overheat without thermostat?

[uhcrandy]

I was having a discussion with someone, the topic of thermostats came up. I was told a car would overheat withou a thermostat, since the fluid would not have enough time in the radiator to cook off. I thought a radiator will give off a given amount of head, regardless of the water flow/speed. Any one care to tell me I am right? LOL. thanks

 

[Joe Reed]

I'd say it would depend on the car, the driving conditions, the condition of the cooling system, etc.

The main issue is that if the coolant flows through the engine too fast, it absorbs less heat...so the engine could run hotter.

 

[bazar01]

I was having a discussion with someone, the topic of thermostats came up. I was told a car would overheat withou a thermostat, since the fluid would not have enough time in the radiator to cook off. I thought a radiator will give off a given amount of head, regardless of the water flow/speed. Any one care to tell me I am right? LOL. thanks

You are correct, assuming the radiator is good (not blocked), fans running, the engine will not reach it's operating temp and will run abnormally cool, will use more gas because the engine temp will tell the ECU the engine is still cold and will run rich.

But what do I know, I only drive an air-cooled car.

 

[Mike83]

Both of my cars had a stuck open thermostat recently. They would not warm up past 1/4 of the way on the scale if I was driving fast (the cold air would cool down the coolant). If I was in slow stop and go traffic it would get *almost* to operating temp. This was in winter, though.

 

[HighVoltage]

If the water is spending more time in the radiator cooling, then there's also water spending more time in the block heating up...

I'm no expert on thermo/fluid dynamics but about 10 years ago, I went and dug up alot of information on cooling for cars. My Nova was having a hard time with it during the summer in the SoCal valley. It was a 250 to 454 conversion (10:1 compression) and I tried a larger radiator and different thermostats to no avail. If the radiator was kept constant, the thermostats made no difference other than how long it took for the heater to work. A lack of a thermostat actually caused the car to overheat faster.

After plenty of reading and asking around, the consensus was an issue with the stock pump (slow flow rate) and radiator (small area of exchange). The experts all agreed, that more flow is better. If you start looking you'll find that every hi-performance water pump just moves more water at a faster rate. Some of the main items that effect heat transfer are:

1) Pressure
2) Area of the exchange (i.e .your radiator size)
3) removal of the Boundary layer (laminar flow)
4) Coefficient of heat transfer (i.e Copper vs Aluminum, etc)

The purpose for a thermostat is to get the engine temperature up but it also serves to introduce turbulence prior to entering the block to prevent laminar flow, which can lead to overheating.

 

[Jim Stabe]

There is a difference between having a thermostat that is stuck open and having no thermostat in place at all. If you measure the area for water to pass through a wide open thermostat it is considerably smaller than the area without one present. That reduced area causes a restriction to the flow causing a head to build up between the pump and the restriction. The head helps to reduce the formation of bubbles from local heating in the head around the exhaust valves. There are a number of racers who don't want to use a thermostat because it is a potential component failure but they do install a restrictor in its place to create head inside the engine.

The feed for the car's heater is always taken after the pump but before the thermostat because the water is hottest right before the thermostat but also because it is at its highest pressure there. The return is always after the thermostat because the pressure is lowest at that point.

Jim

 

[herb101]

Not running a t-stat won't guarantee overheating, but the motor will not cool properly. Jim's comment about the restrictor plate is right on. The system is basically a heat transfer scheme - the way to observe it properly is to follow the path of heat rejection. The "boom" in the cylinder makes the heat and a big chunk goes out the exhaust to atmosphere. However, some heat plus all the fiction load heating saturates the cylinder walls and cylinder heads (and the crank, rods, valves, rockers, cam, etc.) - the coolent soaks this heat up and its temperature rises (while the metal that just transfered its energy cools). The coolant is circulated to the radiator where the heat energy is then handed off to the metal in the fins (cooling the coolant). The air flow across the fins then **** the heat energy into the air stream (cooling the fins) and wisk it off into the atmosphere (where Al Gore blames the woes on the world on it)

Move the coolant too quickly and the rate of thermal transfer from the metal to the fluid exceeds the flow rate of the fluid, leaving heat energy in the metal instead of removing it. Repeat time and time again and the heat energy in the base metal continues to rise until something gives.

One thing to remember is that the oil (not the coolant) is responsible for the majority of the engines cooling via this same heat transfer model. Oil coolers pay big dividends in engine cooling.

