Engine cooling using the heater settings
 

With my 80% grill blocking I keep an eye on coolant temps. I have noticed that keeping the internal fan off while setting the temp selector to hot will bring the coolant temp down, even under prolonged high-load hill climbing. But the reason I am posting is that I recently noticed that I can seemingly the same benefit if I select for the internal cabin air circulation. In that setting, with the heater fan off, no hot air comes into the cabin, but the coolant temp still drops. Anyone know why? I assume the heater is dumping the forced air somewhere else, other than the cabin, perhaps into the engine compartment itself.

The effect is that I can cool the engine, without using electricity for the radiator or cabin fans, and without forcing hot air into the cabin. On warm days, this will be a great benefit (if it works as well during the truly hot months).

james

I have a grill block similar to yours. sometimes my HX runs a bit hot - and when it does, it usually has trouble getting into lean burn. I keep an eye on temps of course, but I havent experimented much with using the heater to cool things down..... i'll try it for a few weeks and let you know

This is what I do with my insight.

Great. The trick with the cabin air recirculation selected but without running the fan was the biggest surprise. I expect it'll work for you too. I also found that I could set the heat level in the middle between hot/cold and get a predictably more modest effect. I like the idea of keeping coolant temps in the low and mid 190s.

my coolant temps seem to be at 183.2 or 188.3 about 95% of the time. sometimes they hover to 190. i drove to Tahoe this weekend, and found that when they were up to 190, i could lower them *surprisingly quickly* by turning on the interior heater. next time i'll try to just turn on the cabin recirculation, but no fan - i'll let u know how it turns out.

The heater valve opening lets the cold coolant in the heater core into the system. Trolla will drop the temperature gauge to cold if I open the heater valve.

Works very well
 

Today, after 10 miles driving to work, the coolant temp was up at 203* sitting at a stop light with the engine off. The temp selector on my dash was still on cold. I turned it to "hot," but with the engine still off the fan blew cold air. I started the car to drive, the air from the fan turned hot as I watched the coolant temp drop to 186* within about 10 seconds. For the remainder of my P&G routine to work the car stayed in the 180s-190s as usual (I normally have "hot" selected on the heater once the car warms up).

It was such a good example of what this thread is about I thought I'd add the story.

The coolant doesn't normally flow until through the heater core until the heater is selected. If you notice a significant drop in temps with the heater on your radiator block is too much and will lead to excessive engine wear.

I think most vehicles in last 20 years or so do not have valve for heater, instead coolant always flows and they just switch a flap to get air through heater core or to bypass it.

This would be wrong. Most engines need heater settings selected to bleed air when changing coolant.

The coolant must work through the heater coil as the pipe work acts to cool.
Would it work if you idled for a long.... period of time?
The fans rarely need to work in most commutes, as the thermostat opens, the coolant through the radiator should do the trick (and do it better than the coil in the cabin).

I've always had cars with 'manual' controls for the heater, that is, levers that move the air flaps and water valve. So I keep the heater at COLD to help the engine warm up and that's always seemed to work.
My current car, a 2007 Mitsubishi, has the heater and A/C controlled by buttons and I am not at all sure there is a water valve. I think this is one where the coolant always flows and the heater simply diverts air over the core or not (and it does take a long time to warm up in the morning so I can't really tell if the heater position matters, and I think it doesn't).

But definitely, I've always had the heater as my last resort to combat overheating.

another basic observation
 

If the engine is very hot after a climb but not hot enough to trigger the radiator fan and if the heater has been selected for "hot" already so that coolant is circulating through the heater core, when I cut the engine to coast a long straight or downhill I can take all the heat out of the heater core in under one minute by running the cabin fan at top speed setting, temp selector on hot. Air starts out hot, but gets cool in 30 seconds or so. When I next restart the engine, that small amount of cooled coolant begins to circulate in the system again as the water pump starts-up, bringing the overall coolant temp down slightly.

Ironically I get the oppsite effect. When my car is cold, putting the selector on hot seems to heat it up quicker (judging by distance travled before it hits 130F for 4th gear to kick in). I always leave the fan off. Factory my car came with a 180 thermostat, and I installed a 195 one, so maybe the hole in the thermostat is too big and not letting the engine get up to temp quickly. The 180F thermostat was stuck open, can't really comapair sadily when it always ran around 130-140F lol.

Now if I turn the fan on, or allow fresh air in while selected to hot, it will cool the engine pretty quickly down to around 185F from ~198-203.

The heat is going somewhere, that's for sure. When the car is moving the cowl vents are pushing air through your ducts. The heat is probably coming out in a non-intrusive manner with the windows down. I can heat my car to a comfortable level on 45 degree mornings with the windows up and the heater set to warm or hot, no fan.

I do the same thing by setting my air setting to fresh air in. Normally have to turn it down 1/2 way or it will get too hot, and this works all winter long, but the fan does get the heat transferred faster lol. It don't help to clear windows that much though, very slow reaction time.

Possible explanation:
1) Lower air pressure below the car.
2) Higher pressure above the hood.

1&2 ->
Air flowing from the air intake on the hood, through the element and into the engine compartment and out below the car.

Wow, day 2 on the forum and ive picked up some great info. Never considered the heater into the cooling cycle but I too am thinking the newer vehicles have no valve to eliminate water from entering the heat radiator just a flap to control and divert the air.

In the 12 ram cargo van you hear a lot of flappin (and not just from the wife) when u go pushin the air controls.

SO: the lite is on. I have noticed a low inlet air temp even with a lot of frontal blockage but maybe a duct that could regulate where that bypass air went. IE a way of regulating inlet air temp from the inside with the heater controls. Who d thunk it ?????? z