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'Summer' and 'Winter' Thermostat?

Old May 8th, 2019, 10:45 AM
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'Summer' and 'Winter' Thermostat?

So, talking to my mechanic, he said that cars like my 72 Cutlass with 5.7L 350 used to run different thermostats in the summer and winter. Ex, 160 in the Summer and 195 in the Winter.

Reading some previous threads, I haven't seen the comment Summer v. Winter thermostats, is it a thing?

I believe I have a 195 thermostat in there now bc each time I've bought one at AutoZone or RockAuto, that's come up as OE temp spec. Note: I'm only dangerously handy with this car tinkering stuff.

I now have a Stant 180 Superstat sitting in a box and thinking about installing. My new radiator seems super hot at the upper hose and noticeably cooler (but hot) at the lower hose after a five mile jaunt. With just an idiot light (not alarming), I suppose its not too hot and I'll need an infrared gun to see how hot its running?

Any opinions? My car lives in the South so never really running it when cold outside. 180 sounds like a happy medium.
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Old May 8th, 2019, 11:09 AM
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I have never heard of swapping the thermostat for summer / winter driving. The hotter thermostat will cause the heater to be a bit warmer in the winter, but again, never heard of anyone doing that on a regular basis - and I worked in auto parts stores all through high school and college. 180 or 195 will work fine year round. I think factory was 195 and cars ran fine with that.
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Old May 8th, 2019, 11:17 AM
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Sounds good. I appreciate your input. You should know a thing or two about heat living in the Valley of the Sun. I used to live there and, when my car was residing there, my Dad only managed to put on about 300 miles total in about 15 years he kept it there. It ran (too) hot when he did drive it and now the thermostat, water pump, all belts/hoses, radiator, and head gasket have been replaced since February.
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Old May 8th, 2019, 11:30 AM
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Originally Posted by SanTan Devil View Post
Any opinions?
I'd suggest finding a mechanic who has a clue...

GM tested these cars in snow in the winter and in the Arizona desert in the summer. They didn't overheat when new and certainly didn't need the t-stat changed every season. Sounds more like a way to milk the uninformed customer for a bi-annual coolant and t-stat change.
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Old May 8th, 2019, 11:49 AM
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Next he'll be suggesting winter to summer tire air changes...
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Old May 8th, 2019, 11:58 AM
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I was just about to post something similar about thermostat temps. I bought a fail-safe type from a local store today but it didn't list a temp. I just wanted to check when I got home and it looks like it is 160F which I don't want based on what I have read. But, NAPA has some fail-safe types that come in 160F, 180F, 192F for some reason, and stock 195F. Any opinions on the 180F and 195F... and I suppose the 192F? There must be a reason they made a thermostat that is only a few degrees lower than stock.
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Old May 8th, 2019, 12:23 PM
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For a street driven car I'd say go with a 180 degree & you'll be fine

Tangentially related - these Mr gasket balanced thermostats used to be a popular item. Thought being that at the set temp they snap open & snap closed, rather than progressively opening & closing. Do people still use them? Thoughts?

Mr. Gasket high-performance thermostats are designed to resist large variations in coolant pressures that can occur at high rpms. Under these conditions, coolant temperature and pressure fight for control of the thermostat, keeping it from opening at its designed temperature. These balanced high-performance thermostats have brass-and-copper construction, and open at the right temperature regardless of engine rpm.

https://www.summitracing.com/parts/mrg-4364/overview/
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Old May 8th, 2019, 12:33 PM
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Originally Posted by 71OldsCut View Post
I was just about to post something similar about thermostat temps. I bought a fail-safe type from a local store today but it didn't list a temp. I just wanted to check when I got home and it looks like it is 160F which I don't want based on what I have read. But, NAPA has some fail-safe types that come in 160F, 180F, 192F for some reason, and stock 195F. Any opinions on the 180F and 195F... and I suppose the 192F? There must be a reason they made a thermostat that is only a few degrees lower than stock.
The difference between 192 and 195 is so small that they are essentially the same.

As for the "fail-safe" thermostats, I recommend staying away from them. I was forced to use one of those in my Jeep several years ago as that was the only thing in stock at the local parts store. Then one summer morning I noticed that the coolant temp was really low, so I pulled the thermostat and found that it was stuck in the open position. That thermostat was designed to lock open if the coolant temp got above some threshold, which apparently happened the afternoon before on my drive home from work in the blazing 110+ temps. So nothing was wrong with anything in the cooling system EXCEPT the thermostat, which stuck in the "fail-safe" wide open state after a brief temperature excursion above its set point. That would not have happened with a regular thermostat - it would have just reverted to normal operation after the temperature excursion was over.

Oh, and the "fail-safe" mechanism was just a stamped steel clip that prevented the thermostat from closing after the temperature came back down. I removed it and put the thermostat back in, where it has been for 3-4 years now and operating nicely.

Last edited by Fun71; May 8th, 2019 at 12:36 PM.
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Old May 8th, 2019, 12:35 PM
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180* Stant Superstat is $3.44 @ Rockauto. Its all you need for a street car,
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Old May 8th, 2019, 07:36 PM
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Originally Posted by SanTan Devil View Post
...my mechanic... said that cars like my 72 Cutlass... used to run different thermostats in the summer and winter.
When I was a child we lived in Minnesota and my Dad drove a '36 Buick. My grandfather ran a gas/repair station and put in alcohol (methanol) antifreeze in the winter with a 180 thermostat to help the heater work better. In winter you would also see people put on radiator grille covers with different opening options depending on the outdoor temperature. Those kept the coolant temperature higher.

