Changing to (or from) Synthetic oil



I recently purchased a nearly new Kia Spectra5 ('07 with 11,000 miles). The dealership I bought it from proudly informed me that they had “converted” it to MobilOne fully synthetic oil. As far as I know, this conversion meant they filled it with MobilOne and then put a sticker under the hood that said I only need an oil change every 7,500 miles.

Now, from what I’ve heard you’re supposed to let an engine (even a new one) get well broken in before changing over to synthetic oil. Is 11,000 miles enough?

Second part of this question, I refuse to allow my car to go 7,500 miles between oil changes. Especially on an engine that’s still getting broken in. I’ve read from many owners that the Kia engines take over 20,000 miles to get fully broken in. Frankly, I’d prefer to stick to my 3.500 mile oil changes with regular old 10w-30 valvoline. Can I just switch back to dino oil? Rip the sticker off at my next oil change and fill up with normal oil, or am I stuck continuing with synthetic? If I do stick with synthetic what is a more realistic oil change interval? I drive in lots of stop&go highway traffic, fairly hard on engines, and I usually do 3,000-3,500 mile oil changes.


Sure! You can switch back and forth between synthetic and regular oil anytime. But you might want to check the owners manual. The manufacturer may recommend 5W-30 oil instead of 10W-30 oil.



Probably sensible answer of the day.


Hi, JL. Well, glad to answer this one. First of all, Mobil 1 synthetic is, in my educated opinion, the best lubricant any car lover can use. Mobil 1 is a true synthetic lubricant; i.e., it is made from non-petroleum gas (not gasoline but a gas). Many so-called synthetics are refined from petroleum products (crude) and then loosely labeled synthetics because they have had parafins removed from them. They are still natural dino oils without the properties of synthetic Mobil 1. And unfortunately the FTC refused to side with Exxon-Mobil which said lubricants made from crude don’t deserve to be called synthetic. I agree with Exxon-Mobil because even though they have had parafins (wax) removed, they still lack all the other qualities of a true synthetic lubricant. (Parafins cause varnish build- up on car engine cylinder walls, which is supposed to be a bad thing.) Now, for some interesting facts about Mobil 1 lubricants. I call Mobil 1 products lubricants instead of oil.

  1. They offers superior heat resistance to high temperatures. Does not burn like oils.
  2. Does not oxidize.
  3. Offers better protection under extremely cold temperatures than dino oil. Lubricates engines much faster than dino oils at startup.
  4. Longer change intervals. I use the 15000 (yes, thousand) mile Mobil 1 engine lubricant on my car and my wife’s and my daughter’s. First oil change for wife’s car, at 2,500 miles, was to Mobil 1 and she now has 153,000+ miles on her car. (It’s always a good idea to look at the engine lubricant, at least once a month to make sure you haven’t picked up any water, though, which would indicate other problems other than the oil or lubricant.)
  5. Slightly better fuel economy since true synthetic libricants are more slippery than conventional oils. This may not be such a great thing, but I am more concerned with engine protection and longer engine life and fewer engine problems since I keep my cars a long time. Wife’s car is 1999. Mine is '04, same model.
  6. Another cool thing is Exxon-Mobil just came out with “green” (environmentally speaking) 0W-20 Mobil 1 which they tout is even slicker than regular Mobil 1, so it should offer even slicker lubrication. It’s going to be the Mobil 1 lubricant which I will be changing to for my wife’s car in about 1,300 miles. I do my own oil changes because I want to make sure I am getting all Mobil 1. Sounds like your dealer is honest enough to be trusted and more than just a car seller.

I am not telling you to use it. I am only leading by example in this case. I use it in my car, my wife’s, my daughter’s, and I understand Dodge sends its Vipers off the line with Mobil 1 i n their crankcases. Maybe those engineers are on to something, too.

I have experienced excellent results with the product and always use it for my vehicles - have since 1980 when I bought my first Supra. It had 110,000 miles when I traded it 16 years later.

Also, changing to Mobil 1 transmission fluid did wonders for the performance of both vehicles. By wonders, I mean the shifting became incredibly smoother.

FInally, I used to work my car hard, as you do, and Mobil 1 was with me all the way. (Sold CATV door to door.)

No, I’m not a Mobil 1 oilman. Wish I was. But, I don’t mind supporting a company that puts out great products and is willing to constantly work to make better products. I think it is cool that your Kia dealer is up to speed on great products for its customers. He/she must like cars.

Great question. Like your “dino oil” remark, too.


Your engine is certainly broken in by now. Use whatever oil meets Kia’s specifications, synthetic or regular as you choose, changed at the interval specified in the owner’s manual.


You are probably too conservative on your 3K oil change regimen, for conventional. Today’s oils are very good quality and can take the longer mileages without a problem. While Mobil 1 is a very good product, and it would be a waste to change it out prematurely, I am not overly brand sensitive, but price sensitive. I have found my vehicles don’t seem to know the difference between the oil brands, and I have had no engine lubrication problems for more than 25 years. I go 5K with conventional or semi-syn, and I go 7.5K on synthetic oils, for all my vehicles. Since you are still under warranty, don’t exceed the manufacturer’s max mileage recommendation. I have kept up my existing oil change regimen for several years without any problems whatsoever.


Well, glad to be receiving some informative (and quick) responses. The Kia Spectra5 owner’s manual does actually recommend 10w-30, BTW, for areas that rearely see below -10* F. For exceptionally cold climates the manual recommends 5w-20, but never 0w-20 (as far as I’ve found in the manual anyway). In MD I rarely see below 10*F, and frankly since I drive 30,000 miles per year I could just make my fall oil change to 5w-20, and then back to 10w-30 in the spring.

