Thermostat myth

Did an experiment due to a faulty thermostat and found that a 180 thermostat will allow the engine to run hotter than a 160. Read on to see why.

Green B would not heat up to proper operating temperature. I put a new no-fail 160 thermostat in for Gary's Run as the OAT was going to be in the high 90s.
The car ran great for the run with no heat issues.

The past week or so the car will not warm up properly. I removed that new 160 thermostat and found that it had failed in the wide open position.

We tested the spare stats and found that a 160 starts to open around 160 and is fully opened at 180........ A 180 starts to open around 180 and is fully opened at 200.
An engine will run at 20 degrees hotter than the thermostat's rating. This is if the system is flowing as it should and the radiator is good.

This would mean that a 180 would give you a max temp of 200. A 160 would give a maximum temp of 180. All this is based on the assumption of the rest of the cooling system operating to spec.

of course it will. from the basic nature of the system it is obvious.

it traps coolant until the release temp.

true, I would have thought a 180° would be full open at 180 and not just start at that point. (and I wonder about that)

if the engine is not producing more heat than the trapped value, the stat will control max as well as min, operating at partial opening or oscillating as required.

if the engine does produce more heat than the rating, then it will not because it will then be woide open and can have no further effect on the operating temp.

once it is fully open, if the radiator can dispose of the excess heat, then it will oscillate about the stat rating. if the radiator cannot, and the overall heat content increases beyond the stat rating, the temp level will increase.

you cannot trust the gage as an accurate "value", since it is relative..relative to original calibration and subsequent changes due to age and plain degraded effectiveness. it should, thou, be consistent within a reasonable time span.

the cooling system SHOULD operate at `195-210 degrees F in most cases. with a 13psi cap, this puts "overheating" at 230° or so. so the B's H on the gage is calibrated at 212° so it it is pegged with a 13# cap you might well be in good shape anyway, depending on loss of fluid since the last time you checked and any odd things that have happened since.

I measured the 180 Failsafe and the standard 180 thermostats. They both open at 180 and were fully open at 195. I used a laser gun and also a meter to find out exactly the open, fully open, and full closed.

At 185 degrees the 180 thermostat is still barely open but after 185 degrees it starts to move rather quickly to fully open.

I also measured a couple 160's and 190's, they all seem to have this 15 degree open to fully open measurement.

They all close were they start.....

I bought one failsafe thermostat and won't buy another. I like the stainless NAPA stats. Recently I put a MR. Gasket balanced thermostat in 195 degrees and it runs cooler by about 15 degrees. It says 195 but operates like a 180. This weekend is going to be warm so I might get a chance to see how it goes in the heat. Our high on Wednesday was 48, couldn't tell much.

Ray, try it with a candy thermometer as the laser guns are not all that accurate. Their readings can be influenced by the type of material and its' ability to reflect.

I have tested my laser gun on various coloured fluids using a commercial quality candy thermometer and have found the laser gun reading inconsistent with the candy thermometer.


The thermostats that I checked all started to open at their marked temperatures and were fully opened at plus 20 degrees F.

Basically what I have found is that with a 160 degree the engine coolant has to get to 180 for full flow (cooling) to happen.
A 180 has to get to 200 for full coolant flow.
The 180 is only starting to open when the 160 already is full open.

Jim, I agree about the laser as it is not exact, but I have also used a $300 digital multimeter that measures temperature with a plug in sensor. It is pretty acurate as my engine temperature matches the exact measurement of my VDO temperature guage.

Either way being fully open at 15 or 20 degrees really does not mean much. Long as it is open and flowing.

Have you ever tried comparing the laser with the known accurate digital one on different material?
It is interesting to note that the thermostats that we independently tested only started to open at their marked temperatures.

I've always thought that only started to open at the specified temperature. Not sure why it is such a big deal as it's not like the engine needs to run at exactly 180º or what ever.

Dan, I run a 180 in the summer and a 195 in the winter and have never had a problem. Putting the 195 in in the winter along with blocking off the oil cooler really help on those bitter cold mornings.

