Yep, they have no cooling lines, so you'd have to plumb your own, a pump, and some kind of small rad. But otherwise they're a great little unit. Compact and super, super light.
There are no lines because there is no cooling jacket in the unit, right? You can add everything external, but that won't make it a liquid-cooled motor unless you create a cooling jacket. I can't remember offhand what builders ended up doing about this, if anything.
The Lexus only ever uses them for very short periods of time IIRC, when power is absolutely demanded. Doesn't mean one way or another that they're not suitable for continuous use, just that they never got it in the Lexus.
Not just the Lexus - the MGR is not used continuously in any Toyota hybrid. It's used when needed for traction, not overall power. Highlander Hybrids are known to shut down the MGR when trying to get out of an extended muddy area because the MGR has been run too long and gets too hot; it's not fatal (doesn't damage the motor), but it needs to "take a break" and cool down.
Ah, I'd completely missed there was a front motor on the 300h drivetrains too- reading here is sounded like only one motor and I could see rear motors on ebay so assumed that was where it was!
(info from here)
There isn't just a motor in front - the front has the engine and power-split transmission that uses two motor-generators to control the engine speed, as well as to regeneratively brake and to boost power using the battery.
Now I see where you're getting the "300h" name. That article is about powertrains - the "300h" part only describes the engine and hybrid system; the model it's in is named by the letters (IS, ES, GS , NX and RC). Most of those models do not use a separate electric-only rear drive unit - they are 2WD. Even with other engines and AWD, the rear motor is not used with the longitudinal version of the system (e.g. LS 600h). The article only mentions a rear motor in the RX, and there has never been a 300h version of the RX model (Lexus equivalent to the Toyota Highlander). The NX (Lexus equivalent to the Toyota RAV4) has a rear motor, and comes as the NX 300h. Other than those rear motors, the motors referred to in the article are in the transmission, not in a drive unit at the rear.
If I'm using this as a power boost hybrid then I guess lack of cooling could be ok, but not if it was to be the only motor driving the car all the time.
I agree, although it could be used as the only motor in a very light vehicle, especially with added cooling.