Water cooled exhaust manifold = 20% fuel economy gain
 

Apparently Volkswagen has a turbocharged engine with a water-cooled exhaust manifold built into the cylinder head. They claim a 20% Improvement in fuel economy, substantially because of the water cooled exhaust manifold. The YouTuber "Engineering Explained" does a good job of narrating the design and the reasons for the claims.

https://m.youtube.com/watch?v=nNendiDFzSM

On start up, protect the catalytic converter.
Sounds like a cracked cylinder head.

Honda had this in the Insight 19 years ago. ;) I really wanted one of the K series engines which had a water cooled header (I believe they started in 2009) but it turned out to be impractical for my purposes.

Really enjoy Engineering Explained btw.

https://i.ebayimg.com/images/g/-X8AA...07u/s-l400.jpg

I didn't know that, about the insight. Which k-series had it tha you considered impractical?

it is a favorite of mine. He is no mechanic, however. That's his only real limitation, as I see it. But he is precisely the kind of engineer I hold up to my engineering-interested daughter as a model: familiar with materials, processes, and wear as well as the math, software, theory, and design.

To my knowledge it was the 2009 Acura TSX and 2012 Civic Si that used the K24Z3 and K24Z7 respectively, and these were the first (high performance at least) K series with water-cooled and integrated exhaust manifolds.

The Insight shares a ton of wiring and sensor signaling with the RSX (2002-2004). It shares a bit less with the 2005-2006 RSX/2004-2008 TSX which moved to drive-by-wire. It shares progressively less with newer ECUs and engines, and the farther forward you go, the more incompatibility you get.

The 02-04 RSX ECU which I chose due to extremely close compatibility with the car's body systems can in theory be used to run any KxxA or KxxZ engine, but a lot of parts and sensors need to be taken from earlier engines to run the later ones, such the crank position sensor, which has very different wiring, and to run the TSX engine I chose I already had to retrofit the throttle body from an earlier-year Accord plus repin most of the other sensors.

The other alternative is to use the correct ECU and wiring harness for the engine, e.g. 2012 K24Z7 ECU with 2012 K24Z7 engine, but then you have issues with things like incompatible body electronics - EVAP/emissions systems, all of the gauge cluster signaling, need to retrofit drive-by-wire to the pedal, and who knows what else. Fuel pump? Haven't the faintest idea if it would work.

Anyhow, I digress. I'm sure someone else the integrated header even before Honda, but the Insight's is the earliest engine I'm aware of.

The complexity of such swaps is like cold water on the imagination.

I've contemplated multiple times brazing soft copper tubing to my exhaust manifolds and plumb coolant to them to help speed up warm up times. I think on short commutes you could definitely see up to a 20% increase in fuel economy from faster warm up times. However, then you have to handle the constant input of that additional heat into the cooling system. That means a larger grill opening, larger radiator, and thus larger aero penalty. Overall, I definitely think its a win, but it would be so nice if we were able to find a way to turn it off like Toyota does with its exhaust heat exchanger on the Prius.

I would be careful of overheating your coolant. This has been a problem since the water cooled egr coolers started in 2004 on the Diesel trucks. The International produced engines used in Ford and International trucks have problems overheating the coolant and plugging the engine oil coolers. Almost all the light duty Diesels have egr cooler failures that lead to coolant consumption.

My Insight 3 cylinder had problems staying warm, not cold, even with a water-cooled exhaust.