Speed of Heat Inside a Vehicle

Could be better engineering, could be bigger heater core vs interior volume to heat in the Sabaru, could be different temperature thermostat, could be larger thermal mass of the Jeeps engine just takes longer to heat up.

I'm sure there are other reasons.

The engine in your Wrangler is larger than the engine in your Outback. The thermostat doesn't open until the engine gets hot. Larger engine= longer warm up time.

I'm not sure on this, but if the Outback utilizes more aluminum components, i.e. block and head, and the Wrangler has cast iron, it will also cause it to warm up a lot faster.

The super-precise tolerances of the Chrysler motor induces less friction and thereby makes for longer passenger compartment warm-up times than those clunky nasty old Japanese motors.

Or you could just be missing your thermostat...your choice.

No prejudice here.

You can always add a little heat....

Warren THR6000C Plug-in Auto Heater 12 Volt 600 BTUs.

$30 online

you could say an infinitesimal amount, if you wanted to quantify it.

You can step it up as high as you like with coleman catalytic heaters, propane powered... This is 3000 btu model...$85 bucks

catalytic heater 3000

Since you incorporated most of the other suggestions, and added a few of your own, I'll just use your checklist to try to narrow it down (as far as fnding an answer to my actual question) And thank you everyone, for your ideas.

This is just the short list of what can affect things.

How big or small is your heater core.

• I don't know. Could be a Wrangler has a small heater core.

How well does it actually circulate hot coolant from the engine.

• Again, don't know. Perhaps Wranglers have poor circulation compared to Subarus.

How efficient is your air ducting.

• Both eventually attain the same temperature inside the cab, so maybe this one doesn't apply.

How fast or slow does your engine warm up.

• This is sort of a paraphrasing of my original question. Sort of.

How big is your engine.

• Mentioned by a few people. But the thought I have with this suggestion is that even though this Subaru is a 4-cyl and the Jeep is a 6-cyl... we previously had a Subaru with a 6-cyl, and it also heated up quicker than the jeep.

How many air leaks does your cab have.

• This doesn't apply, because I'm not talking about how warm inside of cab is. I'm wondering about the actual air that comes out of the blower. Jeep's air is cooler for longer.

How big is your cab space.

• Again, same as above.

How effective is the blower itself.

• Good point. Don't know. Perhaps Jeep has crappy blower.

How do the temperature controls actually work, mechanical linkages or electronic control and are the working properly.

• I'm thinking Jeep is more mechanical and Subaru is more electronic.

How cold is everything when you first start.

• Equal conditions for both

How patient are you.

• Umm... I'm patient. Just wondering why Jeep takes longer to blow warm air.

How conservatively or agressive do you drive.

• On city streets, which is where I am now... I drive both equally.

**** So after all that... perhaps jeeps just have crappy blowers?

Let me add, that the needle on the temperature gauge takes much longer to get into the 200 degree range, on the Jeep. So as far as my original question... that probably eliminates a few things like ducts, etc.

And as I mentioned above, the size of the engine sounded like a reasonable suggestion (larger engine = longer warm up)... but, as I said, I don't think there was all that much difference in the 6cyl Subaru and the 6cyl jeep, as far as engine size. Jeep was still blowing colder much longer.

Look at your coolant capacities also. Bigger radiator= more coolant=longer warmup time.

This would probably apply, since the Jeep is advertised to be for off road use as well as street use.

Okay... makes sense to me.

And yes, jeeps are special. I'm on #4 in 30 years.

Whole bunch of GA's, all around.

Aluminum block vs. cast iron block. The aluminum block will spread the heat quicker than a cast iron block. Your coolant will heat more quickly as a result.

Good suggestions. Thankyou.

Replace with a hotter thermostat, eh? I didn't even know you could do that.

Thermostats come in all different temps and are pretty much standard for US vehicles. Stant makes a complete line.

Don't forget to put the copper to the hot side.

My personal experience with vehicles tend to disagree with a number of theories relating to the small engines are better aspects.

Small engines don't necessarily warm up better unless they are loaded first. I have seen countless 4 cylinder cars that cant produce enough waste heat at idle to even bring the temp gage off its bottom mark in the winter. Where as the bigger engines tend to be less efficient at idle and warm up quicker and can maintain their heat.

To get an engine warmed up quicker don't drive conservatively or keep the RPM's low. Don't redline it of course but by manually shifting an automatic down a gear or two and keeping the RPM's up around 1/2 to 2/3 the way to red line greatly decreases initial warm up time.

Another trick with automatic transmission vehicles is that you can pre load them to warm up the engine and transmission by firmly holding the brakes on while stepping on the throttle while in gear. This puts a load on the engine and nearly 100% of the engine power goes into heating up itself and the transmission. Just don't get carried away on the power level and time. All the engine power is going directly into the torque converter and it heats up quickly. A moderate load for 30 seconds followed by high idle in park or neutral to cool it down and circulate the now hot transmission fluid through the rest of the transmission for another 30 seconds works best.

Flushing out your heater core and related lines every now and then can also have a drastic improvement on your heaters ability. Pull the two coolant lines off of it in the engine compartment and use a regular garden hose with a good flow rate to flush fresh water through the core several times in each direction. You may be shocked at what may come out of there when flushed backwards!

