Is Synthetic Oil Bad for Old Engines?

I am seeing some good deals on synthetic oils. I drive a 99 Camry with 150k miles. I have always changed my oil every 6 mo/7500 miles using regular oil but would like to try sysnthetic. My friend says I should stick to regular since sysnthetics are “lighter” and would leak more in an old engine. But aren’t we comparing oils of the same viscosity?

BTW, there’s nothing wrong with my car but it does have small oil leaks here and there that I am willing to live with (I had never had to top off oil between changes).

There’s no real benefit to using synthetic oil in a Camry. It’s your money, however, so if you want to spend it, go ahead. Synthetic won’t hurt anything, but it won’t help anything, either, and it still costs more.

You CANNOT extend the oil change interval just because you pour synthetic oil in the engine, so don’t think you’ll save money that way.

At 150K miles, I say keep doing what you’ve been doing. Why change now?

Several Decades Ago, I Switched From Low-Fat Milk To Skim Milk. We Know More About The Health Benefits Now. The Same Is True Of Motor Oil.

These types of changes can be made in steps, like going from 2% butter fat to 1% and then to skim.

Buy your car a nice “blend” oil (part dinosaur / part synthetic) and see how it likes it (keep looking underneath for signs of incontinence). If all is well then make the next oil change full synthetic.

You can always go back to dinosaur oil, but I don’t know why you’d want to do it. I’m never going back to 1% or lowfat milk.

As you have noticed we are in transition right now, moving from old fashioned oil to modern oil and the price difference is decreasing all the time. Your Toyota is a car senior citizen, born in the last century. However, I think it’s a good time for you to come up to the 21st century. I say go for it.


Should be no problem and I think the conventional wisdom is that you can go a bit longer between changes with synthetic oil.

However, my particular anecdotal experience is - Last year I switched three of my cars, two '97 BMWs and one '91 Volvo from conventional to synthetic oil. The fourth car, a 2004, has always used synthetic. I switched from 20W50 conventional to 15W-50 synthetic.

All three started leaking oil from one or more locations. The valve cover gaskets failed on all three. All three consumed more oil than they ever had before. They consumed more than they were leaking I am quite sure.

I switched back and replaced valve cover gaskets and some seals. All is well in the driveway again.

I would agree; there is no real benefit in changing to synthetic oil unless you live in an extremely hot or extremely cold area.

If I were you, based on the mileage you drive, 12500 miles/year, I would change oil more frequently, such as 4000 miles or 4 months. Keep using a good quality regular oil in the 5W30 weight. Your engine will likely outlive the rest of the car if you do that.

Happy motoring!

Questions: My Cars Run On Synthetic, But Don’t Leak. Does This Mean That Dinosaur Oil Caused Your Leaks To Begin With Or Is There A Problem With BMWs And Volvos Or Your Particular Cars ?


Did You Know That They Now Market High-Mileage Synthetic Oil For “Leakers” ?

From the Castrol Edge Synthetic Oil 1 QT bottle:
“Guaranteed extended drain interval protection for 15,000 miles or one year, whichever comes first”.

I drive 20k miles a year, 95% of which is interstate highway miles @65-70 mph. I live in North Texas. I based the 6 mo/7500 mile schedule from the Camry Owner’s manual. Based on my driving habits and what Toyota recommends, can you tell me why I should change oil more frequently?

The thought of going 1 year between oil changes is appealing but not at the cost of a damaged engine.

Thanks for the further input. From the age an mileage, I surmised you did a lot of short trip stop and go driving. At 20,000 miles per year in North Texas, you are changing at the right interval, but you still get the best value from using a standard mineral oil and changing it at 7500 miles.

Synthetic is not “bad” for your car, but it is EXTREMELY slippery and gets through tiny openings that normal mineral oil doet not penetrate. So, I predict that when you switch to synthetic your car will “use” more oil, but it will leak out through places you never suspected. However, do the experiment, but don’t go 15,000 miles between changes. Those drain intervals are used to sell the oil and justify the higher price. If the car was new you would be voiding the Toyota engine warranty.

Regardless of the Castrol claim on the bottle, I would not exceed the Toyota drain interval of 7500 miles. Does Castrol also recommend a 20,000 mile oil FILTER?

I use Mobil 1 synthetic in our Nissan Sentra, which has a 4000 miles drain interval for severe service, which this car is used for (short trips). I drain it twice a year at about 4000 miles and change the filter. We live in a cold area, and do short trips with this car.

