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turbo timer/coolant flow analogy

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4K views 21 replies 8 participants last post by  lobsterhat  
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#1 ·
For Cosmo and anyone else who is interested, I tried to come up with a good analogy describing why coolant continues to circulate after the engine is off, thus supposedly cooling the turbo.

Think of a jar of bees; the bees represent the coolant, the jar represents the coolant system around the turbo, the atmosphere represents the rest of the coolant system, and there's a hand shaking the jar that represents the hot turbo.

When the engine is running, the hand is shaking the jar very fast(very hot turbo), making the bees very angry and because the water pump is circulating, all the bees around the jar are angry as well(hot coolant system). Once the engine shuts off the bees outside the jar begin to calm down quickly and fly around slowly(cooler radiator, etc), while the ones in the jar continue to be shaken and remain angry,flying around recklessly(turbo is still hot). Some of the angry bees find their way out of the jar and out into the atmosphere, so they too calm down, however, the jar must have the same amount of bees at all times, (because the coolant system is a closed system) so when an angry bee flies off, a calm one is sucked into the jar(water continuting to circulate). When the calm bee is sucked in, it becomes shaken and angry too, and then in time also makes it way out of the jar sucking in another calm one and so on and on. Eventually the hand gets tired of shaking the jar(turbo cooling), and all the bees are able to calm down and rest where they are(cool turbo and coolant system, no longer circulating).


I dunno if this is actually going to make any sense, it's about 2am right now, but hopefully in the morning I won't feel like a fool. ;)
 
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#3 ·
The hotter water molecules are not happy being near the turbo when there are colder molecules around them. They're more moving around with more velocity than the colder molecules, and they 'pass' the colder ones as they travel away from the turbo. Again, because this is a closed system, as the hotter molecules travel away from the turbo, they are replaced by molecules from elsewhere in the system. These molecules then absorb some of the heat from the turbo, speed up, and then 'pass' their surrounding molecules as the leave the turbo. This would go on until there isn't enough heat left in the turbo to heat the molecules to the point that they would have enough velocity to travel through the system.

I'm not really sure what people think when they say that vaporized coolant is more effective, other than maybe it represents faster moving molecules and thus a faster moving system.

Here's another example I just thought of: When you heat a pot of water on the stove, does only the water that's closest to the pot get hot? No, all the water heats up, because as the molecules near the metal get hot, they become more active and move to a cooler area, and are replaced by a set of cooler molecules. Ever heard the term 'rolling boil'? The water is cycling in order to try and reach an equilibrium. I know when I cook something I don't use a water pump. ;)

And finally, I really doubt that this movement of the water after the car is off is going to be enough to effectively cool the turbo. I'm not trying to post in order to say people don't need a turbo timer, but am just trying to outline the physics involved. :)
 
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#5 ·
Well I know that the new Bugatti Veyron, Hennesey Dodge Viper 800TT, and a TT Ferrari F50 all have turbo-timers on-board, now it might just be me but I think those companies might know a thing or two. Plus while your analogy makes sense (in Physics class it's called convection) and that works fine in a room full of bees or a pot of water, but in a intracate piping system I doubt that the coolant has complete freedom to move, this would envolve the coolant "falling" to the turbo (cold water sinks) and other coolant "rising" to take it's place, i doubt it has the room to do this. Plus it's cool to have someone (after a white knuckle ride of course) get out of your car and tell you that you that your car's still on, and then you show them the keys (maybe that's just me).
 
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#6 ·
Yes I know that these examples aren't completely analogous to the coolant system in our cars. I'm not trying to sell people on whether or not they should or shouldn't have a turbo timer. In a few other threads this arguement has taken place, and Cosmo has stated that he didn't see how the water could circualte w/out the pump running, so I tried to lay it out in some other terms. I absolutely agree that a turbo timer is a great thing to have. And plus I used a lot of polysyllabic words. :p
 
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#9 ·
sumdumgoy said:
This could be a potentially nice thread. I'm very interested to find a final understanding from all of this.
Click to expand...
The only real way to come up with a definitive answer as to whether or not a turbo timer is overkill or not on a stock wrx would be to have 2 cars, one with, and one without a turbo timer. Drive them exactly the same way, same miles, same weather, etc., and see if the one without a turbo timer experienced greater turbo wear than one with. This is not even really possible, and from a scientific point of view, there are FAR too many variables for say, my car and your car to be compared. I only wrote this thread in order to demonstrate how the water continues to circulate to some extent. The convection of heat, to make skiingjohn happy. ;)

Like Cosmo has been preaching, the best thing is to spend $100 and just have the insurance and piece of mind that a turbo timer will bring you. Not to mention the very real possiblity of longer turbo life.
 
