Factory thermostat, really 195º?

[jumpsoffrock]

I'm not happy about seeing my factory temp gauge going very near all the way to the right

I have never driven this truck, it's been in running condition in my driveway since I took it off of a trailer. I have been doing general maintenance to get it drivable.
I replaced the thermostat for the fun of it, a 160º unit came out of the engine. I figured I try and see how it runs with a factory 195º unit so that's what I installed.
I also installed a different thermo housing with two pipe plug holes in it, and in one hole installed a working mechanical gauge.

I ran the truck and the mechanical gauge wasn't barely budging, the top rad hose was not as hot as it should be, however the factory temp gauge was almost all the way over to the right; I'd consider that overheating.

I took the new 195º thermo out and tested in pan of water and it started opening close enough to 195

I put the old 160 back in it and ran it, the mechanical gauge went to maybe 170 sitting still at idle, and the factory gauge was barely at the warm up point on the left side of the gauge.

Are these trucks really meant to run with 195 thermos? I think 160 is too cold and am considering a 180º, but I felt like I was about to seriously overheat a truck I barely just got.....and I DONT wanna do that.
I can't imagine that the factory set thermostat temp would allow the factory gauge to get almost all the way to HOT before it begins to circulate the coolant.
Every thread I read about "correct running temps/thermo" has guys saying they run mostly 195's and they are absolutely happy about it.


Based on my testing I have no reason to believe the factory temp gauge/sender are malfunctioning.

[Mike C]

The 195 was the factory temp rating on the thermostat. IME, a 195 should be almost straight up on the factory gauge. A 180 which is almost always what I run has the temp gauge right on the first line of the gauge (in m y 69 short step) or just to the right of the line (in my kids 72 Jimmy). My old big block truck with a 180 read in the same place as well.

[Minkota]

Maybe get a laser thermometer and confirm the temp at the thermostat housing is the same as what your temp gauge is reading.

[Stocker]

I have a 195 t-stat in my truck and the factory gauge is virtually always to the left of center.

If your known mechanical gauge was reading low and your top rad hose was not hot, you were not overheating, regardless what your factory gauge showed.
As to overheating concerns -- at zero pressure, water boils at 212 and a 50/50 mix boils at 226. Just 8 psi raises water's boiling point to 233 and 50/50 mix to 248.

I agree with Minkota's suggestion of a laser thermometer to see what you really have.

If you still suspect overheating, let's see what your cooling system is like. Radiator, fan, shroud, the works.

[HO455]

Where does the needle on the factory guage point when the key is off? The needles on the factory guages can move off of the factory's setting thus giving an incorrect indication.
Personally I would not give any of this a second thought until I had driven the truck a couple hundred miles.

[body bolt]

Mine does fine with a 195F thermostat. The factory gauge gets just a bit into the normal range of the scale.

[72c20customcamper]

Coolant in the head will get hot much faster than the rest which is where the sender is. I've had cars and trucks go way to the right and then fall quickly as the stat opened. One thing I always do is drill a very small hole in the stat to act as a bypass . Doesn't affect the temp but gets the air out of the system .

[Joesjunk]

I find that a lot of auto parts store temperature sending units don’t read correctly. Buy a good one from a Classic Parts or some other truck parts place. I bet that’s the problem.

Somewhere I have a part number for a good sending unit. I’ll see if I can find it

[tdangle]

I run a 180 in mine. Actually that's what my GM Performance crate motor came with. It runs on the factory gauge about a 1/4 way into the normal operating range.

I think when you put the 195 in there may have been air in the system and that is why your mechanical gauge barely moved yet the factory gauge was way hot. I had a similar issue for a while of wildly fluctuating temperature readings and pegging the gauge until the thermostat opened. then things sorta settled down. Ended up being air in the system causing my problems.

[lil hoodlum]

I don't have too much to add to the discussion.

I thought that 195 degree thermostat sounded pretty high for out years truck, but according to my 1968 Chevrolet truck data book it is indeed listed for small blocks as Harrison 195 degrees. So I learned something new today, thank you.

Having said that, I run a 180* thermostat in my '68 327 but I use an aftermarket mechanical temperature gauge. And like 1972c20customcamper, I also drill a small by pass hole into the flange of the thermostat.

