"I once heard that air-cooled diesels in a hot environment (i.e. desert) can have overheating problems. I(s) this perhaps overstated?"
No. It is an entirely reasonable statement on two levels, depending on which clause you are referring to with 'this'. First, only you can know if you heard the claim, secondly the claim itself is so nebulously phrased that it is scarcely claiming anything.
If you meant to ask if 'aircooled' engines generally suffer from overheating problems more than equivalent 'watercooled' engines, that is a whole different ballgame.
Thank you greg for turning this statement into an actual question.
It is still so extremely broad so as to be difficult to answer precisely, as it very much depends on design and materials and power density and packaging requirements.
A low performance engine with a lot of room for air circulation and large (read noisy) fins can be very reliable as there are very few moving parts in the cooling system. Also, detonation will not cause surface cavitation problems with air.
However if there is no room for large fins the engine has to be relatively quiet, and the output level generates very high temperatures at some points, then water is a better heat transfer medium than air and can better control extreme hot spots and provide more uniform cooling in a tighter basic package. However it needs extra room for ancillaries like the water pump and radiator as well as hoses, all of which can fail. It can cause cavitation corrosion from the vibrations set up in the cylinder wall or head from detonation.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
So what do some of the premier A/C diesels say?? Like Deutz, for example. Do they derate their diesels for hot climate service?? Do they care where they are used.
Frankly, with the temperature differentials between the innerds of the engine, and the cooling medium, I can't see a whale of a lot of difference between 28 C air, and 40 C air, when the delta T is starting at hundreds of degrees in whatever scale you want to use on the inside of the cylinder.
But, I am asking questions here too, not giving answers.
All the Diesel spec sheets I've read, quite a few, state a range of acceptable conditions, inlet air temperature being one, and derate either the engine or the warranty outside of the stated ranges. Some of the electronic control boxes will do the derating for you on the spot.
You're right, the delta T is about the same, the gradients are steeper for liquid cooled systems.
There's something elegant about an aircooled engine, especially after you've changed a few water pumps.
I loved my Corvairs. The second one had a head temperature gauge, which taught me a little. I put in new jugs and bearings, and then it was _real_ sensitive to load. The head temperature would climb fast on ascending a hill. It took ~3000 miles of gentle break-in to get the head temp response back to where it was before the rebuild, i.e., insensitive. Where I'm going with this is that any air- cooled engine is probably at risk for overheating during break-in, but after that, it'll take some abuse. You still have to clean out the leaves, twigs and squirrel droppings once in a while..
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
I have built a lot of air cooled VWs, but they are obviously not diesel and so have some very different design parameters to diesels.
I never had a break in temperature problem, but I was very careful with my specifications and clearances.
They were noisy and gave very good power to weight for the day and age, but they were always only reasonable at best re power per displacement.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
About 1990 I bought an air-cooled Deutz diesel from our local UK stockist for a research project. It ended up at the US Army proving ground at Yuma, where the ambient was 44C. It worked just fine.
These guys have done their homework, and designed the airways round the block to remove as much heat as possible. There is also a lot of heat removed from a diesel by the lube system. The oil is as much a heat transfer medium as a lubricant - particularly squirting oil on the underside of the pistons. The oil coller is often quite big on these engines.
The penalty for the simplicity of the air-cooled engine is the power consumed by the fan - a lot more than the equivalent pump and fan for a liquid-cooled engine. You don't get owt for nowt, as they say in Yorkshire.
