Hello everyone, I have been reading this forum for a while and today I got some free time so as my first post I want to share with you the results of an experiment that I made last year. The story begins when the dealership that serviced my car (Renault Clio) went out of business and I took it to another dealership who overfilled the engine with 2 or 3 litres, (something I thought it will never happen to me!!!), after about 4000 km the car started to be very difficult to start up and that is when I realized the overfill situation, anyway the extra oil fouled the spark plugs and formed deposits in the intake valves and manifold, so I extracted almost 2 litres of oil and cleaned the plugs but that didn't solve the problem; so I had to change the spark plugs, clean the intake, the valves and the fuel injectors and the solvent that I use went into the cylinders and the crankcase so I also had to change the oil. By then someone told me to change the oil, use it for about a week and change it again, so I got on sale a jug of Castrol GTX 15W-40 and put it in the car; but for some reason or another I didn't get around that second oil change; then about a month later I was outside the car when someone else started it and I get to hear a very peculiar sound that I identified from a You Tube video as a cold start rattle So I thought this would be a good opportunity to compare different oils and to get that second oil change, so for the second oil I got Valvoline SYNpower 5W-30 which is what I was going to use in the first place before I got convinced otherwise. So the test conditions were: Car: Renault Clio 2009 Petrol 1.6 16V K4M engine with 48,000 km. Parked overnight (about 16 hours) in a slight incline, start it up at 8:00 AM without touching any pedals or the steering wheel, let it run 20 seconds and shut off. The minimum outside temperature of both nights was 2 ºC. Photo of the engine Test 1: Outside temperature of 8 ºC. Oil: Castrol GTX 15W-40 SN, without API certification. Test 2: Outside temperature of 7 ºC. Oil: Valvoline Synpower 5W-30 SN, ILSAC GF-5, ACEA A1/A5 Both tests were recorded with a SONY Cybershot DSC-W630 resting on top of the battery and aimed in direction of the engine. Video http://youtu.be/mKHwq1b3004 Results:. In both tracks I can identify 4 events 1.- Noise of the starter motor (pretty obvious). 2.- Ticking noise after the start up but quickly disappears; I think those are the hydraulic lifters. 3.- A more deep and metallic sound that fades more slowly, this kind of reminds me of Chewbacca, like if he was screaming inside the engine, I think it sounds better in the filtered versions. don’t know what could possibly produce this sound. 4.- Shut Off: Also obvious but proves that I can not count to twenty in a reliable way (next time I'll use a timer). All tracks start at 0.200 s. 15W-40: Start up time 0.952s, ticking noise until 4.852s; metallic sound until 15s or 16s shut off 20.8 5W-30: Start up time 0.975s, ticking noise until 2.025s; metallic sound until 10s, shut off 19.2 To make it easier to identify the sounds I filtered both tracks using the noise canceling option in Audacity using the last 2 seconds before shut off of each track as the noise profile. I also put the track in reverse since that way is more evident the ticking sound in the beginning. Conclusions: If we work under the assumption of NOISE = WEAR, I think this demonstrates the effect of a low viscosity oil in the start up wear of an engine even in temperatures that are above freezing, we could say that the 15W-40 oil produces 2.5x more wear than the 5W-30; this is supported by the fact that starting up the engine at service temperature the ticking sound is gone. But maybe that assumption is incorrect, maybe the noise and wear are not linearly correlated so we will need another kind of test to further validate this idea. I did the noise canceling bit because I hear something else behind the noise of the engine but that could easily be me hearing things that are not there or could be an artifact of the noise canceling. Anyway, please let me know what you think of all this, if you hear the same things I do or maybe you hear something else like a satanic message in the reversed tracks. Thank You for reading this.