Low Oil Viscosities

timwinters

timwinters

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So,

I just got my oil analysis back from Blackstone and my viscosity was low again. It tested at 82.3 and they list the acceptable range as 86 to 105 when running Aeroshell 100W.

This has been an ongoing problem over the last 10 years (engine OH'ed in 2004) and for 1154 hrs SMOH. Oil viscosities are consistently at or below the lower limits per the oil analysis.

I just went back and reviewed all the oil reports from day one...I've been regularly testing the oil since 98 SMOH (the third oil change after OH)...and what I've found is:

Viscosity has always been on the lower end of the scale.

But

It appears to have worsened since I began using CamGuard in 2006 when the engine had 401 hrs SMOH.

Before that time the viscosity reading were consistently near the bottom of the acceptable range (87 to 95).

Since using CamGuard the viscosity readings are at or below the bottom of the acceptable range (83-88).

So

I assume CamGuard reduces viscosity?

The engine is healthy and all wear levels are consistently low, so I don't think this is an issue...but rather just a curiosity.
 
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Do you add oil in between oil changes?

What is the water level in the oil?

Have you tried using 20w-50?
 
So, what is causing the viscosity to be low?

The engine mechanicals (good or bad) are not going to do that.

Presumably they are comparing to what they know the oil should be.

So, that leaves two possibilities - the long chain molecules in the oil are breaking down (heat) or the oil is diluted with gasoline.

Gasoline would come from running rich, cold starts, priming, etc. Usually more of a problem with frequent cold starts / short runs. Does your oil get up to temp during normal operation?
 
If I remember right they test for lead. What are the lead levels?

I would think the analysis would show fuel?
 
Fuel has been running at 0.5% (recommended levels below 1%)

Lead has been running around 1200 PPM with universal averages of 2929 PPM. (I assume my low levels are from running mostly MoGas)

My oil has issues getting up to operating temps in the winter but not the summer. I always run my oil up to at least 190 dF for 15 minutes on my "pre-oil-change-warm-up-flight."

I used to have an issue with more fuel in the oil but I attributed that to overpriming and quit doing so. Haven't seen an issue with fuel in the oil for almost three years now and that one time was a middle of the winter oil change and the oil probably didn't adequately get to operating temp in the "pre-oil-change-warm-up-flight."

I keep coming back to CamGuard because nothing else stands out but I may be completely off base. I may have to ping Ed to get his opinion.
 
Sound like you need to use an even higher weight oil if viscosity is below the min for your engine. Or as some have said, your oil is being tainted in some weight to cause it to get more sludgy and thicker.
 
It is not from gasoline. Gas evaporates out at running temperatures.

Cessna had "oil dilution" systems on their 180, 185, 206 airplanes as an option.
 
kgruber said:
It is not from gasoline. Gas evaporates out at running temperatures.

Cessna had "oil dilution" systems on their 180, 185, 206 airplanes as an option.
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And in the early 182s...mine used to have one (It was removed long before I bought it).

CTLSi said:
Sound like you need to use an even higher weight oil if viscosity is below the min for your engine. Or as some have said, your oil is being tainted in some weight to cause it to get more sludgy and thicker.
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That was never stated. It's just below the normal range for what one would expect for 100W.
 
timwinters said:
Fuel has been running at 0.5% (recommended levels below 1%)

Lead has been running around 1200 PPM with universal averages of 2929 PPM. (I assume my low levels are from running mostly MoGas)

My oil has issues getting up to operating temps in the winter but not the summer. I always run my oil up to at least 190 dF for 15 minutes on my "pre-oil-change-warm-up-flight."

I used to have an issue with more fuel in the oil but I attributed that to overpriming and quit doing so. Haven't seen an issue with fuel in the oil for almost three years now and that one time was a middle of the winter oil change and the oil probably didn't adequately get to operating temp in the "pre-oil-change-warm-up-flight."

I keep coming back to CamGuard because nothing else stands out but I may be completely off base. I may have to ping Ed to get his opinion.
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Yeah, ask Ed, you'll learn more than you may expect.:yes:
 
Capt. Geoffrey Thorpe said:
So, that leaves two possibilities - the long chain molecules in the oil are breaking down (heat) or the oil is diluted with gasoline.
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dilution, maybe but it'll boil out

oil breaking down (as in losing base viscosity) because of heat? no, viscosity is lost through shearing
 
Clark1961 said:
dilution, maybe but it'll boil out

oil breaking down (as in losing base viscosity) because of heat? no, viscosity is lost through shearing
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Would a tight bearing possibly cause it? Line bore being a smidge off?:dunno: Would surface tension affect the shearing? If so I could see the relation to Cam Guard increasing the viscosity loss since I think it increases surface tension.