[jumpsoffrock]

Originally Posted by HO455

Personally I would not give any of this a second thought until I had driven the truck a couple hundred miles.

I think I'm gonna try this first.
I just buttoned up the truck and spent 30 minutes driving up a 4 lane street(up to about 55) and the factory gauge never even got to the center. However the aftermarket gauge got to about 200-210 at times--all with a 160º thermo.

I'm gonna go get a 180º thermo and install it today and see what that does.

[rockyrivermark]

I thought our trucks always took a 180 stat and thought 195 was more for modern engines.
Im prob wrong in this assumption but alway ran 180 on my classic cars

[Carl Spangler]

I'm running a 180 degree thermostat right now. The primary downside I can see to the 180 vs a 195 is a slightly slower warm up. I do prefer the 180 (over the 195) primarily because the post shutdown carb heat soak isn't as severe. Truth be told, I would prefer something in-between these two, something like a 185................ but alas these don't exist.

[jumpsoffrock]

OK just got back from a solid 50+mile trip--after switching to a 180º thermo--after a good warm up period I found that, according to the mechanical gauge located after the thermo, when cruising 30+mph, it held a temp of 190-195. But if you let it sit at idle it would typically creep up to 210 but it'd take a solid couple minutes to do this. (for fun)I decided to adjust the idle to make it lower, and it took me about 3-5 minutes of idleing. When I got back in the truck the mechanical gauge said 210+; but in the 15 seconds to buckle up and put into gear, it went to 225. Found that odd.

It took about a mile and a half but eventually got back down to a normal ~195º for the remainder of the trip.


If you look inside the radiator tank you can see the walls and tubes covered--not profusely, but very evident--in calcium, I'm gonna guess previous folks ran garden hose water.
It isn't staying at 180º, but it's holding a nice cruising temp; but its getting a little warm at idle. If I were to take a swing at the issue I'd say it needs a new radiator and it wouldn't hurt to switch the "strait driven" fan for a clutch driven fan. I don't think it needs an electric fan.


One of my main goals with this truck in the next couple months is to give it A/C. I need this thing NOT overheating, so investing in a new fancy-ish radiator was gonna happen anyways.

Thanks everyone for chiming in!

[lil hoodlum]

Originally Posted by jumpsoffrock

If you look inside the radiator tank you can see the walls and tubes covered--not profusely, but very evident--in calcium, I'm gonna guess previous folks ran garden hose water.

I've been guilty of that in that past and also of using straight tap water from the kitchen. My results were the same, radiator and engine block coated with minerals from the water. I used dishwasher cleaner to rid the deposits. Not too longer, my heater core went out, so beware dishwasher cleaner can be a little harsh.

[special-K]

Originally Posted by rockyrivermark

I thought our trucks always took a 180 stat and thought 195 was more for modern engines.
Im prob wrong in this assumption but alway ran 180 on my classic cars

Same here. I have always run 180* thermostats in my non-EFI vehicles. They run great, warm up just fine, no negative results. I like the idea of a fair margin from boiling.

[jumpsoffrock]

Originally Posted by lil hoodlum

I've been guilty of that in that past and also of using straight tap water from the kitchen. My results were the same, radiator and engine block coated with minerals from the water. I used dishwasher cleaner to rid the deposits. Not too longer, my heater core went out, so beware dishwasher cleaner can be a little harsh.

Thanks for the info, I'll consider that, but I'd do it with the rad out of the truck. And at this time there is no heater core in-line.

[72c20customcamper]

Problem is if your engine is running hot a lower thermostat wont help it . At over 200 degrees a 195 and a 160 are both full open . There are a lot variables rad condition ,fan shroud, distance of fan to rad and fan placement in the shroud. Engine timing and lean conditions can cause hot running motors.


Also the gauge can read 205 - 210 in the head but the water temp itself is 180-190

[68 P.O.S.]

Originally Posted by Carl Spangler

I'm running a 180 degree thermostat right now. The primary downside I can see to the 180 vs a 195 is a slightly slower warm up. I do prefer the 180 (over the 195) primarily because the post shutdown carb heat soak isn't as severe. Truth be told, I would prefer something in-between these two, something like a 185................ but alas these don't exist.

