thermostat: necessity?

[UncleBob]

I know this will be hard to nail down in generic terms, but I would like to see some discussion about coolant systems: specifically, the removing of the t-stat to "improve cooling" or prevent overheating. I have heard/seen this cause a car to overheat WORSE and I assumed that it was due to there being too much velocity through the radiator, causing less heat transfer where it was needed most. From a recent discussion elsewhere, I'm starting to doubt this.

So. What possible effects will removing the t-stat have? Explain why please.

[bluevp00]

It could prevent the cooling fan from coming on in stop & go traffic. Thus leading to overheating. Most, if not all, cars nowadays have electronically contolled fans. If the car has a seperate coolant temperature sensor then it might be ok, but if the temp is measured by the thermostat then it could screw up the PCM & send it wrong signals. However, if you're talking about an older car, then the fan belt driven, so it *might* not be a problem.

[CraigFL]

The other problem is that without sufficient backpressure, cause by the thermostat restriction, water may not flow thru the engine block properly and pick up enough heat. A lot of cars use special restrictor plates when no thermostat is used.
And of course, an engine runs better when it's hot so no thermostat could cause it to run too cool.

[curtis73]

Originally Posted by CraigFL

And of course, an engine runs better when it's hot so no thermostat could cause it to run too cool.

Exactly. Its important to note that cars are healthier running hot (to a point). Its DRIVERS that like them to run cool.

Its also helpful to think of your coolant as simply a vehicle that carries heat to the radiator. The actual temperature is inconsequential. Its heat in minus heat out. If the engine is giving the coolant 100 joules of energy and the radiator is giving off 100 joules to the air around it, the average temperature of the coolant stays steady. It might stay steady at 50 degrees or 250 degrees, but its not changing. The thermostat simply waits and opens at a target temerature so that's where it remains. That is the reason why changing a thermostat's temperature rating won't prevent overheating. Overheating is caused when the heat in exceeds the heat out. Over heating can only be solved by determining if you have an airflow or coolant flow issue.

Hotter engines tend to make less power, and drivers seem to hate it when their gauge starts registering over 200, but that's just where your oil starts to get in the healthy range. Oil temps and coolant temps are rarely the same, but they are linked. Oil temps up to about 230-240 for regular oil and as high as 275 for true synthetics (those made with esters) are super-happy places for oil. Acids, condensation, blowby, and other junk gets burned or evaporated away.

The biggest misconception I know of in automotive tech (other than warped rotors) is the belief that when a hot engine starts pinging its because the temperatures are too high. That is not the case at all. The explosion inside a combustion chamber can reach 1800 degrees or more. An extra 10 degrees of coolant temp aren't going to make any difference. What's happening is nucleate boiling. The water in the coolant begins to boil on the surface of the water jacket. Where ever there is a bubble, there is no heat being transfered. Its like removing 20% of the surface area. The result is that the heat of combustion is no longer being transferred out as quickly as it was before. The combustion temps spike, and detonation happens. This is the main focus of products like "water wetter" and the like. They contain surfactants that reduce the surface tension. When you get nucleate boiling, the surface of the water jacket looks like the walls of a glass of soda. The bubbles kinda stick to the glass. Adding a surfactant gets those bubbles off returning liquid coolant to the surface.

If you could get by without water, the whole process would be fine. The combustion chamber doesn't care what the temperature of the water is, as long as it is capable of taking the heat its given and capable of giving up that heat to the air. I have one car that runs non-aqueous Propylene Glycol coolant that has seen brief periods of 300 degrees with not a single knock. The oil temp peaked at 245 and it wasn't synthetic so I made sure to change it right away, but since the coolant was still able to carry the same amount of HEAT, no adverse effects were noted.

Side effects to removing your thermostat can be mild or excessive. Removing it does allow for much more flow which as we discussed can help or hurt. It rarely hurts, but it can especially in systems with particularly small radiators. The overall temperature of the oil may or may not reach proper operating temperature which can reduce its life from 5000 miles to literally just a few days. If you have significant blowby and your oil isn't making it to the right temps, it can be a mess in very short order. Cylinder crowns, chambers, and spark plugs can get a pretty thick layer of carbon on them which can lead to lots of trouble. Rings, valves, and other nooks and crannies can fill up with junk that you don't want there. MPG might suffer terribly, especially on an EFI car.

In general, removing the thermostat won't prevent over heating because you haven't changed the fundamental problem... heat in vs. heat out. It will just take longer to get too hot. The jury is still out on whether or not coolant can flow "too" fast. Some say that its moving too fast to pick up heat from the engine and too fast to shed it out the radiator. Since the coolant is moving faster in both the engine AND the radiator it shouldn't matter. Each molecule might be picking up 20% less heat, but there are 20% more coolant molecules flowing past it. Some swear that it hurts, others swear that more flow helps.

I think its safe to say, however that not using a thermostat is generally bad in many ways. I can't think of any situation where the benefits of removing the stat would come close to outweighing the penalties.

[UncleBob]

no argument on the effects of an engine running too cold, I didn't think that would be up to debate. I was more wanting to focus on the other end of the spectrum.

Lets put it this way, if more flow has better cooling efficiency, then why don't manufacturers make the stock t-stat bigger to increase flow potential in a situation where the heat might not be disapated quickly enough. I know this might seem redundant, since a stock engine with a stock radiator will obviously stay within parameters, because thats how and why they designed it....but what determines the best t-stat valve flow at peak opening? Why is it always the biggest restriction in the system, even when its fully open?

[corning_d3]

There's a TSB somewhere(I'll have to look it up) that has a reducer to put inside the radiator hose on certain GM cars.

Curtis, your the man...

[TheSilentChamber]

It may be one of the things you have to look at from the automakers point of view: the thermostats they have now work, they are cheep to make, easy to replace; so why change them.

It may also have to do with (thermal dynamics isnt my highest point so if this is wrong... it may be) if it wasnt the bottle neck of the sytem would it still work the same? Too much flow around it may provide too much cooling to the thermostat it self, causing it not to open and flow properly. It may also be that way to inprove volocity of the water to an excent acting as a ventri of sorts.

[UncleBob]

I thought this was an interesting read: this is from another forum where a simular discussion is going on

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My reasons are not based on any science about bikes but rather by handling warranty service. The thermostat doesn't just pop open but rather slowly opens until it provides full flow through a restricted orfice at a given temperature. Notice that even fully open the stat is still offering some restriction to coolant flow. Now the radiator pressure cap is designed to open and allow coolant expansion into the expansion tank at a given psi usually around 17-21 psi. Tap into the coolant aft, behind the water pump and check your pressure, it's usually much higher, this is known as jacket pressure. The pressure maintained within the water jacket of the block. This pressure helps negate the formation of cavatation or water bubbles bursting on the metallic surface of the water jacket.
Cavatation is devastating to diesels, and accounts for a high percentage of premature engine failure. In diesel engines it is actually visable because the cylinder liners are removable. It manifest itself as small pinholes all around the water contact area eventually leading to errosion and water in the lube oil.
On the other hand, yes, all the oval track engines I've built did not utilize a stat, but did use a restrictor that varied in size based on ambient air temperature and radiator size. The jacket pressure I tried to maintain was 40-50 psi at 7000 rpm. I can't offer any real info on bikes but I would never tempt fate. I'd much prefer to err on the side of caution as this type of damage is frequently catastrophic. There are even specific engines on the road now that are manufactured in a manner that removing the stat completely removes all cooling from the cylinder head. I'll have to check this some time when I'm playing around..........