I'm going to be changing over come my next scheduled oil change. I've got a 96 4WD LTD with just over 100K on it. It's been using Dino forever. I'll be using Mobil 1. Heard that is a great syn.

My engine has a tiny leak somewhere. The oil doesn't even drop per say. There just a little bit collecting at the bottom. I know that when I change to syn it will change considerably.

my 2 cents... if you have a higher mileage car and want synthetic, but are worried about leaks, then go with 10w40 (something a bit thicker) in the summer and switch to 5w30 in the winter.

Um...no. It's not the "thickness" of the oil that makes it leak or not leak. The few times that switching to a full synthetic causes leaks, it's because of cleaning properties or additive package. Using a 10w-40 in 5VZ would probably cause leaks if anything, due to extra un-needed pressure.

The only reason to use a 5w-40 or a 10w-40 in a 5VZ is if you tow constantly and really stress the engine (and I mean alot) or if your engine is going for broke anyway and has low oil pressure, etc. Very few 5VZ's are in these categories. And even if you do tow alot, a 5w-30 is still what I would use.


(And btw, I love Rotella T6. I use it in my 350whp turbo Neon)

Synthetic is FAR better than ANY regular petroleum based oil with no exceptions.

All synthetics have a much higher flash/boil point, have better detergent packages so you will never have to worry about any "sludge" problems.
It would be basically impossible to sludge an engine that is running synthetic.

As for the MYTH that synthetics "cause" oil leaks that is simply untrue.
They may expose a leak you already have.

What causes oil leaks in most cases is over heating, that fries and dries out your seals largely because petroleum oil has deposited gunk on the inside of your engine and under high temps will harden thus the seal dries out.

On rare occasions if someone switches to synthetic oil after they have been running petroleum oil for about a decade the synthetic will clean the engine exposing the seal that the "petroleum oil has caused" to dry out.
In most cases if you allow the synthetic to clean the engine it will rejuvenate the dried out seal as long as the seal is not too far gone.

I have owned 14 cars & trucks in my lifetime so far, I am 52.
Only one was bought new the other 13 used and I have changed over every single one including the diesel to synthetic oil and have never had a problem, in fact just the opposite. The synthetic has cured some problems that I have had.

I just bought my 4Runner a few weeks ago, it had 157xxx miles on it and the first thing I did ASAP was to change it over to synthetic oil.
Not one drop of oil has leaked and if anything the synthetic will prevent the seals from drying out in the future.
I find it incomprehensible that car manufacturers, especially Toyota with their infamous sludge problems does not make synthetic a "requirement" to maintain the warrantee.

Good post above.

Synthetic all the way, and 5W-30. Toyotas best engineers designed the engine to run on it, and you are not smarter then they are.

Its also important to pick one type of oil and stick with it. Seals get used to the particular mix of additives. Without them, there are periods of insufficient lubrication, or seals might dry out on certain parts. Also, some oils don't mix well, even if they are both synthetics. They will form sludge when mixed.

I use Mobil 1 Full synthetic in all my vehicles with the manufacturer recommended weight.

All my vehicles are still running strong. 4Runner = 208k. LC = 289k. I expect my wife's Honda to give me at least 300k before I rebuild it.

First let me say that I have been in the oilfield business for years and have experience with synthetics as well as seen the engineering claims. Most are a bunch of poppycock just to sell the product and once the mind is convinced that synthetic is the cure all it is just about impossible to show a person other wise. That is not to say that synthetic oil is no good. It is if used where it is really needed. However Synthetic is mostly nothing but a hype when it comes to most conventional engines. Unless the engine oil is running above normal temps synthetic is a total waste of money. Now for those who swear by it in conventional engines by all means keep buying it, as it is your money to waste, but I challenge you to take two vehicles and treat them exactly the same and you will see that neither will do better then the other.
While there are claims that synthetic will get you extra miles there is not single study to prove it. No one has ever taken two identical vehicles and put them through exact normal driving one with synthetic and one with conventional oil and proven that synthetic makes the engine last longer. Keep in mind we are talking about the standard engines, not a NASCAR race engine or a dragster. Even the weekend hot rodder does not need synthetic as synthetic will only benefit the engine IF the engine oil is running too hot.
I have a ford truck that I have only used conventional oil in and I have over 400,000 miles on it and it does not use a drop between oil changes. I once had a motor cycle and used synthetic in it. I got about 75,000 mile on the engine. I put a new engine (not rebuilt) in it and went to conventional oil and went just as far on the second engine.
Also if you do the math synthetic costs more without any real benefit except that you can go longer between oil changes. So for 50% extra you can be hyped up and think you are doing something by using synthetic while the manufacture laughs all the way to the bank, but I suggest that you use conventional oil and change it as recommended. You will get the same benefits and have extra money in the bank.
One more thing. Some will try and tell you that synthetic is slipperier then conventional. That is more hype. The industry has standards and they are listed on the oil we buy as to how slippery it is. SM is the highest you can buy and conventional oils come in that grade. Here is a chart Motor Oil Grades and Service Ratings
Here is another article that gives some information. Car Bibles : The Engine Oil Bible
So if the manufacture calls for synthetic use it. If it is not exactly specified (required) then use the conventional and save a ton of money. You will get the same life out of your engine with conventional oil. Believe me IF synthetic oil was as good as some claim every manufacturer would require it for warranty purposes, but very few do. So unless you are building an extremely high performance off road vehicle use conventional oil.

