Very High Finishing Gravity

[dukeellington]

Hey, so I have a Belgian Dark Strong Recipe I've done a load of times: Marris Otter, Caramunich Type III, Golden Naked Oats, Carafa Special Type II, Dark Candy, and Raisins, Dates, Figs, and Vanilla (fruit added in the secondary).
Basically I've really been trying to fine tune it, I wasn't getting quite as sweet as I wanted, so the last time I brewed I lashed up the temp, keeping it ~72C, that times I ended up with SG only 1.052 (guessed the equivalent SG would have been 1.058 counting the fruit not added til later) (I was expecting ~1.090/1.100). I put the inefficiency down to the high temp, and it finished 1.018. The beer tasted nice if a bit sweet, but very drinkable.
This time I really focused on getting the mash high temp without going over the top. Aiming for 69C. I stirred the shite of it at half hour intervals to make sure temp was homogeneous, and started ~67C but brought it up to 69 and held pretty well at 69/70 for the 90 minutes.
Trouble is it's been at 1.040 for a week... I thought transferring to the secondary and adding the fruit might re-bump fermentation but no avail...
Is it too high to bottle? It tastes very nice, so I'm tempted to go ahead but worried I'll explode bottles... any advice appreciated.

[Leann ull]

No mention of your yeast process  or fermentation temps or how you control temp
What are you measuring mash temp with, your 69/70 could in reality be 71/72 which would figure with your high gravity.
Loads of other basic things we need to look at but let's start with the above.
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[dukeellington]

Sorry, yeast is WLP530, one vial in a 1.5L starter for 24hrs.

Mashed in a 33L cooler box. Using a laser thermometer to check temp, not properly calibrated, but checked against known temperatures to within ~1C, so I'm happy enough with that. I'm checking temp during mash by aiming directly at the wort I'm stirring. Mashing for 90 minutes, leaving the lid closed for 30 minutes, opening, stirring, checking temp, if its low I take out a couple of litres and heat and return.

Fermentation was at 22C for the first 4/5days, and held very steady, but then cooled to ~16C. Transferred to the secondary after 7days, and it remained at ~16C for a week. Again checking temp with the laser thermometer on the outside of the plastic bucket. I keep the bucket in my kitchen to prevent wide temperature swings, and also have made a kind of insulation bucket and lid that I put the fermenter into, out of that tinfoil covered attic insulation to try and keep temperature steady. Heating went wonky in our house which was why the temperature dropped, but 15C was as low as it went.
I never took pH readings, during the mash, cooled the wort after the boil (90 mins) with a plate chiller, and pitched the yeast at 22C. Not sure what other factors I've been looking at...

I'd absolutely accept that 69/70 could be 71/72 based on either thermometer inaccuracy or temperature variation within the mash, but would that really create so many non-fermentables that I'd finish at 1.040?

[Qs]

AFAIK laser thermometers only check surface temperature. Worth investing a good thermometer when you use a cooler IMO, I'd recommend the thermapen.

[delzep]

Belgian yeasts tend not to like temperature decreases, only increases (or kept steady)