Hi all. My X300 had a moment today on the motorway. I was sitting at 80 mph for about an hour and all was good then in the rear view mirror I saw a grey ish cloud of smoke bellowing out from the rear of the car. I instantly pulled into lane one and slowed down to 50 mph. The smoke lasted for about 5 is seconds and ended. All the gauge read ok and no warning lights on the dash. Anyway I continued on the motorway for another 100 miles but stuck to a maximum of 70mph and all was fine. No knocking, no burning smells and no oil dripping out the engine. The water, engine oil and gearbox oil was all at the correct levels with no indication of any fluid lost at all.
has anyone got any ideas ?

 

The coolant temp gauge on the dash which is reflective of the head temp but is a rough and not accurate gauge , no red overheat light

At the high speed / engine load you may have been in the range of the radiator fans needing to be in high mode ( ? ) or warping heads just enough

You may have 3.2 liter which would be more applicable

To test for high mode , have key in run but not started

Remove the 3 wire connector on the radiator rear left lower ( coolant temp " switch " )

Notice this is different than the coolant flow thermostat that may not be opening enough ( thermostats whole other ball game but this easier ) If you do change thermostat do not install large O - ring , even if it comes with one , cracks thermostat casting ears / bad for many

Jumper one white wire to black and will get low mode , this test the fans and fan control relay module under car

Jumper the other white wire to black and will get high mode

To test the 3 wire coolant temp switch itself you would have to remove switch and immerse in boiling water for a 100 C and 86 C closing of the switch contacts ( mostly what you are looking for is the water boiling 100 C closing to have high mode )

My fan control relay module was mounted upside down allowing water to go through module connector ruining the high and low contacts when I cut it open , the connector should be on bottem , I could hold my fan control relay module in air and shake and hear water inside , the black fan control module for the X308 ( V8 ) will not work for the inline 6 version ( white ) they are close but not quite

 

I had this exact phenomenon occur to me on a long drive months ago and it has not re-occurred...I am not clear on what Parker7 response to this post means and how the belching smoke relates to the cooling fans. Engine temp was N when the belch occurred.

 

that makes me feel a little better. The car has been driving fine since with no issues at all. The only thing I can think is that I moved home about 2 months ago and now the X300 only does short trips as in only 5 miles each way so doing a motorway trip may of cleaned the engine out?

 

My event was the first long drive after sitting in a garage and rarely being driven except to be serviced before prior owner sold it to me...I later called and described the harrowing event...no good science-based educated guesses at hand, we started the "sounds good" "common sense" speculation of the cause of the fleeting billows of smoke...We both mused it was just "cleaning out the buildup" whatever that might mean...I am glad it only happened once as I was ready to pull over but instead I elected to start making deals with the car and God to get me home from LA to San Diego before rush hour traffic and dark and rush hour to....Made it home safely and now I owe the car I bought! Not sure if God is going to press me for collection....All's well that ends well!