 4 bars on that climb and never wavered. BTW, my car has the full Mountune Induction Kit including the intercooler and I have never had any issues with heat soak or any power loss due to temperature. It doesn't mater if it's mid March or Mid August the car is traction limited in 1st and 2nd gear. It's also why I haven't bothered with a Cobb AP. why boost the power level if your tires won't allow you to see any gain. I'll also note that I've been in many traffic jams with my FiST and since installing the Mountune radiator I only see 4 bars on the temp indicator no matter how hot or cold it is.

BTW, I am cheap about tires, I have a set of Blizzak's for the winter and Firestone all seasons for the rest of the year. As for the original wheels and tires, only dove it for a week with those Firestone 500's before putting them in my basement. Those 17's rode way to harsh and I really don't have any need for "track" tires, they don't last for diddly.

 

[SrsBsns]

I'd recommend doing the radiator. These cars seem to be hit or miss with cooling and I just feel so much better after installing a Mountune on mine. Temps under all conditions (stop-and-go, canyon driving, steep/long inclines, etc.) are so much lower and more importantly, consistent, than when I had the stock radiator. I think the Koyo is fine if it's cheaper than the Mountune. I haven't heard anything bad about it and looks to be almost the same.

I don't think you need to replace the hoses unless they look like they should be replaced. The stock ones are just fine.

 

[TDavis]

#1 thing to do with these cars is get a better rad. I've heard some have problems stock, some haven't. Its a weird mixed bag for some reason. But peoples definition of "overheating" is so different weirdly. ACTUAL overheating would be 240+ and going into limp mode etc. Half the people claiming they've overheated with stock rad probably haven't gotten close to 240.

Can't go wrong with a upgraded rad though. I personally have the Mountune rad, with Bravo Alpha intercooler, Motorcraft 180 T-stat, and with the a/c on in town it never gets above 195 in 95+ degree weather. When you start coasting it cools down FAST

 

[Ludeem1]

It’s possible the radiator just can’t keep up, it was about 95 last weekend and I had the AC on and the fan was super loud, like really loud I was able to hear it from inside the car. I have a Mountune radiator and the temps didn’t go past 195 cruising around town.

 

[Wolfsbora]

Thank you all for your responses! I did 3 flushes using flush and distilled water. I noticed that the distilled water was still coming out slightly orange. I refilled it and now my temps are hovering between 190 to 197 without the AC, up to 215 with it on. I know that temp isn't extreme but even in 90 degree heat here in Pittsburgh my car would run sub-200 with the AC on. I'm probably being paranoid at this point.

 

[FiestaSTdude]

Thank you all for your responses! I did 3 flushes using flush and distilled water. I noticed that the distilled water was still coming out slightly orange. I refilled it and now my temps are hovering between 190 to 197 without the AC, up to 215 with it on. I know that temp isn't extreme but even in 90 degree heat here in Pittsburgh my car would run sub-200 with the AC on. I'm probably being paranoid at this point.

I see my car hit 215 on a regular basis, if you’re in the stock radiator that temp doesn’t surprise me at all. You could always try a bigger radiator, I have the mountune one and never have overheating issues (except for the time my fan quit working)

 

[Wolfsbora]

I see my car hit 215 on a regular basis, if you’re in the stock radiator that temp doesn’t surprise me at all. You could always try a bigger radiator, I have the mountune one and never have overheating issues (except for the time my fan quit working)

Thanks for your reply! It ended up hitting 225 yesterday and I think it would have continued to climb if I hadn't shut it off. Is it safe to assume it's the radiator? And nothing else?

 

[LostInTransit]

based on your comment, you say you did a flush fill, but have you burb the system too? there still could be air pockets in the system

 

[Wolfsbora]

based on your comment, you say you did a flush fill, but have you burb the system too? there still could be air pockets in the system

Are you referring to using the bleeder?

 

[LostInTransit]

Not sure of that term,. But burbing the system implies to placing the car on a hill incline (nose up) and allowing the system to run with the heater on low. This is assuming the system was designed as a closed system. meaning the rad does not have a cap and the system uses the reservoir instead. just to add, if the system has been reinstalled or tampered with and/or a new thermostat was installed.. One should have checked the thermostat before installing it using the boiling water technique. Plus it could also mean the thermostat may have been installed upside down.

 

[Wolfsbora]

I think this will take care of all of my issues. Btw, the fan seems to be functioning as needed so I don't believe that's the issue.

 

[M-Sport fan]

Eventually, I would also like to get all of that order above as well, minus the lower temp thermostat, as it will already run way too cool in the winter for my tastes in combination with everything else listed.

 

[Intuit]

https://www.fiestastforum.com/threads/unable-to-pull-vacuum-on-cooling-system-resolved.28344/

 

[Wolfsbora]

Well, I pulled the trigger on the gear above. What coolant does everyone recommend?