Will an engine over heat without a thermostat? Vote here!

[rang-a-stang]

If you spend any time surfing the web, there are two schools of thought here:
1) if you remove your thermostat, the engine will never reach operating temp. Coolant will flow through the radiator and always be cold. This prevents the engine from running at the temp it is supposed to, increasing wear, fuel consumption, smog, etc. ALWAYS RUN A T-STAT because it is bad for your engine since it will never reach operating temp!

2) If you remove your thermostat, the engine will take a long time to warm up, but then will keep going and overheat because the coolant does not have time to exchange it's heat in the radiator. The Thermostat slows the coolant flow down in the radiator to help cool it down and let the engine run at normal temps. ALWAYS RUN A T-STAT because you will overheat your engine!

SO! I have the ability to record my engine temp, RPM, Speed, and run time, and graph them together. So let's do it! Let's see what happens! For the record, I have a bent toward the school of thought #1 above.

Test configuration:
1979 Jeep Cherokee, 401 (.030 over), mild cam, iron heads, TBI ontop of a Edelbroke performer, Hedman Headers to a single 3" exhaust, BJs Crossflow Radiator with electric fan (fan only comes on below 25MPH) and shroud, about a 60% Distilled water to 40% universal coolant mix, TH400, QT in 2WD front hubs unlocked, 3.55 gears, 33.2" tall tires, heater will remain off for the entirety of the test and the temperature mix switch will be in the cold position.
Test route:
I will drive my truck to work on my normal route (about 18 miles, no freeway, mostly 2 lane, 55mph, flat road with some lights and some street driving). I will start data recording before I start my truck and stop recording when I get to my destination.

Control test:
Monday 22 Feb, I will drive my truck to work in the morning, then home in stock configuration with a 195 degree T-Stat. I will log data both ways and show the graph on here. Weather guessers are saying 80 degrees and sunny in Camarillo for Monday and I work in Port Hueneme which they say is 72 and sunny on Monday.

So... will it overheat? or will it never reach operating temp? Vote here! Let's see what happens!

[iapexl8r]

The jeep IMO will not overheat. but running without a thermostat will let the motor swing in temp with airflow, rpm and OAT. This will effect fuel economy and possibly the operation of the heater. could it be a factor in overheating yes I think it could overheat given the right circumstances.


My jeep had the waterpump bypass hose ran from the upper connection of the water pump to the radiator (basically bypassing the thermostat), in the summer warm weather this was fine although I did notice larger than normal temp swings. But when I drove it into cold temps the engine did not run right and the heater blew cold air,I had to put cardboard infront of radiator to get the motor to run at 160f.


I did not vote because there is no other box to check or even a yes to both never reaching operating temp and overheat.

[Heep-J4000]

No a engine Wil not overheat!

It takes more time to get on a higher temperature ,but would not get at the correct working temperature.

I did have a stuck open thermostat in my dodge 2500 with Cummins 24 valve engine two weeks ago , and along the drive in the morning i did recognise that there was something not like it should. (Stuck thermostat or low coolant niveau)
The heater did not blow warm and the temperature gauge didn't get at the number it normally does.

The engine sounded normal as always and the truck did drive as it does everyday ,so it was not a big problem.
But checked and replaced the thermostat later that day.

btw , the thermostat came from Rockauto and it was the second thermostat in two years that broke down.
FYI it was the cheapest thermostat available.

And about a electric or manual fan ,I say the manual fan is the best for cooling but the fan shroud needs to be there and also match the fan.
Together they do wat they are developed for.
I'm not a fan of a electric fan , have seen enough overheating problems with them.
(Most were builds and or project cars and after putting a manual fan back on with a shroud cooling worked spotless.)

[SJTD]

Someone will want to say it will run hotter because the water passes through the radiator to fast to loose heat completely ignoring that IF that were true it would also be flowing too fast through the engine to pick up heat.

[jeepman42]

To heck with the jeep temp;I'm impressed with the temp prediction of 72-80 degrees Mon. No wonder my brother lives in Long Beach and not in Texas anymore- especially after this last week! Cheers to warm weather!!

