Here are your parts
Replacement parts for YLTE5243DQR0 models | AppliancePartsPros.com

[COLOR="Blue"]Also, I've changed the thermostat...[/COLOR]
Which one the hi-limit or the operating thermostat (4 wire)?

Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 13 to 20 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostats cannot regulate it so the thermal cut-off (fuse) blows.

I am sort of betting on the grounded element theory.
The hi-limit should have regulated the temperature so the fuse did not blow.
Note: That unless there is another problem in the unit the hi-limit should never have to open. It is just a safety device with the fuse being a backup safety device.

Just in case it is not a grounded element.
With all the below the high limit will also have to be replaced.
Check that the belt is OK.
Check the seals (drum etc) in the unit. The air is pulled over the heating coils, through the drum and pushed out the exhaust. So any large seal leak will pull in room air and the cycling thermostat on the blower will run the unit hot.
Check that the lint filter is not coated with fabric softener residue which greatly reduces air flow.
Check/clean your vent system.
Check/clean the blower wheel.

If all OK you may want to replace the cycling thermostat as it's contacts may not be opening (welded shut)

[COLOR="Blue"]maybe the heating coil has lost its original properties (13 to 20 ohms). Is it possible?[/COLOR]
I do not think so. It could increase it's resistance but I cannot see how it could reduce it.

Check inside the heater for any sign of a weld mark or scorch, it could be the heater warms up and then sags touches the case, overheats and blows the fuse. Then when it cools it breaks the connection to the frame.

Also which thermostat did you replace?

Did this unit used to work OK for you or is it new to you?

OK

Since everything looks OK I would replace the following (Item 5 in Section 4). It is your main control thermostat.

Note: That it has 4 wires, 2 for the contacts and 2 for it's internal heater so be sure to note what wires go where.

Part number: AP2975271