This is one of the better reasons to use the old standby: heat the pan dry, then add fat, then add food. If you do it exclusively with oil it really depends on which oil, how hot or cold it was to begin with, how much you added, and so on. Besides, you may not be adding fat.
In any event, to tell if the pan is hot, the water test works quite well, and can be given greater range: if a droplet of water instantly zaps into steam, the pan is VERY hot, and ready for high-heat stir-frying (e.g., a good deal of Chinese wok cooking). Another test popular with many professionals is the cheek test: pick up the pan by its handle and hold it several inches to a foot from your cheek. You will detect heat very precisely that way, whereas your hand may become rather inured to high heat as you cook more and more. I do not recommend the cheek test with a wok, not so much because the heat is high as because the shape is such that by the time your cheek is close enough, the edge is searing your ear.
The metal skewer test is excellent for fish. Stab into the thickest part, wait several seconds, and then press the tip sideways just below your lower lip. Cold: raw. Warm: ready (depending on what you're cooking, of course). Hot: probably overcooked. Remember that the temperature will continue to rise just a bit after you remove the fish from the pan or oven, so it needs to be just underdone when you take it out. Anyway, it's much faster than any "instant-read" thermometer, and with practice easy and automatic.
All these temperature tests require practice, of course. If you get used to skewer-probing fish, you just shove it in there a few seconds before you think it's really going to be ready, yank it out, test, and then either pull the fish or wait a bit longer -- and if you're used to this test and the cooking method, you don't have to test again, because you know how hot it's going to be. You see?
Incidentally, if you are being tentative about pan heat, you're going to have trouble with a number of things. Just crank it up. You're not going to hurt anything. I'll give you an example.
Cut up about a cup each of onion, celery, and bell pepper, and mix well. Cut up some peeled raw potatoes. Cut some boneless, skinless chicken into large cubes. Have on hand about 8 cups of chicken stock, preferably unsalted homemade, but certainly low sodium. You can also use stock diluted with water, if you prefer. Get some of your favorite hot sauce (Tabasco, Crystal, etc.) and a couple Tb of some kind of Cajun/Creole/Louisiana premade seasoning mix. You'll also need a few Tb of high-smoke-point cooking oil, e.g. canola, and a big, deepish skillet or saucier.
Toss the chicken with half the seasoning mix and a couple shakes of hot sauce, and let sit for a few minutes or so.
Crank the heat. Maximum. Wait a minute -- literally a minute, not a few seconds. Flick water: does it run or flash into steam? In between would be great, but it really doesn't make a whole heck of a lot of difference so long as it's in that range.
Pour in the oil, swirl the pan around to glaze the bottom, and toss in the chicken. Toss it up in the pan with a wooden spoon, kind of scraping up stuff that sticks if need be -- but if the pan is very hot, chances are it won't stick. When the chicken is distinctly brown in a lot of parts -- not tan but golden brown -- pull it out with a slotted spoon and immediately add half of the onion-celery-pepper mix. Stir and scrape the bottom vigorously for about 15 seconds. Notice that the moisture in the vegetables deglazes the pan, i.e. removes the brown stuck chicken stuff. Let the mixture cook undisturbed (yes, still over very high heat) for 2 full minutes. Add the remaining seasoning mix and stir vigorously, scraping up any brown stuff -- there won't be much. Wait another 2 minutes and repeat the scraping. Repeat this process another couple of times, until you cannot scrape everything up and some of what's down there is looking worryingly close to black, i.e. burnt. Now add 1/2 cup of stock and scrape everything down there -- this is normal deglazing. When it's all cleared, add 3 cups of stock and the potatoes. Cook over high heat, stirring occasionally; if you have a cover for the pan, that's helpful, but not necessary. When the liquid has nearly boiled off, start stirring pretty often, and pay attention. As you get close to dry, the starch in the potatoes and other vegetables is going to start to stick HARD, and you need to scrape scrape scrape it up. Continue this process until you can't get it to clear and it's close to burning, and, once again, add 1/2 cup of stock. Stir-scrape to clear, add 2 cups stock, and boil off again as before. This time, deglaze with 1/2 cup stock, then add the reserved chicken and the remaining stock. When it comes to a rapid boil, turn down the heat and simmer gently until the chicken is cooked through. The stew will be brown and thick, with chunks of chicken; very little of the potato will be recognizable, because it should have broken down nearly completely. The flavor will be intense, both because of all that stock reduced to nothing and because that process of boiling off, crusting, and deglazing turns a lot of the vegetable starches into sugars.
The point of the exercise, of course, is that you are doing this entire dish, until the very last step, over as much heat as you can muster. The fact that the dish is also extremely healthy and inexpensive is just icing on the cake.