This last summer the car was running about a needle's with over hot, but my radiator had a pretty decent leak which I think caused the system to run at a lower then normal pressure. I'm curious to see how she runs with a rodded out radiator and the electric fan with adjustable thermo switch.

You guys have too much free time on your hands!!! :)

Wonder how much hotter AC makes temp run???

I did some tests of thermostats in a pan of heated water several years ago using an AC thermometer and found the results to be similar to those posted by Jim. Yep, I sometimes have too much time on my hands, the benefits of retirement. Checking thermostats or playing around with other mechanical and electrical devices sure beats watching TV.

Clifton

Retirement has given you a new job, Gordon ~ helping others. I have followed your sage comments (often from your experiments like the one above) for many years and really appreciated your willingness to add your findings to the greater Knowledge and myth busting concerning our cars.

For my money, I use the "balanced" type T-stat shown below, which I have used now for many years. There is some discussion of it on my site: http://www.cibolas7.net/12299.html

The big deal about a "balanced" T-stat vs. a regular pellet type is that a balanced T-stat is designed to NOT be influenced by pressure surges of the coolant as the engine revs up quickly and the pump develops some extra pressure to the coolant flow. It probably is not that big a deal in most cars driven moderately, but does help in engines used for racing, drag racing, or which simply require high revs to extract max HP. A good street example would be, say a Honda rice rocket capable of something near 10K rpms or better. In our cars, the need is not as great, and the effect is not as telling either, but it is just a measure I use to help control coolant flow a bit better than the more ordinary type T-stats.

Andrew, what you describe is essentially what I have had and have done with my 68 GT for over a decade and I have not had any real problems with overheating even tho I lived in a mountainous and hot and cold climate in Idaho, not unlike your own there in Bend. The balanced T-stat and the addition of the blanking sleeve (see web page linked above) have done a very good job of restoring the cooling system's circulation to something like what had been originally intended when this engine was designed, and I think that has helped make overheating harder for the engine to accomplish than when the blanking sleeve (either as a part of the OE T-stat or the separate "racing" sleeve you can buy from Moss) have been missing.

I think you are missing the point - the stat does not have to be fully open for cooling to occur, in fact it's job is to slow the coolant to maintain engine temperature. Not sure why you think this is a myth - it is the way I have always understood them to work.

You will find that you normally need very little coolant flow to maintain engine temp - the stat barely open is sufficient. A 1/4" hole in the stat will slow the engine warm up time by as much as 30 minutes, and if the engine is not working hard, it will overcool the engine!

I run a 180 degree and I've stood outside my car and watched as the needle rose to above 180, sometimes to the 212 mark only to see it open and drop back to 165 and make it's way back to the 190 mark. The temp rises while sitting at a light or in traffic
but it cools right back when running along. Since it get rather warm here, I've tried running a 160, how ever the car didn't run quite the same at a cooler temperature, so I
went to back to a 180 and it's fine. The biggest improvement noticed is making sure you system is clean and free flowing.

Jim,

I understand what you have said....even though I still don't understand, figure that one out...LOL

My feeling is if an engine is going to run hot it will do it, no matter what type of thermostat you use. Using a different temp T stat will allow the engine to get warm faster or slower.

Respectfully

Paul

I agree with Paul. I hope he is right. I thought that the stats job was to help maintain a minimum engine temp. It makes sense that it would not start opening until its rated temp. As the engine temp increases, finally the stat will be wide open and have no further effect on temps of a higher degree. When the engine begins to cool, the stat will begin to close in order to maintain the minimum temp. Is this not correct thinking?

Mick,

You are correct. A thermostat has nothing to do with overheating, but it can cure overcooling. My car with a 160 would not reach 180 degrees. I installed a 180 and now my engine stays between 180-190 degrees operating temperature. Your point about maintaining minimum temperature is also correct.

Ray

You said it better than I Mick.

I have a 165 deg thermostat, furnished with the Moss AC kit, installed and my temp gauge runs between N and H on about 87 deg day at about 70 mph. Im wondering if a blanking plate would help cool it down more toward the N mark. Of course in the mountains my gauge runs above normal then also.
What is a safe reading on the temp gauge?

GILMGA Wrote:

Paul if you run a 160 stat it is fully open by around 180 degrees.
If you ran a 195 stat it would be fully open by around 215 degrees.