I disagree. Its not the oil that breaks down during use, rather the additives to the oil. Synthetic oil is a better medium for these lubricating additives, so it lasts longer. Dinosaur oil will hold them just as well for a little while, but failure to stay on top of the interval can quickly lead to engine damage. Spinning up for too long or excess heat buildup like we see in heavy towing or off road use makes the dino oil medium less then ideal.

Now which type of oil you are using matters much less then the fact that you stay on top of regular maintainance. The fact that you put 400k on your Ford was no coincidence. I'll bet you rarely if ever missed an oil change interval. Failure to perform regular and preventitive maintainance is the single biggest cause of mechanical failure, period.

I change oil every 5k in all my vehicles. I would rather spend a little more and sleep better knowing that my old trucks are better lubricated now then they ever have been!

You are not "saving money" using conventional oil, in fact just the opposite.

Also in several engines like my wifes Lexus for example I don't care how often you change conventional oil you can get sludge because of how hot that engine gets.
When you shut that engine off and the oil runs back down a thin film of oil remains on top and if it is convention oil it sits there and literally cooks and starts clogging up those tiny oil channels.
Synthetic oil has a MUCH higher flash point thus will not cook in that engine.

Conventional oil after just a couple hundred miles has broken down quite a bit because of it while the synthetic is basically untouched.

Since I only drive usually less than 8000 miles a year I change my oil once a year using synthetic.
If using conventional I would have to change oil at least twice if not 3X during that year.

You don't waste money using synthetic at all.

As far the effectiveness of synthetic oil what sold me back in 1977 was I used to own a Baja Bug, really nice engine in it a 2180cc nicely built, VW racing heads putting out about 220hp.
Only problem I had with it was it would get hot and lose considerable power especially if I took it to the desert and romped on it.
I tried everything, put in a deep sump, all stainless lines and a oil cooler on the roof under a scoop which added A LOT of extra oil and cooling on and oil cooled engine but to no avail. Used every kind of conventional oil there was. Still would over heat and lose power.

A friend of mine tried amsoil in his bug and liked it, at the time all they had I think was what they called 20/50 racing oil.
I put that in my Bug and Viola, never over heated again, never lost power no matter how hard I pushed it. SOLD!
So I KNOW that synthetic is superior oil, I have seen the results of it too many times.

Also my wifes Lexus when we first got it had a fresh oil change of conventional oil in it from Carmax so we let it go about 1000 miles prior to changing it because they just put it in the day we bought it.
We went through about 3 tanks of gas and one tank was a long trip.
we got just over 26 mpg. That was with whatever 5W30 dino they put in.
Changed to 0W30 Amsoil and have gotten up to 31mpg on a long trip straight hwy miles.
Also this engine is one of the worst for sludge because the top end gets so hot.

We have had it for 7 years now and I had my mechanic take a look at it last year and it was clean as a whistle inside, zero sludge.
My Jeep I just sold with its straight 6 was same way, mechanic said it looked new inside it was so clean and it was a 94' YJ with 150xxx miles.

Synthetic makes a huge difference in some engines.

Also I might add if you have an older vehicle that runs flat tappets etc, those engines were made to use very high ZDDP oil which all oils used to be many years ago, high levels of Zinc & phosphorus was the norm.
You are basically killing your classic car engine if you run standard conventional oil in it today.
Most synthetics have higher ZDDP.

Personally I have yet to own a car/truck that has not benefited from Synthetic oil and that is everything from VWs both raced out and dead stock, diesels, 4/6/8 cylinders Hondas, VWs, Fords, Dodge, Lexus, Jeep and now that I think about it even my motorcycle and outboard engines on my boat which were 2 & 3 cylinder.

I will trust my 34 years of using synthetic exclusively in every engine I have owned over whatever I read any day.
Oh hell I even run it in my pressure washer in an old Briggs and Stratton forgot about that, so that is the whole gambit 1,2,3,4,5,6,8 cylinders.

In general in most applications running synthetic will probably "save" you money, has for me for 34 years.

wow, there is a lot of info being tossed around here. This is an age old debate.

From my personal experience:

While I attended post secondary for Petroleum Engineering we had to do several Chem. labs on the lubricating properties of various oils at various temperatures. Most oils we tested were conventional and we also tested Castrol Syntec and Mobile 1 at 5W30 weights for all of the oils. Mobile 1 literally destroyed ALL of the other oils in this experiment. (I did this approx. 8 years ago, sorry I wish I could remember all of the exact details....)