Stant has a 186 and ACDelco has a 190

[custom10nut]

Originally Posted by jumpsoffrock

I'm not happy about seeing my factory temp gauge going very near all the way to the right

I have never driven this truck, it's been in running condition in my driveway since I took it off of a trailer. I have been doing general maintenance to get it drivable.
I replaced the thermostat for the fun of it, a 160º unit came out of the engine. I figured I try and see how it runs with a factory 195º unit so that's what I installed.
I also installed a different thermo housing with two pipe plug holes in it, and in one hole installed a working mechanical gauge.

I ran the truck and the mechanical gauge wasn't barely budging, the top rad hose was not as hot as it should be, however the factory temp gauge was almost all the way over to the right; I'd consider that overheating.

I took the new 195º thermo out and tested in pan of water and it started opening close enough to 195

I put the old 160 back in it and ran it, the mechanical gauge went to maybe 170 sitting still at idle, and the factory gauge was barely at the warm up point on the left side of the gauge.

Are these trucks really meant to run with 195 thermos? I think 160 is too cold and am considering a 180º, but I felt like I was about to seriously overheat a truck I barely just got.....and I DONT wanna do that.
I can't imagine that the factory set thermostat temp would allow the factory gauge to get almost all the way to HOT before it begins to circulate the coolant.
Every thread I read about "correct running temps/thermo" has guys saying they run mostly 195's and they are absolutely happy about it.


Based on my testing I have no reason to believe the factory temp gauge/sender are malfunctioning.

I was wrestling with this issue for a while. Everything was fine in the system until my son flushed it out in his Automotive Class, and then it started “Reading Hot” all the time, but never overheated. After replacing all components of the cooling system (thermostat, water pump, and sending unit. The radiator was recently replaced.), I then suspected the gauge, which is original.
Just recently, I took the old girl out on a Trash Run and everything is back to normal. It’s fixed, but I don’t know for sure what caused the issue, since I replaced all the possible cause at once.
In accordance with the Factory Manual, the 195 degree thermostat is “Stock”. That’s just when the engine is up to that prescribed temp. I know my engine is Cold Blooded and is just sluggish when it’s not fully warm. It not highly modified so most settings and components are near factory stock.
Many will run the 180 or even the 160, based on what works best for them.
Running “Normal”, mine will read “Just Left of Center”, AFTER the T-stat opens. like a few members have said.

Check all your connections to make sure there’s no corrosion built up. If you don’t have a problem with over heating that could be the issue.

[gmc684x4]

I would use clr to flush the rad out
You have build up in your rad you will have build up in the engine

I did the t stat change when I was young asking for a summer tstat from listening to my dad's crowd
The parts shop owner explained your engine is designed and built to run with a 195 tstat year around
You have over heat issues check rad water pump fan and shroud and never use tap water for top ups

Only once did I overheat in my old trucks that was not pump related
Stuck in bumper to bumper traffic for 2 hours hot day changed the fan and added a fan shroud after that no issues

[Chevys4life]

Originally Posted by lil hoodlum

I've been guilty of that in that past and also of using straight tap water from the kitchen. My results were the same, radiator and engine block coated with minerals from the water. I used dishwasher cleaner to rid the deposits. Not too longer, my heater core went out, so beware dishwasher cleaner can be a little harsh.

Will that dishwasher magic clean out the entire system if it is flushed with it?

[Carl Spangler]

Originally Posted by 68 P.O.S.

Stant has a 186 and ACDelco has a 190

Can you post the part #'s please.

The only 'oddball temp thermostats' I found looked like they wouldn't fit a standard thermostat housing.

[68 P.O.S.]

Originally Posted by Carl Spangler

Can you post the part #'s please.

The only 'oddball temp thermostats' I found looked like they wouldn't fit a standard thermostat housing.

I found them on summit. https://www.summitracing.com/search/...%3a190-degrees

The 186 one looks weird, not sure if its correct. https://www.summitracing.com/parts/s...make/chevrolet

[Steeveedee]

Generally, running hot at speed is blockage, like the radiator is clogged.
Generally, running hot at idle is from lack of air flow. Running hot in both regimes is what I had. After a lot of flogging, I put in a high flow thermostat. It's cooling fine, now. I run a 180º t-stat personally, also due to wanting to reduce heat soak. This truck had always started hard when hot, in the 40 years that I have seen it in operation, before and after the rebuild about 25 YA. Now I can repair the AC and use it. My didn't even know it has AC.