White smoke coming from the tail pipe

You should see the level dropping in the coolant reservoir. There are two tests for a leaking cylinder head gasket. One is to add a small bottle of dark purple dye to the coolant, then check a day or two later with a black light. The dye will show up as a bright yellow stain. If the head gasket is leaking, you will find the dye inside the tail pipe. Auto parts stores will have the correct dye for the fluid being tested, and those that rent or borrow tools should have a black light.

https://www.2carpros.com/articles/head-gasket-blown-test

You can also have your mechanic perform a chemical test at the radiator, with the engine running. This involves drawing air from the radiator through a glass cylinder with two chambers partially-filed with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow. You can borrow this tool from auto parts stores too, but they will make you buy your own bottle of fluid. That is because it will be rendered ineffective if it freezes or becomes contaminated with antifreeze. They do not want to risk borrowing it to the next person with contaminated fluid. Paying your mechanic to perform this test, which just takes a few minutes, is less expensive than buying the bottle of fluid.

If cost of repair is an issue, consider looking for a nearby community college with an Automotive program. We were always looking for live work to give our kids real-world experience, but since they are only in the shop a few hours per day, it can takes weeks to get the car back. The cost will be very low, but you will also have to wait until they are teaching Engine Repair class. That might be only once or twice per year.

The labor time for replacing the head gasket is about 8.4 hours just in case you want to go that route and if you multiply that by hourly rates of $50.00 to $100.00 you get around $420.00 to $840.00 depending on who does it with the lowest just being a local garage or gas station mechanic and the highest being the dealer, although they could be even more than $100.00 an hour.