Help: Overheating WITHOUT a thermostat
02-14-05 | 09:27 PM
#26
All of the sensors will read the same, as they are reading the temperature of the coolant. The problem is that the coolant temperature is cooler than it should be. The coolant is flowing too fast to absorb a lot of the heat from the metal. So every guage in the world will be reading the same nice low temps - as they are measuring the coolant temp. But the metal is hotter than it should be. In essence, the coolant isn't cooling the metal like it should. You need the t-stat in there to ensure that the coolant will flow at a rate that will allow a proper heat-transfer.
02-15-05 | 07:32 AM
#28
Originally Posted by Nick86
All of the sensors will read the same, as they are reading the temperature of the coolant. The problem is that the coolant temperature is cooler than it should be. The coolant is flowing too fast to absorb a lot of the heat from the metal. So every guage in the world will be reading the same nice low temps - as they are measuring the coolant temp. But the metal is hotter than it should be. In essence, the coolant isn't cooling the metal like it should. You need the t-stat in there to ensure that the coolant will flow at a rate that will allow a proper heat-transfer.
02-15-05 | 07:59 AM
#29
The mystery of the prize.
Joined: Aug 2002
Posts: 832
Likes: 2
From: Bay area
Originally Posted by Nick86
You have to be careful when you say 'the car never ran hot without the thermostat'. What you are saying is that the coolant temperature never read more than a certain temperature. Other than bypassing the radiator, the thermostat is there to slow the flow of coolant throughout the engine. If the coolant is travelling too quickly throughout the motor, it cannot properly and efficiently absorb heat. In essence, the transfer of heat from the engine to the coolant cannot happen well enough.
So, while the coolant temperature (and that on the guage) may seem ok, the engine is cooking. What may read 1/4 on the guage may actually be 3/4. You need the thermostat in there to regulate the flow rate (and therefor heat transfer rate) of the coolant as well as the flow path.
So, while the coolant temperature (and that on the guage) may seem ok, the engine is cooking. What may read 1/4 on the guage may actually be 3/4. You need the thermostat in there to regulate the flow rate (and therefor heat transfer rate) of the coolant as well as the flow path.
This is BS.
Running without a restrictor is not a problem because the coolant will flow too fast, you want fast flow! That crap about it moving too fast to pickup heat is not true, it's a myth.
The problem with running restrictor-less is the water pressure inside the engine will drop. If the water pressure drops too low you will get hot spots, the water will boil around the exhaust ports and if you start getting localized areas with boiling those areas are not going to be cooled effectively anymore. You need pressure.
What you want is to balance flow and pressure, the higher the flow, the better, as long as you do not compromise pressure too much in the process.
Now I know this is going to get flamed, but here I will quote a pretty reliable source of information on the subject, I've quoted from this book on the forum before:
----
4 stroke performance tuning - A. Graham Bell, lubrication and cooling section page 300.
However, what if the engine was too hot on the first test with the 16mm restrictor If going t oa 19mm hole did not bring the temperature down and we were losing block pressure, we would have three options: a larger radiator, more pump speed, or a combination of both. Assuming that it was a hot day test I would go for more pump speed with a limit of around 6200 rpm. However, if the temperature was way up on a cold day, more pump speed might not get you out of trouble when the weather warmed up. Therefore a larger radiator might be the way to go.
Some of course would just go for bigger and bigger restrictors, or discard the restrictor altogether. This is not a good move; certainly the temperature gauge may come down to where you want it, but consider what is happening inside the engine. With no outlet restriction, water pressure in the block and head will be right down. With lowered water pressure steam pockets will form in the hottest areas of the engine. The combustion chamber, exhaust valve, and piston crown will then overheat, driving the engine into detonation. At this point hp will fall, and if the situation continues the engine will be destroyed.
An old wives' tale states that if you discard the thermostat or the restrictor the engine is damaged because the water is flowing through it too quickly to draw off excess heat, or it is flowing through the radiator too fast to give up its heat. This is not so; what causes the engine damage is insufficient water pressure to pack the coolant in tight around hot spots in the engine. Then any water that hits these hot spots dances about like water droplets on a sizzling barbecue plate without drawing off any heat. As the water boils off, the size of hte hot spot grows as a bigger and bigger steam pocket forms.
In reality we want reasonably rapid flow through an engine, as this tends to reduce the incidence of stagnant high-temperature pools. Additionally the rapid flow will scrub off gas bubbles as they appear in the hottest parts of the engine before they have a chance to congregate into an impenetrable steam pocket. In fact, the solution to cooling problems is not so much a matter of moving more water through an engine, as moving less more rapidly. This will pay large dividends in more hp and better engine reliability.
---
Smokey Yunick goes into this a bit also, but I don't feel like typing it out.
02-15-05 | 08:19 AM
#30
Originally Posted by pengarufoo
This is BS.
Running without a restrictor is not a problem because the coolant will flow too fast, you want fast flow! That crap about it moving too fast to pickup heat is not true, it's a myth.
The problem with running restrictor-less is the water pressure inside the engine will drop. If the water pressure drops too low you will get hot spots, the water will boil around the exhaust ports and if you start getting localized areas with boiling those areas are not going to be cooled effectively anymore. You need pressure.
What you want is to balance flow and pressure, the higher the flow, the better, as long as you do not compromise pressure too much in the process.
Now I know this is going to get flamed, but here I will quote a pretty reliable source of information on the subject, I've quoted from this book on the forum before:
----
4 stroke performance tuning - A. Graham Bell, lubrication and cooling section page 300.
