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Air cooled vs water cooled


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#1 Boss 448 OFFLINE  

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Posted March 02, 2011 - 12:23 PM

This is a hypothetical question and I realize that there are a lot of variables that would influence the answers but I am going to ask it anyhow.

Generally speaking are water cooled diesel engines more fuel efficient than air cooled diesel engines? I would think that they are because it is easier to maintain optimum operating temperatures with a water cooled engine which I imagine allows engineers to design the engine to run constantly in the most efficient heat range.

Similarly, do air cooled diesel engines tend to be lighter weight and/or smaller dimensionally in relationship to the power they produce?

Which design is the easiest to use in conversions (output shaft, water pump, etc)? Clearly air cooled engines don't require a radiator and some don't even require a drive belt system for an alternator.

While I doubt none of these questions have exact answers I am interested in hearing what others have observed and learned in their experience (or opinion). I know some here have more exposure to and experience with small diesel engines than I do.

JN

#2 jrk OFFLINE  

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Posted March 09, 2011 - 08:35 PM

You hit the nail on the head in your last sentence ... a lot of variables but I'll take a stab at a couple of them.

Given the same displacement water cooled engines are usually more efficient not only because they can maintain a more consistent temperature but also because they are able to operate at a higher compression ratio (this is what actually helps in efficiency) without a great increase in temperature. A general rule of thumb is that liquid cooled engines are heavier than air cooled engines by the time you add the coolant, radiator, and water pump ... plus the added block material for water jackets - although the fins on an air cooled engines do add weight. I'm sorta partial to air cooled engines because there are less things to worry about - however water cooled engines may be more reliable long term if you are really "straining" your engine on hot days.

If your using this powerplant in a swap I'd say to strictly worry about the external dimensions rather than the above criteria. Furthermore, you should be able to locate an air cooled diesel much cheaper than a liquid cooled engine (new) if that is of any concern.
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#3 Boss 448 OFFLINE  

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Posted March 11, 2011 - 03:54 PM

Good observations and thank you for the input.

I agree with everything you said. I too like the simplicity of air cooled engines but dimensionally I'm not sure the twins are any smaller than water-cooled engines. In particular they tend to be very tall making it difficult to fit them under a hood.

Not all air cooled models are less expensive than water cooled - here again you have to consider a lot of variables. This looks like a lot of engine for the money in a water cooled model: YANMAR NEW DIESEL ENGINES 2TNV70-PGA 2 CYL ENGINE 13 HP - eBay (item 120696387678 end time Mar-17-11 16:59:34 PDT)

While on the other hand here's an air cooled twin engine costs considerably more (though I'd sure like to have one) Hatz 2G40 Diesel Engine - eBay (item 330341668563 end time Mar-23-11 11:14:19 PDT)

So it's not possible to simply state that one design is better than the other. Still it is interesting to compare the generalities such as the compression issue you mentioned. That's one thing I had not considered.

I do wonder if it would be safe to assume that a water cooled engine will provide slightly better fuel efficiency per amount of work performed?

In researching various engines (used and new) that I have seen for sale I have collected a few PDF brochures with dimensions and other specs that others may find useful. In an earlier thread it was discussed creating a listing of various engines for comparison and if the moderators still feel the idea has merit I will be glad to upload them.

JN
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#4 Utah Smitty OFFLINE  

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Posted August 25, 2011 - 09:40 PM

I'd appreciate seeing the list. I have 2 diesels that I want to put in Garden Tractors... a 10 hp Chinese-built Yanmar Clone, and a Kubota Z482. If I could figure out how to build a bellhousing for the Kubota, I'd put it in my Power King 2414. The 10 hp I may put in my Case 444 or the Case 195.

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#5 Cvans ONLINE  

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Posted August 25, 2011 - 10:03 PM

Interesting that you should bring this up at this time. I just pulled a 10hp. 2 cylinder water cooled Kubota out of a garden tractor and I'm replacing it with a ListerPetters air-cooled single cylinder 8hp. engine. Just guessing from the effort used on the chain hoist I would say they weight about the same. If I could figure out a way to check this with the wife's scale without damaging it I would. The ease of installing an air-cooled engine rates very high in my book. I know of no water-cooled engine that can come close to the Lister for fuel economy. 40,000 hour engine life is worth something also. To be honest with you though the price of these new really places them off the chart. It's just that air-cooled engines are soooo simple to install compared to the others. Put it this way, installing a water-cooled engine is work, air-cooled is fun. Either way I think you will be happy with your results.
I really want to try a China diesel when the right project comes up. The V-twins look very good.

#6 Boss 448 OFFLINE  

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Posted August 26, 2011 - 08:27 AM

I'd appreciate seeing the list.

Smitty,

After going to find those various PDF's I got to thinking that it would make more sense to list links to the original sources. That would be more efficient than uploading all the different stuff and it would refer people to the current information so that they could pick and choose the information that they want to download.

I will start another thread and begin with some links today or this weekend. If others will also contribute perhaps the Moderators here will make the thread a sticky. As we go along people that possess information not available on the web could upload that information as well (manuals, specs, sources, etc).

JN

#7 Big John OFFLINE  

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Posted August 26, 2011 - 02:10 PM

If money is no object, Northern Tool has a V-twin air-cooled 25.2 hp Kohler for $5000.:say_what:




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