[MysticRob]

I voted that it won't overheat. Might take forever to warm up in colder temps but with coolant constantly circulating with no thermostat, I don't see how it could possibly overheat.

[Brynjminjones]

I've not had a missing thermostat, but I've driven with one that was stuck open for a while in my 4.0 XJ.

I found (as expected!) that it took forever to warm up, and would usually not get up to operating temperature.
The times when it would normally (with a thermostat) start to get a little hot, it also ran a little hot without a thermostat. The difference was that once it cooled down again, it would overcool to well below operating temperature.

Basically, it made no difference to maximum temperature reached, but the operating temperature below that was much more variable.

[rang-a-stang]

Control drive to work complete. Here is "normal" conditions. Red dots at the bottom on the time axis represent times when I was sitting at a red light or stop sign. The purple'ish color on the far right is engine run tim in seconds. All the other values are self explanatory.

I'll log drive home as well. I plan to run the "No TStat" runs in mid March to allow a few more comments.

[oregonphil]

That's a pretty neat chart. " driving on base" Port Hueneme?

[J20 project]

Funny, funny. Any real world practical knowledge here? Just curious. The one thing missing in the conversation is that "they" the dudes that designed engines understood a couple things.
1) an engine works best...i.e. cooling, vaporizing fuel, heated up to the right op temp.
2) If you have a pump, i.e.(water pump) it is designed to circulate a certain amount of gpm in a certain pumping system. Volume, rates, all relative
3) the gpm is specific...specific
4) the tstat is an orifice,
5) it is a restriction which slows the flow....it is.
6) this allows for a certain amount of gpm passing through the radiator at a certain pump speed=rpm...
7) Depending on where you live, the rpm you run, the ambient temp, humidity=dew point, the quality of your pump and radiator....

The answer is not straight forward.

I had an issue w/ a 440 dodge...I had the timing set a bit high=more hp at rpm..it overheated. I removed the tstat....=it got worse.
Personally,,, i do not believe that backyard, yank the fixes are worth much of anything. Anyone(well nearly anyone) can make a small block chevy run like a raped ape for about 2 passes on the dragstrip,,,,but GM made an engine that would run every day for about 100k miles.


J20 project

[J20 project]

May have not stated one thing clearly....the tstat(being a smaller orifice) tends to slow the flow through the radiator to where the time spent there,,,exchanges more heat than just screaming through the radiator.

[rang-a-stang]

Had to go home a different way but still a valid sample. This one includes some freeway driving. Yep. Port Hueneme, my desk is on station.

Some of my observations:
1) It's interesting that the TStat opens at about the same run time even though my engine started 30F warmer
2) I think it's cool that when the TStat first opens, the coolan in the rad is super cold and drops the temp quite a bit, then as the aluminum rad heats up, the temp goes to 200F plus or minus 5.
3) My engine runs cooler at lower than 25MPH because my fan runs at that temp.
4) When I left home this morning, it was 70 degrees and sunny. When I get to work it was 68 and sunny. When I left work it was 74 and sunny. When I shut my truck down in Oxnard this afternoon, it was high 70s and sunny, no breeze. I did not get dew point or humidity measurements.

You guys all put some good stuff in these comments! The answer isn't as simple as I thought it would be! I'm excited to see what happens when I pull the TStat.

For the record, if coolant temp goes over 210 during the "No TStat run" I will pull over, pop the hood, and let it cool down. That will be a successful test showing it will over heat without a TStat.

[Ristow]

if your cooling system can keep the engine cool with a thermostat,it will keep it cool without.

if it were not so,your engine temps would continue to climb anythime the thermostat opened under engine load. right? it aint brain surgery.

[SJTD]

It took a while but someone said it.

Heat transfer is a funcfuncfunction of several things, one of them being the Reynolds number which is dependent on the flow velocity. If velocity increases, Re increases and heat transfer increases.

[fulsizjeep]

if your cooling system can keep the engine cool with a thermostat,it will keep it cool without.

if it were not so,your engine temps would continue to climb anythime the thermostat opened under engine load. right? it aint brain surgery.

That's really good because if you have a QuadraTrac, you already have your frickin hands full.