 

[nova65ss]

They did not design a thermostat for nothing.

 

[JerseyJim]

A thermostat is absolutely required. It's not just the amount of time spent in the radiator that counts, it's the amount of time spent in the engine. The water/glycol mix is no where near as good at absorbing heat as straight water would be and it doesn't give it up as easily either. It takes a certain amount of dwell time to get the job done. Removing the thermostat is not the cure for an overheating problem.

A lot of old drag guys run a much higher percentage of water for just this reason. Additives such as Royal Purple are used to make up for the missing rust and corrosion inhibitors that would normally be provided by the antifreeze as well as to add surfactants that improve the wetting capabilities of the coolant.

You certainly do want a good, high flow water pump and wide open passages through the engine to allow the water to flow at the maximum rate that the thermostat allows in any given situation. Keep in mind that the water pump pulls rather than pushes. A poorly designed water pump usually exhibits cavitation. What we would refer to as a high volume water pump to me is one that will keep water moving even when the engine is at low RPMs.

 

[Charles (in GA)]

I was having a discussion with someone, the topic of thermostats came up. I was told a car would overheat withou a thermostat, since the fluid would not have enough time in the radiator to cook off.

This is true of many engines.

Charles

 

[e-tek]

In my mind, the thermostat is there to get the engine up to operating temperature faster. Once the engine coolant temp is 190 (usually) then it opens the gate for the rad water to flow into the engine to maintain the 190 temp. Once the thermostat is open, it's open - and the design/cleanliness of the system is what's going to either keep it cool, or allow it to overheat, so at that point, it matters not if you have a thermostat or not - unless it gets so cold (driving in Canada say...) that the thermostat actually closes to maintain engine temperature. As was said above, if it gets too cool, performance and gas mileage suffers and it's hard on the engine. Isn't that the case?

 

[ImportTuner]

In my mind, the thermostat is there to get the engine up to operating temperature faster. Once the engine coolant temp is 190 (usually) then it opens the gate for the rad water to flow into the engine to maintain the 190 temp. Once the thermostat is open, it's open - and the design/cleanliness of the system is what's going to either keep it cool, or allow it to overheat, so at that point, it matters not if you have a thermostat or not - unless it gets so cold (driving in Canada say...) that the thermostat actually closes to maintain engine temperature. As was said above, if it gets too cool, performance and gas mileage suffers and it's hard on the engine. Isn't that the case?

That's what I thought ..

 

[herb101]

Compare the free flow area of an open thermostat to the outer diameter of the thermostat. The that acts as a flor contol device - close = no flow, open = calculated flow through center opening, missing = uncontrolled full flow. Works just like Cv calculation for controllability of valves in hydronics systems (because that's what this is).

 

[ddawg16]

I was having a discussion with someone, the topic of thermostats came up. I was told a car would overheat withou a thermostat, since the fluid would not have enough time in the radiator to cook off. I thought a radiator will give off a given amount of head, regardless of the water flow/speed. Any one care to tell me I am right?

Chalk the first part to urban ledgends.....on the second part, you are more or less right.

On the first part, about the only way you could push water through the engine fast enough so that it did not cool is if you used some type of turbo and the water was going so fast that it basically cavitated across the metal....hence, I don't think it's possible to do that.

If the water flow is faster...about all that happens is that the heat rise is less...but the total amount of thermal energy moved is the same.

Overheating is when you reach the saturation point of the water...or more commonly known as boiling....when water turns to steam, it's lost it's ability to absorb more heat, or cool your engine.....one of the reasons for pressure caps.

An engine has an ideal temp that it runs at....which for most fuel injected engines is around 95 to 110 deg F.

The thermostat serves two purposes....helps the engine get warmer fast...and helps keep it above the min operating temp.

A very common misconception is that removing a t-stat or putting in a colder one will solve an over heating problem. Unless the over heating problem is a stuck close t-stat...it will not help. If the engine over heats with a good t-stat, it will over heat without one as well.

One last thing....as correctly stated above...glycol does not have as good a thermal transfer as water....running more than 50% does not help.....50/50 works well....you can get good protection with 25% glycol if you are not in real cold climates.

 

[oldgoat]

I had a 65 Plymouth that I took out the thermostat and it certainly did overheat. Now maybe in all models it won't, but I do know that it will in some cases. Even a stuck open thermostat will restrict it enough to cool a engine.