I am, I suppose, a bit antiquated in my oils but this is my first new car (close enough anyway). Having mostly been a smallblock Chevy man this is all new to me, but a longer commute necessitated such a car purchase. I now slog my way through 40 miles of DC-metro area traffic every morning and evening. I keep 10w-30 Valvoline and STP-additive around for my vette (built the engine myself and intend to take care of it) but I can quite easily keep whatever the Kia wants around. Feels weird to go 7,500 miles between oil changes, and I do my own always.

The manual makes it very hard to choose an interval. For “normal use” it says 7,500 mile oil changes and 105,000 mile trans service. For “severe use” it says 3,000 mile oil changes and 30,000 mile trans services. That’s quite a jump. I don’t mind paying for a high-quality synthetic, just want to make sure that it actually can live up to its claims of mileage.

Oh, and as for trans fluids, the Kia uses SPIII instead of familiar old DexIII. Is it safe to change to a synthetic and/or aftermarket trans fluid or should I stick with Kia’s own brand?


Good posts! Yes, you can switch back & forth between synthetic and regular oil. Conversion is a religious term. Switching is more a more suitable term.

Your engine by now is well broken in and I would suggest 5000 miles as a good interval for mixed city/highway driving. If you spent all your miles on the highway, 7500 would be OK. Mobil 1 does not have a lot more additives than regular oil, and it is additive depletion that governs you oil change interval. Mobil 1 has a wonderful base oil, but that just means good stability and lubrication properties.


Given your traffic conditions I would go with the severe interval. Normal is driving pure highway with no traffic, my previous commute was 45 miles each way with one stop sign the entire ride and never any traffic unless there was an accident. 43 miles was with the cruise control set at 70 mph.


I did a quick Google on SPIII, and there appears to be no US aftermarket equivalent. Apparently Hyundai, Mitsubishi and Kia use SPIII and no US aftermarket brand has been certified to be the same. I would then default to buying the Kia brand, as much as I hate to do so, personally. I would shop around as there might be a major variance in pricing in your area, amongst the dealerships. For MD, 10W-30 is probably fine year round for your application.


Check out the web site for Blackstone Laboratories ( Their business is analyzing used oil samples to spot engine problems and determine when the oil needs to be changed. If you poke around in their web site (Technical, FAQ), you will see that they don’t encourage people to spend extra money for synthetic oil.

Thirty years ago, I had a small Japanese sedan that I drove on the street during the week and raced during summer weekends (SCCA Showroom Stock). Service ranged from stop and go traffic in the winter to full throttle on the track. My employer, a large transportation company, had its own oil lab. As a favor, they ran periodic oil analyses for me. Their data showed that the oil was still good after 6,000 miles.

If you want to combine caution with economy, I suggest you use conventional oil and follow the manufacturer’s recommendations for viscosity and severe service change interval. Synthetic is specified for some cars, but yours isn’t one of them.


Actually Mobil 1 is now and has been for some time made with a group III base oil. Other motor oils like Penzoil Platinum and I think Royal Purple and Redline are made with a group IV base oil which is more desirable than a group III base oil.


Lots of good info here. has a good primer on oils. I recommend a visit.


You certainly can change back, assuming the oil you change to meets the specifications in the owner’s manual. Switching from standard to Synthetic and back is no longer a problem with today’s oils.

As for your concern about synthetic and breaking procedure, I suggest you break out that owner’s manual that came with your car. It will tell you want you need to do or not do for break-in.

Today’s oils and engines are far different than they were when I was a kid and 3,000 mile oil changes were the limit. You can safely follow the manufacturer’s recommendations and oil change periods safely. With the change in engines and oils that break-in procedure is not really the same as the good old days. Stick with what the owner’s manual says. BTW,you are right not to trust every thing the dealer may say. The manufacturer, not the dealer is the authority.

Don’t be surprised if it does not tell you to change the oil that soon, times have changed. Of course if you like you can change more often it you like, but it really is a waste of time and money. There has been at least one study that showed more wear when you change modern oils too soon. It seems the perform best after they have been in there for a while. but the difference appears to be rather slight.

Oh yea that owners that the Kia engines take over 20,000 miles to get fully broken in. is likely true, but that really is referring to obtaining maximum fuel mileage. You have no reason to do anything special for the car after the period specified in the owner’s manual.

So, don’t worry be happy!


For your type of driving, you don’t really need synthetic oil; a good mineral oil changed at the SEVERE freqency will ensure low wear and long life for your Kia.


Now, from what I’ve heard you’re supposed to let an engine (even a new one) get well broken in before changing over to synthetic oil. Is 11,000 miles enough?

This is pretty much an old-mechanics-tale. Some cars come with synthetic oil from the factory. You can switch back to regular dino oil if you like. It won’t hurt either way.


Talk to your dealer or e-mail your questions to Mobil. I never read on any of the containers I bought that there were certain vehicles Mobil 1 was not for.


Six thousand miles is the old standard for changing to synthetic. 11,000 is more than enough miles.


Our new GM car came with a factory fill of Mobil 1 and broke in just fine. It burns no oil at 8000 miles. Modern machine tooling, cutting tools and cutting lubricants permit greatly reduced engine break-in demands.

The oil change computer readout showed 40% oil life remaining at 8000 miles so we were on our way to a little over a 13,000 mile oil life. I changed the oil at 8000 miles but in the future will let it go to about 25% remaining or more likely no longer than once per year as specified in the owner’s manual.

Regarding changing from dino to synthetic and back, go by the information on the oil container. If it was an issue, you would clearly see warnings and there are none. Who would know more than the oil companies who certainly would not want ruined engines to answer for.


Unless you have an extremely high performance engine, you can use either synthetic or mineral oil under mormal driving conditions. Synthetics really shine in extreme cold, heat, ,and bearing loads, such as in towing heavvy loads.