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Changing to synthetic oil

If you have a high mileage car that has always used conventional oil, what is recommended if you want to change to synthetic. Is that evan a good idea ?

We’ve had many posts on this one. There is generally no point switching to expensive synthetic oil if conventional oil has served you well.

The only exceptions I’d make is if the car has a turbocharger or if you are living in an area with severe winters. Then synthetic makes for easier starting. and would have been a good idea from day one. But some makes, like Chrysler did not specify synthetic in their older turbo cars for fear of scaring away buyers.

Please tell us make model year and type of engine, and we can refine it further for you.

Unless you have a European car like a turbo VW or BMW, almost any kind of synthetic will be OK. Just make sure it is the right viscosity, like 5W30 or 5W20 as recommended in the manual. On very old cars a 0W20 will likely result in oil consumption.

If you want to change to synthetic, use the weight and spec specified by your owner’s manual.

Is it a good idea? Not in my opinion. Synthetic is not a magic elixir, nor will it extend the life of an old engine that only requires dino oil. Chemically, synthetic and dino oil are the same. The differences are in the purity and in the consistency of the molecular size. These things mean nothing to a regular engine.

Synthetic is for engines that place high heat and/or large stresses on their oil, such as engines with turbochargers. These engines use their oil to lubricate bearings spinning at very high RPMs that are heated by the exhaust stream gasses. Normal engines don’t subject their oil to these conditions.

If you want to be sure you get the maximum life out of your old engine, change the oil more often and take good car of the rest of its needs. A properly tuned and operating engine places less stress on everything, but when it’s old it typically does have more “blowby”. Blowby is combustion gasses being forced by the rings. Normal wear and natural relaxation of the rings allows more of this in old engines. Those gasses contaminate and dilute the oil, and IMHO the only way to counter that is to change it more often.

There’s an old axiom I like: keep doing what you’re doing and you’ll keep getting what you’re getting. In your case, if what you’re doing is working, keep doing it. Change what you’re doing and you might change what you’re getting.

The other advantage to synthetic is extreme cold weather. We do a lot of skiing in the White Mountains and we drive my SUV. We’ve woken up to -30…synthetic oil is great when temps are like this.

During the summer we go camping at least a couple times a month. Hauling a trailer can be very stressful on an engine…and again synthetic is better for this type of driving.

My wifes Lexus - she just drives to an from work and when we travel (not camping). So my wifes cars - I’ve been using just regular dino oil.

My only experience in changing from regular oil to synthetic was with a lawnmower engine. I have a,23 year old push mower in which I was using the straight weight heavy detergent 30 weight oil. It was burning oil so badly that I would almost be asphyxiated when I mowed the yard. I found full synthetic 10W-30 oil on sale at my local Rural King store for $2.79 a quart for the RK house brand. Since it was only $1 more than the non-synthetic house brand, I decided to take a chance. The mower uses much less oil–I can mow the yard twice before I have to add oil. The exhaust doesn’t smoke nearly as much–now I only see the smoke when the engine is pulling hard to cut tall grass. I was ready to buy a,new mower last year before I tried the synthetic oil. Now I may even get through this season.

The reason I don’t buy a,new mower is that 1) I am a cheap skate and 2)_the mower has a cast aluminum deck that is in good condition. I would replace the engine or get a,short block, but parts are no longer available for the mower–not even blades. The mower is a,Homelite-Jacobsen and Homelite sold ifs mower division. The mower has two blades–a long blade and a short blade that are perpendicular to each other. If I replaced the engine and used the present blade set-up and then bent a blade, I would have to get a new adapter and go with a single blade that might not work as well with this specially designed deck. The synthetic oil saved the day for me with the mower. Whether it is worth it in a car engine is something else.

I don’t see any harm but also not much gain. You might get a little more leakage with the syn. In extreme cold or heat you can get better performance such as starting a car at 20 below. I had an old riding mower that sat out all winter, with a pull start, and was a beast to get going in the winter for plowing. I switched to synthetic oil and there was quite a difference in the effort required to turn the engine over.

In the 70’s or early 80’s, I had an old Datsun 510, and an old 9 pass Pontiac wagon. I tried synthetic oil in them, mostly out of curiosity, and both started leaking from part of the motor. By memory it seems the oil sender switch, but I cannot clearly remember. People told me, “Oh, no! That can’t be!” But, it was.

Now, of course, I use synthetic for everything.

Save your money and stay with dino oil.

I’ve done the switch on high mileage cars I’ve purchased. I am a “synthetic oil in everything” kind of guy. About half the time I’ve made the switch and NOthing has happened, at all. The other half, the engine burned about twice the amount of oil as normal and dirtied the oil up very quickly.

With that experience, I’d suggest if you change to synthetic, check the oil frequently in the first 2500 miles and change it at that mileage and then you can extend change intervals to 5000 or 7500 miles or what ever your manual says or you feel comfortable doing.

@irlandes – I too owned a Datsun 510. Two actually, from the early 70’s. Great little car with NO rust protection at all. In the midwest they dissolved long before the engines wore out.