Is 10w30 oil really ok?

There are no problems using 5w30 oil in fact there may be a small gain in mpg. Some people myself included run 0w20 oil and gain a little more mpg. Rest assured you have nothing to worry about.

John (Britprius)

 

You should be ok with the 10w30 but ask for a discount for the next oil change with 5w30 synthetic.

I think there is a label under the hood that specifies 5W30 so that the mechanic doesn't need to check the owner's manual. It might be inside the door jamb as well.

Check you tire pressure, there is a good chance that the mechanic didn't pay attention to the recommended tire pressure as well.

 

10w30 is fine. However, it is stupid. You are in prime location to run 0w20 not 5w30.

Also depending on how many miles are on the car, switching formulas can be disastrous. Stick with what the car knows.

 

Without getting to complicated the first figure in the numbers before the W is the cold viscosity of the oil, and basically the lower the number the thinner the oil.

So a lower number means the engine turns more freely when cold less electrical power used for start up and quicker starts also the oil flows more readily round the engine giving better lubrication (quicker).

The high number after the W is the hot viscosity of the oil "in your case the same for both oils" so when the engine is hot "most of the time" there really is no difference between the two oils.

John (Britprius)

 

TK1Toaster was pointing out that you could use 0w20 oil to advantage, but stop worrying and leave the oil that you have in the car as is you do not have a problem.

John (Britprius)

 

Conventional oil and synthetic oils mix perfectly ok. It would do no harm to find what oil you have in your car (ordinary dino so called in the US) or synthetic. Synthetic is good for 10,000 mile change interval but ordinary oil only 5000 miles. The important thing is that you check your oil level on a regular basis some users on here have damaged engines for the sake of checking the oil level, but do not!!!! over fill.

John (Britptius)

 

It is fine to leave it in, especially since you do not drive much (2005 @ 64K miles).

But you are in a prime location (geographically) to switch to a thinner oil i.e. lower weight. BritPrius explained the viscosity. I run 0w20 which means it is super thin when cold. After it heats up, it is still lighter than what you have. New Prii use this too. It wasn't really available when the 2005 was manufactured. So 5w30, 10w30, 20w30, all will be fine in your car, but not optimal. 0w20 is optimal for your location and vehicle.

After deciding the type, you need to decide what flavour essentially. Synthetic or not, and brand. At 64K miles, you can still make the switch to synthetic. I do not like recommended people to switch to synthetics much after the 80K mark. The uniform size of oil molecules in synthetic is great. However it may break free crud or holes that were plugged naturally by larger particulates in regular oil. If you have no such holes or problems, then the switch is painless. The newer the engine, the less of a chance of these wear items making the switch no problem.

If it were my car, I would go to the store, buy 4 quarts of Mobil 1 0w20 Advanced Full Synthetic and have the mechanic change it out. From now on, only ever put in this oil. However I am a "car guy" and treat my cars rough some days and baby their treatments so they last. This is great oil, but there are betters. This is an oil you can find at any auto parts store or even Amazon.com without having to special order. Any mechanic should honour an oil change using your oil. Make absolutely sure to see them pour it in if you doubt the scruples of the shop. This is good oil, and if you appear to not have a clue, there is no reason for them to not just put it on their shelves and give you the cheap crap they buy in 55 gallon drum bulk sizes like what you already got.

 

Synthetic oil is a superior product to conventional oil keeping the engine cleaner and freer of lacquers.

It also has a longer life "in the UK/Europe the oil change interval for this oil is 10,000 miles (Toyota spec) and this is the oil I use.

If you decide to change your oil change the filter as well and consider the old oil as being an engine flush. The decision is your's, no harm will be done either way.

As I said previously the important thing with the Prius is not to neglect checking the level on a regular basis, "basic maintenance".

John (Britprius)

 

Like the OP, I don't put many miles on my Prius per year. Less than 5000/year. If I went to synthetic, would I still be needing to change it out at 1 year intervals? Or could it go even longer? I have always used plain dino oil in my previous vehicles, which likewise didn't get many miles per year. I have always changed at 1 year intervals, and have never had any concerns about engine performance or oil consumption. I know dino oil is supposed to be changed at 6 months, but I didn't do that and have lived to tell the tale.

 

Well the synthetic will generally last a couple years. Mobil 1 if it sits on a shelf will last 5 to 10 years with no problems. So I don't see why it wouldn't work in the engine if not driven much. I would just drive it until the oil didn't look good anymore with that few of miles per change.

The risk with changing to synthetic grows as the engine gets older, but the risk is only there if there is a problem to begin with that is masked with old dino. Ideally you pick the car up from the dealership with 0 miles on it, and switch to synthetic until the day it is crushed.

 

Warren is (one of) the suppliers for Wallmart's "supertech" oils. It will be a basic bulk workshop oil, nothing special, but nothing wrong with it either. It wont hurt your engine.

Given that your part of the world will be warming up over the next few months, why don't leave it in over summer and change it out come autumn. Or something like that, I mean give it a short run at least.

Edit: I was assuming above that you're doing fairly low annual miles. Now however I notice you said this car is new to you, so we cant really guess your annual mileage from the odo reading. Can you tell us roughly how many miles do you drive per year? And do you drive lots of high speed freeway trips, or do you mostly drive short or low speed local trips?

 

Not as much as you have noted above, low 50's down to 44, that's about 15%. More likely you should only see 2% to about 3% maximum. As you know there can be a lot of variability from one tank to the next, so you definitely want to run it over several tankfuls before jumping to conclusions. If you were doing mostly long trips, or if you were operating in very warm conditions then I'd expect you'd see no difference at all. But with mostly short trips and cold conditions you will see the maximum effect.

That being said, there are other properties of an oil, besides viscosity, that can effect fuel economy. Different additive packages and friction modifiers can make a difference too, so you may get more than predicated.

I check mine either stone cold or warm after sitting for 10 to 15 minutes. I don't notice much difference (if any) between thee two measurements. If I check cold then the car's usually been sitting overnight in the garage. If I check warm then I usually do it about 10 to 15 minutes after returning home from a drive. Just make sure that if you're doing the hot measurement that you wait at least 5 min for the oil to drain back to the sump before doing it.

Either way the oil should not be above the top dimple. If it's more than 1/4" over then it could be affecting your fuel consumption. You really should check this immediately upon picking up the car after the oil change. If it was say 1/2" over, then by now that top 1/4" will probably be frothed and sucked away and nicely fouling up your throttle body anyway.