Temperature readings with and without a Thermostat

[Bob Johnson]

I have recorded the temperature for a 13 mile drive on the highway with and without a thermostat. It includes the drive to the highway and the exit off the highway. I am including a graph comparing the two drives. I am also including a blow up of a 2 minute section of the drive with the thermostat to show how the temperature oscillates. Both drives were with my PU which has a Model B engine, Mitchell overdrive, B carburetor, A distributor. I tested the the thermostat by placing it an a pan of hot water and it started to open at 160 degrees and was fully open at 180 degrees. I used 3 thermometers to make sure I was getting the correct temperature when I tested the thermostat in a pan of hot water. The thermostat is located at the bottom of the water return hose from the engine to the radiator, just above the head. It is held in place with a clamp so it cannot move up the hose. The drives were done on different days but the weather conditions were about the same.

Bob

[Kurt in NJ]

Where are you measuring the engine temperature?

[Bob Johnson]

The temperature is measured at the top of the water return hose just before the inlet to the radiator. It is the temperature of the coolant. It is measured in the coolant flow. Also note that the probe is not very big so it reacts quickly to temperature changes.

Bob

[marc hildebrant]

Bob,
Nice data. Why did you locate the thermostat in the return line ?

Marc

[Bob Johnson]

I may have cause confusion with the term "return". The thermostat is located in the hose at the top of the radiator that moves the water from the engine back to the radiator. Just after the water pump.

Bob

[quickchange]

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Marc, the water flows into the top of Radiator, so is in the outlet side top of the head not down on the block , unless you are from down under like me where the water turn anti clockwise . Nice data , really apreciated , Once back from Vancover i will also do test & beleive the thermostat is what has caused my overheating because thats the only thing changed apart from alloy head , Time will tell. Thanks BOB J.

[Kurt in NJ]

The temp of the coolant after the thermostat is not the same as engine temp, that is why you have so much variation with the thermostat, try the same test with the sensing probe the other side of the tstat---the engine side, I think you will see a quick rise to a near constant temperature.

[Old182]

Nice work, Bob. The tstat dithering is quite clear - I'm sticking with my non-thermostat engine.

[Bob Johnson]

Kurt,

I am confused, please explain how the temperature can be near constant on one side of the thermostat and change 25 degrees on the other.

Bob

[Jawman]

Originally Posted by Bob Johnson

Kurt,

I am confused, please explain how the temperature can be near constant on one side of the thermostat and change 25 degrees on the other.

Bob

here is an example when the engine cool and not running all the water is at room temperature. now start the engine and what water on the engine side will get wormer and wormer, but the water on the radiator side of the thermostat is still at room temp. until the thermostat opens and the water from the engine is now in the radiator. basically when ever the water is on the radiator side it has a chance to cool in between the openings of the thermostat. does that make sense?

[Jawman]

I bought a car once with out a thermostat in it and finally had to put one in it. when it was cold it would never warm up unless it was sitting running with no air flow other then the fan through the radiator. after a while of just sitting it would start to over heat and then I had to drive at least MPH before it would start cooling down. I put a thermostat in it and the temp always stayed at 195 degrees. SO my question is with out a thermostat can a modal A or B drive around at slow speeds or idling and not over heat.

[Bob Johnson]

Jawman,

If you look at the second graph you will see that the hot/cold cycle is about 20 seconds. So the water has about half that time, 10 seconds, to cool in the hose while the thermostat is closed. I highly doubt that the water in the hose above the thermostat can cool 25 degrees in 10 seconds.

Bob

[TerryH]

Bob--from your graph it appears that even with that 160 thermostat the water temp at certain times was getting awfully close to 210.........does that worry you at all? I guess that it does not boil over, but sure seems like it is getting close at times, then cooler again.....very interesting. I tried a stat in my car when I first got it several years ago, but it did not like it....it puked out water in short order, went back to no stat, and it never overheats or uses water.

[Bob Johnson]

Jawman,

On the 4th of July I was in a local parade with my PU. It was around noon time and the temperature was quite hot. We when 3 blocks and it took over 30 minutes. I never shut off the engine so there was lots of idle time. I did not have a thermostat and the temperature never when above 160 degrees.

Bob

[Bob Johnson]

Terry,

Yes it did spit out some water once on that trip. It occurred at about the 8:30 mark when the temperature when above 205.

Bob

[PC/SR]

A good clean efficient cooling system will keep an A cool under most any condition, sometimes too cool. A "warmer" engine will run more efficiently than a "cooler" engine, and will vaporize the combustion by products that causes corrosion and gunk. One guru says that 180 will produce power and 160 will produce sludge. I run a 180 with no problems and it never gets above the 180. If you over heat with or without a tstat, it is time to check the cooling system. If you run cool all the time, you should try a tstat. While I enjoy very much the discussions here on the Barn, one problem with individual tests is that conditions on one car may be and probably are different than another car so that what works for one car may not be valid for another.

[Ron in Quincy]

I have driven model As for forty seven years and have never used a thermostat; the one thing I have always had was a good radiator. The first 27 years I lived in Sacramento, Ca.; I believe the normal average temp. this time of the year is 92 degrees and have seen 107 a number of times.

I recall on one outing a member lost his fan belt; said he wanted someone to get a trailer so he could get his A home; His battery was fully charged, I told him he could drive the A home without the water pump working and as long as he was moving the A shouldn't run any hotter than normal; he followed the suggestion. He called me that evening and said the A ran just as cool as it did with the water pump working; said when he came to a stop a couple of times, with no air moving through the radiator that the heat did rise but as soon as he resumed normal speed the temperature went right down.

I'm inclined to believe the subject of using or not using a thermostat will not be solved on the Forum. I's kind of like what kind of oil to use !!!

Ron

[pdora]

The purpose of an automobile thermostat is to keep the water temperature UP, not to keep it DOWN. It exists to solve cold weather problems.

It would be interesting to get some real-world temp readings during very cold winter driving. Perhaps some of our friends in the southern hemisphere might care to conduct some experiments?

[Larry Brumfield]

Bob,

Nice post but inaccurate results.

If I weren't such a cheapskate I'd donate a head so you could bore a hole in it and install the temperature probe BEFORE the impeller, completely submerged and surrounded in more stable but still moving water. As it is now the impeller is sloshin' and throwin' the water up the pipe intermittently at the probe. Moreover, that electronic device has probably gone plum crazy trying to read all the rapid fluctuations being sent by the probe.


Larry B.

[Old182]

I ran a 50+ mile tour on Sunday in over 90 degree heat mostly at 35-40 mph, many hills, then back home at 45-50 mph. Top radiator was 196F, bottom was 148F after a hot soak - no tstat. As the attached table indicates, my coolant will boil at ~227F with 50/50 Prestone/water. Being at least 25 degrees away from boiling under those conditions keeps me from putting a tstat in the system and creating a restriction. I guess I'm luckier than some as my coupe warms up nicely in cooler weather - not an issue.