diff --git a/common/prefix.py b/common/prefix.py
index c1744e8ff7..d027e3e5a1 100644
--- a/common/prefix.py
+++ b/common/prefix.py
@@ -6,12 +6,14 @@ from typing import Optional
 
 from openpilot.common.params import Params
 from openpilot.system.hardware.hw import Paths
+from openpilot.system.hardware.hw import DEFAULT_DOWNLOAD_CACHE_ROOT
 
 class OpenpilotPrefix:
-  def __init__(self, prefix: Optional[str] = None, clean_dirs_on_exit: bool = True):
+  def __init__(self, prefix: Optional[str] = None, clean_dirs_on_exit: bool = True, shared_download_cache: bool = False):
     self.prefix = prefix if prefix else str(uuid.uuid4().hex[0:15])
     self.msgq_path = os.path.join('/dev/shm', self.prefix)
     self.clean_dirs_on_exit = clean_dirs_on_exit
+    self.shared_download_cache = shared_download_cache
 
   def __enter__(self):
     self.original_prefix = os.environ.get('OPENPILOT_PREFIX', None)
@@ -22,6 +24,9 @@ class OpenpilotPrefix:
       pass
     os.makedirs(Paths.log_root(), exist_ok=True)
 
+    if self.shared_download_cache:
+      os.environ["COMMA_CACHE"] = DEFAULT_DOWNLOAD_CACHE_ROOT
+
     return self
 
   def __exit__(self, exc_type, exc_obj, exc_tb):
@@ -42,5 +47,6 @@ class OpenpilotPrefix:
       os.remove(symlink_path)
     shutil.rmtree(self.msgq_path, ignore_errors=True)
     shutil.rmtree(Paths.log_root(), ignore_errors=True)
-    shutil.rmtree(Paths.download_cache_root(), ignore_errors=True)
+    if not os.environ.get("COMMA_CACHE", False):
+      shutil.rmtree(Paths.download_cache_root(), ignore_errors=True)
     shutil.rmtree(Paths.comma_home(), ignore_errors=True)
diff --git a/conftest.py b/conftest.py
index d8cbe25b0a..c4eb259a35 100644
--- a/conftest.py
+++ b/conftest.py
@@ -25,13 +25,13 @@ def pytest_runtest_call(item):
 
 
 @pytest.fixture(scope="function", autouse=True)
-def openpilot_function_fixture():
+def openpilot_function_fixture(request):
   starting_env = dict(os.environ)
 
   random.seed(0)
 
   # setup a clean environment for each test
-  with OpenpilotPrefix():
+  with OpenpilotPrefix(shared_download_cache=request.node.get_closest_marker("shared_download_cache") is not None) as prefix:
     prefix = os.environ["OPENPILOT_PREFIX"]
 
     yield
@@ -77,3 +77,6 @@ def pytest_configure(config):
 
   config_line = "nocapture: don't capture test output"
   config.addinivalue_line("markers", config_line)
+
+  config_line = "shared_download_cache: share download cache between tests"
+  config.addinivalue_line("markers", config_line)
diff --git a/selfdrive/car/tests/test_models.py b/selfdrive/car/tests/test_models.py
index a66bd180b4..973101d4ca 100755
--- a/selfdrive/car/tests/test_models.py
+++ b/selfdrive/car/tests/test_models.py
@@ -22,6 +22,7 @@ from openpilot.selfdrive.car.honda.values import CAR as HONDA, HONDA_BOSCH
 from openpilot.selfdrive.car.tests.routes import non_tested_cars, routes, CarTestRoute
 from openpilot.selfdrive.controls.controlsd import Controls
 from openpilot.selfdrive.test.helpers import read_segment_list
+from openpilot.system.hardware.hw import DEFAULT_DOWNLOAD_CACHE_ROOT
 from openpilot.tools.lib.openpilotci import get_url
 from openpilot.tools.lib.logreader import LogReader
 from openpilot.tools.lib.sanitizer import sanitize
@@ -64,6 +65,7 @@ def get_test_cases() -> List[Tuple[str, Optional[CarTestRoute]]]:
 
 
 @pytest.mark.slow
+@pytest.mark.shared_download_cache
 class TestCarModelBase(unittest.TestCase):
   car_model: Optional[str] = None
   test_route: Optional[CarTestRoute] = None
@@ -183,6 +185,8 @@ class TestCarModelBase(unittest.TestCase):
     assert cls.CP
     assert cls.CP.carFingerprint == cls.car_model
 
+    os.environ["COMMA_CACHE"] = DEFAULT_DOWNLOAD_CACHE_ROOT
+
   @classmethod
   def tearDownClass(cls):
     del cls.can_msgs
diff --git a/selfdrive/locationd/test/test_locationd_scenarios.py b/selfdrive/locationd/test/test_locationd_scenarios.py
index 4cfbd6f8a9..f48c83ce46 100755
--- a/selfdrive/locationd/test/test_locationd_scenarios.py
+++ b/selfdrive/locationd/test/test_locationd_scenarios.py
@@ -97,6 +97,7 @@ def run_scenarios(scenario, logs):
 
 
 @pytest.mark.xdist_group("test_locationd_scenarios")
+@pytest.mark.shared_download_cache
 class TestLocationdScenarios(unittest.TestCase):
   """
   Test locationd with different scenarios. In all these scenarios, we expect the following:
diff --git a/system/hardware/hw.py b/system/hardware/hw.py
index a8967520e3..694299d72e 100644
--- a/system/hardware/hw.py
+++ b/system/hardware/hw.py
@@ -3,6 +3,8 @@ from pathlib import Path
 
 from openpilot.system.hardware import PC
 
+DEFAULT_DOWNLOAD_CACHE_ROOT = "/tmp/comma_download_cache"
+
 class Paths:
   @staticmethod
   def comma_home() -> str:
@@ -31,8 +33,8 @@ class Paths:
   @staticmethod
   def download_cache_root() -> str:
     if os.environ.get('COMMA_CACHE', False):
-      return os.environ['COMMA_CACHE']
-    return "/tmp/comma_download_cache" + os.environ.get("OPENPILOT_PREFIX", "") + "/"
+      return os.environ['COMMA_CACHE'] + "/"
+    return DEFAULT_DOWNLOAD_CACHE_ROOT + os.environ.get("OPENPILOT_PREFIX", "") + "/"
 
   @staticmethod
   def persist_root() -> str: