How a thermostat ACTUALLY works

[@jozefsk7456]

yay, the board is back

[@NickTaylorRickPowers]

School's back m'fers

[@templartoto4416]

Love to see you in front of the board again , this is how I first saw you . More of this please 👍

[@thisisyourcaptainspeaking2259]

The purpose of the air bleed hole is to avoid trapping air in the recirculation. If the system is free of air, the bleed hole serves no purpose. Have a closer look, there's a loop that recirculates coolant independent of the thermostat being open or closed. This loop passes across the wax plug of the thermostat in order to expose it to the warmed coolant.

[@Surestick88]

Yup. The system recirculates coolant through the engine and bypasses the radiator until the thermostat opens then coolant starts going though the radiator. Circulating coolant through the engine with the thermostat closed helps warm the engine equally throughout. Some thermostats actually have a little pin in the bleed hole that closes it when coolant is flowing and allow air bubbles to escape when the engine is stopped.

[@dirtygarageguy]

Nope.

[@dirtygarageguy]

It's right in front of your face...

[@dirtygarageguy]

Who thumbed up the first comment in this thread come on, own up.

[@thisisyourcaptainspeaking2259]

@@dirtygarageguy Check it again.

[@ravishkasilva2851]

Thanks Matt BMW TIS got a grate explanation about this it’s basically the same thing as you said. Now they have MAP controlled thermostat that got a heater inside the wax compartment.

[@gutserker]

This reminds me of an old video a while back and I mentioned there's some people that modify their coolant loops to allow more flow to bypass the thermostat until the coolant gets up to temp. Old carbureted bikes with water cooling struggle to keep warm enough for best performance. I had modified the coolant loop of my 89 ninja 500 to have a bypass loop before the thermostat, and that helped some in cold days. This year I finally did the same thing with my 2000 ninja zx6e/zzr600. It was much less affected by this modification, but I still imagine it helps a tiny bit, since this bike does run better on hot days.

[@A_S_100]

What you are saying, doesn't make sense. You're saying the bike 'can't keep warm enough for best performance' but you fix that by bypassing the thermostat which is actually closed to restrict the coolant flow while the engine is warming up. If you bypass the thermostat then, hypothetically, if the engine temperature were to drop then coolant flow would not be controlled by the thermostat (because you've bypassed it), and the coolant would flow round unrestricted when the engine is supposedly cold. How does that help the engine to 'keep warm enough for the best performance' when it's cold outside or warm up? Your going to have to explain that one.

[@gutserker]

@@A_S_100 maybe I didn't go into enough detail to fully explain my system this time around, but it's very similar to how a car cooling system behaves. During cold operation the thermostat will be closed and the coolant will circulate around the engine. As the temperature warms up the thermostat opens and the coolant behaves like normal other than a small amount of water flow that recirculates bypassing the radiator. This system does not cause sudden shocks and temperature because the engine doesn't stop producing heat, the engine doesn't produce cold. Since there is a bleed hole inside the thermostat there is always a small amount of water flow going through the radiator I think, but for some engines that is still too much slow for an ideal engine temperature in Cold environments. I originally came across this modification where someone did the thermocouple sensing and coined the term the thermo Bob. They showed that a stock configuration will have those highs and lows of thermostat opening, cold air goes into the engine And repeats until the temperature stabilizes after many many minutes of operation. This allows the coolant to keep its flow rate but to bypass the radiator until the thermostat starts opening up more. It's not a complete bypass of the thermostat, it's not a one-to-one ratio coolant hose. It's usually about a quarter of the diameter of the stock coolant hose so the coolant will still prioritize going through the thermostat if it's able to

[@denniselenson560]

Everybody knows how a thermostat works (obviously not, judging by the comments) but this was a really good explanation of how the whole system works and why it's designed like that, good job Matt, great video, glad to see the board again.

[@233kosta]

Thinking about it for a second, the thermostat's sensing element is well... inside it. So you have to have hot water right there to actuate it. If you had no flow, you'd be reliant on the water (and surrounding materials) to more or less purely conduct that heat until the wax core gets warm enough to crack open. Not a recipe for reliable operation, especially if you want the thing to be insensitive to other factors (i.e. where you put it, OAT, etc.). Sticking a tiny hole on the side solves all those issues neatly - water moves very slowly, but still faster than waiting on pure conduction, so when it gets hot the thermostat will do its thing relatively quickly.