In the summer he changed our Buick to water with a 160 thermostat for better cooling.

Permanent antifreeze (glycol) came along in the mid '20s but was more expensive and didn't have universal acceptance for many years. Lots of people were frugal at that time, the Depression having changed their spending habits.

Our next new car, a '53 Buick, came with permanent antifreeze from the dealer and my Dad continued to use that thereafter. The thermostat dances were thing of the past. The heaters had also made a quantum leap in performance by that time. The '53 even had an auxiliary heater under the passenger seat to keep the back seat passengers warm. No more blankets for us kids on winter trips.

Your mechanic must be really old to recall that practice and have selective memory loss to confuse the era when it was practiced.

Last edited by VC455; May 8th, 2019 at 07:38 PM.
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Old May 9th, 2019, 02:42 AM
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Originally Posted by VC455 View Post
Your mechanic must be really old to recall that practice and have selective memory loss to confuse the era when it was practiced.
My mechanic is older, yes. Funny, I have second opinion mechanic who is actually older (in his 80's) than my local mechanic. He's as sharp as a whip though. I've been leaning on his secondary opinion so much lately that I didn't call him on this one. Need to go make a trip to see him though. My car might just make it there/back without issue now that the cooling system has been worked over.
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Old May 9th, 2019, 02:57 AM
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I don't have that problem. This is hanging in my garage to remind me

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Old May 9th, 2019, 06:36 AM
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I grew up in Cleveland, Ohio and my dad also did the alcohol anti freeze and summer/winter thermostat change out as mentioned above by Gary, VC455. As stated, when "permanent" anti freeze became prevalent, thermostat change out went away.
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Old May 10th, 2019, 02:48 AM
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Despite realizing it probably is not necessary I do the stat swap seasonally, I run a 160/165 in warm months an 185/190 in cooler months for warmer running temps & more heat. The lower temp stat seems to keep the temp down, run fans less & at lower speed and recover from any creep upward more quickly. Car runs cool enough that in cooler weather (below 65ish) the water will drop below the opening point if Im on a down grade for a bit even with the warmer stat
For the most part it runs @ whatever I have the electric fans set for, appx 180 in warm weather, 165 for a track day and 200 in cold weather (CT winter). For the 10 minutes it takes to swap stats (twice a year) I like the difference.

Last edited by bccan; May 10th, 2019 at 02:53 AM.
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Old May 10th, 2019, 06:24 AM
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So, I now have an infrared thermometer on its way. Not much of an investment and I'm really curious to see the temps on my upper radiator hose, lower, and even what my home AC vents are spitting out. IF running a 195 thermostat, should the upper radiator hose be just above/around 195 in an ideal world or maybe more like 210/215 before it enters the radiator? I'm guessing the lower hose will tell me approximately what the coolant is being cooled down to.

I don't have a Rally Pack, just an Idiot Light gauge. Would be super cool to have the Rally Pack but, I can figure something better to do with $600 (depending on my source).
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Old May 10th, 2019, 06:39 AM
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I see no reason not to run a 180 degree thermostat year round. Keep in mind that is not going to make your car run at 180 degrees. It is just the temp your thermostat opens and your cooling system starts working.
While we are discussing thermostats I will through something out you guys may have never heard of. Way back in the 80's, I used to do some work on Saturdays for a fairly well to do guy. He had a 67 Rolls Royce and I replaced the thermostat in it for him. He had purchased the thermostat from the dealer. The thermostat had little inserts in the middle of it that would melt if the thermostat stuck closed and overheated. I think the thermostat was about $30 at the time. I thought that was pretty creative. Would not want a Rolls owner to be inconvenienced.
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Old May 10th, 2019, 10:26 AM
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Originally Posted by SanTan Devil View Post
I don't have a Rally Pack, just an Idiot Light gauge. Would be super cool to have the Rally Pack but, I can figure something better to do with $600 (depending on my source).
The temp gauge in those doesn't give a degree reading, it just shows variations of hot / cold. What temperature is the needle indicating on the Rallye Pack gauge below?
For under $25 you can get a real temperature gauge and mount it wherever you want. You could get a 2 gauge set and have oil pressure as well. Or a 3 gauge set and have temperature, oil pressure, and voltage.






Amazon Amazon

Last edited by Fun71; May 10th, 2019 at 10:30 AM.
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Old May 10th, 2019, 03:09 PM
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Something like this below, very easy to install. There are others more or less $$
Amazon Amazon

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Old May 12th, 2019, 07:04 AM
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...And following up. I received my infrared thermometer yesterday and took the Cutlass out for my usual test spin today. Came back and here's the stats:
  • T-Stat housing at 201F
  • Upper Radiator Hose at 194F
  • Lower Radiator Hose to Water Pump at 151F

Given the above stats, everything seems pretty good?
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Old May 13th, 2019, 06:51 PM
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Finally the real reason for this temperature issue: get another cool toy! I have been wanting infrared forever. Super cool for exhaust viewing as well . Good acquisition!
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