Why Aren't There More Air Cooled Truck Engines?

[rbattelle]

It seems to me that if you eliminate the entire liquid cooling system you eliminate a lot of complexity, failure points, and maintenance. Of course, you trade off aerodynamics and probably add an air-to-oil heat exchanger.



Are those tradeoffs really that bad? I mean, 911s were air cooled until relatively recently, and that's one of the finest sports cars ever made.



Are there problems with air cooled engines that I'm not aware of?



-Ryan

 

[DonTX]

I suspect the objection to noise level is the primary reason. I had a two cylinder Lombardini diesel generator installed in an RV, had to remove it, noise was terrible. The water jacket does wonders for making a diesel quieter.

 

[2-ND TIME]

air cooled engines

They went to liquid cooled engines because of the tighter tolerances this made for better power output the Merlin engine was a prime example of this technology in increased power output.

 

[opjohnny]

A good heater would be nice. All the air cooled bugs I drove never had much of one.

 

[rbattelle]

They went to liquid cooled engines because of the tighter tolerances this made for better power output the Merlin engine was a prime example of this technology in increased power output.

I don't understand the relationship between tolerancing and liquid cooling. What, exactly, is built to tighter tolerances because of liquid cooling?



In my opinion, the switch to liquid cooled aircraft engines was driven overwhelmingly by the need for improved aerodynamics. I mean, an R2800 double wasp makes 2500 hp, whereas the Merlin made only 2100 hp (both ratings achieved with superchargers). Obviously, the package on the Merlin was much more aerodynamically convenient.



-Ryan

 

[JApol]

Weight and aerodynamics are big in aircraft, the more weight that is shaved off the airframe equals out to increased flight time and or more weight carrying capability.



The question about tolerances.

My bet on this is with a liquid cooled engine all the parts can be machined closer togeter because the water is only going to get so hot unless you run out. With an aircooled system it all depends on airflow, if there is not airflow through the engine compartment there is not going to be any engine cooling.

I don't know about you but when I get on the skinny pedal with my box turned all the way up I can see the water temp slowly rising. Its takes quite a bit of heat to get 7 gallons of water to raise 20*. The engine would probably have to be at least 3 times the physical size it is now just to get all the cooling that ti needs.



If you have 1300* EGT's I bet that explosion inside the cylender is at least 2000* at 1000 times per minute.



opjohnny, how many times did that bug overheat? Thats a little 4 banger with little to no exhaust restrictions

 

[JJuday]

Air cooled engines do have their ups and downs. I have personally seen many of the Deutz-Gleaner combines that have burned because of poor maintenence on the owner's behalf. When the manual says to clean all of the cooling fins and the fan once a week or more, you'd better double it to be safe. I don't know what the tolerance issue is all about. Deutz is German and the Germans are notorious for tight tolerances in mechanical applications, so I am not sure what impact the fact that they are air cooled has on the engines. I guess what I am trying to say is, air cooled engines can overheat just as easily if not cared for. Forgot to mention, air-cooled engines typically need more surface area to cool more efficiently, end result being they are usually longer. This also means more maint. as you have to clean these engines thouroughly. If they have a layer of dust and oil on them they will not cool well. Segmented heads, singles or doubles are common too. They work well in some applications.

 

[JHerr]

I understand that it is easier to control emissions in an automotive water-cooled engine. With increased pressure for lower emissions, I am sure that would be true for truck engines, as well.



Deutz diesel engines were pretty noisy, at least the ones that I remember. For me, that isn't negative, just an observation.

 

[ezcurra]

I suppose that a cylinder surrounded by a water jacket is going to be cooled FAR more uniformly than a similar cylinder surrounded by fins with air running through them. Also, I suppose that while a thermostat keeps the engine temp very stable by controlling the coolant flow, varying airflow through an air-cooled engine makes temperatures vary quite a bit. Do air cooled engines control the airflow other than the cooling fans being RMP-dependent?



