Menu Sign In Contact FAQ
Welcome to our forums

Diesel: why is it not taking off?

It is really great to see that the forum taking off.

I did not see the appropriate category for this post. Sorry.

About 10 years ago Thielert (later Centurion) started selling Diesel conversions. I am genuinely interested why it is not taking off.

  • Did the bankruptcy of Thielert has damaged the trust of potential buyers?
  • Why are not all C172's and PA28's converted?
  • Are the economies that bad for the conversions?
  • With rising AVGAS prices is it not still not economical to convert to Diesel?

Is it wise to buy a C172 with a diesel conversion or is it a long shot.

Any thoughts are appreciated.


All I can offer is opinion.

I would say that the Thielert thing damaged a lot of trust. The clutch thing left people wary of new technology as has a few failures based on the loss of electrical power.

Most of the Cessna and Piper fleet are old, and the cost of conversion is just too much relative to the cost of the airframe and takes too long to recoup in fuel.

There is also the danger that if many people switch to Diesel, than it will be taxed in the same way as Avgas and therefore the recouping will never happen and you'll be left with an expensive conversion cost and no payback.

I think it would be a tougher call if buying a new aircraft and both options were on offer.

If you were buying a new one and expecting to fly it a lot so that the engine life would only be a few years, then the Diesel would be a lot more attractive.

All my opinion of course and not really based on anything other then what I read and see ;)


EIWT Weston

•Why are not all C172's and PA28's converted?

Besides the cost thing that dublinpilot mentioned, for me it just a lasting memory from when I heard a diesel PA28 taking off when I visited Elstree aerodrome once, and it just sounded weird. Maybe there was something else in the surroundings muffling the noise that day, but do diesel converted PA28/C172's really sound different? This is obviously not a very 'green' statement, but when I fly or hear a plane, especially a SEP, I want it to sound like a plane. OK, a PA28 overhead will never sound like a Merlin powered Spitfire, but if it sounds like a old Fiat 500, I think that's wrong. I'm the same with cars, I just like a car to sound like and never really like diesels, or these electric hybrid things. It's purely an emotive thing for me.

Hello, I have some experience with the 135hp engine in a C172 and did my PPL exam on it. Short version is run as fast as you can and never get on any of those planes.

The W&B got a lot worse than with AVGAS

The plane never saw a drop of Diesel. Just JET-A1 available killing some of the expected economy.

The plane misses power down low. Acceleration in really bad combined with the weight issue. Up in the FL the turbo helps a little.

The FADEC is horrible. It will stop if you have no electricity. In the end the plane had 3 separate batteries... In addition to that the FADEC is just too complicated. Once the red light came on just after takeoff one FADEC went away the plane lost 10 knots and then the second FADEC kept the engine running in backup mode for the rest of the traffic pattern. Landed shut down the plane and never flew in that thing again.

It had more airworthines bulletins than any other plane I can image.

The time limited parts have been vera expensive. These costs have been far more than any posile little saving from the fuel.

With another engine this might be different but I think if you want to save on fuel go for Mogas.

There is also the danger that if many people switch to Diesel, than it will be taxed in the same way as Avgas

It already is in the UK, for all private use. It is a self declaration system so relies on honesty, however. But its existence alone kills the retrofit market.

Mr Thielert's little adventure (on both lack of engine reliability and dodgy accounting practices in his company) coupled with "Mr Diamond's" desire to deliver airframes and get the money from customers no matter what the longer term result would obviously be, damaged trust (and investment) in diesels for many years.

I also think contributory factors were

  • The original 135HP is not enough for most of the applications. A PA28-140 is almost the bottom end of the just-about-usable market so this was a backwards step. A 180-200HP engine would have sold much more. A 250-300HP engine (especially 300HP) would have sold well into the upper end of the market where most fuel is burnt, delivering much needed extra performance. No pilot who flies for real wants to go backwards in performance, unless there are absolutely stellar payoffs elsewhere (and there weren't).

  • The stupid FADEC implementation where loss of battery power stops the engine. It would have been trivial to put in a little alternator to power the FADEC. This set the most basic systems redundancy back to the pre-Lyco age (1940s) and killed the market in the USA, and among technically savvy potential customers everywhere.

  • Diamond "customer service"...

  • The economic recession came at just the right time...

Time will tell, but if it has not been for the above we would now be 10 years further down the road and maybe with a proven diesel package which in something like a DA42 would have been brilliant.

Shoreham EGKA, United Kingdom

At present, the available diesel engines seem to have a poor return on a big investment. They are a great idea, and someone has to fund advancing technology. You might not want it to be you!

I liked the Thielerts in the DA-42's I flew, but I was aware of high operating costs, and short times in service relative to maintenance schedule. A few times, I had a sick engine, and it seemed to be silly simple things going wrong, but I had to fly to the service center for repairs.

I spent three years working with SMA to buy a diesel for a C182 project. It did not end up with a purchase, so my client bought a brand new IO-550, and that was that.

I really like diesel, but I think it is still GA technology at it's infancy, and somewhat unproven. My money would not be there yet....

Home runway, in central Ontario, Canada

So, what does everyone here make of the new Cessna 182 production diesel?

A c172 will do about 6gph. At € 3,00 per litre which is the price in Holland that makes for € 67,- per hour.

a diesel would do maybe 5gph at €1,7 for jet a1 totalling € 31,50 per hour.

For this saving you invest a lot in athielert engine which needs gearbox overhauls every x hours and a tbo which is considerably less.


If you look at the faster aircraft like the tb20, c182 or the 114 .. they will burn about 12gph. the sr22, sr22tn or Commander 114tc will go up to 14-18 gph. Here it starts to make alot of sense..

my 114tc roughly does 17gph rop. equalling almost € 200,- where a good diesel would burn maybe €70,- worth,

The c182 is equipped with the next gen SMA with 230 bhp and no gearbox. If they can make a 300bhp version at right weight I am all in.

If they can make a counterrotate version as well they are ideal for the Seneca V which currently burns 26 gph totalling € 290,- versus 14 gph jet totalling € 88,-.

The DA42 outsells all other piston twins by a large factor. So diesel engines do have a market.

The main issue is the US market where diesel engines are non existent and where the business case is even weaker because Jet A-1 and Avgas cost roughly the same.

Earlier problems and ADs on engines is water under the bridge. Not really relevant. The electric system with the backup battery has been improved years ago. Diesel engines will find their market but it takes time. The Centurion 2.0S is not a bad engine. The SMA is a good engine.

So, let's remember what the diesel alternatives today are:

  • Austro for new Diamonds
  • Thielert retrofit for older Diamonds, 172s and PA28s
  • SMA/Continental for new Cessna 182s

That's about it. Thielert apparently ruined not just their own business but also diesels' reputation in GA. Diamond's current Austro ruined the DA40, being better adapted to the DA42.

Cessna's new JT-A 182 appears like the best bet from a technology perspective to me. It's also the only "pure" aviation engine. This would be my engine and implementation choice if looking for a new SE to keep.

Overall, the question will boil down to 100LL availability and cost. The EPA in the US will sooner or later affect the "LL" in 100LL. What's left then? Jet A.

What's generally the cheapest fuel in Europe? Jet A.

Where's the biggest growth in GA? Asia. What do they run? Jet A.

454 Posts
Sign in to add your message

Back to Top