thicker oil causes valve seal damage (?)

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Found this post on the MMO forum -

"If you go thicker, you risk wearing out your valve guide seals at the least, and valves at the most. Staying with the recommended oil viscosity, except high mileage, seems to work well. I went 185K on 10-30W, and it still did not need additional oil between changes; but I smelled oil at startups near my exhaust. O/W, its running like a new truck, except with Lucas stabilizer added to high mileage oil. My engine is set, and just try to replace components with the best quality I can afford at the time (I get a few go wrong about every 75K, especially in mid-FL heat). Hopefully, I’ll have less go wrong now that I’m an MMO convert!!

Yes, thicker oil feels better for a brief time, but keep an eye on your exhaust at startup. You will soon see blue clouds coming from your exhaust!"

Any truth here ?
 
Originally Posted By: TurboTravis
Zero


Disagree, completely.

If thicker oil doesn't place more stress on engine oil seals, then there are some basic laws of physics which are being re-written. Whether or not it 'matters' depends on the engine.
 
Without taking a side in the debate (I have no experience running overly thick oil...), I think I can explain the thinking:

A minute amount of oil has to get past the seals to lubricate the valve stem itself. Thicker oil will not get past the seals as readily as the recommended viscosity.

Ergo, less lubrication of the valve stems leading to the early demise of either stems or guides. Worn out stems will kill the seals and voila' - blue smoke.

The likelihood of this is unknown to me...depends on how critical the stem/guide lubrication is, how overly viscous the oil is for that application and how susceptible the stems/guides are to wear.

But I see the logic in the thought process...
 
Last edited:
Originally Posted By: JoeWGauss
nonsense. But then again MMO is nonsense as well.


Gonna have to agree that MMO in gas/oil is a placebo-based cleaning experience
 
Originally Posted By: JoeWGauss
nonsense. But then again MMO is nonsense as well.


Disagree. MMO has it's place for certain apps.
 
Originally Posted By: ericthepig
Originally Posted By: JoeWGauss
nonsense. But then again MMO is nonsense as well.


Disagree. MMO has it's place for certain apps.


Door hinges, model car wheels..
 
Originally Posted By: ericthepig
Found this post on the MMO forum -

"If you go thicker, you risk wearing out your valve guide seals at the least, and valves at the most. Staying with the recommended oil viscosity, except high mileage, seems to work well. I went 185K on 10-30W, and it still did not need additional oil between changes; but I smelled oil at startups near my exhaust. O/W, its running like a new truck, except with Lucas stabilizer added to high mileage oil. My engine is set, and just try to replace components with the best quality I can afford at the time (I get a few go wrong about every 75K, especially in mid-FL heat). Hopefully, I’ll have less go wrong now that I’m an MMO convert!!

Yes, thicker oil feels better for a brief time, but keep an eye on your exhaust at startup. You will soon see blue clouds coming from your exhaust!"

Any truth here ?

I don't think the viscosity of oil affects the endurance of the valve seals that much. Most valve seals are metering type and they meter the oil that passes through the seal and for thinner viscosities, more oil will pass through. But there should be a descent oil film between the seal and stem with any viscosity. These seals are working in boundary-lubrication regime I believe and even in the boundary-lubrication regime, I think thicker viscosity is better for wear. I think the failure of the seals happens mostly due to failure of the rubber thanks to heat hardening.

All said, I've replaced my valve-stem oil seals about 700 miles ago, which was a lot of difficult and tiresome work. A shop would probably either not do it or charge a small fortune.

Here is how they look like. Note that the inside of the Viton seal is metal-clad:

IMG_2052.jpg
 
Yes that the logic but given the wide tolerance even heavy oils can provide enough lubrication to the stems.
Many engines run heavier oils for the life of the engine without issue or stem/ guide failure, e.g. Diesels and Euro engines.
Just a guess on my part but i would think with emission regulations being what they are manufacturers would want to keep oil consumption through the guides to a minimum.
Many guides are bronze and tend to hold lube.


From SKF.
Quote:
Oil metering to the valve guide /
s tem interface is the prime function of a
valve stem seal. Although the requirements
for each engine differ according to the design
parameters and operating conditions, the oil
metering rate is generally within the range
of 0.1 - 1.0mg per valve per hour.
 
Originally Posted By: TurboTravis
Originally Posted By: ericthepig
Originally Posted By: JoeWGauss
nonsense. But then again MMO is nonsense as well.


Disagree. MMO has it's place for certain apps.


Door hinges, model car wheels..


Lmao exactly!
 
Originally Posted By: Gokhan
Most valve seals are metering type and they meter the oil that passes through the seal and for thinner viscosities, more oil will pass through. But there should be a descent oil film between the seal and stem with any viscosity. These seals are working in boundary-lubrication regime I believe and even in the boundary-lubrication regime, I think thicker viscosity is better for wear. I think the failure of the seals happens mostly due to failure of the rubber thanks to heat hardening.

All said, I've replaced my valve-stem oil seals about 700 miles ago, which was a lot of difficult and tiresome work. A shop would probably either not do it or charge a small fortune.


Yup most valve stem seal failures are related directly to heat, no surprise when they fail at 200K+ miles... Mostly the type of material the seal is mfg'd from dictates it's longevity... The the early Ford Modulars used a seal that failed before 100K mi(another engine that they are a PITA to repl, got my T-shirt), begnning '96 an improved seal was introduced that generally lasts the life of the engine...

New stem seals can a major difference, I've seen OHC engines that were using a quart in 200mi, improve to less than a quart usage in 3K mi...
 
Hijacking my own thread -

Plenty of safe legitimate uses for MMO. eg, I've run OCIs w/ 15w40 or 5w30 in my Sienna and change it in the Spring. Top off with a quart of MMO in December (the van needs it by then). Safe app for MMO and it (IMO) provides smoother starts for December thru February temps. (put some in the freezer overnite - super low viscosity the next morning). And it's only in the crankcase a few months.
 
Thicker oil generally causes LESS oil use.

MMO in the engine is not normally recommended - special needs only.
In the fuel? Yes. A bit of lube for the fuel pump, valves guides, and rings. Also a bit of sealing for the valve seats.

There is no placebo effect. It is a good idea to use extra lube with alcohol infused fuels. It's not something that you can feel.
It is for long term use and benefit.
But some do report some extra smoothness at idle.
 
Another any truth question -

Is there any truth to the belief that ethanol has a slight "drying effect" in the fuel system? (Previous poster may have alluded to this.) Thus more motivation for MMO in the fuel?
 
Yes ethanol has a drying effect on the fuel system. The more alcohol, the harder it is on stuff, and not just drying, it also is corrosive in larger concentrations.

When carb kits started coming with composite floats instead of bronze ones, we saw ethanol gas soften, deform, and in some cases eat through them until they got the formula right.

I run MMO as a top lube in my old cars and bikes built before ethanol was the law of the land, but you can run TCW3 2 Stroke oil, or something like Lucas UCL as well.

As far as thick oil leading to valve seal damage, its usually heat and time that shrink or just decompose the things. Look at the small block chevy. They uses the same type of seal for decades on those things with everything from straight 30, to 10w30, 10w40, and 5w30 speced on them.
 
Manuals given with cars state that oil changes should be more frequent with E85. So we can clearly see the results of any alcohol [even E10] is not good.
It diminishes the lubricity of pure gasoline - the fuel pump is the main part hard hit.
 
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