An engine with a 160 will probably not get much hotter than 180 degrees as the thermostat is fully open at 180.
While the engine with a 195 will only begin to open at 195. This would mean that the engine when hot would never be cooler than 195.

graflexmaster Wrote:

Mount Logan is close to 20,000 feet. The only way to drive close to the top is with an extremely high performance helicopter. The last 2000 feet or so you would have to walk.

The only place in NA that there are real mountains is on the left coast.

I wonder what kind of thermostats they use to keep their oil from freezing.

I had a "fail safe" thermostat fail open almost immediately after installation.

Failsafe thermostats are a joke! Get the engine a little hot and they stick open. I have NEVER had a thermostat stick closed because I change them every few years. It's just a gimmick to make you think need that protection. Like much advertising, fear is the main thing they are selling.

Limey Wrote:

MICHael

uhhhhh.... They have mountains in Tenn. Gil?? Last time I drove through there I thought they looked more like speed bumps.....

but then again I'm from our West... where it's not uncommon to see mountain passes at over 5oooft.....(highest point on the East coast is Mt.Washington at just over 5000ft)lol
Geographically challenged, eh? Every Southern MG fan knows Mt.Mitchell in the Pisgah Forest is the highest at 6684 ft, having driven up and the surrounding area it many times. Mt. Washington is mere 3rd.

Ive lived in CA and CO and much rather have my mountains.

Ours are green and much more fun to drive in. Dragons Tail is a chalenge

Jim, you make an assumption at the end of your statement saying that:

This would mean that a 180 would give you a max temp of 200. A 160 would give a maximum temp of 180. All this is based on the assumption of the rest of the cooling system operating to spec.

The MAX temp has NOTHING at all to do with anything that a termostat can fix.

The thermostat SOLELY controls the LOWEST temp of the engine - once it has heated up!

Since the thermostat opens at 180, as soon as the thermostat opens, cool water rushes in, and it closes again.

Having the thermostat FULLY OPEN is only really desireable, if you are having OVER heating problems. At which time, full water flow is needed, to avoid overheating!

As has been my experience of more than 25 years of MGB enjoyment, they ONLY overheat when SOMETHING is BAD. Otherwise, the stock radiator and mechanical fan (with the exception of the 3 balded early fan) is plenty to keep an MGB engine cool. Even in 120 degree weather that we get here in the Southern California desert areas.

Some people tend to comfuse a thermostat with keeping an engine COOL, they actually serve the OPPOSITE EFFECT, they keep the engine HOT, or rather AT NORMAL OPERATING TEMP. You experienced this, when your "FAILSAFE" 160 degree thermostat failed. The result is an engine that won;t heat up properly.

It has also been my experience that an MGB engine runs cleanest and best at around 210-215 degrees fahrenheit. Which is why I usually run a 210 thermostat in my MGB. This also works great in the winter, when you need the heater.

Good Luck All!

B

Cooling problems are not much of an issue with the MG if the cooling system is working correctly and the engine is in good tune.

Yes I agree that once the stat is fully open the system is cooling its' maximum ability. I grew up in the sub zero prairies and realize that the thermostats job is to control the minimum temperature of an engine. I have seen times when the radiator never gets too hot to touch and the heater struggles to give a bit heat.

I can understand what you are saying about the thermostat opening at 180, then as soon as the thermostat opens, cool water rushes in, and it closes again.
My only question is where is the cool water coming from?

I had always thought that the wax pellet expanded from the increasing heat of the coolant in a linear fashion. The hotter the fluid the larger that the opening becomes until the wax pellet is at its maximum size. This maximum size happens at about 15 to 20 degrees above the stamped temp on the stat.

If you test a 210 stat I will bet that it is fully open at 225 to 230 degrees.

An engine with a 210 would run hotter than one with a 160 because the 160 is fully open at 180. All being well this engine should not see more than the 180 degrees.

Where as the engine with the 210 would never be cooler than the stats' lowest opening of 210 degrees.

The engine with a 180 should run cooler than the engine with a 210.

