I got thinking and poking around things and came across this thread. Pretty interesting idea/concept. Basically use an EGR "cooler" as a heat exchanger to heat the coolant temp during cold start.... sounds like exactly what I'm effectively trying to do. I was trying to solver the coolant flow side of the issue when you didn't want heat, didn't really dawn on me to stop the exhaust gasses instead. From what I've been seeing, my cat is bad on this car, so either run it as is, or straight pipe it. Deleting it gives room to fab up a heat exchanger and some sort of valve to redirect the exhaust flow.
https://ecomodder.com/forum/showthre...ger-29085.html
I probably should data log some trips to measure warm up times, air temp and such so I have a base line to start with. Full grill block (at least until it warms up more) and engine compartment sealing/insulation I suspect should help tons. The EGR cooler seems like a pretty logical way to go. Clearly a micro controller would be a good idea to have hooked up so it can automate the open/close cycle. I'd say 160F and colder have it heating the engine, and over it's closed.
I suspect a 12v based heater on the oil pan and maybe a 12v heater in the coolant circuit would help things too. The inverter can put out somewhere around 1000w more than standard draws, so probably safe to have 700-800w to heat the engine. Maybe a slight pre-heat if time allows. This is sort of like a plug in block heater, but runs off the stored up energy in the hybrid battery effectively (and in turn, ideally from fuel burnt when the engine is warm and efficient).
It seems like these kinds of mods not many people do, so there's not too much info out there about this stuff. The core concept seems to make sense to me though.
I should probably grab some of those cheap temp gauges that runs off dc power to be able to see some temps under the hood. Inverter, transmission, oil pan, etc.
I haven't looked into it at all, but I'd assume the prius has some sort of coolant to oil heat exchanger setup. At least the 92-96 era toyota camry did, it went right on the oil filter threads and coolant lines ran to it and the oil filter spun onto it.
Oh just ran across this pic, pretty interesting to see the temps charted on a longer trip to compare against. Seems like inverter coolant runs around 115F in their case. I didn't realize the inverter and transmission are on the same loop. I guess a slight side benefit from running in EV mode at first is quicker transmission warmup. Ideally the inverter would be kept to air temp and I'd think letting the transmission warm up a bit more could be good, but I'm not sure what kind of temps the electric motors are seeing.
Source:
https://priuschat.com/threads/invert.../#post-2749272
This is also an interesting video I saw referenced.... I guess just dumping excess heat from the exhaust manifold into the coolant can be fine as long as there's enough cooling at the radiator. Benefit is the faster warm up times, just can't heat the coolant too hot to cause issues. A simple copper pipe wrapped around the manifold some, or early in the exhaust pipe should exchange a bit of heat but not be too overkill. Fun part would be doing the wrapping lol. It seems like this head design would be pretty ideal for a hybrid engine.