Why some engines warm up faster? (vehicle, 2011, idle, fuel)

[HappyRider]

We all want quick heat output in the winter. My rule always was that with a bigger engine you get heat quicker but that doesn’t seem to be necessarily the case. My 4.7L Dodge V8 doesn’t seem to make the heater go any faster that the Ford 4.0 V6 SOHC in the Explorer.

[jazzlover]

Two big factors are the mass of the engine and how much fuel it uses at idle or low speed conditions. Larger, heavier engines generally burn more fuel at idle and low RPM's, but also may have more mass (block, etc.) to warm. Lighter mass engines usually use less fuel, but may actually warm faster due to their lighter weight. Of course, a lighter mass engine will also cool off more rapidly when turned off.

Fuel injected gas engines generally burn less fuel at idle and low RPM than does a similar size carbureted engine. A diesel engine burns even less fuel at idle and low RPM, to the point that a diesel engine may have trouble maintaining operating temperature at very low outside ambient temperatures. Gasoline engines generally burn enough fuel at idle and low RPM not to have that issue. I do wonder, though, as gasoline direct injection engines become more common, will GDI engines burn sufficiently less fuel at idle and low RPM to also lose temperature in very cold ambient conditions the way that a diesel engine can?

[HappyRider]

I was having this conversation with someone and he said aluminum heads have a lot to do with quick heat.

[mshultz]

Good knowledge on this thread.

You want the biggest displacement in the smallest block for quick warmup. A 400 small block Chevrolet will warm up much faster than a 283, because it is using 400/283 times as much fuel at idle. This assumes equal efficiency.

A 402 Chevrolet big block is going to be much slower to warm up than the 400 small block, because you have at least 100 pounds of additional mass to warm up.

[sunsprit]

in addition to the issues of engine mass, fuel and fuel delivery system ...

there's the cooling system topography and strategies that the manufacturer used in a given engine.

For example, an engine using a two-stage thermostat; ie, where the coolant is recirculated through the head and block to the heater core may deliver functional heat faster than a cooling system with a single-stage thermostat.

The difference is that the t-stat has two control surfaces: (1) that controls the coolant flow through the engine to the radiator, and (2) a block-off plate which controls the recirculation loop through the engine for the warm-up cycle. Initially, no coolant flows to the radiator, but as the engine/limited amount of coolant warms up the recirculation loop is blocked off. Then, as the engine warms up, the larger amount of coolant in the radiator and overall system is fed into the engine and ultimately has the flow to the radiator controlled by the main portion of the t-stat. The advantage in this design is that there is significantly less coolant circulated to handle the cooling during the warm-up cycle so the coolant is heated faster.

Some cars use this to great advantage; ie, a Subaru 2.5ltr engine can begin to deliver functional heat from cold start-up within a few hundred yards of driving at modest speeds (no more than 30 mph) even on a 0F day. If you let the car idle for the time it takes to clear the windows ... especially if there's ice to be scraped ... you may even find that the engine temp gauge is up to the normal engine running temp by the time you get back into the car and drive off. Of course, it's just a small amount of coolant that has reached this temperature, but it's a dramatic difference compared to getting into a diesel pick-up truck in the same conditions and needing to drive several miles before any functional heat is delivered ... and that includes the Dodge/Cummins where a two-stage t-stat is used which doesn't warm up any faster than a Powerstroke with a single-stage t-stat. It's a combination of thermal mass and cooling system design at work.

This type of comparo isn't new. Such differences in cooling system strategies were present even in cars of the 1960's ... Fords were slow to deliver heat compared to Chevy's of comparable engine displacement. Worse still was to get into an IHC Scout and need to drive 15-20 minutes before the old cast iron lump out front delivered hot water to the heater core.

[need4speed2012]

I would say that you have a leaking thermostat, its not sealing causing the vehicles heater to get hotter slower.

[Malloric]

Prius also uses what is basically a 3 liter thermos to store the coolant. As long as the vehicle hasn't been sitting for several days, you've got heat pretty quickly.

[MckinneyOwnr]

As was stated, the weight of the engine and material is a big part of it. Just like in welding, aluminum heats up much quicker than steel/iron, also cools down quicker too.

Another thing that really heats an engine up quicker is if there is a turbo. Instead of all that wasted hot exhaust leaving the car, it heats the turbo up and that air gets put back into the engine.

My turbocharged cars have always warmed up much faster than a naturally aspirated one.

[jazzlover]

sunsprit and Malloric are correct. Most engines built in the last 20-30 years also have some method of warming the intake air (usually by pulling it from next to the exhaust manifold) until the engine is reaching operating temperature. A few newer cars are borrowing the trick from big trucks of having radiator shutters that will close when the engine is cold to restrict airflow into the engine compartment.

All of this serves two purposes, to warm the engine faster for better emission control and to enhance fuel economy. Diesels are harder to warm up in very cold temperatures because the only way to warm them is to burn more fuel, which means elevating the idle speed. For example, the 2011+ Ford Super Duties actually have a cold weather idle control that will elevate the idle speed if the vehicle is sitting in Park and the engine begins to lose temperature. It will do the same thing when the vehicle is started in very cold weather.

The quickest way to warm up any vehicle is to start it, let it idle just long enough to get the oil circulating, then drive it at moderate RPM. That does not over-rev the engine, but puts it under enough load to warm it faster. Not to mention that an engine sitting idling for 20 minutes or longer warming up is getting 0 mpg.