diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 0.4.2
+
+The reaper thread for a manager will go to sleep completely when there are no connection to manage. See: https://github.com/snoyberg/http-client/issues/70
+
 ## 0.4.1
 
 * Provide the `responseOpenHistory`/`withResponseHistory` API. See: https://github.com/snoyberg/http-client/pull/79
diff --git a/Network/HTTP/Client/Manager.hs b/Network/HTTP/Client/Manager.hs
--- a/Network/HTTP/Client/Manager.hs
+++ b/Network/HTTP/Client/Manager.hs
@@ -32,7 +32,7 @@
 import qualified Data.Text as T
 
 import Control.Monad.IO.Class (MonadIO, liftIO)
-import Control.Monad (unless, join)
+import Control.Monad (unless, join, when, void)
 import Control.Exception (mask_, SomeException, bracket, catch, throwIO, fromException, mask, IOException, Exception (..), handle)
 import Control.Concurrent (forkIO, threadDelay)
 import Data.Time (UTCTime (..), Day (..), DiffTime, getCurrentTime, addUTCTime)
@@ -47,6 +47,7 @@
 import Network.HTTP.Client.Types
 import Network.HTTP.Client.Connection
 import Network.HTTP.Client.Headers (parseStatusHeaders)
+import Control.Concurrent.MVar (MVar, takeMVar, tryPutMVar, newEmptyMVar)
 
 -- | A value for the @managerRawConnection@ setting, but also allows you to
 -- modify the underlying @Socket@ to set additional settings. For a motivating
@@ -112,6 +113,7 @@
 putSocket man key ci = do
     now <- getCurrentTime
     join $ I.atomicModifyIORef (mConns man) (go now)
+    void $ tryPutMVar (mConnsBaton man) ()
   where
     go _ ManagerClosed = (ManagerClosed , connectionClose ci)
     go now mc@(ManagerOpen idleCount m)
@@ -153,10 +155,12 @@
     tlsConnection <- managerTlsConnection ms
     tlsProxyConnection <- managerTlsProxyConnection ms
     mapRef <- I.newIORef $! ManagerOpen 0 Map.empty
+    baton <- newEmptyMVar
     wmapRef <- I.mkWeakIORef mapRef $ closeManager' mapRef
-    _ <- forkIO $ reap wmapRef
+    _ <- forkIO $ reap baton wmapRef
     let manager = Manager
             { mConns = mapRef
+            , mConnsBaton = baton
             , mMaxConns = managerConnCount ms
             , mResponseTimeout = managerResponseTimeout ms
             , mRawConnection = rawConnection
@@ -169,8 +173,8 @@
     return manager
 
 -- | Collect and destroy any stale connections.
-reap :: Weak (I.IORef ConnsMap) -> IO ()
-reap wmapRef =
+reap :: MVar () -> Weak (I.IORef ConnsMap) -> IO ()
+reap baton wmapRef =
     mask_ loop
   where
     loop = do
@@ -183,8 +187,13 @@
     goMapRef mapRef = do
         now <- getCurrentTime
         let isNotStale time = 30 `addUTCTime` time >= now
-        toDestroy <- I.atomicModifyIORef mapRef (findStaleWrap isNotStale)
+        (newMap, toDestroy) <- I.atomicModifyIORef mapRef $ \m ->
+            let (newMap, toDestroy) = findStaleWrap isNotStale m
+             in (newMap, (newMap, toDestroy))
         mapM_ safeConnClose toDestroy
+        case newMap of
+            ManagerOpen _ m | not $ Map.null m -> return ()
+            _ -> takeMVar baton
         loop
     findStaleWrap _ ManagerClosed = (ManagerClosed, [])
     findStaleWrap isNotStale (ManagerOpen idleCount m) =
diff --git a/Network/HTTP/Client/MultipartFormData.hs b/Network/HTTP/Client/MultipartFormData.hs
--- a/Network/HTTP/Client/MultipartFormData.hs
+++ b/Network/HTTP/Client/MultipartFormData.hs
@@ -3,14 +3,14 @@
 --
 -- > {-# LANGUAGE OverloadedStrings #-}
 -- > import Network
--- > import Network.HTTP.Conduit
--- > import Network.HTTP.Conduit.MultipartFormData
+-- > import Network.HTTP.Client
+-- > import Network.HTTP.Client.MultipartFormData
 -- >
 -- > import Data.Text.Encoding as TE
 -- >
 -- > import Control.Monad
 -- >
--- > main = withSocketsDo $ withManager $ \m -> do
+-- > main = withSocketsDo $ void $ withManager defaultManagerSettings $ \m -> do
 -- >     req1 <- parseUrl "http://random-cat-photo.net/cat.jpg"
 -- >     res <- httpLbs req1 m
 -- >     req2 <- parseUrl "http://example.org/~friedrich/blog/addPost.hs"
diff --git a/Network/HTTP/Client/Types.hs b/Network/HTTP/Client/Types.hs
--- a/Network/HTTP/Client/Types.hs
+++ b/Network/HTTP/Client/Types.hs
@@ -50,6 +50,7 @@
 import qualified Data.Map as Map
 import Data.Text (Text)
 import Data.Streaming.Zlib (ZlibException)
+import Control.Concurrent.MVar (MVar)
 
 -- | An @IO@ action that represents an incoming response body coming from the
 -- server. Data provided by this action has already been gunzipped and
@@ -505,6 +506,12 @@
 data Manager = Manager
     { mConns :: I.IORef ConnsMap
     -- ^ @Nothing@ indicates that the manager is closed.
+    , mConnsBaton :: MVar ()
+    -- ^ Used to indicate to the reaper thread that it has some work to do.
+    -- This must be filled every time a connection is returned to the manager.
+    -- While redundant with the @IORef@ above, this allows us to have the
+    -- reaper thread fully blocked instead of running every 5 seconds when
+    -- there are no connections to manage.
     , mMaxConns :: Int
     -- ^ This is a per-@ConnKey@ value.
     , mResponseTimeout :: Maybe Int
diff --git a/http-client.cabal b/http-client.cabal
--- a/http-client.cabal
+++ b/http-client.cabal
@@ -1,5 +1,5 @@
 name:                http-client
-version:             0.4.1
+version:             0.4.2
 synopsis:            An HTTP client engine, intended as a base layer for more user-friendly packages.
 description:         This codebase has been refactored from http-conduit.
 homepage:            https://github.com/snoyberg/http-client