I have heard that air cooled engines are limited in how hot they can run, and that hurts emissions. Supposedly that is what killed the VW bug.

 

[Gary - K7GLD]

The reference to "more" air cooled trucks implies there currently ARE a few in service? What would those be?



A current liquid cooled high HP/displacement diesel engine in an 18-wheeler would seemingly require a far larger space for a similarly powered/displacement air cooled replacement!



Seems that the usual far wider temperature swings of an air cooled engine vs a water cooled one is the issue where mechanical tolerances are concerned.



And where longevity is concerned, motorcycles such as a water cooled Honda Goldwing will pretty commonly see in excess of 200K miles with decent maintenance...



What will an equivalent air cooled motorcycle engine do - and if there aren't any equivalent air cooled motorcycle engines to compare with, why not?

 

[Rebel Ram]

I don't have a degree in thermal dynamics but it makes sense to me that the cooling prosses is much easier to control with liquid cooling. Also the size and sound levels mentioned earlier here. But look at it on a smaller scale. Modern 4 stroke offroad motorcycles are making HP levels only dreamed of 10 years ago. And do it reliably. This would not be possible with air cooling for more than 30 seconds.

This is a good discusion though.



Oops,, Gary beat me. What will an equivalent air cooled motorcycle engine do - and if there aren't any equivalent air cooled motorcycle engines to compare with, why not? ..... Read Harly Davidson :-laf

 

[rbattelle]

Great answers. I guess it really comes down to emissions, noise, and packaging. A real shame, though.



-Ryan

 

[SGibson]

The BMW flat twin,Moto-Guzzi V-twin and the Harley are all aircooled motors that can last damn near forever providing they have a breeze over the cylinders.

 

[WStephens]

The Deutz diesel is available in trucks or heavy equipment, they use oil circulated in the heater core instead of water to heat the cab. Duetz makes air cooled, water cooled and oil cooled engines. I considered a 4 cylinder Deutz for a repower of my Land Cruiser but the Cummins 3. 9 made more sence for a conversion.

 

[opjohnny]

JApol, you got me there, they would never overheat. Had trouble with the carb iceing up in the winter. Twin carbs would fix that.

John

 

[Cummins Pilot]

A Pratt & Whitney R2800 aircraft engine is cooled less by air than you'd think. 60% comes from oil cooling, another 15% comes from the intake air (fuel). Aircraft also travel at a more uniform speed. ie less stop and go. And they move a lot faster.



Air cooled engine are notorious for sticking valves also.



Also there was no "switch" to liquid cooled aircraft engines. Quite the opposite. Early airplanes were water cooled and the weight was the factor that drove them to extinction along with complexity problems. The Merlin and a few others are a rare breed. Most fighters were air cooled.

 

[Gary - K7GLD]

Not many heavy duty air cooled airplane engines face stop-and-go traffic, or low speed steep grade loads that involve high temperatures and reduced airflow at the same time...

 

[JJuday]

There are some air-cooled medium duty trucks around, the world that is... . Magirus-Deutz is a company co-partenered by KH Deutz of Germany. They are used mostly in Africa and the Middle East countries that can afford them. The Belgian Army and The South African Army use them as the equivilant to our Deuce and a Half. I saw many when I was in Baghdad, mostly 4 and 6 wheel drive. Flatbeds, dump trucks, small cranes, they had many attachments for them and they all sounded pretty good, for a Deutz anyway.

 

[Lnwing]

I have an Iveco box truck with the 5 cylinder Deutz engine. It runs good enough, but the Iveco part is getting tough to keep on the road. I've been thinking for a while that the Deutz might be a repower candidate when I park the truck.

Has anyone used this engine for a repower?

 

[Sageair]

The more cooling available the more power you can safely extract from an engine. Aircraft engines typically develop about 1 hp for every 2 cubic inches, while the highest hp ratings you typically see for a given engine is in the marine version, where cooling is never a problem.