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How much does a radiator cool down the system?
- Thread starter riz
- Start date
The VAST majority of cooling is done by the radiator.
Why do you ask?
Why do you ask?
I know that......... I was just talking to another gear head guy at work and we were wondering how much of a temperature change the radiator actually makes....... What is the temperature range from the time it enters the radiator to the time it exits back to the engine? 30° ? 60° ? 10° ?
RIZ
RIZ
There is no set amount. It varies according to a ratio between the coolant temp vs the ambient temp of the air, modified by the amount of air flow.
With the added variables of coolant flow speed and volume, amount of and effectivness of wetting agents in the coolant, and insulating properties of dirt, dust, and other things coating the outside of the radiator.
The higher the difference between the coolant temp and the ambient air, the more heat will flow.
100 degree coolant with 85 degree air, will result in not much cooling.
240 degree coolant with 20 degree air, will suck the heat out big time.
With the added variables of coolant flow speed and volume, amount of and effectivness of wetting agents in the coolant, and insulating properties of dirt, dust, and other things coating the outside of the radiator.
The higher the difference between the coolant temp and the ambient air, the more heat will flow.
100 degree coolant with 85 degree air, will result in not much cooling.
240 degree coolant with 20 degree air, will suck the heat out big time.
it's not that much, take an IR gun to the in/out hoses on the rad... but in addition to Fordum's points, it also has to do with the fact it is a thermostatically controlled system.... the flow is controlled by the thermostat, which only allows it to get to a certain temp... it's not like it exits the motor at 250, and comes back in at 150...
another huge variable is what the motor is, it's cooling passage routing, cylinder construction (can we all say, 400 SB...) , etc, etc that effect how much and how fast it wants to nuke the coolant..
but in all automotive cases, I'd bet you wont see more than a 10% to 15% difference... now, come play on boats where everything is raw water cooled and I'll show you some funky #'s...
but even with that, a lot of the same principles still apply... surface area of cooling fins, ocean temp, therms, yada, yada......
I did as Paul mentions....My BBC with a wide 2 core Aluminum radiator had temps around 185 at the thermostat, and 90* at the bottom outlet...this was in a 70* shop, with both electric fans running.
hmmm, surprised it was that much....
My first draft had the thermostat in it, but I left it out. There is a large controversy about the effect of one, and I decided to not bring it in.
There can be little doubt that it sets the lower limit of engine temp, but there is a lot of discussion about it's effect on temps above its limit.
I have pulled thermostats out of engines in the past, and usually they take much longer to warm up, and in most cases, run at a lower temp.
In fact that was and is a favorite way to solve a cooling problem.
I personally have not run into an engine that ran hotter with the thermostat out, but some people I have reasonable trust in say that they have.
In one discussion I got into, I had an otherwise seemingly rational fellow assure me that the thermostat "set" the temperature that an engine ran at and if one was left out the engine was free to run at any temperature and might get so hot it would seize because there was nothing to tell it not to run that hot...........
I did not disagree with him.
He was happy, and had done nothing to me, so why should I destroy the delusions that made him happy?
Yet otherwise sober clear-eyed people that had never donned the feathers and run amok before, kept assuring me that they had removed the thermostat and the engine promptly overheated and was almost damaged but cooled off after the stat was put back in.
The theory I have heard to explain that is that without the stat, the water moves through the radiator too fast and does not have time to lose enough heat.
At first glance, this sounds rediculous. Sure if the coolant stays in the radiator longer it will lose more heat.
But, while that coolant is losing more heat, the coolant in the block is gaining heat, and one would think that it is doing so at a faster than the radiator is losing it.
However, I have since seen some studies where the flow rate was varied in an engine while all the other variables are held steady, and it seems that there is a sweet spot where you get maximum cooling.
Any slower and you don't get the heat out, and any faster the heat does not transfer to the air as well.
There can be little doubt that it sets the lower limit of engine temp, but there is a lot of discussion about it's effect on temps above its limit.
I have pulled thermostats out of engines in the past, and usually they take much longer to warm up, and in most cases, run at a lower temp.
In fact that was and is a favorite way to solve a cooling problem.
I personally have not run into an engine that ran hotter with the thermostat out, but some people I have reasonable trust in say that they have.
In one discussion I got into, I had an otherwise seemingly rational fellow assure me that the thermostat "set" the temperature that an engine ran at and if one was left out the engine was free to run at any temperature and might get so hot it would seize because there was nothing to tell it not to run that hot...........
I did not disagree with him.
