Help solve a debate - engine cooling and AC

[tri-pedaler]

I've gotten different advice on this issue, so I thought I'd ask the experts...

Our cars love to overheat, and I compete in a Street class so I can't upgrade the radiator. I run the heat during and pop the hood in between runs.

Someone suggested also running the AC when stopped to activate the system fans. Otherwise you can't run the radiator fans when stopped.

Others say (rightly) that this adds heat to the system when the AC cycles.

My question is: are the gains from running the fan worth running the AC when stopped, or not?

 

[Frisk]

you're literally pumping heat back to the engine by running your AC. I couldn't imagine that fans are enough to offset this in any way. All mechanical losses in the AC system are going to be converted to heat as well.

You'd probably be better off looking into installing a fan override switch of some kind rather than running the AC.

 

[TDavis]

Just get a radiator. Problem solved lol.
Putting A/C on puts more stress on the engine. Theres a reason in the hills and mountains in Arizona there are literal street signs that tell you to turn your a/c off to keep the car cooler when going through the hills

 

[Dialcaliper]

Running the A/C is absolutely worse for cooling in all situations. The compressor adds mechanical load to the engine (which puts additional heat into the coolant) and to make matters worse, the A/C condenser is in front of the radiator, and heats up the cooling air going to the radiator - literally pumping heat from the cabinDouble whammy.

We only have a single fan, so if the engine temp is high, the fan will be running, A/C or no A/C. We don’t have a separate A/C fan like many older cars, and even then you’re still making the heat load worse. The thing to do in that situation (two fans) is Hotwire the A/C fan relay to come on whenever the primary engine fan comes on, but don’t turn on the A/C compressor!

One old trick you *can* do is turn the cabin heat (to foot or face vents) on full blast, as the heater core is effectively a small radiator dumping heat from the engine coolant. It will be miserable on a hot day, but will cool the engine faster. Many a vintage car has made it up a hill on a hot day by running the heater in 100F+ degree heat.

But don’t turn on the defroster, as that also engages the A/C compressor. If that seems counterintuitive, it is. The goal of the defrost is not just to heat the air to the windshield, but to dry it out first (by cooling it to condense out moisture) and then heating the dry air back up. My pet peeve about modern cars is there’s no option to just send normal hot air out the defrost vents without “conditioning” it with the A/C on.

 

[LostInTransit]

Seems to me that someone has been following my thread about removing the Active shutter system.. So far we're happy to report that our MPG's have reached 23.8 and this is a new high because for more than 3 years, (not knowing the van had these slats) they were closed off. Again for more than 3 years our city MPG's would never get any higher than 23.0 and as of this afternoon we reached a new high and as far as we know. it's still accumulating and with a roadtrip coming up.. we expect to see even better fuel economy.

With that in mind.. Automakers claim these shutter system would close while at highway speeds to allow for better fuel economy.. doesn't say anything about keeping the engine and trans cool. But now that we've removed 10 of the 14 slats.. it's clear we're cooling the engine more and gaining better fuel economy.

I'm saying this just to see if any of you have actually edited/altered or removed this shutter system on car built after 2015. it could make a big difference.

Our testing will continue in a few days.

 

[dhminer]

Seems to me that someone has been following my thread about removing the Active shutter system.. So far we're happy to report that our MPG's have reached 23.8 and this is a new high because for more than 3 years, (not knowing the van had these slats) they were closed off. Again for more than 3 years our city MPG's would never get any higher than 23.0 and as of this afternoon we reached a new high and as far as we know. it's still accumulating and with a roadtrip coming up.. we expect to see even better fuel economy.

With that in mind.. Automakers claim these shutter system would close while at highway speeds to allow for better fuel economy.. doesn't say anything about keeping the engine and trans cool. But now that we've removed 10 of the 14 slats.. it's clear we're cooling the engine more and gaining better fuel economy.

I'm saying this just to see if any of you have actually edited/altered or removed this shutter system on car built after 2015. it could make a big difference.

Our testing will continue in a few days.

Fiesta didn’t have the shutter system on any model years

 

[foodtruck]

Since OP is autocrossing their car in HS, I would double check with SCCA if altering grille is allowed before going ahead with any such mods (I'm guessing not, but doesn't hurt to check).

 

[SteveS]

In the dark old days of autocross (back in the late 70's and early 80's) we used to return to your pit, leave the engine running with the hood open, and use a pump-up Indian can to spray a mist of water onto the radiator from the front. And Indian can is a big metal precursor of the pump up sprayers for misting plants or spraying insecticides/herbicides. Something like this: https://www.amazon.com/Chapin-International-20000-1-Gallon-Translucent/dp/B000E28UQU/ref=sr_1_5?crid=2TKD5H2A1D20W&keywords=pump+up+sprayer&qid=1698795728&sprefix=pump+up+spraye,aps,258&sr=8-5

The mist evaporates from the outside surface of the radiator, which cools it faster than just airflow.