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#10 ·
Agreed....but we all know that test will never happen.

I think I mostly just wanted to learn something out of the different explanations people provide. I don't fully understand the process and thought I might get some good info. I'll keep reading!! ;)
 
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#11 ·
Here's what Subaru themselves has to say on the issue, as of 2001:

"2002MY WRX TURBO COOL DOWN PROCEDURE
FHI's position regarding this is that it is not necessary to perform a "cool down/idling" procedure, as was recommended with past turbo models. Our current 2.0L turbo engine has a far greater cooling capacity and, coupled with technology advances, makes this practice no longer necessary. This explains why information about cool down is not included in the 2002MY Impreza Owner's Manual.

The heat contained in the turbo charger will begin to vaporize the coolant at the turbo charger after the engine is stopped. This hot vapor will then enter the coolant reservoir tank which is the highest point of the coolant system. At the same time the vapor exits the turbo charger, coolant supplied from the right bank cylinder head flows into the turbo. This action cools the turbo charger down. This process will continue until the vaporizing action in the turbo charger has stopped or cooled down."

http://www.subaruwest.com/PDF_files/Tech_PDF_Folder/june_2001_techtips.pdf
 
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#12 ·
I know this is a bit off topic but I have two questions. In my manual, it says when the coolant needs a bit filled up like when it is around the low level, it doesn't say exactly where to fill it up, so I am guessing just in the tank where the min and max lines are. Is that right? Because when changing the coolant it says to fill the coolant by the upper radiator cap by the intake manifold.

Also what kind of coolant should I put in. I know it should be 50% soft water and 50% coolant but can I just buy the mix already made? If not would I just mix it with tap water from my house that is softened?
 
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#14 ·
T WREX said:
Here's what Subaru themselves has to say on the issue, as of 2001:

"2002MY WRX TURBO COOL DOWN PROCEDURE
FHI's position regarding this is that it is not necessary to perform a "cool down/idling" procedure, as was recommended with past turbo models. Our current 2.0L turbo engine has a far greater cooling capacity and, coupled with technology advances, makes this practice no longer necessary. This explains why information about cool down is not included in the 2002MY Impreza Owner's Manual.

The heat contained in the turbo charger will begin to vaporize the coolant at the turbo charger after the engine is stopped. This hot vapor will then enter the coolant reservoir tank which is the highest point of the coolant system. At the same time the vapor exits the turbo charger, coolant supplied from the right bank cylinder head flows into the turbo. This action cools the turbo charger down. This process will continue until the vaporizing action in the turbo charger has stopped or cooled down."

http://www.subaruwest.com/PDF_files/Tech_PDF_Folder/june_2001_techtips.pdf
Click to expand...
Subaru says that because they don't sell turbo timers. Again, the vaporized coolant thing. Vapor is hotter than liquid, therefore not being able to cool as well. Subaru proved my point for me.

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#15 ·
Yes, water cools better than vapor, but they're not saying that the vapor is what's cooling the turbo. What they're saying is the the vapor leaves the turbo and goes to the reservoir, in turn drawing liquid from the cylinder head into the turbo. This liquid is then heated, changes to vapor, leaves the turbo and draws in more liquid from the cylinder head. The turbo is cooled by liquid, not vapor.
 
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#17 ·
IBAUCLAPla said:


Do you know where I should buy it from (Scooby dealer?)? Also any idea on where to pour the coolant to top it off.?
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Dude, go to VIP, Autozone, Pepboys... whatever it is that you have in your town and buy some anti-freeze. This is not going to be that complicated. Dump it into the reservoir, not the radiator, close the hood, and call it a day.
 
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#20 ·
The real question here, in my opinion, is not whether or not the water continues to cool the turbo after the engine is off, but how MUCH the water cools off the turbo after the engine is off. When the turbo is no longer hot enough to vaporize the coolant, is it still hot enough to cook the oil that remains? Cooking the oil is the problem that is trying to be avoided with a turbo timer if I'm correct. I have no idea at what temp coolant will stop being vaporized, what temp the oil is getting cooked and building up within the turbo, etc. Due to the lack of these figures, again I reiterate, I agree with Cosmo that a turbo timer is a cheap, easy, effective way to insure against premature turbo problems.
 
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#21 ·
I would say that someone with a temp gun and a turbo timer should do an experiment. Drive a certain distance and then turn off the car (no timer) and check the temp of the turbo over some period of time, then when the outside temp is the same do the same thing and have the turbo-timer set to 1 or 3 minutes (or whatever yours is) and check the turbo temps periodically again. That would solve this once and for all, I'd do it if someone wants to hook a brotha' up with a temp gun.!Thumbs Up
 
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