Viscousity 5W20-5W50 ?

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Dec 14, 2005
OK I'm new here so pardon my spelling. My question is, what is the difference between 5W20 and 5W50 engine oil. From what I have been told the 5W stands for winter flow or cold starting flow rate ( viscousity )and the last number 20 or 50 is the rating for high temperature protection of a single grade oil. The oil does not thickin to 20 or 50 it just protects to that weight. Hondas recomend a 5W20 and I question why a 5W30 or 5W40 can't be used in that or any engine being that the 5W oil is used. I have used 5W50 with no problems in my last car for 100,000 miles and never gave it much thought. I think that it cost more to produce oil of 5W that protects up to 40 or 50. European blends of oils are also comimg into our markets and wonder why we are behind or are they any different then ours? My MB C Coupe only recomends certain oils that pass 229.3 testing. What makes their engines different from other cars? Thanks for the help here!! [Smile]
Hi Mitch. Your figures are a bit technical for me. What I was trying to find out is that both 5W20 and 5W50 are the same thickness when cold and when the oil gets hot the thickness doesn't change, does it? I thought the 50 had more additives to protect as well as a 50W single weight oil at higher temps then the 20. I can remember hearing that oil doesn't thicken when hot, it just holds its viscousity as stated by the first number ( 5W )
The numbers given are average actual viscocities. The bigger the number, the thicker the oil. So, you see, the 5W20 oil is a LOT thinner at 40dC and remain a lot thinner at 100dC. All oils get thinner as temperature increases. If you search you can find a viscocity calculator that you can plug in the 40dC number and the 100dC number and then querry the viscociy of that oil at any selected temperature. You will see a definate pattern of thinning with temperature. In (very) general, the additives are independent of the spread between the 5W number and the -xx number (excepting the polumers that govern the viscocity spread.) The fisrt number (5W) telly you a little about what the oil will be like when you start the car on a typical spring day. The second number (-xx) tells you something about the viscocity of the oil as you drive down the highway. Since all automobiles are operated at a controlled temeperature (water thermostat) the oil ends up rather near the 100dC viscocity number when the vehicle is used in a low power condition (like cruising down the interstate). This happens both winter and summer with only a few degrees different in the actual oil temperature. So for actual long term operating conditions (e.g. after warmup), only the last number is relevent. For startup conditions (e.g first 15 minutes) only the first number is relevent. For high power environments (race track use) the HTHS number is relevent.
The simple answer is that the 5W-50 oil will be much thicker at operating temperature than the 5W-20. At around -30C, where the 5W spec is determined, you could expect both types to have a similar thickness.
Wow, it is confusing. Lets straighten out a few things. 1. As oil gets hotter it gets thinner. (always) 2. The point of multiweight oils is to make oils thinner when cold and thicker when hot - as compared to a straight weight oil. 3. The first number tells you how the oil behaves at VERY cold temperatures like around 0 deg F. Not a typical spring day. At say 50 deg F, a 5W20 will be much thinner than a 5W40 oil. In fact a 5W20 oil will be thinner than a 5W40 oil at all temperatures your car will ever see, unless you like to start your car at colder than minus 10 deg F. 4. The 50 oil does not have more additives than a 20 oil (necessarily)
OK, Now I understand. I wonder why companies only recomend 5W20 for their engines? I think they are concerned about MPG figures. I don't think 5W50 will hurt any engine though. I know MPG might drop a bit but as long as there is no damage to the engine then it wont hurt. If you can read between the lines, I have some 5W50 in my garage that I would like to use up and have given some thought to mixing it with 5W30 to dilute it maybe 3 to 1. Waste not want not, as the saying goes. I have a habit of buying oil when it goes on sale and as I have said I used it in my Montana van and now want to use it in my daily driver ( Vibe AKA Matrix ) Many Thanks for the info, Tony
Wright now in the outback of Australia the outside temp is 44C and ive always use 5w40 BP Visco 5000 or mobil 1 5w50. Tried the 5w20 and 10w30 in this heat but the 5.4lt V8 engine sounds like a diesel after a 400km run.
Based on the data in:;f=1;t=009433 And averaging several candidates:: ..........40C........100C 5W20..... 46cSt ..... 8.9cSt 5W30..... 65cSt .....11.2cSt 5W40..... 88cSt .....14.2cSt 5W50.....108cSt .....17.6cSt So the 5W does not have an absolute meaning at 40dC and shows at least a full factor of 2X in thickness over the 20-50 spread in operating weight. While, on the other hand, the "other" number after the 'W' does seem to have a small band (25%-ish) between viscocitys and weights. European cars have a different driving regimine than American cars. Over here (USA) we have a rather constant maximum speed of 70 MPH (little slower in bigger cities, a little faster here and there). Also, over here, we have the EPA which can fine/tax the automakers big money unless they achieve fleet economies of x MPG (that city/HW lunicy). So, it is prudent to specify an oil that enables the car to last through its emissions warentee (120K miles) it is also prudent to save as much gas as possible. Modern thin oils do this. In europe, it is possible to drive into Germany, get on the autobahn and drive at 120-150 MPH (at least for short durations). This changes the operating conditions enough to warrent different oils and why Europeans look to the HTHS number.
Thin oil *may* lubricate the top piston ring better, since more of it can get past the other rings. My Subaru survived climbing mountains in warm weather, with the radiator half covered, using 5w30 that thinned to a 5w20 near the end. Lead was 1 ppm, iron 6. Underhood temperatures were above 70 celsius and the oil pan was sheltered by a belly pan so there was no oil cooling at all. The engine made quite a rattle when decelerating. Next time, I'm putting in a cold air supply for the alternator.
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