Oil question

[DaleInTN]

I picked up the wrong weight oil and was wondering if I could use it or should I take it back. I have been using 5w-30 but picked up 5w-20 instead. Is it ok to use?

I live in the Chattanooga Tennessee area and the engine has 300,000 miles on it. I can't think of anything else that would be of importance concerning the oil weight.

Thanks

[blkfordsedan]

It won't hurt it. With that many miles, It may run slightly lower oil pressure when warmed up. May burn a little more oil & be a little noisier as well.

[tooldude]

When asking around about this subject I have always gotten differing opinions. I don't know why anyone thinks they know better than the engineers who test these things. I would not use 5W-20 in the warm months unless it is a synthetic oil, which has a higher film strength. We never know the long term results of anyone using lighter or heavier oils than recommended. I believe it's a testament to the engineering that we can vary the weights at all.

[blkfordsedan]

5W-20 should be at least a synthetic blend. That said, the engineering involved around oil viscosity and selection is not really that technical. Especially with the clearances involved in these older engines. From a lubrication perspective, thinner oil is much safer than thicker, as long as it is sufficient to provide adequate boundary layer seperation. Anything more is wasted as excess pressure, generating increased heat and resistance to flow. The viscosity at cold start up is much more critical, and in this case, both oils should be the same. If one is a synthetic or blend, it would be even better. In terms of the climate, it's really insignificant to the application. If the cooling system is functioning properly, the oil operating temp will be the same...Or very close. The actual difference between 5W-20 and 5W-30 at 212*F operating oil temp is only a few centi-strokes, depending on the actual brand. Different...but not enough for concern. Manufacturers have switched recommendations from 5W-30 to 5W-20 with no changes to the engine design...for no reason other than the fractional increase in the CAFE ratings. The main issue in this application is the high mileage of the engine and not so much what particular oil the manufacturer recommend when it was new and the clearances were in spec.. In fact, with 300K miles, I would probably be running 5W-40 and invest in an oil pressure gauge.

[tooldude]

blkford from what little I've read on the subject that sounds right on. Every engine in which I've run synthetic oil has always pumped too much oil past the rings as the mileage climbs, though it's the best oil to use. Actually, more synthetic (vs. conventional) will get past the rings in all engines. A blend will do better but I prefer to use all synthetic because of the way I'm doing my oil changes. With the conventional oil, I used 10W-40 and even 20W-50 in the hot weather (in Houston,TX) in engines with 100,000+ miles. These were trucks that I ran all day making hot shot deliveries. With lower viscosities than 10W-30 I would always hear relatively more clattering sounds in the engine. I switched to synthetic for the better properties. When I use a blend, I buy both types of oil and mix them myself because the blend doesn't reveal the percentage of synthetic in the mix.

[navdoc101]

Check out www.bobistheoilguy.com
Bob is the Oil Guy.
Lots of good info there.

Go through the Motor oil University.
It explains all about the grading system 5W-30, 10W 30, etc.

[DaleInTN]

The oil is full synthetic

[blkfordsedan]

Have you ran full synthetic before? If so, then great. If not, I would caution against switching to full synthetic in an engine with that many miles. Full Synthetics do a MUCH better job of cleaning the engine. That sounds great, but that can create issues in engines that are well worn and have years of carbon and deposit buildup and can lead to increased blow-by. It's not the fault of the oil, it just cleans it so well that it reveals the full extent of the engine wear.

[DaleInTN]

I've been running full synthetic for about 9,000 miles. The engine doesn't smoke at all. I do have to add oil every now and then, but it runs great. It does have some oil leaks, but nothing bad. I don't know if the engine has 300k on it or not, but the odometer has 300k. I'm getting a solid 47 mpg the last 30 days and have 44 mpg average for the past 14 months of owning this car. I don't drive faster than 55 mph.