For most animals that can see IR, the resolution is pretty low*. Wouldn't expect "dazzling engines", but maybe rather a blob of something warm around / behind.
Also the dragon's "third eye" is delivering no real resolved image, but just some kind of a sensation. I would guess comparable what we can see out of the corner of the eye: Movements, and everything more shadow-and-blob-like.
*It's just a physics thing: The wavelength. Longer wavelength (IR is significant longer than optical or UV) means lower resolution under otherwise the same conditions. Same thing why astronomical images from radio telescopes (much longer wavelength than optical) look ways less detailed than those from conventional optical telescopes. One can use certain tricks to overcome this, especially how the data are processed (= in animals: what the brain does with it) like combining with higher-resolution images in other wavelength ranges or taking images under a slight offset angle, but "there is only so much".