 

[nissan_crawler]

I was having a discussion with someone, the topic of thermostats came up. I was told a car would overheat withou a thermostat, since the fluid would not have enough time in the radiator to cook off. I thought a radiator will give off a given amount of head, regardless of the water flow/speed. Any one care to tell me I am right? LOL. thanks

I have fixed 3 overheating problems that were caused by no thermostat. The best solution if you have one stuck closed and can't replace it immediately is to take a pair of dykes/diagonal cutters/whatever you like to call them, and cut the bars that hold the thermostat guts in, leaving you with just the disk with the hole in it.

You can indeed run water too quickly through a radiator.

A guy at work had farted around with overheating on his cherokee, replaced the radiator, water pump, fan clutch, still didn't fix it. I got to talking to him, and he mentioned "I even tore the entire thermostat out and it didn't help". BINGO! I asked if he still had the old one, it was on the passenger floormat. We cut the guts out, slapped the disk in, it ran fine. ***** just had a bad t-stat from the get-go.

 

[tdkkart]

When I built my trike I was on constant watch to make sure that the cooling system was as efficient as possible. After all, mounting the radiator in the back is not typically regarded as the best idea.
Along with the large radiator, I used a high flow water pump, made sure not to underdrive the pump, and installed a high flow thermostat.

Guess what??
It cooled TOO well. My initial shakedown runs were made on 50* days in Nov. The temp gauge would not go over 140 on the highway, and 160 in town unless I was at a dead stop.
Taking a look at the the wiz-bang thermostat I bought, even when closed it had 3 rather large bypass holes in it, 3/16 or so in diameter. These holes by themselves were too much flow to allow the motor to warm up.

Ended up with a standard 195* T-stat, now it does as it should, never goes over 200* even with extended idling.

 

[slimshady_2469]

ive had 2 cars that when i bought them someone before had completely cut the functioning part of the t-stat out so it was just a hole. i think this would be similar to the restrictor plate? anyways, i live in wisconsin and in the winter if you would start the car it would warm up almost to regular, but as soon as you started driving it would drop and low heat. i dont know why anyone would want to do such a thing to a street car but they did to 2 of mine.

 

[herb101]

ive had 2 cars that when i bought them someone before had completely cut the functioning part of the t-stat out so it was just a hole. i think this would be similar to the restrictor plate? anyways, i live in wisconsin and in the winter if you would start the car it would warm up almost to regular, but as soon as you started driving it would drop and low heat. i dont know why anyone would want to do such a thing to a street car but they did to 2 of mine.

It would be almost identical to the restrictor function. Here a link to the devies:

http://store.summitracing.com/partdetail.asp?part=MOR-63440&autoview=sku

 

[e-tek]

My old man always said: If you want to cover all your based, you should check a thermostat (old or new) before replacing it. Just hang it in some very hot or boiling water - you can watch it open. Seems like 1 of 10 is bad from the factory!

 

[chaingang]

If you want to see what removing the T stat does to cooling install an oil temp gauge. As most everyone has mentioned the t stat is there for a reason and yes once it is open it for the most part stays wide open. The restriction it causes is the reason for it being there as has also been mentioned. People will argue that the car runs cooler by watching the temp gauge and seeing that it shows cooler as is usually the case. But, if you could watch the oil temps at the same time you will find that they go up. Heat is no longer being transfered from the block, heads etc... because the coolant is moving to fast to absorb it. However, oil drains back to the pan by gravity, slowly and will absorb more heat that would have been carried away by the coolant. Without an oil cooler it has no way to give up this heat and will continue to cook. In reality the engine is hotter, you just can't see it. Neither will the computer because it moniters engine temp through the coolant. You can run without the t stat if you like but I'll keep mine in.

 

[Shocker]

An engine has an ideal temp that it runs at....which for most fuel injected engines is around 95 to 110 deg F.

I don't believe that this is correct. Most modern fuel injected engines run temps anywhere from 195f to 210f depending.

Maybe you meant Celsius? That would be closer. I haven't seen many engines running 230f on the temps, but most certainly in the 200 to 205 range.

VW VR6 engines run around 210. Modern Corvette's run around 215 to 220.

