Stop leaks from synthetic oil

[dadbeau]

Two or three months ago, we changed to synthetic oil (Mobil 1) in our 1972 FJ40, 1972 FJ40 FST and 1984 Fj40. All were tight with no leaks prior to the oil conversion, now they all have significant leaks. Any opinions or experience out there in converting back to conventional oil and have the leaks stop or slow?

Sent

 

[BEE-JAY42]

My 2 cents, stop putting lipstick on a pig.

 

[brian]

now you get to replace all the leaky seals.

 

[Cruiserdrew]

I thought it was pretty much disproven at this point that synthetic oil causes leaks. I've never noticed it and I've used in in a lot of old Land Cruisers. Worn seals cause leaks, not synthetic oil.

Anyway, not enough info here.

Hard to believe all those old Cruisers were "tight" prior.

In 2Fs at least, the most common leak, by far, is the oil pan gasket, especially in the arches. Try tightening them up a bit and see what happens.

What viscosity oil was used? Thinner viscosity=more leaks.

 

[71FJ40]

I thought it was pretty much disproven at this point that synthetic oil causes leaks. I've never noticed it and I've used in in a lot of old Land Cruisers. Worn seals cause leaks, not synthetic oil.

You are right - it does not cause the leaks, it is just that the smaller uniform molecular structure seeps through cracks in seals and gaskets that regular oil would not.

The main difference between synthetic motor oil and conventional motor oil is found in the molecular structure. In a mineral oil, the molecules come from organic, natural materials - which are not consistent, have different sizes and odd shapes. There can also sometimes be a few oddball molecules in mineral oils.

Synthetic oils, on the other hand, were created by scientists in a lab. The molecules are uniform, and they line up like good soldiers inside of your engine, and air more likely to leak out of existing defects.

 

[45Kevin]

I have heard people complain of the same thing with old motorcycles.

What was explained to me was that dino oil will cause gaskets to swell and sit tighter against the two surfaces they are between.

Synthetic oil will not cause the gasket to swell, ergo you don't get as good a seal.

 

[1911]

I have successfully used fully-synthetic oil in many older vehicles (motorcycles especially), as old as 1928 models, without ever having observed it to cause any new leaks that weren't already there. Not saying that it couldn't or doesn't happen, just that it is not a given that it will. My 40 runs on synthetic and doesn't leak a drop anywhere - but I've replaced the oil pan and side cover gaskets and the rear main seal myself so I know they were done right. Agree with Andrew that the oil pan (and the side cover) gaskets are the most common culprits by far for oil leaks on a 2F.

 

[TJ96TLC]

I noticed my first round of Amsoil turned dark after less than 5k in my 96lc. I think it cleans a lot of deposits out, which could unplug a potential leak. Since then the oil stays clean progressively longer. I did notice my first seepage around the valve cover this week. I have ran Amsoil since 90k for 57k so its probably just time for a new valve cover seal.

 

[Tigerstripe40]

Synthetic motor oil is great for high performance sports cars with tight tolerances and high rpms.
A 2F does not fit that description.

While synthetic motor oils can be changed more infrequently than conventional motor oils, typically that would assume that you are regular street driving. A Land Cruiser isn't typically used that way.

Where we use Cruisers, there is a greater chance of the oil getting contaminated by other stuff (like dirt from a dusty road). So having 8000 mile oil changes doesn't make too much sense IMHO.

Run quality conventional motor oil. Change it every 3000-5000 miles or 50 hours of run time.

Personally, I think that running synthetic motor oil in a F/2F/3F is simply a waste of money. The motor wasn't designed for it, and has pretty loose tolerances to begin with. Now you've got another problem (leaking seals) which will only be corrected by replacement. You might be able to put in a high mileage motor oil that contains seal swellers, but that might just buy you a few more months.

 

[zags]

You are right - it does not cause the leaks, it is just that the smaller uniform molecular structure seeps through cracks in seals and gaskets that regular oil would not.

The main difference between synthetic motor oil and conventional motor oil is found in the molecular structure. In a mineral oil, the molecules come from organic, natural materials - which are not consistent, have different sizes and odd shapes. There can also sometimes be a few oddball molecules in mineral oils.

Synthetic oils, on the other hand, were created by scientists in a lab. The molecules are uniform, and they line up like good soldiers inside of your engine, and air more likely to leak out of existing defects.

This makes sense to me. I have seen oil leaks start after switching to synthetic, but only on higher mileage engines.

 

[howyadoin]

Synthetic motor oil is great for high performance sports cars with tight tolerances and high rpms.
A 2F does not fit that description.

While synthetic motor oils can be changed more infrequently than conventional motor oils, typically that would assume that you are regular street driving. A Land Cruiser isn't typically used that way.

Where we use Cruisers, there is a greater chance of the oil getting contaminated by other stuff (like dirt from a dusty road). So having 8000 mile oil changes doesn't make too much sense IMHO.

Run quality conventional motor oil. Change it every 3000-5000 miles or 50 hours of run time.

Personally, I think that running synthetic motor oil in a F/2F/3F is simply a waste of money. The motor wasn't designed for it, and has pretty loose tolerances to begin with. Now you've got another problem (leaking seals) which will only be corrected by replacement. You might be able to put in a high mileage motor oil that contains seal swellers, but that might just buy you a few more months.

Well said, much like people running "high octane" fuels in a vehicle not designed for it...makes zero sense. .02