 

[LostInTransit]

thanks for the clarification @dhminer

 

[M-Sport fan]

you're literally pumping heat back to the engine by running your AC. I couldn't imagine that fans are enough to offset this in any way. All mechanical losses in the AC system are going to be converted to heat as well.

Without fail, when sitting in stop and go traffic while idling in summer heat, my engine coolant temps run cooler when the AC is on, due to the fan coming on instantly when that system is engaged.
I literally watch the temps drop from 212-215 down to 186-192 (on my UltraGauge EM) when the AC is engaged from no HVAC controls being on at all.

This is with the factory radiator, and of course, any hard driving in those hot summer temps will sent it right back to that 215 running temp, but NOT at idle.

You'd probably be better off looking into installing a fan override switch of some kind rather than running the AC.

Not being an electrical engineer (like some on here), or even as much as an incompetent electrician, I WISH that someone made something like this that would not set codes in our ECM when installed and activated, and have been begging for someone to make up something like this for our rides.

I had one, made by an aftermarket company, on my last car ('00 LS1 Z28) and loved it!

 

[tri-pedaler]

Since OP is autocrossing their car in HS, I would double check with SCCA if altering grille is allowed before going ahead with any such mods (I'm guessing not, but doesn't hurt to check).

Yes - not allowed, correct.

 

[tri-pedaler]

Just get a radiator. Problem solved

Street class - can’t 🤷‍♂️

 

[tri-pedaler]

We only have a single fan, so if the engine temp is high, the fan will be running, A/C or no A/C.

Great post. But in my experience the fan never engages at idle without running the AC. Perhaps that points to a different issue with the car.

Also, I do run my heat (and direct it out the open windows), but sometimes it seems to not blow hot. Would this be the common BDA issue?

 

[Frisk]

Without fail, when sitting in stop and go traffic while idling in summer heat, my engine coolant temps run cooler when the AC is on, due to the fan coming on instantly when that system is engaged.
I literally watch the temps drop from 212-215 down to 186-192 (on my UltraGauge EM) when the AC is engaged from no HVAC controls being on at all.

This is with the factory radiator, and of course, any hard driving in those hot summer temps will sent it right back to that 215 running temp, but NOT at idle.



Not being an electrical engineer (like some on here), or even as much as an incompetent electrician, I WISH that someone made something like this that would not set codes in our ECM when installed and activated, and have been begging for someone to make up something like this for our rides.

I had one, made by an aftermarket company, on my last car ('00 LS1 Z28) and loved it!

The real measure would be Fan On No AC vs Fan On w/ AC. You're running a heat pump and pulling cabin heat into the engine with the AC on, it's just a very bad idea to add that extra heat and then try to blow it away with a fan when the entire goal is to cool the engine.

Real question is whether you'd be allowed to run a box fan blowing at the radiator when you're off-track. Seems like that would be a cheap and (maybe, dunno) legal way to achieve the same thing without running the AC condenser pump

 

[tri-pedaler]

The real measure would be Fan On No AC vs Fan On w/ AC. You're running a heat pump and pulling cabin heat into the engine with the AC on, it's just a very bad idea to add that extra heat and then try to blow it away with a fan when the entire goal is to cool the engine.

This is the question. Can anyone confirm that the fan comes on at idle without running AC? It doesn’t on mine my ‘15.

Re: box fan, never seen this, and would need a power source, but I like it. Maybe a leaf blower, as in F1 for the brake ducts?

 

[Frisk]

yeah, that could work, but you'd want a wide nozzle. Other option is those fans they use for dyno testing, where they move a large volume of air.

You can get those milwaukee/dewalt battery bank power sources that would probably do the job for you if you already own a bunch of their batteries. Otherwise dedicated battery banks would do the job and would cost less overall.

 

[TDavis]

Street class - can’t 🤷‍♂️

The more and more I hear these rules for AutoX makes me stick to road courses lol. Unless theres something I don't know, a radiator isn't going to give you a power advantage in AutoX. Unless you don't have time between sessions to cool down

 

[SteveS]

The more and more I hear these rules for AutoX makes me stick to road courses lol. Unless theres something I don't know, a radiator isn't going to give you a power advantage in AutoX

The point is to make it so stock means stock.

 

[kivnul]

You can replace the thermostat and stay in class. Not sure if it would help in your situation though.

As to the draconian rules of AutoX: I always felt it is to keep like to like: The joy of a stock class is that anyone can join with the car they have and not be racing against someone who dumped money into their car. There is a class for anyone and everyone.

 

[foodtruck]

This is the question. Can anyone confirm that the fan comes on at idle without running AC? It doesn’t on mine my ‘15.

My 2014 does when I just parked after a run and I have full heat bars on the indicator (at least for a while).

But yeah, the solution that worked for me is just heater on full blast during the run; its not that bad cause windows are usually open.