Anyway, it'll be interesting to hear what Ed has to say.
 
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Send them a sample of unused W-100 and ask them to test it for viscosity.

Run for one cycle without using Camgard and see what the viscosity is.

Compare the results to previous reports.
 
I'll give unwanted advice
Change to 15W50 and leave out the Camguard. Fly the engine more often
Camguard is not likely diluting your oil viscosity or the testing labs would have keyed on it by now
If there was a total synthetic oil approved I would tell you to change to that
Synthetic oil chains are vastly more resistant to mechanical shear and coking
Oil loss/burn is not decreased by using higher viscosity oil - and conversely is not increased with lower viscosity oil
Oil loss is decreased by increased ring conformance to the barrel and tight(er) valve guides.
Oil loss is increased by the opposite conditions.
Wear is not increased by lower viscosity oil, and vice versa
3 quarts per 50 is not excessive and likely has little to do with the shearing of hydrocarbon chains that is the likely culprit to your lower viscosity - based on the information given
 
Problem with synthetics is they all use the same base stock and it does not work will with 100LL and the by products of its combustion as it's formulated to work with UL Mogas.
 
Are you adverse to changing to P66 XC for one oil cycle? Change one thing, and see if there's a difference. Since the oil is the system under test, try changing brands. It's possible that during your viscosity decline that Shell may have changed additive package, and adjusted something that isn't playing well.
 
Henning said:
Problem with synthetics is they all use the same base stock and it does not work will with 100LL and the by products of its combustion as it's formulated to work with UL Mogas.
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YESSIR! Just ask Mobil how thing went with their 100% synthetic. :eek:
 
Dr. O said:
I'll give unwanted advice
Change to 15W50 and leave out the Camguard. Fly the engine more often
Camguard is not likely diluting your oil viscosity or the testing labs would have keyed on it by now
If there was a total synthetic oil approved I would tell you to change to that
Synthetic oil chains are vastly more resistant to mechanical shear and coking
Oil loss/burn is not decreased by using higher viscosity oil - and conversely is not increased with lower viscosity oil
Oil loss is decreased by increased ring conformance to the barrel and tight(er) valve guides.
Oil loss is increased by the opposite conditions.
Wear is not increased by lower viscosity oil, and vice versa
3 quarts per 50 is not excessive and likely has little to do with the shearing of hydrocarbon chains that is the likely culprit to your lower viscosity - based on the information given
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Best post yet.....:thumbsup:
 
docmirror said:
Are you adverse to changing to P66 XC for one oil cycle?
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No, not at all. In fact there's three cases of it sitting in my hangar as I've decided to start using it as my winter oil instead of Aeroshell 80W. I plan to stay with 100W in the warm months though.

I'll be switching to XC for the first time come November.

I change my oil about every four months regardless of time so I'm usually running summer weight for 8 months and winter weight for 4.
 
Henning said:
Would a tight bearing possibly cause it? Line bore being a smidge off?:dunno: Would surface tension affect the shearing? If so I could see the relation to Cam Guard increasing the viscosity loss since I think it increases surface tension.

Anyway, it'll be interesting to hear what Ed has to say.
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Tight bearing? prolly not - the oil just wouldn't go there (or would burn) and the bearing would wipe

Shearing is mechanical so think drive gears of some sort chopping the oil. Run automotive oil in a motorcycle and you get chopped up oil. In an aircraft engine about all you have is the oil pump and the mag drive (and maybe a vac pump) so no idea what would be shearing the oil in Tim's engine. The numbers he is quoting are within 10% so prolly no big deal. He probably has more flow because of the lower viscosity and flow is the important part, not pressure.
 
It might be the Camguard.

I've noticed in my Blackstone reports that my viscosity is detectably higher if I use less Camguard.

I don't know what Camguard is like when it's hot, but at room temperature it sure flows a lot more easily than Philips 20W50. It's easy to see that when you pour it in.

I'm tempted to use less than the recommended amount of Camguard in the summer, when I'm flying more regularly. The anti-corrosion ingredients of Camguard makes most sense when the plane sits idle for a few weeks.
 