[@stco2426]

Agree with this, but I know about cars and vans more. Without the hole the thermostat might also be slow to open as it could (depending on the type of plumbing) sit in a cool pocket. I've also seen in manuals to put the hole, (which sometimes has a little metal piece in it too) orientated uppermost. Presumably this way, it does help any gases / air to escape.

[@markmenzies4218]

Car makers have thrown this in the bin now. it's now all controlled by the ecu using a motor. all in a big plastic housing bolted to the block. they break apart & spew the coolant out in a hurry. i done a ford kuga recently. £200! instead of what a tenner for a tried & trusted old waxtat. progress? bollocks.

[@mazdamaniac4643]

Aye, why leave it to proven simplicity when a highly complicated computer system can fuck up your day even more spectacularly?

[@sm400]

Or 400 euros for Pcr abortion😂😂😂top job

[@chyrt]

I really missed these video's

[@kingduckford]

I suppose this explains the telltale sign of a thermostat starting to go bad is temperature spikes, as the thermostat actually is jamming shut and opening up leading to fluctuations rather than a smooth temperature? Thanks for the lesson.

[@espenschjelderup426]

This had me wondering what's up with the thermostats that has a small plunger thingy in the bleed hole? On a side note, have you ever seen a datalogg with coolant temperature plottet against time? I have never seen one from a bike, but on some cars I have seen that when the thermostat opens the first time from cold it's often at a slightly higher temp than the following ones. This is the temperature the ECU sees.

[@dirtygarageguy]

A jiggle pin... that's for another video

[@mikedelcaribe7422]

About using fuel for cooling, my brother had a 3 cylinder air cooled bike that used fuel for cooling. The three cylinders were butted up against each other so the one in the middle didn't have as much external surface area to receive air cooling. To compensate for the reduced cooling on the middle cylinder the manufacturer used a richer carburetor jetting for that one cylinder, but otherwise, the three carburetors were identical. For a two stroke it worked well as long as no one interchanged the carburetors.

[@anotherhonda9402]

A few Honda V Twins have bigger jets on the rear cylinder, I've heard it was for this reason?

[@mikedelcaribe7422]

@@anotherhonda9402 Seems plausible if it was air cooled or if the cooling was compromised for some other reason.

[@anotherhonda9402]

I knew about the bypass hole in the thermostat though I thought the expansion circuit works off the radiator pressure cap? When working properly if there is too much pressure then coolant pushes the cap open, sending coolant to the expansion tank, but if the rubber seal on the cap that closes off the expansion circuit is damaged it can allow coolant to overflow from the expansion tank. I had this happen on one of my bikes so as a short term fix I borrowed a radiator cap from a Nissan Terrano (Ford Maverick) at it was the same size and was a similar or same pressure rating, I just topped up the coolant and it was fine to get me home.

[@mikedelcaribe7422]

If the thermostat were to completely shut and didn't have the dribble hole, is it likely that enough heat would reach the thermostat element to activate it to open in a reasonable amount of time, or would it be sluggish to open?

[@chriswilliams1096]

Just what I was going to ask! Beat me to it.

[@mikedelcaribe7422]

@@chriswilliams1096 I was the second to ask.

[@dirtygarageguy]

@mikedelcaribe7422 the wax element is on the hot side...

[@mikedelcaribe7422]

@@dirtygarageguy Does the wax work like hydraulic fluid that expands with heat to open the valve blocking element?

[@abyssmanur3965]

​@@mikedelcaribe7422yes.

[@saifcathum3423]

I've heard that there are fail open and fail closed thermostats. Do you have any experience testing them? I'm curious about the engineering of a fail open mechanism. Is there any reason why you wouldn't want fail open thermostats exclusively other than cost?

[@butunercouk]

This is your topic Matt. I think you should expand that. Air, water, oil cooling. Materials iron, aluminium, cast, billet expansion differances. Radiator types serpentines bar and plate types. Pressure management and all that kind of shyte... I think bike & automotive hobbyists really need that. 💩

[@branch2000]

Matt can you do a video about rev matching (also mention what would happen if you screw it up/ hard downshifts and their consequences) note: im not talking about clutchless shifting ive watched your video about that

[@guillo88]

all heil the blackboard! great vid, and now we know!

