Well, by “heat efficient” I meant capability of less energy being lost as heat versus a gas engine, and so less fuel wasted.
The Dasher was called the Passat in Europe. The 1.6/1.7-liter diesel put out 48 horses, about the same as the Beetle. The Quantum was based on the next generation Passat, too.
Well, if I wasn't "working" the engine, it didn't make any heat. You could probably put your hand on the exhaust manifold if it had been idling for a while. Don't try that with the gas version.