diff --git a/.changelog/2946.txt b/.changelog/2946.txt
new file mode 100644
index 00000000000..307f2798104
--- /dev/null
+++ b/.changelog/2946.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+compute: fixed `google_compute_router_nat` timeout fields causing a diff when using a long-lived resource
+```
diff --git a/google/resource_access_context_manager_access_level.go b/google/resource_access_context_manager_access_level.go
index 0594dc0ad95..dfc2496102b 100644
--- a/google/resource_access_context_manager_access_level.go
+++ b/google/resource_access_context_manager_access_level.go
@@ -462,9 +462,10 @@ func flattenAccessContextManagerAccessLevelBasic(v interface{}, d *schema.Resour
 	return []interface{}{transformed}
 }
 func flattenAccessContextManagerAccessLevelBasicCombiningFunction(v interface{}, d *schema.ResourceData) interface{} {
-	if v == nil || v.(string) == "" {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
 		return "AND"
 	}
+
 	return v
 }
 
diff --git a/google/resource_access_context_manager_service_perimeter.go b/google/resource_access_context_manager_service_perimeter.go
index 9f91c189d9a..990630d4e03 100644
--- a/google/resource_access_context_manager_service_perimeter.go
+++ b/google/resource_access_context_manager_service_perimeter.go
@@ -407,9 +407,10 @@ func flattenAccessContextManagerServicePerimeterUpdateTime(v interface{}, d *sch
 }
 
 func flattenAccessContextManagerServicePerimeterPerimeterType(v interface{}, d *schema.ResourceData) interface{} {
-	if v == nil || v.(string) == "" {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
 		return "PERIMETER_TYPE_REGULAR"
 	}
+
 	return v
 }
 
diff --git a/google/resource_compute_address.go b/google/resource_compute_address.go
index d627d470946..e8a831e1300 100644
--- a/google/resource_compute_address.go
+++ b/google/resource_compute_address.go
@@ -353,9 +353,10 @@ func flattenComputeAddressAddress(v interface{}, d *schema.ResourceData) interfa
 }
 
 func flattenComputeAddressAddressType(v interface{}, d *schema.ResourceData) interface{} {
-	if v == nil || v.(string) == "" {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
 		return "EXTERNAL"
 	}
+
 	return v
 }
 
diff --git a/google/resource_compute_router_nat.go b/google/resource_compute_router_nat.go
index fa8c82a4306..dd5c3d07275 100644
--- a/google/resource_compute_router_nat.go
+++ b/google/resource_compute_router_nat.go
@@ -721,42 +721,58 @@ func flattenComputeRouterNatMinPortsPerVm(v interface{}, d *schema.ResourceData)
 }
 
 func flattenComputeRouterNatUdpIdleTimeoutSec(v interface{}, d *schema.ResourceData) interface{} {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
+		return 30
+	}
 	// Handles the string fixed64 format
 	if strVal, ok := v.(string); ok {
 		if intVal, err := strconv.ParseInt(strVal, 10, 64); err == nil {
 			return intVal
 		} // let terraform core handle it if we can't convert the string to an int.
 	}
+
 	return v
 }
 
 func flattenComputeRouterNatIcmpIdleTimeoutSec(v interface{}, d *schema.ResourceData) interface{} {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
+		return 30
+	}
 	// Handles the string fixed64 format
 	if strVal, ok := v.(string); ok {
 		if intVal, err := strconv.ParseInt(strVal, 10, 64); err == nil {
 			return intVal
 		} // let terraform core handle it if we can't convert the string to an int.
 	}
+
 	return v
 }
 
 func flattenComputeRouterNatTcpEstablishedIdleTimeoutSec(v interface{}, d *schema.ResourceData) interface{} {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
+		return 1200
+	}
 	// Handles the string fixed64 format
 	if strVal, ok := v.(string); ok {
 		if intVal, err := strconv.ParseInt(strVal, 10, 64); err == nil {
 			return intVal
 		} // let terraform core handle it if we can't convert the string to an int.
 	}
+
 	return v
 }
 
 func flattenComputeRouterNatTcpTransitoryIdleTimeoutSec(v interface{}, d *schema.ResourceData) interface{} {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
+		return 30
+	}
 	// Handles the string fixed64 format
 	if strVal, ok := v.(string); ok {
 		if intVal, err := strconv.ParseInt(strVal, 10, 64); err == nil {
 			return intVal
 		} // let terraform core handle it if we can't convert the string to an int.
 	}
+
 	return v
 }
 
diff --git a/google/resource_compute_target_https_proxy.go b/google/resource_compute_target_https_proxy.go
index 9d3bce7c78b..3b7777f6b2e 100644
--- a/google/resource_compute_target_https_proxy.go
+++ b/google/resource_compute_target_https_proxy.go
@@ -457,6 +457,10 @@ func flattenComputeTargetHttpsProxyName(v interface{}, d *schema.ResourceData) i
 }
 
 func flattenComputeTargetHttpsProxyQuicOverride(v interface{}, d *schema.ResourceData) interface{} {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
+		return "NONE"
+	}
+
 	return v
 }
 
diff --git a/google/resource_dns_managed_zone.go b/google/resource_dns_managed_zone.go
index 67473e8a7f1..0a937382f63 100644
--- a/google/resource_dns_managed_zone.go
+++ b/google/resource_dns_managed_zone.go
@@ -544,9 +544,10 @@ func flattenDNSManagedZoneLabels(v interface{}, d *schema.ResourceData) interfac
 }
 
 func flattenDNSManagedZoneVisibility(v interface{}, d *schema.ResourceData) interface{} {
-	if v == nil || v.(string) == "" {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
 		return "public"
 	}
+
 	return v
 }
 
diff --git a/google/resource_logging_metric.go b/google/resource_logging_metric.go
index 87e6dab1f33..e69bff67fd8 100644
--- a/google/resource_logging_metric.go
+++ b/google/resource_logging_metric.go
@@ -586,9 +586,10 @@ func flattenLoggingMetricMetricDescriptorLabelsDescription(v interface{}, d *sch
 }
 
 func flattenLoggingMetricMetricDescriptorLabelsValueType(v interface{}, d *schema.ResourceData) interface{} {
-	if v == nil || v.(string) == "" {
+	if v == nil || isEmptyValue(reflect.ValueOf(v)) {
 		return "STRING"
 	}
+
 	return v
 }