Best oil for small oil leak timing cover?

[MoreCowbellAz]

Just 2 weeks ago I went through this exact issue in my Rav4 (112k), had switched to 0w30 and 5w30 HM but the leak slowly got worse over time. I finally bit the bullet and replaced the timing cover. And it ain't cheap once you add in all the "may as well do's" like serpentine belt, replace pulleys and tensioners, etc. The vehicle is otherwise is such great shape it was worth it to see if I can get another 3-5 yrs out it without more major repairs.

FWIW the issue for me is I would notice a hot or burning oil smell in my garage after I parked it. But I could never find anything actually dripping. Chased it around for prob 2-3 yrs, replaced pcv, switched oils, etc, was driving me crazy. Finally I noticed an actual drip off the oil pan, which I traced up to the pulley area and voila apparently it was the timing over. They didn't have to remove the engine, but they had to remove a whole bunch of other things.

 

[The Critic]

The cover is sealed using RTV. HM oil will not help. It is not a rubber seal.

Dropping the powertrain to reseal a 3.5 is the only realistic way of doing it. It only takes about an hour to drop the subframe with the engine/trans still attached. The job can be done in-car but would be very very very difficult.

 

[Trav]

Nothing will help with RTV that has broken its seal (that is the great benefit of Hylomar, it will reform its seal if disturbed for some reason). RTV and esters commonly found in greater amounts in HM oils and sealing additives do not play well together.

 

[LeakySeals]

Originally Posted by StevieC
Originally Posted by PimTac
I was under the impression that high mileage oils will not do anything for bead sealed parts? They work on gaskets and things like valve seals and cam seals but not the stuff being applied by robots.

They typically don't but it's worth a try considering what he has to do to fix the problem right.

True. But this seal is a rubber gasket. So it should respond to HM oil. I would also try 1/4 turn on the bolts.

 

[Trav]

Timing cover with a rubber gasket? RTV doesn't really qualify as a rubber gasket. It tends to deteriorate instead of swelling in the presence of products designed to swell rubber seals.
Many modern rear seals today are Teflon, good seals, can be difficult to install and totally unaffected by additives when they do leak. Today these products and HM oils have an ever decreasing market and unless you are sure you have a fully gasketed engine like the ones that were the norm when I first started in this business its best IMO to leave them alone.

 

[Leo99]

Until it drips, it's not really a problem. Used cars have issues. This one is very minor. Could go another 100k+ miles before it drips.

 

[oil_film_movies]

Originally Posted by The Critic
The cover is sealed using RTV. HM oil will not help. It is not a rubber seal.

Originally Posted by Trav
Timing cover with a rubber gasket? RTV doesn't really qualify as a rubber gasket. It tends to deteriorate instead of swelling in the presence of products designed to swell rubber seals.
Many modern rear seals today are Teflon, good seals, can be difficult to install and totally unaffected by additives when they do leak. Today these products and HM oils have an ever decreasing market and unless you are sure you have a fully gasketed engine like the ones that were the norm when I first started in this business its best IMO to leave them alone.


I looked at all the "elastomer shrink/swell compatability" tests done in SN & dexos1 to see what they expect oil to affect.
NBR nitrile rubber
FPM flourine rubber (Viton)
AEM Ethylene acrylate copolymers
ACM polyacrylates
VMQ vinyl methyl silicone (polydimethylsiloxane)

Silicone rubber does indeed appear on the list, VMQ, as it has methyl (CH3) groups hanging of the siloxane backbone. That said, most of the discussion around the properties of VMQ appears to indicate they usually fail due to mechanical stress, as in vibration & shifting around due to repeated expansion-contraction & structural metal flexing where it seats.

Despite the methyl groups in the silicone rubber gaskets, it may well be the High Mileage oils don't actually do much to those.
It could be the SN/dexos1 tests just make sure nothing wicked is in the oil to attack those seals, and its actually rare when they do.

Originally Posted by Leo99
Until it drips, it's not really a problem. Used cars have issues. This one is very minor. Could go another 100k+ miles before it drips.
That is right. A little sludge or vanish in an older engine can wedge into the gasket & help it seal too. That could happen.