My dryer [Kennmore series 70] recently stopped working. I cleaned out the lint tray and hose, then installed a new thermal fuse.
It started to work again but is very hot and at a high temperate. The timer does not seem to work.
Does it now needs a thermostat or timer?

My suggestion is to check the thermostat.

General dryer check and test procedure :

Make sure you NOW FIRST disconnect the power cable from the wall socket , and put it on the ground in front of you.
Remove the top and/or rear panel and have a look as to what is going on inside.

Check thermostat(s), fuse(s) and the thermal cut-off'(s) in the dryer. Use a multimeter (Ohm function) to test for continuity.

Now the more dangerous part of testing : measuring voltages on a "life" machine! From here you have to work very carefully :

ALWAYS HAVE SOMEBODY AROUND WHO CAN PULL THE POWER CORD FROM THE SOCKET : IT CAN SAVE YOUR LIFE !!! Instruct the person what to do : NOT to touch or pull you, but to pull the power cord from the socket in case of problems. Once the power is disconnected they can help you.

Plug in the power cord. Close the door (empty drum) and switch the dryer to full power and start the machine.

Is the drum rotating properly? Is the fan blowing air in one continuous flow?
Measure the voltage over the heater element : is it Voltage stable or cycling?
If the voltage is cycling, is the frequency stable?
What is the speed of switching in seconds? Test 2 minutes to make sure. Note down the results, or call the switching to your assistant and let him/her note down the passed seconds.

Repeat the measurement, but now with the heat setting on half power.
Note down the results once again.

Of course you can also come back to the board and discuss your findings!

Success !

:)

Note 1 : Info on heating power arrangement :
The heater element is normally one single unit that has 2 connections.
One is neutral, the other is hot.
There are two ways of powering : Full power and regulated power. Both are protected against overheating by a thermal cut-out switch.
Half power is either obtained by thermostat cycling of the power, or by time switching via a relay.

Note 2 : ALWAYS clean the air filter from lint before running any drying cycle.
Lint can cause unnecessary heating up, fire, equipment failure, and it cost money for extra electricity use.
It also may cause your thermostat to cut out.

;)