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Clark1961 said:
Tight bearing? prolly not - the oil just wouldn't go there (or would burn) and the bearing would wipe

Shearing is mechanical so think drive gears of some sort chopping the oil. Run automotive oil in a motorcycle and you get chopped up oil. In an aircraft engine about all you have is the oil pump and the mag drive (and maybe a vac pump) so no idea what would be shearing the oil in Tim's engine. The numbers he is quoting are within 10% so prolly no big deal. He probably has more flow because of the lower viscosity and flow is the important part, not pressure.
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Anywhere you have metal to metal contact that is NOT pressure fed, the shearing can and will take place.. Like ... Idler gear to crank gear, Idler gear to cam gear, Lifter face to cam shaft in non roller motors... Even small surfaces like pushrod to rocker arm, rocker arm to valve stem and numerous other high load per sq inch contact points will shear oil...

The whole idea behind Cam Guard is to add a " clingability" formula to it stays attached to metal parts to lubricate them during start ups after extended storage times.... It also has some ( EP) extreme pressure properties, similar to high load gear oil...

Cheapest and easiest way to address this issue is to just add a pint of STP oil treatment at each oil change.. IMHO...
 
N801BH said:
Anywhere you have metal to metal contact that is NOT pressure fed, the shearing can and will take place.. Like ... Idler gear to crank gear, Idler gear to cam gear, Lifter face to cam shaft in non roller motors... Even small surfaces like pushrod to rocker arm, rocker arm to valve stem and numerous other high load per sq inch contact points will shear oil...
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The point is that there is nothing unusual in Tim's engine. Note that I'm not agreeing with or disputing your claims about shear. I have already pointed out that gear contacts result in shear.
 
Clark1961 said:
The point is that there is nothing unusual in Tim's engine. Note that I'm not agreeing with or disputing your claims about shear. I have already pointed out that gear contacts result in shear.
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I concur 100%.....
 
N801BH said:
I concur 100%.....
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As do I. That's why I ended my original post with...

timwinters said:
The engine is healthy and all wear levels are consistently low, so I don't think this is an issue...but rather just a curiosity.
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Thanks for all the input, especially Clark who actually knows what he's talking about on this topic! :yes:

I'm still going to try to get in tough with Ed when I get a chance. I'll report back with his thoughts if I'm successful in reaching him.
 
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timwinters said:
As do I. That's why I ended my original post with...



Thanks for all the input, especially Clark who actually know what he's talking about on this topic! :yes:

I'm still going to try to get in tough with Ed when I get a chance. I'll report back with his thoughts if I'm successful in reaching him.
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you may want to have a10 hr and a 25 hr sample checked for viscosity to see what is happening with the oil - I noticed a change in oil consumption around 25 hrs before adding the air-oil separator on the 'kota
 
That's an idea. I could always drain the oil using a clean hose into a good clean bucket, get the sample from the middle, and refill with the same oil.

BTW...in reading my last post...when I said "especially Clark who actually knows what he's talking about on this topic!"...wasn't to infer that you usually blow smoke. Rather, it was to suggest that others might be blowing some smoke in this thread (but surely that never happens here!) ;)

It could be interpreted either way...and I wanted to be clear that I wasn't insulting you. Not that I would ever hesitate to insult you. :)
 
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And Ed says that there is nothing in CamGuard that would lower viscosity.
 
timwinters said:
BTW...in reading my last post...when I said "especially Clark who actually knows what he's talking about on this topic!"...wasn't to infer that you usually blow smoke. Rather, it was to suggest that others might be blowing some smoke in this thread (but surely that never happens here!) ;)
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No worries, I took it in the worst possible way and you are now off my Christmas card list...
 
NoHeat said:
It might be the Camguard.

I've noticed in my Blackstone reports that my viscosity is detectably higher if I use less Camguard.

I don't know what Camguard is like when it's hot, but at room temperature it sure flows a lot more easily than Philips 20W50. It's easy to see that when you pour it in.

I'm tempted to use less than the recommended amount of Camguard in the summer, when I'm flying more regularly. The anti-corrosion ingredients of Camguard makes most sense when the plane sits idle for a few weeks.
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There is a flip side as well. Viscosity is a factor in being able to transfer heat, less vis will transfer better IIRC, and the biggest role the oil plays in your engine is not lubrication but the removal of heat.

If you aren't seeing any issues besides the viscosity issue, no heat, no wear; then no worries.
 
I told Blackstone that I might send them a 10hr and 20hr sample on this run to see how the oil is changing over time...and maybe even a sample out of the bottle. Here is the response:

Tim: Sounds like an interesting experiment. W100 typically starts out with an SUS reading of about 94 at 210F, so it's dropping somewhere along the lines. But it is a pretty harmless drop. In theory, the starting SUS should be 100, that's where they get the name W100, and W80 oil should have an 80 SUS at 210F. In practice though, the readings are normally less. I'd guess that's from changes in the base-stock and additives over time.
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