Progressive thickening in cold over time?

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Kitchen lab work 101. This may simply be a process issue but I need a reality check. Over 1 month ago I placed various oil samples in sealed canning jars in a freezer. They thickened as expected during the first day and from there remained stable for weeks. No apparent change in viscosity. (swirl test) But just yesterday I checked again and now I notice changes. The castrol HD30 is essentially frozen. Zero movement inverted 10 seconds. Mobil drive clean dino 10W30 is close behind. Both flowed, albeit slowly, just two weeks ago. Mobil1 TS 10W30, SS 0W40, Ams 0W30, Havoline 5W30 appeared thicker, relative to their xW rating. I checked freezer temp and it still fluctuates ~-2 to -5*f during the day. Containers are sealed tightly. No signs of moisture inside. Is this normal or is a control out of whack? Given equal temperatures, would a total lack of agitation for two weeks have an effect on their viscosity? David
 
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903
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CA
I'd think the freezer would be the best place to store samples. It should slow down any chemical reaction and physical changes. Some things don't like to be frozen, like latex paint, but oil should be OK.
 
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47,640
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Duvall WA - Pacific NW USA
It almost sounds like some moisture slowly got into the oil containers over time. When you say "sealed", do you mean the canning lids were heated and the rings screwed on good and tight? Sometimes those lids don't make a good seal if they aren't heated a bit. I only postulate this because it happened to all the samples, almost as if your freezer suddenly went into -50°F mode! Maybe let a couple thaw and do a water analysis!
 

OneQuartLow

Thread starter
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874
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Pacific NW
That's a thought Pablo. I didn't seal them in official canning style, but the lids were new and are on tight. Also, I have versions without lids, and the moisture on those is an obvious frost layer. Nothing appears to have changed with the sealed jars, besides their fluidity. Don't think I can afford analysis for these stupid pet tricks but I'll submerge them today to see if anything leaks in. This wasn't anything I had expected so I'd have to start over with better process to confirm it. Just wanted to hear if anyone nad seen something similar.
 
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2,480
Wow, just -2F...when I measure mine with a digital thermometer it went to -20F...now that's cold! Can't explain the freezing though...can you stick the thermometers directly into the oil?
 
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58
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USA
quote:
Originally posted by OneQuartLow: That's a thought Pablo. I didn't seal them in official canning style, but the lids were new and are on tight. Also, I have versions without lids, and the moisture on those is an obvious frost layer. Nothing appears to have changed with the sealed jars, besides their fluidity. Don't think I can afford analysis for these stupid pet tricks but I'll submerge them today to see if anything leaks in. This wasn't anything I had expected so I'd have to start over with better process to confirm it. Just wanted to hear if anyone nad seen something similar.
If you don't want to spend money, I can think of something you could try. You could thaw a thickened sample, and see if it appears to flow normally at room temp. Assuming it does, you could then refreeze the oil. This should tell you if the change was reversable or permanent. For example, if the oil picked up moisture and that was causing the thickening, then I would imagine that it would re-thicken as soon as the sample got back down to it's prior, stable temp. Also, I don't know how your freezer is, but I've seen my 'frost free' freezer vary over time from -20 F to +5 F depending on whether it's 'defrosting', etc. -Greg Bohn
 
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