I need a reality check on my prewar gas oven in Bed-Stuy. It's one of those old 20-inch gas ranges with the dial that looks like it came with the building. I set it to 350, put an oven thermometer on the middle rack, and after 20 minutes it read 425. Then the burner cycled off, swung down to about 300, and eventually came back up to 415 before settling into a rhythm around 335–415. This is not a one-off: it happened three times last week. I roasted a chicken on Sunday and the breast was borderline dry while the thigh was just barely at temperature, and a tray of chocolate chip cookies spread like crazy on one rack and then underbaked on the next.

The burners on top are fine, and I had the gas company out to check the line and they said pressure to the stove is normal. My super says 'they all run hot' and won't replace the range because it still lights. I'm not trying to get a new stove; I just want to know if this is a bad thermostat, a calibration issue, or something else I can work around. If you've dealt with this, what actually helped? I already keep an oven thermometer in there full time, but I'm still guessing every time I bake. Is there a fix that doesn't involve me taking apart a gas appliance in a rental, or should I just learn the offset and stop trusting the dial?

I had a nearly identical range in my Astoria prewar, and the short version is: the dial is a suggestion, but the swing you're describing usually means the oven thermostat's sensing bulb is losing accuracy. The thermostat in these old gas ovens works by a capillary tube running to a bulb inside the oven; when the bulb stops responding correctly, the gas valve cycles late, so the oven overshoots, then overcorrects down, then overshoots again. Some thermostats also have a small calibration screw inside the knob shaft, but on the 20-inch prewar models I've seen, that screw is often frozen or stripped, and forcing it can make the thermostat worse. If you can find the model, the service manual sometimes shows the adjustment, but honestly the screw route is hit or miss.

What helped me more than fighting the thermostat was adding thermal mass. I keep a pizza stone on the lowest rack, all the way in the back but not covering the vent. I preheat the oven for about 45 minutes before baking, and the stone smooths out some of the wild swings—not perfectly, but I stopped getting cookies that were burnt at the edges and raw in the middle. The offset you choose matters less than keeping an eye on the thermometer and learning how your oven cycles. For a whole chicken, spatchcocking and starting it lower, around 325 on the dial in my oven, gave me much more even results. Also check the door gasket: if it's cracked or flattened, the burner cycles even more aggressively because heat dumps out the front. That's another cheap fix that a super might actually do.

Truth. I got a 20-inch prewar oven in East Harlem and the dial is basically fiction. I clipped a cheap oven thermometer to the middle rack and I write the real temp on a piece of masking tape stuck to the backsplash. Set to 350 gets me 440 some days, 310 others. I just set it to 325 and rotate whatever I'm baking halfway. It's annoying but I baked decent focaccia last month with the thermometer and a stone on the bottom. Don't even bother calling the gas company for the thermostat; they only care if it's leaking. My super laughed and said 'cook by eye like the rest of us.'

Appreciate the detail, astoria_arch. That confirmed what I suspected about the thermostat bulb. I looked at the gasket and it's definitely flattened in a couple of spots, so maybe the oven is dumping heat out the front. I also tried the masking tape thing EastHarlem_E mentioned, but my readings were still jumping enough that the tape would need to say '335–415 depending on mood.'

Question for you both on the pizza stone trick: does it help more with the wild swings, or does it just make the bottom of whatever you're baking hotter? I have a pizza stone I use on the floor, but I've been afraid to leave it in for cakes or a delicate tart because I don't want the bottom crust to burn before the middle sets. Do you bake directly on the stone or put a sheet pan between the stone and the pan? I'm considering a baking steel too, but if it's just going to give me a hotter floor I'd rather save the cabinet space. For now my plan is: heat the oven with the stone on the lowest rack, bake cakes on the middle rack with my thermometer clipped next to the pan, and start chicken lower. Let me know if I'm overcomplicating this.

For cakes I do have the stone on the bottom but I never bake the cake directly on it. I put the stone on the very bottom and use a regular sheet pan on the middle rack with the cake pan on top of that. It acts like a buffer. If it's a thin tart, I'd maybe lower the oven and rotate halfway. But yeah the stone mostly evens the swings so the air temp doesn't crash as hard when the burner turns off. It's not a miracle but better than nothing. Also try not opening the door for the first 20 minutes or you lose all the heat. I still burn the bottom of focaccia sometimes, so I put a little cornmeal and watch it close after 25 mins.

Bedstuy_bill, if your gasket is flattened, that's probably making the swing worse because the thermostat is reacting to the burner cycle rather than the actual oven cavity staying sealed. You can sometimes have the super replace just the gasket; it's not a gas part. On most prewar ranges, the gasket is a fiberglass rope glued into a channel around the oven opening. If the channel is intact, it's a pretty easy swap, but don't use random adhesive because it has to withstand oven temps. A service person can do it, or a thorough super might if you ask nicely and mention the front of the stove is getting too hot.

As for the stone vs steel: for a gas oven, I'd stick with a thick stone for buffering. Stainless baking steel transfers heat faster than stone, so yes, it can make the floor hotter and scorch delicate bottoms before the center is set. If you already own the stone, don't buy steel. Put the stone on the lowest rack as a heat sink, not as a baking surface. For cakes, do exactly what EastHarlem_E said: stone on the bottom, sheet pan on the middle rack as a thermal shield, cake pan on top of that. It won't fix the thermostat, but it will clip the worst of the swing.

One caveat: don't block the oven vent. In these old ranges, the vent is often a small slot along the back or the top of the door frame. If the stone covers the vent, you'll overheat the control panel or the burner won't cycle properly. Keep the stone back but not fully covering that slot.

Good call on the vent, astoria_arch. I checked and there's a small vertical slot on the back left of the oven floor; my stone was close but not covering it. I also tested the dollar bill trick on the gasket and it telegraphed exactly what you said — some spots grab and some pull out with no resistance. I can see the black rope in a couple of places. I'm going to ask the super about replacing just the gasket; if he won't, I'll see if the building's plumber can do it without touching the gas side.

So far the workaround is actually decent. I preheated the oven with the stone on the bottom for 40 minutes, set the dial to 325, and the thermometer on the middle rack held in the 350–390 range instead of swinging to 425. I made a batch of cornbread in a cast iron skillet, placed on a sheet pan on the middle rack, and it baked evenly with no burnt bottom. Spatchcocked chicken also worked better at a lower dial setting. I'll probably still want the gasket fixed, but at least I'm not blindly guessing every time.

Nice, that's basically how I run mine now. 325 dial, stone on the floor, thermometer clipped next to the pan, and I leave the damn door closed. The gasket swap is a good move if you can get it done; I never thought to check mine. Might give the super a polite headache about it next time I see him. Otherwise, prewar oven gang for life.