Most know I'm the RX importer for Australia though my friend Ron pays/distributes it. I have an 89 Mazda 626 2.2 turbo (GT in the U.S I believe) that has had 3 complete RX cleans/rinses with various oils and PureONE filters (not a good choice for RX duty IMO) in the distant past. Rx maint dose every OCI since. I've been running Pennzoil Performax 100 5W50 real syn for two OCI's with a M1 10W30 top up and no RX maint dose. A while back my 194F thermostat was changed after dying by my workshop for a 180F by mistake and consequently the engine runs much colder. I just had some work done at my workshop and provided my own oil (Castrol Magnatec 10W40) as they use very thick (up to 40W70) oils. Now intermittently I get masses of white smoke from the exhaust pipe. As a long term RX importer/user I'm very surprised. I Have 140km's on this oil/RX mix and I'm trying to get my head around what's going on? On the original 3 RX cleans nothing like this happened so I'm mystfied. Still the engine is quiter/smoother already which is a nice surprise. Maybe the long runs (10-15,000kms) with 5W50 and a colder thermostat have given me some unwanted sludge/nasties. Opinions welcomed....s