I'm running this on a 3 member replicaset, on different machines.

/usr/bin/mongod --replSet rs --bind_ip 192.168.1.101 --dbpath /ramcache --port 35001 --logpath /var/log/mongodb/minimongo.log --storageEngine wiredTiger --logappend --wiredTigerCacheSizeGB 1 --nojournal

If i run them all with --nojournal, the following operation takes a few seconds to run:

from pymongo import MongoClient
pm = MongoClient('192.168.1.101: 192.168.1.102:35001, 192.168.1.101:35001', w=3, wtimeout=480000, j=False)
pm.testdb.testcol.insert_one({"asdf": "123"})
# this one here
print pm.testdb.testcol.update_one({"asdf": "123"}, {"$set": {"value": 1}})

Running db.currentOp() at the right time, can get the following info:

{
...
        "secs_running" : 2,
...
        "msg" : "waiting for write concern",
...
}

However, if i remove the --nojournal flag, it runs instantly, even with w=3. I've also noticed that if the primary member is running with --nojournal and the other 2 secondaries without --nojournal it still runs ok. I haven't managed to replicate this behaviour on a single machine with 3 mongod instances on different ports, so i can't completely say it's not a network issue, but i'm not sure how to investigate further.