5w-20 in an engine that specs 5w-30

[Gene K]

By the time 5W30 "Energy Conserving" gets through shearing its 5W20 anyway so whats the difference?

Now if you are going to run a shear stable oil like Rotella T5 or Maxlife I might see the point of going with a 30 weight.

 

[Gene K]

Originally Posted By: JRed
Originally Posted By: JOD
People seem to be completely ignoring the relationship between viscosity and temperature...


That was what I was wondering - and hope to find out (since I changed the oil this evening to Mobil Super 5w-20). Since the oil rarely if EVER reaches operating temp (I have a car I can drive long distances if I need to) I figure I may as well just go with the thinnest oil I possibly can. Guess we'll find out if it's worth it or not.


Going with 5W20 to start with will save you having to wait thousand miles for 5W30 to shear.

I really cant see what the big fuss is about oils that are going to end up 8.9 cSt (5W20) vs 9.1 cst (5W30 EC) anyway.

 

[4ever4d]

Originally Posted By: JOD
Obviously, a lot of responders on this thread really struggle with reading comprehension. A 30W oil is not going to 'protect your engine better'?? You oil is 'too thick' as it is, even if you're using a 10W oil... People seem to be completely ignoring the relationship between viscosity and temperature. If you're never getting the oil up to temperature, you're to be best off using the thinnest oil possible. It will at least be closer to the correct operating viscosity, and it'll get closer to operating temps than a thicker oil (since it heats up more quickly).

I do agree with the suggestion to try and actually take it for a drive every now and then.

As far as the mention of the RX8, what on earth does a oil weight for a rotary engine have to do with a guy with a regular engine who drives it 3 miles at a time?

+100 Your beater or any new car will run fine on a 20wt oil no worries use with confidence.

 

[Patman]

I agree with JOD, an engine that doesn't get up to full operating temperature very often is a perfect candidate for a thinner oil. Think about it this way, that 5w20 oil in an engine that only gets up to an oil temp of about 170-180 max, is probably going to be about the same viscosity as a 10w40 oil might be at 220 degree oil temps.

 

[Jeff_in_VABch]

Originally Posted By: JRed
So, I bought a beater car and it specs 5w30. Trouble is, it gets driven on very short trips (less than 3 miles) and the coolant rarely gets to operating temp - much less the oil.

I went to Walmart, bought Mobil Super 5000 5w-20, and plan to change the oil in this car to that oil tomorrow. I figure since the oil isn't getting up to operating temp I might as well give it the thinnest economically feasible oil I can.

Then again, there's really very little difference between 5w30 and 5w-20 when cold, especially at summertime temps. Who knows - maybe I'll see a magical MPG increase or something. I doubt it, but I've never even thought of using 5w-20 in anything else (hate the stuff) but figured I'd give it a shot in this situation.


In your situation, the 5W20 will be fine. Almost any oil will be fine. You still need to change it at an appropriate interval.

The only reason you wouldnt want to is if the engine is very worn and has low oil pressure.

At the dragstrip, many cars run relatively light oils as there is little warmup and heavy oils would create excessive oil pressure. A 3 mile trip is essentially the same thing.

 

[sunfire]

Not sure if I agree with the xW-20 = premature failure comments. There are plenty of good used oil analysis documenting xW-20 will protect engines just as well as a xW-30.

What is the different between the two grades anyways? A few centistokes difference is going to ruin an engine? What happens when the xW-30 sheers, becomes a little fuel diluted, or a little out of viscosity spec right out of the bottle? Nothing.