Mike

 

[ddawg16]

I don't believe that this is correct. Most modern fuel injected engines run temps anywhere from 195f to 210f depending.

Maybe you meant Celsius? That would be closer. I haven't seen many engines running 230f on the temps, but most certainly in the 200 to 205 range.

VW VR6 engines run around 210. Modern Corvette's run around 215 to 220.

Mike

Shocker....you would be correct and I had a case of fat fingers and brain fart.....I ment 195 to 210.....too many numbers in my hear right now.....

I'm doing start up on an autoclave in Tulsa and I'm dealing with a lot of temperatures....95 to 110 is where I try to keep the water tank under full load cooling....with the cooling towers going....150 is the max for the fan motor....and I'm dealing with a 1000HP fan that is pulling 1800 amps when it should only be pulling 1200A with a full load of 160 PSI....too many #'s......it's been one of those weeks....

 

[jerk_chicken]

If you want to see what removing the T stat does to cooling install an oil temp gauge. As most everyone has mentioned the t stat is there for a reason and yes once it is open it for the most part stays wide open. The restriction it causes is the reason for it being there as has also been mentioned. People will argue that the car runs cooler by watching the temp gauge and seeing that it shows cooler as is usually the case. But, if you could watch the oil temps at the same time you will find that they go up. Heat is no longer being transfered from the block, heads etc... because the coolant is moving to fast to absorb it. However, oil drains back to the pan by gravity, slowly and will absorb more heat that would have been carried away by the coolant. Without an oil cooler it has no way to give up this heat and will continue to cook. In reality the engine is hotter, you just can't see it. Neither will the computer because it moniters engine temp through the coolant. You can run without the t stat if you like but I'll keep mine in.

Your reasoning of the physics and chemistry of energy transfer is flawed. I guess it's easy to do such a thing when there is an answer that's quite easy to make up. You are apparently not looking at matter, in this case, coolant, as it really operates on a molecular level.

I have run several cars with and without thermostats and never did I see oil temps rise. I don't advocate removal of thermostats, except in extremely hot climates, and even in that case, I recommend removal of the guts, but not the disc.

As far as checking if a thermostat works, all one has to do is boil the old one and see what it does. Even though you're likely going to put a new one in, this will eliminate the guesswork should you have a temp problem.

 

[rcleaver]

Last summer the thermostat in my 2000 SUV failed. I was puzzled at first because it failed in the open position. I didn't know this type of thermostat was being used back in 2000 (I'm still not sure -- maybe I was just lucky it failed open and not closed).

Anyway, the temp stayed low and the oil temp didn't rise, whether driving at low or high speed. I don't get it but I suspect there is something I don't know about the cooling system in that vehicle -- and I never bothered to investigate further.

 

[herb101]

It's also not a bad idea to boil test a new stat before installation. This is usually one of those trivaal dollar jobs where the labor and consumable (friggin antifreeze prices) far outweight the part cost. Over my wrenching career, I have had 3 bad stats new in the box (all brand name units) - one of these I was smart enough to find with a pre-install boil test.

When something goes wrong after a part change, you normally don't think "hmm - bad part" - you usually look for the installation error. This trait makes finding a bad new stat pretty time consuming.

 

[jerk_chicken]

Not a bad idea.

 

[JerseyJim]

Love these types of discussions. Everyone has their own opinions... Even their own science! I think that circumstances vary from case to case. I have had over heating on vehicles where a complete rebuild has been done. Everything new and clean in the engine, new water pump, re-cored radiator... When the old engine never did it before.
I have an old Econoline with the engine in a box between the seats. Ford put a belly pan under the front of these trucks to direct air through the radiator. Some guys swear removing the pan has solved their over-heating problems. The answer is usually a combination of things. And once we get fed up with the problem, we typically make a number of changes that somehow do the trick.
I know experts who claim that vapor lock is an urban myth. I had all kinds of problems when NJ went to ethanol blend. If I stopped at a light, the heat would build up in that box. Boil off the fuel in my carb bowl and create an air bubble in the fuel line. Couldn't re-start until I would remove the fuel line and burp it out. Just so happens the first tank of the blended fuel coincided with the complete engine rebuild. I was probably running just as hot before but I wasn't vaporizing the fuel at idle. A six blade fan, a phenolic carb spacer, and an insulated fuel line later and the problem was fixed. Which one did it? Well the insulating the fuel line wasn't enough. Between isolating the carb from the manifold and dropping water temp... Problem solved.
We can all argue the physics of coolant... But we all know that thermostats are required and if a car overheats with a functioning thermostat... We need to look elsewhere.
One word of caution... With so many aluminum parts being used - radiators, heads, etc. we need to chaange the coolant more frequently to avoid corrosion.

