diff --git a/hysop/backend/device/autotunable_kernel.py b/hysop/backend/device/autotunable_kernel.py
index bbe6e21c760e015fb3ad22c39974ae9ab7b1494e..32d2d6359606ce48f4becb1d79becd79d39e5c35 100644
--- a/hysop/backend/device/autotunable_kernel.py
+++ b/hysop/backend/device/autotunable_kernel.py
@@ -23,7 +23,7 @@ class AutotunableKernel(object):
         self.symbolic_mode = first_not_None(symbolic_mode, autotuner_config.debug)
 
     def custom_hash(self, *args, **kwds):
-        HASH_DEBUG=True
+        HASH_DEBUG=False
         assert args or kwds, 'no arguments to be hashed.'
 
         def _hash_arg(a):
diff --git a/hysop/backend/device/codegen/kernels/directional_advection.py b/hysop/backend/device/codegen/kernels/directional_advection.py
index fb0b1cfc4bb3f6346c594985543cc508bdda8384..7a5a0b438f03b711c3d4e3b2e19853365d1449d0 100644
--- a/hysop/backend/device/codegen/kernels/directional_advection.py
+++ b/hysop/backend/device/codegen/kernels/directional_advection.py
@@ -701,6 +701,7 @@ if __name__ == '__main__':
         symbolic_mode=True,
         relative_velocity=0.66,
         nparticles=4,                        # MONOLEVEL TEST
+        tuning_mode = True,
         #nparticles=1, is_bilevel=(256,64,32), # BILEVEL TEST
         known_vars=dict(
             V_mesh_info=vmesh_info,
diff --git a/hysop/backend/device/kernel_autotuner.py b/hysop/backend/device/kernel_autotuner.py
index 4f09b4c4faa02ee9440848c471e8fe50833736cd..5e8b840f5e9f94ea0659d6078f5bffd02a87fd05 100644
--- a/hysop/backend/device/kernel_autotuner.py
+++ b/hysop/backend/device/kernel_autotuner.py
@@ -22,7 +22,7 @@ class KernelAutotuner(object):
 
     FULL_RESULTS_KEY = '__FULL_RESULTS__'
     DUMP_LAST_TUNED_KERNEL    = False
-    STORE_FULL_KERNEL_SOURCES = True
+    STORE_FULL_KERNEL_SOURCES = False
     
     @staticmethod 
     def _hash_func():
diff --git a/hysop/backend/device/opencl/autotunable_kernels/advection_dir.py b/hysop/backend/device/opencl/autotunable_kernels/advection_dir.py
index 8a1fb8793ac4d132a74589acf50db843a12efb9e..9c8ef420c0bad770b50385c533b89a7510b45ce6 100644
--- a/hysop/backend/device/opencl/autotunable_kernels/advection_dir.py
+++ b/hysop/backend/device/opencl/autotunable_kernels/advection_dir.py
@@ -61,8 +61,10 @@ class OpenClAutotunableDirectionalAdvectionKernel(OpenClAutotunableKernel):
         vboundaries = (velocity.global_lboundaries[-1], velocity.global_rboundaries[-1])
         
         eps = npw.finfo(precision).eps
-        dt = 10*eps
-        assert (dt > +0.0), 'Precision {} cannot represent 1e-7.'.format(precision)
+        dt = velocity_cfl
+        velocity.fill(1.0)
+        velocity.exchange_ghosts()
+
 
         make_offset, offset_dtype = self.make_array_offset()
         make_strides, strides_dtype = self.make_array_strides(position.dim,