Fact or fiction? Switching to synthetic with high mileage.

[Luke]

I really like using mobil 1 synthetic, and i just got my 240sx, it's got about 94k miles on it. I'm not sure if the person before used synthetic or not, but i just changed it with conventional oil. Now i looked around and i can't find a definitive answer to the question, "Will switching to a synthetic oil on a higher mileage engine cause oil leaks?" People say that synthetic oils will cause old seals to start to leak. Can anyone give me some truth behind this statement?

[MasterMan]

with my car i went from normal oil, to semi synthetic, to full synthetic.. it hasnt leaked any oil yet.. oh and my car has 161k miles on it.. just changed over to full on synthetic about 159k

[sultan]

synthetic doesn't cause leaks, but because it is thinner than conventional it may leak where a conventional does not. my Q used regular oil until i bought it and switched to synthetic at 108,000 miles. it doesn't leak at all.

[PalmerWMD]

I have switched all my recent cars to full synthetic with no ill results (none of them below 80k engine miles)

Modern full syn formulations dont even need seal swellers like normal oils some;many full syn base oils (!) have seal swelling properties.So you can use the space left by not needing sealswellers for extra of all other additives.

Fred...

[Luke]

Ok, thanks for the reassurance. I figured that if regular oil didn't have any leaks, there's a good chance synthetic wouldn't. Glad to hear other people with experience in it. Next oil change will be synthetic. :ylsuper

[stickgoat]

My '96 240 has 122k miles on it and the previous owner had been using full 10w30 synthetic with no problems. I plan to keep up with that when it's due for a change again.

Penzoil and some other companies have come out with special high mileage oil. Penzoil's HM has synthetic additives which help to recondition gaskets and seals and prevent leaks and even help stop minor ones. I've never heard of anyone having leakage problems as a result of synthetic oils.

[UncleBen]

i have valvoline full PAO sythetic 5w-40 sittin in my room just waitin for an oil change in my car. i haven't ever put synthetic oil in it, and i can just about assure you the previous owner didn't cause they seem to have been big huge ****s, just by the way the car was when i got it. but she's all good now the car has 115k miles on it BTW. just about to role over 116k

[AZhitman]

A good rule of thumb is for a higher mileage car, switch to syn. But once switched, don't go back, as the conventional oils will have less seal-conditioning properties and may exacerbate any potential leaks.

[91nis240]

I got my 91' 240sx w/ 77,000 miles on it, now currently has 90,000. The previous owner used 10w30 catsrol GTX (bunch of ****) I now and ever sense i bought the car have been using 10w30 mobile 1 synthetic, w/ absolutly no leaks. The one thing is that if the car has not been gettin synthetic then give it a engine flush before converting over!

[EyeStabPeople]

AMSoil 10w40 here, if you become a meber of their... thing for 20 bucks a year you can get quarts of AMSoil for about the same as regular price mobil1, AMSoil lasts a good 6 thousand miles, i usd it on my last car which was heavily boosted, and after 5 thousand miles the oil was still thick and Amber, AMSoil is REALLY good stuff, i highly recommend it

[Bubba]

I have over 185K miles on my '89, and I even run it 4 times per year on race tracks and I use good,old-fashioned, non-syntheticoil. I've never had to add a drop between changes, and she still runs great. It the oil/filter changing that's important not whether or not it's synthetic. Save your money, go fossil.

[Spectre]

The one thing is that if the car has not been gettin synthetic then give it a engine flush before converting over!

I switched both of my cars to synthetic without an engine flush. If your car has a lot of miles, you don't want to flush the deposits out. Some of them are detrimental, but others need to be there(I'm getting this from a chemist). Read the back of any quart of synthetic. All of the ones that I've seen say that it blends with any conventional, or synthetic oil. I had a shop trying to upsell me with that gimmick and I told them that I had already switched a car over without a hitch. That shut them up.

[Silvia007]

Well my car had 130k on it when I got it, it's never been on synthetic and there's definately a difference. I went straight to Amsoil 10w30 and that stuff has worked wonders on my car. Better gas milage was one. I had no problems and will never use any other oil unless it's advertised somewhere saying they are "better" then amsoil.

[Shogun]

Go for semisynthetic oil. The fully synthetic has caused rather many problems in Motorbikes (high rev engines).

The best would have been a fully synthetic oil with sticky performance but as far as I know there are no brands like that on the market.

[TheProfessional]

i agree, if you plan on keeping the KA, then run semi syn... i typically never advise a full syn switch to cars over 100k because to me it seems pretty pointless. obviously, you want to run syn from day one (not literally) because itll keep the motor running mint for years; wont wear as fast, better oil, etc etc. but if you plan on keeping the motor for a while, run somewhere in between = semi synth. thats just my opinion.