Your Toyota Is On The “Most Wanted” List, The List Of Cars Most Wanted By Oil Sludge, That Is. Synthetic Handles Temperature Extremes Better And Is Less Likely To Form Sludge.

Any car that is known for oil sludge problems would especially benefit from synthetic. It could just save a sludging engine’s life.

Click and have a look at one of many engine people advocating synthetic oil:

csa; the conclusions I draw from these sludge posts is that you need to CHANGE OIL MORE FREQUENTLY than even the manufacturer recommends, rather than switch to synthetic. My 2007 Toyota and all their other 2007 models have a 5000 miles interval for all conditions. Their experience with sludging has made them wiser.

Synthetic oil is useful only for EXTREME conditions, such as very high and very low temperatures, heavy loads, turbo-charged engines.

OP should heed the posts and never exceed his current oil change interval, regardless of the oil used.

If OP goes to the long drain interval with Castrol synthetic he will certainly have sludging problems.

However, people will always try to get something for nothing, sometimes with diastrous results.

Doc, I Agree With Your Advice. I Change Mobil-1 At 5,000 Mile Intervals.

I think most of the folks who blame the car manufacturers for their car’s sludge problems and / or blown engine are the same folks who get a little negligent in the oil change / maintenance department.


[b]csa; the conclusions I draw from these sludge posts is that you need to CHANGE OIL MORE FREQUENTLY than even the manufacturer recommends, rather than switch to synthetic. My 2007 Toyota and all their other 2007 models have a 5000 miles interval for all conditions. Their experience with sludging has made them wiser.

Synthetic oil is useful only for EXTREME conditions, such as very high and very low temperatures, heavy loads, turbo-charged engines. [/b]

…or perhaps design flaws/characteristics that would promote sludge at a given distance for conventional???

Good point; some cars are more “failure resistant” than others. The sludge-prone Toyotas would not sludge if the oil was changed exactly in accordance with the directions, such as more frequently when encountering “severe” conditions.

When such a car is brought into the dealer with a sludged up engine because of severe conditions, and the oil has been changed accoding to the light service schedule, the garage does not know what happened. And it has to be treated as a warranty case.

Synthetic oil is not a cure for stupidity or lack of observing the directions. I have several friends who owned these “sludging” engines and drove them several hundreds of thousands of miles before disposing of them.

There are engine designs that require synthetic due to the severe operation temperatures and pressues.

Car manufacturers have to treat the customer as being negligent from day one, and design the engine to be as idiot-proof as possible. Toyota learned the hard way that practically all driving is severe, with a few execptions and that owners usually do not follow the drain interval directions.

Toyota manuals now do not differentiate between light and severe, and specify 5000 miles for all driving, knowing that most owners would pick the long interval to “save money”.

The early GM V6 engines, for instance, had very small oil galleries, which plugged easily causing lack of lubricant flow. This caused many failures.

No, synthetic oil is not bad for your older engine but the more important question is: Does your engine need it? No… it’s just a waste of money in my opinion. It does nothing for your engine that conventional oil can’t do.

I have a 99 Toyota with the engine flaw that overheats the oil. After Toyota finally acknowledged the sludge problem back then, they lowered the oil change interval from 7.5K down to 5K miles.

I currently have 160K miles on my car - all dyno oil changed every 5K. No sign of sludge.

I’ve read about many others who have used synthetic and stayed with the 7.5K oil change interval. I choose not to do it, but they’ve had no problem.

Will it hurt your engine? I don’t think so.

Is there a benefit to switching? I don’t think so.

If what you have been doing has been working, why switch?

This has been a great discussion. here’s what I have learnt and will be doing:

  1. Change oils every 5000 miles for since Toyota has apparently moved away from the 7500 mile recommendation (almost all my driving is highway)

  2. Keep using regular dyno oil in an old engine. (I may use sysnthetic on my wife’s car which has 50k miles and is primarily driven for short stop-go trips. But only if I can find synthetics on huge sale!)

Thanks everyone for your inputs.

There are two synthetic bases. One shrinks rubber seals and the other swells them. Properly combined, the seals are safe(?). Like most everyone else I must depend on the experts and synthetic oils offer some great benefits but I question the effects on old, hardened seals. On older engines I have decided it best for engines to “stick with the one you come in with.”

This site provides a good primer on oils:
I recommend a visit.