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Old 01-17-2010, 03:13 PM   #1
carp
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Default Problem with Thermometer in Cooler MLT

I recently installed weldless fittings and a Blichmann thermometer into my 10 gallon Igloo MLT, but am totally disappointed with the results.

With hot water only in the MLT, with constant stirring, it reads correctly. But once I add grains and everything stabilizes, it reads at least 15 degrees cooler than actual (as measured with a thermocouple immersed in the mash at the top of the cooler). Stirring does not appreciably affect things.
During lautering (draining of batch sparge) temperature does read more sensibly.

The thermometer has a 4" stem and protrudes into the MLT at least an inch. I have calibrated the thermometer against another one like it and against my Cole Parmer thermocouple.

My theory is that all the metal outside the cooler - the thermometer itself, and coupler and half the nipple, is closer to ambient temp (40F) and is affecting the reading.

Anyone else have this problem, and/or ideas on its cause and its resolution?

thanks,

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Old 01-17-2010, 03:38 PM   #2
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Sometimes the bi metal thermometers will stick. I have a different brand of thermometer mounted in my two kettles and they read accurately over the entire mash.

At least they agree with my thermocouple thermometer.

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Old 01-17-2010, 03:48 PM   #3
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I wondered about that, but don't think sticking is the problem. I haven't observed it to stick during any of my calibration efforts, and I tried tapping it when it was reading low during the mash.

I have a similar setup in my BLK (a keggle) and don't get the same problem at all.

I'm wondering if the problem is unique to the cooler, that perhaps in a keggle there is enough heat transfer to the fitting holding the thermometer that it gets warmed up, but that in the cooler the fitting is cold.


It does occur to me that for my next brew I'll swap the thermometers, put the shorter-stem one from my BLK into the MLT and the new 4 incher into the BLK.

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Old 01-17-2010, 05:53 PM   #4
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I have a 4" stem in my Mash kettle and 2.5" in the boil kettle.

I don't think you would get that much temp wicking away by the fitting / thermometer. If you did you would feel it get hot.

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Old 01-18-2010, 02:44 AM   #5
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I think you are probably on the right track. If you have nearly three inches of the probe in the wall of the cooler (colder temp than contents) or outside the cooler all together, the net reading is going to be pretty far off if the inside/outside temp differential is large. I have heard of people warming up their coolers for a while before they mash to get rid of the "thermal mass". Maybe that would keep the difference between wall temp and inside temps closer and get better readings?

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Old 01-19-2010, 01:59 AM   #6
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I do preheat the cooler, but in any case the low temp reading occurs throughout the mash, i.e. until the end.

Bargain, I'm not sure if your logic about it not wicking heat if it doesn't feel warm is correct, or is completely wrong. I guess my thought is that the fitting is cold, due to be being insulated from the hot mash by the cooler, and is therefore causing the thermometer to be cold.

However I have my doubts. I'd love to hear from folks with cooler (not keggle) MLTs with thermometers.

Thanks all for the feedback,

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Old 01-19-2010, 06:34 PM   #7
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I used to use a dial thermometer, but was experiencing similar results to yours. I now use a digital thermometer and get more accurate results, plus it has a built in timer, and audible temperature alarms.

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Old 01-20-2010, 01:51 PM   #8
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I am a little baffled by the 15 degree difference if you say the thermometer is calibrated. I do get a small difference in temp over time on my metal kettle without any insulation on it but not 15 degrees.

Did you swap the thermometers to see if they are reading the same?

Try using your thermocouple lead right next to the end of the thermometer stem to see if they agree on the temp during the mash. You could attach it with a twist tie or something to be sure it right next to the probe end.

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Old 01-20-2010, 03:31 PM   #9
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I think lehr had a problem with the Blichmann thermometer sticking. The True temp bimetal that I have has been dead nuts on with my thermapen .

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Old 01-20-2010, 10:43 PM   #10
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I haven't brewed since I last observed the problem, but when I do again (probably 2 weeks) I'll swap the thermometers. I like the thermocouple idea as well - my current probe is not long enough, but I was planning to order a different anyway.

Just to reiterate - the thermometer is definitely calibrated, and it definitely not sticking.

Thanks again all for the feedback.

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