However, what if the engine was too hot on the first test with the 16mm restrictor If going t oa 19mm hole did not bring the temperature down and we were losing block pressure, we would have three options: a larger radiator, more pump speed, or a combination of both. Assuming that it was a hot day test I would go for more pump speed with a limit of around 6200 rpm. However, if the temperature was way up on a cold day, more pump speed might not get you out of trouble when the weather warmed up. Therefore a larger radiator might be the way to go.
Some of course would just go for bigger and bigger restrictors, or discard the restrictor altogether. This is not a good move; certainly the temperature gauge may come down to where you want it, but consider what is happening inside the engine. With no outlet restriction, water pressure in the block and head will be right down. With lowered water pressure steam pockets will form in the hottest areas of the engine. The combustion chamber, exhaust valve, and piston crown will then overheat, driving the engine into detonation. At this point hp will fall, and if the situation continues the engine will be destroyed.
An old wives' tale states that if you discard the thermostat or the restrictor the engine is damaged because the water is flowing through it too quickly to draw off excess heat, or it is flowing through the radiator too fast to give up its heat. This is not so; what causes the engine damage is insufficient water pressure to pack the coolant in tight around hot spots in the engine. Then any water that hits these hot spots dances about like water droplets on a sizzling barbecue plate without drawing off any heat. As the water boils off, the size of hte hot spot grows as a bigger and bigger steam pocket forms.
In reality we want reasonably rapid flow through an engine, as this tends to reduce the incidence of stagnant high-temperature pools. Additionally the rapid flow will scrub off gas bubbles as they appear in the hottest parts of the engine before they have a chance to congregate into an impenetrable steam pocket. In fact, the solution to cooling problems is not so much a matter of moving more water through an engine, as moving less more rapidly. This will pay large dividends in more hp and better engine reliability.
---
Smokey Yunick goes into this a bit also, but I don't feel like typing it out.
Running without a restrictor is not a problem because the coolant will flow too fast, you want fast flow! That crap about it moving too fast to pickup heat is not true, it's a myth.
The problem with running restrictor-less is the water pressure inside the engine will drop. If the water pressure drops too low you will get hot spots, the water will boil around the exhaust ports and if you start getting localized areas with boiling those areas are not going to be cooled effectively anymore. You need pressure.
What you want is to balance flow and pressure, the higher the flow, the better, as long as you do not compromise pressure too much in the process.
Now I know this is going to get flamed, but here I will quote a pretty reliable source of information on the subject, I've quoted from this book on the forum before:
----
4 stroke performance tuning - A. Graham Bell, lubrication and cooling section page 300.
However, what if the engine was too hot on the first test with the 16mm restrictor If going t oa 19mm hole did not bring the temperature down and we were losing block pressure, we would have three options: a larger radiator, more pump speed, or a combination of both. Assuming that it was a hot day test I would go for more pump speed with a limit of around 6200 rpm. However, if the temperature was way up on a cold day, more pump speed might not get you out of trouble when the weather warmed up. Therefore a larger radiator might be the way to go.
Some of course would just go for bigger and bigger restrictors, or discard the restrictor altogether. This is not a good move; certainly the temperature gauge may come down to where you want it, but consider what is happening inside the engine. With no outlet restriction, water pressure in the block and head will be right down. With lowered water pressure steam pockets will form in the hottest areas of the engine. The combustion chamber, exhaust valve, and piston crown will then overheat, driving the engine into detonation. At this point hp will fall, and if the situation continues the engine will be destroyed.
An old wives' tale states that if you discard the thermostat or the restrictor the engine is damaged because the water is flowing through it too quickly to draw off excess heat, or it is flowing through the radiator too fast to give up its heat. This is not so; what causes the engine damage is insufficient water pressure to pack the coolant in tight around hot spots in the engine. Then any water that hits these hot spots dances about like water droplets on a sizzling barbecue plate without drawing off any heat. As the water boils off, the size of hte hot spot grows as a bigger and bigger steam pocket forms.
In reality we want reasonably rapid flow through an engine, as this tends to reduce the incidence of stagnant high-temperature pools. Additionally the rapid flow will scrub off gas bubbles as they appear in the hottest parts of the engine before they have a chance to congregate into an impenetrable steam pocket. In fact, the solution to cooling problems is not so much a matter of moving more water through an engine, as moving less more rapidly. This will pay large dividends in more hp and better engine reliability.
---
Smokey Yunick goes into this a bit also, but I don't feel like typing it out.
02-15-05 | 09:01 AM
#31
The mystery of the prize.
Joined: Aug 2002
Posts: 832
Likes: 2
From: Bay area
Originally Posted by KNONFS
Thanks for the tech info, now my question still remains, if there were hot spots, will it show on a gauge?
You're welcome.
And no, localized hot spots that are not right at the gauge sender will not show on the gauge. I imagine they will eventually though, after the hot spot has spread, if it gets bad enough to do that. There would be some damage by then though and I imagine pretty obvious overheating signs, boiling out of the overflow etc.
02-15-05 | 09:58 AM
#32
Originally Posted by pengarufoo
You're welcome.
And no, localized hot spots that are not right at the gauge sender will not show on the gauge. I imagine they will eventually though, after the hot spot has spread, if it gets bad enough to do that. There would be some damage by then though and I imagine pretty obvious overheating signs, boiling out of the overflow etc.
And no, localized hot spots that are not right at the gauge sender will not show on the gauge. I imagine they will eventually though, after the hot spot has spread, if it gets bad enough to do that. There would be some damage by then though and I imagine pretty obvious overheating signs, boiling out of the overflow etc.
A motor could be toasted because of hot spots, but they are hard (or almost impossible) to find
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