[@seanylewl]

Was hoping you'd explain how the thermostat actually functions, what causes it to open once it gets to temperature. This video should be called What a thermostat does, not How it does it.

[@dirtygarageguy]

How it does it and how it works are different how?

[@seanylewl]

@@dirtygarageguy What it does and how it does it are different, yes.

[@cliveadams7629]

@dirtygarageguy I think he means how does the thermostat open and shut with temperature.

[@seanylewl]

@@cliveadams7629 exactly

[@dirtygarageguy]

This is all good, but not what the video is about, I feel sorry for your "expectations"...

[@backyardmechanical]

my pet hate is people who remove the thermostat to try fix an issue or think by removing it the engine will run cooler.

[@sm400]

I generally leave the exterior there still if I have to resort to abortions..😂😂..I've explained this in various languages...I'm not a fluid dynamicist.....but the furthest cylinders maybe faltar circulation...

[@cliveramsbotty6077]

the immaculate misconception

[@sm400]

When im scared i drill a small hole😂😂

[@danielwoodhouse1870]

Brilliant

[@Manuqtix.Manuqtix]

Wait I forgot how the coolant flows in my motor

[@Ken_Myette]

Expasion

[@vikingbiker]

Is everyone in this comment section being deliberately obtuse?

[@bananabrooks3836]

Only about spelling.

[@vikingbiker]

@@bananabrooks3836 pointing out speelling mistakes on the internet must make you feel smart ?

[@bananabrooks3836]

​@@vikingbikerNo, l was hoping you would enlighten me on the 'obtuse' nature of the comments you have perceived.

[@keithf8890]

Mmmmmmmm,spelling.

[@Trumplican]

wanna see a garbage thermostat/coolant system? Enter the Kawasaki KLR 650. no bleed hole/bypass or anything. top half of the cylinder runs hotter than the bottom and they soon start to smoke like pigs. luckily theres the aftermarket upgrade called the thermo-bob

[@dirtygarageguy]

Wow thermo bob is really stupid...

[@Trumplican]

@@dirtygarageguy its a really stupid name ill give you that but it fixes the shit cooling system on the KLR. even dumber is the upgrade for the counter balancer tensioner. they call it the doohickey. great video BTW as always.

[@Matt-we7si]

drill some small holes in the thermostat surely ?

[@ItsAllJustBollox]

Without the small hole the warmer water would not reach the wax capsule before the engine overheats the system needs a flow to move the cold water away from the thermostat so it can respond to water temperature.

[@dirtygarageguy]

No, no and no. Wanna see a demo of why this isn't true?

[@ItsAllJustBollox]

​@@dirtygarageguy it is true, water is a poor conductor of heat without a flow the water at the thermostat will be a lot cooler than the water in the cylinders resulting in overheating, remember not all thermostats are at the highest point of the water system. Do a demo and put the thermostat in various positions some low some high without any flow.

[@dirtygarageguy]

Water is a poor conductor of heat... it's only bested by ammonia and mercury... Edit sorry it's mercury, HF acid and water then ammonia.

[@vikingbiker]

​@ItsAllJustBollox if water is a poor conductor of heat what do you cook your padta in ? Moden society exists because water is used in powerplants over 200 years, even in nuclear reactors which get unbelievably hot. What are they using the water for?

[@freezingDaniel]

​@@vikingbiker transporting heat, not transmitting heat The thermal conductivity of water is worse than say aluminium. [ Thermal conductivity: Water: ~0.6 W/(m·K), Aluminium: ~237 W/(m⋅K) ] The reason water is used is that moving water around is much faster than relying on thermal diffusivity of other materials. [ Thermal diffusivity: Water at 25 °C: 0.143 mm^2/s, Aluminium: 97 mm^2/s ] Additionally the high heat capacity of water helps it move more heat given the same volume. [ Heat capacity: Water: ~75 J/(mol·K), Aluminium: ~24 J/(mol·K) ] So we - use metals to quickly conduct the heat away from the source and flatten spikes - then we further conduct the heat from metal to water - we circulate the water between source and dissipation point to maximize rate of heat transfer (influenced by temperature-difference) between the water and the source/diss. p. - ... reverse at dissipation point for cooling

[@gafrers]

Blackboard videos FTW