Used to be that full synthetic oil was considered unwise in high mileage older motors as it was likely to cause oil leaks. I have read recently that modern full synthetic oils are less likely to do this. My T4R has 225k miles on it, a couple slow leaks, mostly or completely from the valve covers, it is less since I torqued the bolts down.

Would like to use Rotella full synthetic, what do people think? Will I leak more oil or the same?

Why not give it a try and see what happens? Nobody is going to be able to give you a concrete answer on whether or not any existing oil leaks will become worse and whether or not any new leaks will pop up when you switch to full synthetic. The worst case is you switch back to conventional if it doesn't work out.

If I were you, I'd go ahead and perform the valve cover gasket job. Unless you pulled off your plenums, you weren't able to get to all the valve cover gasket bolts so you only tightened some of them and not all of them.

I don't see any advantage running synthetic on my type of use. Frequent highway heavy use. I run conventional Castrol GTX 10-30. About 7-8K between changes at running about 1K per week. I have 330K on my motor (387K chassis) and it uses about 1 quart every 4K miles.
I bought a valve cover set but never had time to put it in. So I tweaked all the bolts I could get at, pushing aside the covers and was able to stop the leaking. I didn't torque to spec (they loosen anyway), just tightened them to what felt right, been over a year and 50K and no leaking since.

If you have a leak, it is likely to leak more. Why not fix the leaks?

Otherwise, I switched to Rotella T6 a few years back around 250 or 260k miles and am over 290k with no problems or leaks (valve cover gaskets replaced in that time period though). No noticeable oil burned per 5k oil change interval.

-Charlie

I was using syn-blend on the 4R and 2000 LC until 210K and 232K miles respectively, and then switched to full synthetic Castrol oil. No leaks so far. The 4R is at 215K and LC is at 237K.

If you are replacing the valve cover gaskets, use OEM and apply a small film of Toyota FIPG to the bottom surface on the head.

I've always used amsoil synthetic, even in my older ones approaching 400,000. If there is a leak, it's 'cause you need to replace a seal as Charlie said, not because of the oil.

I second Nissanh, non toyota seals will give you the opportunity to replace them twice.

If you do the valve covers don't for get all the half moons

Do the valve cover job. It’s very easy, Once you do your research. Then if you get stuck at some point there is a video or instructions online somewhere on how to get past the obstacle. Haven’t lost any oil since doing mine and I’m using mobile 1 synthetic.


2001 SR5 4x4 Premium
2017 SR5 4x4 Premium

I like conventional oil in my old rig. The pros of this in my opinion is that I get to get a thorough look at my truck every 3-5k miles. With synthetic you may go almost a year before having to change the oil. Just my 2 cents. Also I think the leaks will exacerbate with synthetic.

oil is 100% personal preference. I see the value of synthetic, others obviously don't.

Your leaks aren't going to go away by switching to synthetic, they May get worse but I doubt it if they actually are valve cover related. Fix the leaks, switch your oil (if you're so inclined), nothing bad will happen. If you find something about the new oil you don't like, drain it and try something different. It's not like running oil for a change cycle is going to be irreversible.

I bought 2 saturns with over 140,000 miles plus a 96 4Runner with 220,000, a 97 4Runner with 120,000 and switched them all over to either Rotella T6 or T5 or Pennzoil platinum or ultra and the leaks never got worse.

To me the leaks going to synthetics are a wives tale. I’ve never experienced it.


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This! Exactly what I did/do

I appreciate all the posts but no one really answered the question about whether modern fill synthetic oils tend to leak less.

It is my understanding that once a synthetic (or any) oil has found a way out, changing back will will not stop the new seepage, hence the advice against changing to full synthetic oil late in a vehicles life that has only had dino oil.

I am also not about to try to cure the leaks in this vehicle, it not that brisk but also likely not from just the valve cover gaskets. But if they got worse with a
fully synthetic oil I would be pissed. And seitching back to my current oil, from many reports, would not return to my current leak rate.

If you have a leak, it is Possible for that leak to get worse with a change of oil. Doesn't matter if you change brands but stay dino, or change from dino to synthetic.

Having a "minor" leak that's minor because of all the sludge on the inside isn't exactly more desirable than having a bigger leak. Clearly, neither are ideal. Take your chances or don't, but there's no guarantee that the next time you change the oil you won't have worse leaks.

As for the idea that All leaks get worse with a switch to synthetic, that's false. It's 100% dependent on why and where it's leaking. A cracked and worn valve cover gasket is going to leak regardless of the oil and it's not going to leak More just because that oil is now synthetic.

A men.

It’s a wives tale.

Fix the leak and it will go away. Synthetic oil has an inherently lower pour point than conventional oil does so it’s thinner. Just that, in and of itself will cause the leak that is already there to flow more.

I hate google for making irrelevant things relevant because of all the people that looked at it. I also dislike all the armchair chemical engineers on Bob Is The Oil Guy website.


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