diff --git a/scrapy/core/engine.py b/scrapy/core/engine.py
index 1bbf8921f..d5e3f4064 100644
--- a/scrapy/core/engine.py
+++ b/scrapy/core/engine.py
@@ -102,7 +102,6 @@ class ExecutionEngine:
         )
         self.start_time: float | None = None
         self._start: AsyncIterator[Any] | None = None
-        self._started_request_processing = False
         downloader_cls: type[Downloader] = load_object(self.settings["DOWNLOADER"])
         try:
             self.scheduler_cls: type[BaseScheduler] = self._get_scheduler_class(
@@ -135,7 +134,7 @@ class ExecutionEngine:
         )
         self.running = True
         if _start_request_processing:
-            self.start_request_processing()
+            self._start_request_processing()
         self._closewait: Deferred[None] = Deferred()
         await maybe_deferred_to_future(self._closewait)
 
@@ -207,13 +206,9 @@ class ExecutionEngine:
                 self._slot.nextcall.schedule()
 
     @deferred_f_from_coro_f
-    async def start_request_processing(self) -> None:
+    async def _start_request_processing(self) -> None:
         """Starts consuming Spider.start() output and sending scheduled
         requests."""
-        if self._started_request_processing:
-            raise RuntimeError("Request processing already started")
-        self._started_request_processing = True
-
         # Starts the processing of scheduled requests, as well as a periodic
         # call to that processing method for scenarios where the scheduler
         # reports having pending requests but returns none.
diff --git a/scrapy/shell.py b/scrapy/shell.py
index 14bc31137..bb39eccc3 100644
--- a/scrapy/shell.py
+++ b/scrapy/shell.py
@@ -128,7 +128,7 @@ class Shell:
         await maybe_deferred_to_future(
             self.crawler.engine.open_spider(spider, close_if_idle=False)
         )
-        self.crawler.engine.start_request_processing()
+        self.crawler.engine._start_request_processing()
         self.spider = spider
 
     def fetch(