If you don't have good air flow out of the vents check your air ducting for blockages and broken or out of adjusted mechanical damper door linkages. If the heat door does not fully direct the air through the heater you will never get hot air. If you just don't get much air flow even in the high fan position you may have a partially blocked or stuck door. Don't be surprised to find a mouse nest and or a dead mouse blocking something from moving or letting air through. Same with any filters that your air system may have. Find them and clean them out if you have them.

Lastly talk to others who own the same vehicle. If everyone has crappy heaters then it not necessarily you who has problem its just a crappy design that was likely designed by people who do not live in a cold region of the world.

More good suggestions. Thanx.

Okay, so it appears that my question has been answered. I'm now reasonably sure I understand why it takes longer to blow hot air in the jeep.

But the conversation seems to have shifted over to suggestions on how to get it to warm up faster. This too is interesting. Several things have been mentioned. Is there any consensus on which one of these suggestions might have the most drastic effect, and get hot air blowing the quickest? After 8 years in the desert, I'll now be subject to a winter of cold bitter snowy lake-effect winds off Lake Erie. (thank you Canada ) The quicker I can get warmer, the better.

I vote for a 195° thermostat and cardboard in front of the radiator, not grill as someone suggested.

If overdone, this could cause overheating, so you may need to trim the cardboard.

Mandated gas mileage squeezes everything, including luxury stuff, like heating or cooling. Those detract from the mandate.

So, follow Lyn's example, and cut down on the airflow thru the radiator. Heat, that does not go out, comes to you.

If I know Jeeps, and I humbly have known a few, once the beast gets good and warm it produces plenty of heat.

If this is the case you are experiencing AND you are facing cruel north winds all winter - go with a block heater. Cheap to install and cheap to operate.

Diesels warm up slowly, even with a block heater when it gets cold enough. But they start like a top and are comfortably delivering heat before I can clear the drive even in the coldest.

To facilitate traveling I used to carry a 50 foot extension cord and also handy was an old fashioned lamp bulb outlet replacement. Even hotels didn't mind if I unscrewed an exterior bulb to plug in my truck.

As to other options:

Higher temperature thermostat: This will raise the temp at which water is released from the block to the radiator and heater. The engine will warm faster and to a higher level, but take longer to get to your heater core and continue to run warmer.

Covering the radiator even partially: I'm on the fence, it will not cure the problem you describe, but will contribute more heat to the cabin eventually. The downside is if you do not have a temp gauge to keep an eye on, the first warm day you risk overheating it.

Good luck and have fun, all the more effective with gas engines.

Try an experiment on a cold morning. With two observers, simply start both cars at the same time and watch the coolant temp gauges. They will sit at the bottom until the thermostat opens. You can quickly see if one opens well before the other.

The second way is to start the cars with radiator caps off and accurate thermometers sitting in the top of the radiator. When your thermostats open, you will see the quick rise of the circulating coolant.

Yes different brands have quicker heating systems !

That's actually a pretty valid point. The jeep's comes off of the downside of the water pump and off of the thermostat housing, which is "in" the radiator loop. I don't know about the subie...anyone?

The Jeep is using the water pump to suck the water through the heater core, and the heater core gets the water from the water that is being pushed out of the engine after warming up. It would go through the radiator if the stat was open, but instead it is drawn through the heater core. That sounds right to me.

Virtually all European and Japanese makes use this arrangement;

The core connections are actually wrong as the author of this blog seems to think the water pump is pumping - not sucking [as they all do]

But the 'source' out of the water heated intake manifold [or pump bypass circuit, or rear of head] is correct [and 'ahead' of the thermostat].

Note the valve: This is controlled by electronics interlinked with other sensors that monitor combustion conditions, so warming must reach a particular level before the heater can heat.

Most main thermostats are progressive, meaning in cold conditions this system will put most of the heat through the heater and only 'spare' through the radiator.

No cardboard required.

^{BTW, thanks for the vote}

Most main thermostats are progressive, meaning in cold conditions this system will put most of the heat through the heater and only 'spare' through the radiator.

Thermostats in cars are progressive only in so much as they will open only as much as the heated water causes the valve in the stat to move. As soon as some cold water from that radiator hits that wax pellet, it closes again until the wax pellet warms up again from the warm water. This may go on again many times till all of the water reaches a sufficient temperature to keep the thermostat open. Even at that point, the thermostat may partially close if the conditions are right for the radiator water to start to cool off again.

Very true of the 'wax-stat', it tends to be open, or closed, following events. The fast and accurate 'following response' is much favored high performance cars and racing.

Bimetal ones are more 'progressive' and 'averaging' [and tend to loose accuracy over time]. They'd probably be the better choice if consistent heater output is the center of one's world.

Then there are the electronic and hydraulic versions.

As who fits which to what and why, is another thread in itself - I used 'loose terms' - Sorry

34point5 hit the bullseye. Newer vehicles are plumbed such that the heater core is fed from just in front of thermostat after doing a loop through engine. In other words the heater core comes up to thermostat opening temp rapidly in Subaru.

Quote- Is there some kind of booster...

I've always thought that there was some kind of electric assist in some luxury cars because I've noticed how quick you'd get heat in them. Maybe not?

I'm guessing the difference is related to when the engine coolant arrives at the heater core. It seems likely that the Jeep coolant may be routed around the heater core while the engine is warming up. This might be done in order to get the emission system working as soon as possible and delay the arrival of coolant to the heater.

Hello." But the actual air that blows from the vent is hotter much sooner, also. While my Wrangler is still blowing lukewarm air... the air coming out of the Subaru's vents is already hot for quite some time." It seems you are describing two issues.1.Warm up times and 2. Heat transfer.1.Warm up times or the time it takes to reach operating temps is dependent on how much heat can be transferred from the cylinder walls into the coolant and remain in the coolant for use by the heater core.As mentioned previously a thermostat that is opening too soon will send the hot coolant to the radiator before operating temperature is reached and depriving the heater core .A clutch fan that is stuck in high volume mode will also delay the warm up with a similar effect.To reach the desired operating temperature as soon as possible has prompted many manufacturers to install electric fans rather than clutch fans as the latter always is moving some air which removes heat. 2. Heat Transfer from the cylinders to the coolant is often impeded by a build up of corrosion and sediment in the walls of the water jackets on older vehicles (The Jeep is 6 years older)due to the corrosion inhibitors in the anti-freeze losing their effectiveness.This same corrosion/sludge also reduces heat transfer in the heater core and reduces volume of coolant circulated as the blades of the water pump impeller rust away.I will mention here that their are garages with machines and chemicals to remove much of this corrosion and sludge through flushing.I have flushed cooling systems on Jeeps whose owners did not change the antifreeze at the recommended intervals.The flushed out coolant had the consistency of pond mud.Last is design differences.The length of heater core hose routing on Jeeps is often longer than the Subarus.This puts the heater core further from the heat source contributing to more loss of heat.Insulation wraps are available in hardware stores to reduce this loss.Much of this was already shared by other posters. I am simply relating my own experiences.Hope this helps.

My only comment to an otherwise well written post is that the fan clutch should not have any affect on the speed of the heater operation. The fan clutch and fan can only remove heat from the radiator after the the thermostat opens. Blowing air across a radiator filled with stagnant water will not affect the heater operation. And the electric fans became necessary for packaging with the front wheel drive combinations. As the desire for increased fuel efficiency became necessary, anything that could be done to remove drag from the engine when not needed was used . In some of the current big vehicles, the manufacturers are using hydraulics to turn the fan only when needed.

Air cooling does happen in a water cooled engine. So reducing the amount of cold air flow from around the engine will speed up how quickly the engine comes up to operating temperature.

Putting cardboard in front of the radiator to regulate the engine's temperature is the dumbest thing I've ever seen. Making sure your thermostat is working properly is the key to staying warm in the winter.

Is that a Lyn-Door industries design?

It's a LynDoor™ Industries transport truck. We have a huge fleet of these to distribute our products.

Not really dumb at all, that's a pretty bold anonymous statement.

If you have ever driven across some of the colder parts of the US, you would see that this is common place.

Maybe you're just against seeing a Pamper's box flattened and bungeed to the front of my truck?

Around here in the middle of winter its almost mandatory on many vehicles.

A common one is school busses. Most of them that are properly set up for winter around here have so much interior heater capacity the actual engine radiator does not function most of the time.

I have driven newer school busses that had to be driven flat out at the rev limiters just to keep the engine heat up high enough to keep the interior warm even with the radiator completely covered in cardboard.

As modern vehicles go the cab heater is not on the outgoing side of the thermostat where the radiator is. Its in the block side and is part of the main circulation system going from the pump to the heads and back. Many vehicals now have full time circulation through the heater core and a damper system is what directs air through or around the heater core itself. Ford, Chevy, Dodge and most other American market vehicals are set up that way and blocking off the heater coolant circulation path can actualy be damaging to the engine in some vehicals.

My Pamper's box isn't going to block the coolant path.

I used blinds in my Bronco a few years back and did overheat the truck on an unexpectedly warm day though. I was just too lazy to pull them out and paid the price.

The most effective improvement would be to get an engine block heater. But it requires you to use it to get the benefit of it. What should give you good results would be to flush your heater core, Make sure that the heater hoses are free and clear. There may be a valve in the heater hoses that limit the volume of water going to the heater at times of maximum cooling. This valve must not be a restriction to coolant flow when open. Is the valve actually opening all the way?

Using a higher temperature thermostat will raise the temperature of the coolant to a higher level before allowing the water to be routed to the radiator for cooling. Buy a good quality thermostat. It must cycle every time you start for the next 5-10 years. If the old thermostat is not closing fully when cold, it may be allowing some of the engine water to flow through the radiator when it should not be. This would slow the warm up process.

Another thing that would cause a slower cabin warm up(not what the op questioned) would be a recirculating air supply. If the Jeep is pulling only cold outside air, and the Subaru is recirculating some inside air, the Subaru will be throwing warmer air faster.