diff --git a/README.md b/README.md
index b1bbb79..6409309 100644
--- a/README.md
+++ b/README.md
@@ -81,7 +81,7 @@ COW 将以下错误认为是墙在作怪：
 
 无论是普通的 HTTP GET 等请求还是 CONNECT 请求，失败后 COW 都会自动重试请求。（如果已经有内容发送回 client 则不会重试而是直接断开连接。）
 
-用连接被重置来判断被墙通常来说比较可靠，超时则不可靠。COW 每隔一分钟会尝试估算合适的超时间隔，避免在网络连接差的情况下把直连网站由于超时也当成被墙。
+用连接被重置来判断被墙通常来说比较可靠，超时则不可靠。COW 每隔半分钟会尝试估算合适的超时间隔，避免在网络连接差的情况下把直连网站由于超时也当成被墙。
 COW 默认配置下检测到被墙后，过两分钟再次尝试直连也是为了避免误判。
 
 如果超时自动重试给你造成了问题，请参考[样例配置](doc/sample-config/rc)高级选项中的 `readTimeout`, `dialTimeout` 选项。
diff --git a/estimate_timeout.go b/estimate_timeout.go
index 8adc5ca..0eec2b3 100644
--- a/estimate_timeout.go
+++ b/estimate_timeout.go
@@ -10,7 +10,6 @@ const minDialTimeout = 3 * time.Second
 const minReadTimeout = 4 * time.Second
 const defaultDialTimeout = 5 * time.Second
 const defaultReadTimeout = 5 * time.Second
-const maxTimeout = 20 * time.Second
 
 var dialTimeout, readTimeout time.Duration // initialized in runEstimateTimeout
 
@@ -30,7 +29,8 @@ var estimateReq = []byte("GET / HTTP/1.1\r\n" +
 // considering non-blocked sites as blocked when network connection is bad.
 func estimateTimeout() {
 	debug.Println("estimating timeout")
-	buf := make([]byte, 4096)
+	buf := connectBuf.Get()
+	defer connectBuf.Put(buf)
 	var est time.Duration
 
 	start := time.Now()
@@ -44,9 +44,6 @@ func estimateTimeout() {
 
 	est = time.Now().Sub(start) * 5
 	debug.Println("estimated dialTimeout:", est)
-	if est > maxTimeout {
-		est = maxTimeout
-	}
 	if est > config.DialTimeout {
 		dialTimeout = est
 		info.Println("new dial timeout:", dialTimeout)
@@ -68,12 +65,10 @@ func estimateTimeout() {
 	if err != io.EOF {
 		errl.Printf("estimateTimeout: error getting %s: %v, network has problem?\n",
 			estimateSite, err)
+		goto onErr
 	}
 	est = time.Now().Sub(start) * 10
 	debug.Println("estimated read timeout:", est)
-	if est > maxTimeout {
-		est = maxTimeout
-	}
 	if est > time.Duration(config.ReadTimeout) {
 		readTimeout = est
 		info.Println("new read timeout:", readTimeout)
@@ -92,6 +87,12 @@ func runEstimateTimeout() {
 	dialTimeout = config.DialTimeout
 	for {
 		estimateTimeout()
-		time.Sleep(time.Minute)
+		time.Sleep(30 * time.Second)
 	}
 }
+
+// Guess network status based on doing HTTP request to estimateSite
+func networkGood() bool {
+	return (readTimeout == config.ReadTimeout) &&
+		(dialTimeout == config.DialTimeout)
+}
diff --git a/sitestat.go b/sitestat.go
index 03d8752..4604f19 100644
--- a/sitestat.go
+++ b/sitestat.go
@@ -143,6 +143,9 @@ func (vc *VisitCnt) visit(inc *vcntint) {
 }
 
 func (vc *VisitCnt) DirectVisit() {
+	if !networkGood() {
+		return
+	}
 	if vc.userSpecified() {
 		return
 	}
@@ -153,6 +156,9 @@ func (vc *VisitCnt) DirectVisit() {
 }
 
 func (vc *VisitCnt) BlockedVisit() {
+	if !networkGood() {
+		return
+	}
 	if vc.userSpecified() || vc.AsTempBlocked() {
 		return
 	}