HunnaLs400

I have a 1998 Lexus Ls400 with 228k

I and the previous owner have been running high mileage full synthetic oil.

Since the car is so old there a very high chance the upper and lower oil pan gaskets haven’t been replaced. Full synthetic oil is more acidic than regular oil. Older cars’ gaskets weren’t made to be able to handle full synthetic oil since it wasn’t very prevalent back then. Therefore, I was wondering if since they are older gaskets and I’ve been running full synthetic… if the gaskets may have worn out because of that? I know they are because they are leaking hahahaha but I was just wondering if that may have been the cause.

I obviously have the 1uz-fe vvti. I was wondering if the vvti solenoids may have been effected by the full synthetic oil as well. I’ve been needing to replace those becuase I get a vvti code in both banks.

overall the main question is should I not run full synthetic and just change my oil more often or should I keep running full synthetic?

LeX2K

I drive cars daily that are much older and I've been using synthetic oil for many years, no issues with leaking or anything like that. In theory synthetic oil can leak more since it tends to flow easier for lack of a better description. I would keep using the same oil along with the OEM oil filter.

CLLEXUSS

If you have been running conventional motor oil for a long time and were considering a switch to full synthetic then maybe there is a case not to do that. But this is all the car has known. I think that's an engine oil myth about the full syn acidity being an issue, I don't believe that is correct. But I could be proven wrong but I don't think so, until proven otherwise.

LeX2K

Even if it was, what is the difference between seals and gaskets 30 years ago vs. now? For example a cam seal (same part number) was used in Toyota and Lexus models from about 1987 to 2014.

Losiracer2

Lexus used FIPG silicone back then to seal the oil and transmission pans, so it wasn't a typical inferior gasket. My 99' was still leak free to this day, and I used full synthetic, until I wanted to inspect the filter and make a valve body adjustment from 2 to 3 for more line pressure and had to crack open the pan and reseal. I used the same FIPG 1281 Seal Packing tube they did at the factory for the reinstallation.

timmy0tool

iTrader: (7)

i agree with the sentiments here: i have yet to see hard evidence that synthetic cause more leaks than conventional. most people immediately correlate leaks to when they switched out to synthetic which is hard to prove the cause/effect.

leaks (like all other car problems) usually have more straightforward explanations (e.g. seal failure). driving conditions and habits, ambient temps, and maintenance are other factors that would contribute more directly to leaks than just the oil used.

RA40

iTrader: (6)

Have an oil analysis done at varying intervals to see how this car is with oil longevity. Doing 5K intervals is fairly easy with synthetic and have plenty of good additive left in it. I did ours at 7-8K when it was driven regularly.

The one main leakage point will be the valve cover gaskets with age. The rest of the engine should be tight if it retains the original seals on the oil pan. The cam seals have been replaced at the TB intervals.