tomf

At my last oil changed I switched to full synthetic oil. After 600 miles, I have oil leaks from both the valve covers. Previously no leaks at all in the last year I've owned my 1999 ES300 with 138,000 miles.

I'm posting this as a warning to those with high mileage cars considering switching to fully synthetic. Doing so can cause leaks.

Lexmex

What brand and weight of oil were you using before and currently?

Trexus

138,000 miles appears to be low mileage. Be sure to change the valve cover gaskets...

PFB

Synthetic oil WILL NOT cause leaks. It may however make already worn-out gaskets/seals more evident, by leaking past them, and/or cleaning any sludge and other gunk that was sealing the existing leak. This is because Synthetic oil has much better cleaning properties, flows much better than conventional oil, and hence also lubricates much better than conventional oil (This is a good thing).

I don't know which synthetic Oil you are using, but I know that Mobil-1 Synthetic oil (and maybe others) have been formulated specifically to swell gaskets and seals, potentially stopping the oil leak. It may however take 5,000 Miles or so before the leak will stop. Make sure that you use the correct viscosity.

Your switch to Synthetic, and the subsequent oil leak, could also have been purely coincidental.

Phil

WAES300

I put synthetic in mine after purchasing it at around 200K miles; there were no leaks then or now. I don't know if it had regular dino or synthetic beforehand..

miltonlin

I have been running Mobil1 since 1K, now have 145K. I too had valve cover leaks just fixed. It seems to be common problem from my research of the 1MZ-FE?

tomf

No brand in particular. Used 5W30.

tomf

I thought of that but given the fact that both the front and back valve covers started leaking makes me inclined to think its not a coincidence.

fatboypup

i put mobile one 5w30 in my 97 with 162k on it after running a can of engine restore thru it ......... it actually leaks less now

PFB

If that was my car, I would change the valve cover gaskets (a very common problem on these models especially at that milage), and go back to Synthetic (Mobil-1 5w30). Amsoil Synthetic would have been my first choice, but its hard to find and also much more expensive.

01ES300NYC

iTrader: (2)

change your valve cover gaskets...and if u can change your oil seals and oil pan gasket...you should be good after that...
01 es300 with 164,000miles... using royal purple 5w 30 and royal purple filter and never had a drop of oil leak. but i changed the seals and gaskets when i bought the car(wasn't leaking when i bought it, just wanted to avoid a headache)...then i switched to synthetic...

dcapo

yup, what "PFB" said

is it a fact that if u go synthetic, u gotta stick with it for good, unless u fully reflush the whole system

LeX2K

This is not a "fact" at all. You can switch, mix, change, or do whatever you want between synthetic and conventional oil, they are 100% compatible with each other. If you have a leaking problem when using synthetic oil, then you need to fix the source of the leak, or go with a high mileage dino oil, which can help alleviate the problem.