The Stovebolt Site Forums The Shop Area Engine Shop 170° thermostat for 235

So after 235 installation it was running a little warmer than I prefer. I was running 180 thermostat. Could not find a 170 at the parts store only 160. Didn't want that either. So after some research found a 170 for a mid 90s small block but had a extra piece on the bottom. Tried it and I believe when it opened it got wedged down because it was getting hotter than before. So I cut it off and reinstalled. Couldn't be happier. In traffic it climbs just a fuzz over 180. Perfect and availability is better because the flaps keep them in stock. Just an FYI for anyone that wants to run a little cooler. Picture shows what I did .

Thermostats do not regulate engine operating temperature. Your engine is going to operate at whatever temperature it normally operates at regardless of the Thermostat rating.

Thermostats only regulate the amount of time it takes the engine to reach its normal operating temperature. A thermostat with a lower temp rating will open sooner allowing more water to flow through the radiator causing the engine to take longer to reach the operating temperature that it is used to running at.

It the winter, it will take longer for your heater to feel like it's working.

Otto, a thermostat indeed regulates engine temperature, assuming that the radiator is big enough to provide the required cooling.

Just the name "thermostat" is made up of thermo or heat and stat or constant. The engine will heat up initially, with the thermostat closed, then will open to regulate at or near to the rated thermostat temperature. If the engine generates less heat (moderate speed on flat ground), the thermostat will close a bit, and if you mash the gas to climb a hill, the engine will generate more heat and thermostat will open to provide more cooling from the increased flow thru the radiator.

klhansen - I am sure that goes on quite often in the great white north of Alaska. Not so much around Paulaskifield, Missouri.
Down here in much of the lower 48, given warmer temperatures, the engine generates enough heat to keep the thermostat wide open whether you're climbing a steep grade, at idle in traffic, or moderate speed on flat ground.
The main goal of the thermostat is to attempt to prevent the engine from falling below the optimal temperature for ideal performance.
The OP was concerned about his maximum temperature which a thermostat has no bearing on unless it is stuck closed.

OK. I guess I worded that badly. I did mean to indicate that the thermostat will not prevent the engine from running at it's uppermost temperature.

Changing the T stat to a lower rating to bring down operating temps will not work.

Carl, you are absolutely right, although I did say "assuming that the radiator is big enough to provide the required cooling."

Even in "Paulaskifield, Missouri" or the middle of the Mohave Desert, if you had a humongous radiator installed, the engine would operate at or very near the thermostat rating, and not overheat. Now if you lived somewhere that the ambient temperature was over 250F, then all bets are off. But then you wouldn't need to worry about your engine, because you'd probably expire first.

The therm. opens just enough to keep the temp. at the rated setting. It will not fully open until the temp reaches the capacity of the cooling system.

George

Thanks for the info. Can you post the part number for that particular thermostat?

Napa 170562 1998 chevy 350

Talking about thermostats, we have a 216ci which calls for a 180 degrees thermostat. Our engine runs hotter than we’d like. Would it hurt to use a let’s say 160 degree thermostat? We are in Texas and it’s pretty hot here. Also we’ve also learned that having a ⅛ inch hole on the thermostat makes them operate much better.

NAPA sells a "Safe-T-Stat." I don't remember the brand name they use but no matter that. These T'stats have a very short lifespan, essentially until the stat opens fully, then it's over. Time for a new one. There are a couple of little hooks that grab onto the movable part once fully open and won't let it close again.

On a hard pull the stat will fully open rather soon and when you go over the top and watch the gauge on the way down, you'll see the temperature drop to around 140 on an 80 deg. day. Then it's time for a new stat because it will never close. 2-ton trucks with 261s have bigger radiators but it's still not enough for long mountain grades in hot weather. Remember these trucks came with an 85 HP 216, not a 150 HP 261. There were only so many square inches available within the sheet metal design so they made the radiators thicker but at some point you really need more square inches. GM did that post ''55 and you'll notice from the truck spec books that the 2 tons with 261 I6 had larger radiators than the 283 V8s.

Another interesting factoid is that the temperature where the gauge sensor is, between #5 and #6 cylinder, will be lower than at the thermostat housing. I've checked. When the gauge pegs on hot (GMC one reads 220), the sensor I added in the t'stat housing reads about 235. This is on a low-waterpump 235. Same for the 261. The part that the OP cut off the NAPA170562 is the valve that allows internal recirculation with the thermostat closed on the later engines. Without that feature, as soon as you start up a hill and the engine starts producing heat, some spots in the engine will boil the coolant before the t'stat can open. Not good. Many 261 truck engines had such a setup but that replacement part number is NLA, so they've nearly all been changed out for the 235 design.

The secret to cooling under load is to flow as much water as possible, which will reduce the tendency to form hot spots that boil water locally in places in the system. AC equipped GM V8s came with slightly smaller water pump pulleys spinning the pump and fan faster. To maintain temperature under light load, add a restriction to water flow, air flow or both. Back in the day before fast-acting thermostats, heavy trucks had shutters in front of the radiator that closed as soon as you topped the hill. You could hear the pitch of the fan change when they closed. This was also before the days of de-clutching fans. On some routes the shops would remove the fans altogether in winter to save fuel; not on I-5 from Seattle to LA but on the Seattle to Chicago route or Seattle to Edmonton.

Installing a lower temperature t-stat in your area only means you'll have full flow to the radiator sooner, it won't help with a hot running engine. It might be time to service the cooling system and confirm everything is working correctly.

You didn't say, but how hot is it running and what temperature would you like it to be at?

Mike B

A properly operating thermostat only brings the engine to the temperature rating of the thermostat. A 170 deg thermostat opens when the engine coolant reaches 170 deg. If the engine runs hot then it is not the thermostat's fault... you have other issues. Radiator stopped up, hose collapsing on the inside, faulty waterpump etc.

My 54 3100's 235 has a 180. Yesterday I drove 20 miles 60 mph. Outside temp was 92 at 85% humidity. The engine temp didn't quite reach 190.