 

[chaingang]

Your reasoning of the physics and chemistry of energy transfer is flawed. I guess it's easy to do such a thing when there is an answer that's quite easy to make up. You are apparently not looking at matter, in this case, coolant, as it really operates on a molecular level.

I have run several cars with and without thermostats and never did I see oil temps rise. I don't advocate removal of thermostats, except in extremely hot climates, and even in that case, I recommend removal of the guts, but not the disc.

Never claimed to be a physics or chemistry major. Can't prove scientifically anything about thermal dynamics. Nor did a just make something up just for the case of argument. Are you saying that oil does not share any responsibility for shedding heat? So squirting cooled oil on valve springs to reduce heat related fatigue failures in high RPM overhead valve motors is made up too. My response was one of logic. If the oil temps are higher and coolant temps are lower then it stands to reason that oil is now carrying some of the heat away. I simply reported what I have seen in my 25 years or so of playing with cars. Mostly purpose built cars and I have seen it on numerous occasions. I don't know of any production US cars that actually come with an oil temp gauge. So if you removed the t stat or it failed open you would not be able to see the temp. Also, if it fails open then you still have the restriction offered by the body and willl still get good heat transfer due to the increase pressure and reduced flow. Yes most racers install restrictors instead of the thermostat for this reason. I stand by what I said. I have seen oil temps higher with no thermostat or any form of restricting flow.

 

[jerk_chicken]

Are you saying that oil does not share any responsibility for shedding heat?

No, I did not, and no one else read that. It's a poorly played deflection on your part to invent that.

 

[chaingang]

No, I did not, and no one else read that. It's a poorly played deflection on your part to invent that.

Not trying to invent anything. This certainly is not getting either one of us anywhere and appears to be getting personal on your part for some reason. Bear in mind I am not talking about huge temperature swings. Only about 10 to 15 degrees F. We both seemed to have experimented with and without thermostats. Your results are yours and mine are mine. Both are opinions based on these results. Simply stated for others to take as they wish.

 

[jerk_chicken]

This certainly is not getting either one of us anywhere and appears to be getting personal on your part for some reason.

It did not turn personal, either. I stated the experience I had and refuted a portion of yours due to flawed understanding of how matter in this case works.

 

[ddawg16]

I don't have the exact numbers handy....but water has a higher heat transfer ability than oil. Hence, a water cooled engine can get rid of heat better than an oil cooled engine.

With that said....keeping the oil cool is not a bad thing. My jeep has an oil cooler (came with the SBC). Oil can tolerate a higher temp than the water...but oil starts to break down if it gets too hot....hence, this is one of the reasons you typically see oil coolers on trucks....they typically run under higher loads which puts more stress on the oil...keeping it cooler helps it last longer.

So...to summerize....

The t-stat is a part of the cooling system that makes it a closed loop system for regulating the temperature to keep it in a desired temperature range.

Removing working t-stat will not solve a cooling problem.

Putting in a cooler t-stat will not improver performance

Having the water flow too fast does NOT decrease cooling

Additives in the water for the most part do not help (glycol excepted)

To learn more, go over to the Off-Road.com site...find Short Wheel Base jeeps and search on thermostat's.........that topic has been worn out many times over there......

 

[e-tek]

My old man always said: If you want to cover all your based, you should check a thermostat (old or new) before replacing it. Just hang it in some very hot or boiling water - you can watch it open. Seems like 1 of 10 is bad from the factory!

Does anyone read threads before posting????:wtf:

As far as checking if a thermostat works, all one has to do is boil the old one and see what it does. Even though you're likely going to put a new one in, this will eliminate the guesswork should you have a temp problem.

It's also not a bad idea to boil test a new stat before installation. This is usually one of those trivaal dollar jobs where the labor and consumable (friggin antifreeze prices) far outweight the part cost. Over my wrenching career, I have had 3 bad stats new in the box (all brand name units) - one of these I was smart enough to find with a pre-install boil test.

.

Not a bad idea.

Really.....