[Diesel_Dave]

So lately I’ve been thinking about ways to improve cold start warm up times. Here’s my latest brainchild. Why not put in a coolant-to-exhaust heat exchanger? In a cold startup (before the thermostat opens), you circulate coolant from the engine block through an exhaust heat exchanger (after the turbo) and then back to the suction side of the coolant pump. You then put in a control valve so that after the thermostat opens, no more coolant flows through the heat exchanger.

I can’t think of any downside to this. You are taking heat away from the exhaust, but it’s after the turbo so there’s no harm to that. At that point it truly is waste heat. After things have warmed up, the control valve would be closed, so after the thermostat opens you’re back to your original system. Depending on how you constructed the heat exchanged, there could be just a tiny bit more backpressure on the turbo, but it would be really, really small and if you sized the heat exchanger correctly there wouldn’t be any additional backpressure.

As far as how it could be practically constructed, perhaps the easiest way to make the heat exchanger would be to use an EGR cooler from an engine much larger than the one being used. That’s already designed to handle exhaust conditions, and coolant. I haven’t quite figured out the control valve. I think there should be some way to do it mechanically, but maybe you’d have to do something electrically. For somebody that’s good with electronics, it shouldn’t be too hard.

Has anybody else tried anything like this? Any comments or suggestions?

I’ve attached a (crude) schematic.