I switched to Mobile 1 on my last Toyota. It had 145 000 miles on the clock when I switched. I had a few leaks "appear" after the switch to synthetic which cost quite a bit to fix. (Synthetic doesnt cause leaks, but I DO believe that is lubricated and cleans better therefore as said above, the synthetic just revealed an existing issue. I had no increase in fuel economy with the switch.

In the Honda Accord I owned prior to my last Toyota: Switched to synthetic at 100 000 miles. No leaks were revealed and my gas mileage increased 10% after the switch, which still amazes me.... must have been because of the better lubricating properties.

I have also heard that the technology going into conventional oils is getting progressively better and that the gap in oil performance between conventional and synthetic is constantly decreasing. However, I have no proof to back that claim up.

I like your statement about having a FORD with 400,000+ and not using a drop.......B.S.!! plain and simple.

I've owned a few vehicles from Ford ranging from brand spanking new to cars with over 150,000 miles when I bought them.

EVERY.......yes EVERY one has used oil. Fords will use a quart of oil every 5000 miles. And that you can take to the bank.

Synthetics will also reduce oil tempature by 20+ degrees. And can also provide an extra mile or 2 to a gallon of gas due to reduced friction.

I run Synthetic in my motorcycle and it reduced oil temp by 25 - 30 degrees on an Air-Cooled V-Twin.

And were talking about a motor that will cost you $8 - $9g to replace (a 124ci S&S show polished V-Twin).

Your claims that Dino oil matches up to Syn oil is NUTS!!

Alot of the turbo Subaru guys swear by Rotella, branded for diesel use or not. It deals with the rigors of a turbocharged engine quite nicely, and won't hurt a gas engine by using it.

I think synthetics have their place. Not in my 4runner though.

I have an Audi A6 Bi-turbo and it requires synthetic. If you ran regular oil in it, the turbo journals and drain tubes would cake up so quickly, the turbos would die a violent and painful death.

I am doing the schedule A in Mercedes CLK 500 and Mercedes recommended service interval is 13,000 miles. It comes from the factory with Mobil1 0-40w. This engine has sludge in the valve cover area. So don't tell me an engine running synthetics won't sludge because it will.

My 4runner has been using castrol gtx for the past 100k miles and there is not one bit of sludge in the valve cover area.

The bottom line is - If you are going to change your oil every 3 to 4k miles, then stick with Dino Oil. If you are going to change it every 10k miles, then use Synthetic oils.


Definitely don't run Synthetic oils in the 4runner's diffs. That is a sure way to start and cause problems. It is too thin and doesn't offer the tackiness that conventional oils have. Gears and bearing run dry after sitting for a while and that leads to other issues.

I recommend using Lucas oils in the diffs.

Tractor guys use it in their gas tractors--it has the ZDDP they took out of all the gas dino oils. I use syn in my cars(6-7K OCI), but the tractor gets Rotella 15W-40 every six months.

I have seen guys like you. All mouth and no back bone. Here the deal. I will put up 10,000 dollars and you do the same both in one account. We will sign an agreement with witness'. We will change the oil on this truck together and then take a 5000 mile trip. We will then drain the oil. If it is 1 quart low after 5000 miles you get both mine and your 10,000. If not I get both. Now put up or shut up. By the way I am willing to bet you cannot reproduce the same results you boasted about on your other stats either but lets take care of this other first. Let's see who is slinging BS!

There is zero difference in viscosity between conventional oil and gear lube Vs Synthetic oil & gear lube.
I cant understand why people believe the synthetic is "thin".

5W30 is 5W30 period whether it is Dino or Synthetic same with gear lube 75W90 is 75W90. The advantage of synthetic is it adheres to the metal much better the superior additives form an iron-sulfide barrier that stick to the gears no matter how long they sit.

If anything it keeps its viscosity longer at temp than dino oil does and like all multi viscosity oils & lubes the hotter it gets the higher the viscosity becomes.

There is zero difference between dino gear lube Vs synthetic other than the synthetic last longer and protects better.

I wouldn't run anything but synthetic gear lube, ran it in my Jeep for 10 years without a single problem, ran it in my Ford F250 4X4 diesel without a single problem and I am running it in my 4Runner and no doubt will be without a single problem.

The problem with a Mercedes sludging while using synthetic is because of the 13,000 mile interval while using Mobil 1.
With Mobil 1 I would not exceed 6000 to 7000 miles tops.
Synthetics could also sludge if the head gasket is leaking coolant into the oil.

But you use a quality synthetic and "decent" intervals and you don't have any other problems like coolant leaking into oil then you will never get sludge. Under normal conditions synthetics have more life left in them at 8000 miles than conventional oils do at 2000, plus always much higher flash point so if an engine sludges with synthetic oil then you got either serious problem with your engine or you let the oil go WAY longer than it should and let it break down to conventional oil levels of protection.