He was happy, and had done nothing to me, so why should I destroy the delusions that made him happy?
Yet otherwise sober clear-eyed people that had never donned the feathers and run amok before, kept assuring me that they had removed the thermostat and the engine promptly overheated and was almost damaged but cooled off after the stat was put back in.
The theory I have heard to explain that is that without the stat, the water moves through the radiator too fast and does not have time to lose enough heat.
At first glance, this sounds rediculous. Sure if the coolant stays in the radiator longer it will lose more heat.
But, while that coolant is losing more heat, the coolant in the block is gaining heat, and one would think that it is doing so at a faster than the radiator is losing it.
However, I have since seen some studies where the flow rate was varied in an engine while all the other variables are held steady, and it seems that there is a sweet spot where you get maximum cooling.
Any slower and you don't get the heat out, and any faster the heat does not transfer to the air as well.
I also Paul, my temp gun works best when pointed at black surfaces, not silver or other shiny metals, so I pointed it at the rad hose where it connects to the thermo housing, and the bottom where it connects to the rad. And thats a Northern Rad. too, with the Windstar fans on it.
cdoggwsu
1/2 ton status
If the coolant is moving through the radiator too fast to lose the heat couldn't we also assume that it's moving through the engine too fast to gain enough heat to properly cool it?
That being the case it makes sense that the coolant in a system with no thermostat would run at a lower temp but then it's really not doing it's job as effectively because all the residual heat is now soaking into the mechanical components, oil, etc. In essence, the hotter the coolant temp the "cooler" the engine internals will be. I doubt that extra heat would truly be enough to seize an engine but I suppose it could lend some validity to the argument.
Possibly, but it gets complicated when you start comparing coolant flow through a radiator and coolant flow through an engine block.
Rad flow is fairly straightforward, has no internal turns or eddys, and in some cases approaches laminar.
Plus its just in and out.
Block flow twists, turns, and may circulate around the block before going into the rad. And is going to be turbulent.
Plus I am not sure that there is a set ideal amount of water in a rad vs amount of water in a block.
I'm sure that some radiators hold much more water than the engine they are cooling while some may even hold less.
So, on a straight GPM basis, the length of time a given molecule of water spends in a block vs the time it spends in a rad is going to be different.
Those are some of the problems with this subject, and the main reason all the discussions I have had on it wind up breaking down.
Too many variables, not enough data.
I'm quite sure that the data exists, water cooled IC engines have been around long enough for the experiments to have been done, but I haven't see much of the info, and its too much trouble for me to go in depth.
If I have an engine that is overheating in the application I am using it in, I just slap in a bigger radiator and/or fan.
I just let the data that is already known do my work for me. If I were to put a 351W on a dune buggy I was building, I would look up the radiator that engine used when put in a truck, and mount one of those.
No sense in reinventing the wheel.
Rad flow is fairly straightforward, has no internal turns or eddys, and in some cases approaches laminar.
Plus its just in and out.
Block flow twists, turns, and may circulate around the block before going into the rad. And is going to be turbulent.
Plus I am not sure that there is a set ideal amount of water in a rad vs amount of water in a block.
I'm sure that some radiators hold much more water than the engine they are cooling while some may even hold less.
So, on a straight GPM basis, the length of time a given molecule of water spends in a block vs the time it spends in a rad is going to be different.
Those are some of the problems with this subject, and the main reason all the discussions I have had on it wind up breaking down.
Too many variables, not enough data.
I'm quite sure that the data exists, water cooled IC engines have been around long enough for the experiments to have been done, but I haven't see much of the info, and its too much trouble for me to go in depth.
If I have an engine that is overheating in the application I am using it in, I just slap in a bigger radiator and/or fan.
I just let the data that is already known do my work for me. If I were to put a 351W on a dune buggy I was building, I would look up the radiator that engine used when put in a truck, and mount one of those.
No sense in reinventing the wheel.
Not really surprising. Just in normal fire up and making sure things are right on the race car I can barely touch the incoming water line to the rad. I can hold my hand on the outgoing water line easily. This is at idle one 16" fan running.
Never the less the bottom line is that you can calculate the temp loss in the rad. You just need to know; The makeup of the coolant, the speed of the coolant in the fins, the pressure of the coolant, the rad. material, the airflow across the rad, the temp of the air flowing across the rad., the incoming temp of the coolant, make some assumptions about the cleanliness of the rad. both inside and out and probably a few variables that i can't think of.
Then it's just a simple math equation from there.
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