Heat immediately?
 

OK, all we theoreticians, I'd like some answers. Living in the southeast, I seldom face weather in the teens. Not so lately! Suppose one enters his truck in the early AM where a thermometer inside shows temps in the upper teens. Say you assume the coolant must be above this to stay liquid--just assume 20. If you immediately turn on heat to max as soon as you start up, would the 20-degree coolant allow the heater to immediately begin raising the temp inside the truck? I recently argued "No".

And now, where could there be a flaw in answering "Yes"?

I thought it was interesting.
Sam

Re: Heat immediately?
 

The heat won't work til water temp rises.

Re: Heat immediately?
 

I don't know if this is a serious question or not. You will not notice or feel any heat until the coolant starts to warm up. The engine will need to run for a while to build heat in the coolant which can then be blown through the heater core.

I don't know how specific an answer you are looking for. A super technical answer would take into account if the coolant was the same temperature as the ambient air. Say it is 20 degrees in the cab and the coolant was 25 degrees ( antifreeze will not freeze at 25 degrees). The metal of the heater core would be 20 degrees along with the duct work, etc. The air being pushed by the blower fan would also get cooler due to motion and also being channeled through cold ducts.

The 25 degree coolant pushing through the system would probably result in the air coming out of the ducts being slightly closer to the ambient cab temperature until the ducts and heater core absorbed some of the warmer air. Would you be able to detect the difference? No.

Once there is enough heat to open up the thermostat, you will get some nice warmer air which also has to heat the cold air occupying the interior area of the cab. The colder the ambient temp, the longer it takes for a cold vehicle to build heat and eventually warm the interior. It has been sub zero here for the past ten days. I have to let my car run about fifteen minutes before it will begin to push warm air inside.

Re: Heat immediately?
 

Just my 2 cents worth. Here in Central Arizona the temp at 5 am now is in the high 20's and it takes about 10-15 minutes just to get my Suburban tolerable. Thats after letting it run in the driveway for about 5-10 minutes

Re: Heat immediately?
 

I'm not smart enough to attempt to answer this question, but it kinda fits into what I do day in and day out and I'm not afraid to look silly on the interweb so here is my thoughts.

I think the main flaw in "yes" is that the btus put off by the "20 degree coolant" (which would be minuscule) can't over come the load being put on the cab interior by the ambient temp outside. Meaning the heater can't overcome the heat loss.

Re: Heat immediately?
 

The coolant will be the same as the outside temp and remain liquid as long as you have enough antifreeze in it. The time it takes you to get heat will depend on how long it takes the engine to make water warm enough to ad heat to the air circulating over the the heater core and as said above warm the duct work enough to still be warm when enters the cab. The cab will start to feel warm once the heater has had time to start warming the air and all the other stuff in the cab. My motor builds heat slow and as cold as it has been here takes a while to get warm in the cab.
Jimmy

Re: Heat immediately?
 

This is why I have driven my 07 all this past week. Remote start and a great heater lol. I can't wait to get a real system in my 65

Re: Heat immediately?
 

Until the coolant that is held back in the motor by the thermostat warms to its setting lets say 180 degrees you will not get heat. When it opens and allows the heated coolant to flow thru the heater core you have heat. Keep in mind you are heating sort of a cold tin can so it takes awhile to warm up. It was -15 here this morning with a wind chill of -28 so it took along time for my 65 GMC to begin to feel remotely warm.

Re: Heat immediately?
 

Just to add, don’t let engines warm up at idle. 30-69 seconds max and drive gently until warm. The old wives tale of warming up a car is actually bad for your engine.

Re: Heat immediately?
 

Hotrodder you will get heat before the thermostat opens. The lines to the heater are both before the thermostat. As the engine warms up so does the water to the heater.
Jimmy

Re: Heat immediately?
 

Due to the thermal mass of the engine block and coolant, it will take a while for the coolant to cool down to ambient temps. It is possible that the coolant will still be slightly warmer than the ambient temps (not more than 5 degrees after 8 hours), so it is possible that it will transfer heat to the air in the heater as soon as you crank it up. However, the temp difference will be so small that it will be offset by the motion of the air over your skin which will make the temp seem cooler. The temp difference between the coolant and the air will be dependent on how fast the air cools overnight.

As has been noted, when you crank your truck and the coolant is warming up to the temp that opens your thermostat, the coolant is being circulated between your water pump and engine thru the heater core- so it should warm the interior as fast as possible. Note that the thermal mass of the interior also has to be overcome, so it takes a while for everything to warm up.

Re: Heat immediately?
 

I have a diesel pickup (2004 model year) and need to plug the block heater in so it will start in cold ambients. It's been right around zero degrees F and below around here lately.

I fire it up and I usually can feel the heat blowing by the time I get to the end of the driveway.

K

Re: Heat immediately?
 

Up here on the weather networks they are always talking wind chill, which makes it seem even colder when the wind blows. I always let the truck run a bit before putting on the heater fan. Mine still has metal floors so the heater doesn't do much anyway but at least the tank has been moved out of the cab.

Re: Heat immediately?
 

Canadian equipment for 67-72 trucks has a heater hose preheater RPO, does anyone know exactly what this does? Quicker heat?