High Mileage Oils Help Stop Small Leaks ?

Odd_Ball said:
Seals on rotating surfaces pretty much universally have some elastomeric sealing surface and should be improved by seal swell agents if they've hardened and contracted.
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Except for some newer Rear mains are now teflon, and high mileage oil won't do jack for a leaking teflon seal.
 
ZeeOSix said:
Anyone have success on using a High Mileage oil with respect to stopping small oil leaks? GF has a G35 Infinity with 165k that has a small valve cover leak, and the valve covers are a royal pain to get to on this 3.5L V6. Was thinking of using "Valvoline High Mileage with MaxLife" next oil change and see if it helps. Anyone seen a high mileage oil actually help out with something like a slight valve cover leak?
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I've used HM oil in many different vehicles with small leaks. I've used it in a few Chevy vans, a GMC Savana 3500, a Ford Transit 250, and a Ford Escape. I have never noticed a bit of difference. It could be that once it starts leaking it's already too late. Or it could be HM oils don't really do a whole lot to begin with.
 
Odd_Ball said:
High mileage oils contain seal swell agents. As seals age, they become less elastic and can shrink dimensionally.

Seal swell agents reverse this trend, making the seal more elastic (lower durometer) and causing them to expand dimensionally.

If a seal is non-elastomeric then seal swell agents aren't going to do much. Some static seals may be non-elastomeric, but many are. Particularly in more modern cars. So I don't think you can say they won't help across the board. It will depend on the composition of the gasket. Valve cover seals are generally elastomeric these days so they may be helped by a high mileage oil. In the old days they might have been cork or cork/rubber but I haven't seen those in a long time.

Silicone rubber gaskets are probably a special case and I suspect they aren't improved by HM oils. Those are pretty common on valve covers as well.

Seals on rotating surfaces pretty much universally have some elastomeric sealing surface and should be improved by seal swell agents if they've hardened and contracted.
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I give up...:(
 
I understand HM oils are designed to treat symptoms of high mileage including oil leaks, oil consumption, etc.
If I had a reason to start using HM oils, I would expect at least a small reduction for any existing leaks, if the leak is not entirely stopped.
 
I've seen good results (all seeping stopped) with just GENTLY snugging down the valve cover bolts in situations like this on numerous engines. . The VC bolt torque specs are not high, so don't get carried away and strip threads or crack the valve covers.
 
blufeb95 said:
I'm more familiar with the newer G37 and G25, but I think they're also dual TB, dual MAF, dual air box, so there's a lot of crap in the way on each side.
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This is a 2004, so there isn't a dual TB and intake system. But the big intake manifold needs to come off to get the the valve covers.
 
I have. I've used Valvoline and am now using Castrol HM in my 98 Chevy K3500 with the 7.4L that has a leak at the front bottom of the oil pan. It originally stopped it from dripping on the ground to just seeping. Lately I've noticed it has started to drip again but the oil has been in the engine for almost two years and 3,000 miles.

I'm probably going to change the oil tomorrow and will probably use Castrol HM again. I have no idea if the new oil will stop the drip again.
 
ZeeOSix said:
Anyone have success on using a High Mileage oil with respect to stopping small oil leaks? GF has a G35 Infinity with 165k that has a small valve cover leak, and the valve covers are a royal pain to get to on this 3.5L V6. Was thinking of using "Valvoline High Mileage with MaxLife" next oil change and see if it helps. Anyone seen a high mileage oil actually help out with something like a slight valve cover leak?
Click to expand...
Had the same problem with my previous car, tried M1 10W-40 HM, it was useless.
 
Last edited:
blufeb95 said:
I'm more familiar with the newer G37 and G25, but I think they're also dual TB, dual MAF, dual air box, so there's a lot of crap in the way on each side.
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You know that rings a bell...

I have seen pictures of the underside of a hood G37 and that is very, very true... No room at all because of the air box and maf setup.
 
If you plan to keep the car longer say another 100,000 miles then I would change the valve covers/gaskets. If not just check the oil level every week or other week and just fill when the level goes down.
 
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