One question is why would the BL shop manual list the follow specs for the thermostats?
Standard............165
Hot climate.........165
Cold climate........180
This info is from the original loose leaf BL Workshop Manual that I bought when I purchased my first MGB back in 1971.

These specs seem to be out of line with what many of us are doing.
Did the BL engineering guys get it wrong?

Jim1971 Wrote:

The thinking that I have is twisted perhaps but once the engine hits the point where that stat is fully open the effect on the cooler water from the bottom of the radiator is not going to cause the thermostat to close very much as this water is at the maximum temperature that it can be at by the time it reaches the thermostat. The only time the stat would stat to close would be if the engine coolant temp was to begin to drop. This could happen on a coasting down a long gradient at highway speeds.

If an MGB B engine had a radiator the size of the one on a Mack truck. This radiator would always be able to disperse any heat that the little 4 cylinder could produce.
In this case the stat would always hover between closed and open. This would result in the internal engine coolant temps being kept within the 20 degree spread of thermostat operation.

A thermostat in you home does the same thing it controls the heat or AC to maintain a constant predetermined temperature spread. (usually around 5 degrees)
The only way that the room temp with be out of this spread would be if the AC or heat could not keep up to the demand.

The low temperatures for the stats in the factory manual may result from the old design of the engines.
Modern engines are made of different materials and can operate safely at much higher temperatures.

GILMGA Wrote:

Jim, WAX PELLET???

What wax pellet are you talking about?

I haven't worked on many later model MGs, but, I've never seen a wax pellet in the cooling system.

Most thermostats have what's called a b-metallic coil in them. Basically two different types of metal fused together to form a spring of sorts that is very sensitive to heat changes. As the water surrounding it heats up, it expands or collapses and this causes the "trap door" that the coil is attached to to open and close. That's basically how a thermostat works.

The cold, and that's a relative term, comes from the radiator. and you'd be surprised, a new or in good condition MGB radiator will cool the water very rapidly. It's not until the insides get corroded and constricted or the air flow over the outside deteriorates that the efficiency of the radiator goes down.

As far as the temps that the BL Manual gives, I have no clue. But, you have to remember, the thermostat doesn't really help to COOL the water, it's actually the OPPOSITE, it helps to KEEP IT AT A DESIRED TEMP.

The reason they list the 180 for a cold climate is so that the car stays warmer and the heater will work properly. Of course, we've found in later years that the car actually is most efficient at a slightly higher temp of around 210. Back then there weren't any smog constraints, they didn't care about unburned fuel, heck, it was 25 cents a gallon, right?

NOW, if you have a breakdown in your cooling system, then you have a problem. That's when people start changing the thermostat to a lower temp. BUT, this really only delays the inevitable until the car overheats. By allowing cooler water to enter the engine sooner, it keeps the guage down lower, BUT only until the whole system can no longer keep the engine cool, and the car overheats.

This scenario is caused by a poor cooling system though, and NOT the thermostat.

The thermostat solely regulates the introduction of cooler water from the radiator into the engine.

I have lived in SoCal my entire life, and it gets hot here, in the central valley of CA, the temps were above 110 the entire summer. We would pack the MGB full of gear and travel to all sorts of Brit Car Events. My car never overheated. The only change I made was to add the later plastic fan, I think it has 6 or 7 blades. I ran a stock water pump and stock radiator, and NEVER overheated. No electric fans are needed, assuming that your radiator is working efficiently.

The rad is key, these are always overlooked, and they don't have to be. Moss sells them for less than $200, and they're good quality, made in England products that last for years. People add stopleak rather than getting the leak soldered, and this leads to clogs eventually. Think about it, that stop leak doesn;t know the difference between a good hole and a bad hole, so it clogs everything eventually, this coupled with corrosion from old antifreeze or NO antifreeze is the rads downfall.

Good Luck,

this has been a good discussion!

B

http://auto.howstuffworks.com/question248.htm gives a simplified explanation about "wax pellet type" T-stats.

http://64.78.42.182/sweethaven/MechTech/Automotive01/default.asp?unNum=5&lesNum=1&modNum=9 gives a bit more "in-depth" explanation and the advantage of some drawings to help make their operation and innards more easily understood.