New Turbo coolant tank option potential
05-10-2014, 10:48 PM
#1
Racer
Thread Starter
New Turbo coolant tank option potential
Hey Rennlisters, I've been working on this little project, and I think this could be useful to everybody here who feels like $285 is a bit much for a new coolant tank... Basically, I'm graduating next week with a degree in polymer science engineering and I feel like with my experience with plastics, I should be able to design something to get around paying that much for a glorified piece of polypropylene.
tl:dr: I'm going to spend $130 on a nonturbo tank, and put an extra brass fitting on it with some sealant and save $150. I'll let you know how it goes.
Heres the issue with the discoloration, obviously much of the problem comes from the accumulation of grit on the inside of the tank - this can be cleaned off with the coffee ground method, or really sloshing around anything that can abraid the inner surfaces of the tank. However, the root of the issue is that the plastic is degrading from the heat. polymers are very susceptible to unfavorable reaction kinetics between the molecules when exposed to heat and UV in particularl. It is through a similar process that they get brittle. but basically these side reactions which often result in chain scission. This causes a decrease in molecular weight, and a resulting decrease in toughness. (molecular weight of a polymer is the difference between the polyethylene used for garbage bags and that used for hip implants.) These side reactions also cause browning in the presence of oxygen and other chemicals.
Essentially the material itself is degrading from the inside out. I cut a piece out of my ballooning tank to show the cross section. See how it's more brown on the inside (right) than on the outside (left)? Disregard the white on the left side of the piece, that is chain crystallization due to when I broke the piece off.
So what are the issues with buying a used tank? it will get old (obviously). A new tank while still inherently full of these issues will last another 20 years.
What are the issues with adding a port to a nonturbo tank? ($135 instead of $285)
-it must hold pressure (15 psi)
-it must be able to withstand the force of a stuck hose being pulled off
-it must not expand or contract much more than polypropylene
-it must be thermally and chemically stable
This is what I have found:
With a 1-inch spade drill bit, this fitting will screw right into the side (or top) of the coolant tank.
The fitment is secure enough that it will not move no matter how much force I put on it, and just based on how tight it threaded in, will likely withstand the pressure by itself. When I put it on the new tank I will use Permatex ultra grey around the edges just to be safe.
The CTE of brass is 1.7-2.07x10^-5%/degC
The CTE of polypropylene is 1.22-1.8x10^-4 %/degC
different by a power of 10, but considering this will only experience a temperature swing of roughly 150degC, this is insignificant.
Brass is thermally stable up to 800degC, so no issues there, and is chemically stable in both water and ethylene glycol.
I'm going to buy the new tank and have it shipped to me within the week, and will be posting updates to the process as I go. Stay tuned, the car is currently out for a few more weeks with a burnt valve, so I won't get to test this new tank for a while for those of you who will be waiting around eating popcorn to see how this turns out.
tl:dr: I'm going to spend $130 on a nonturbo tank, and put an extra brass fitting on it with some sealant and save $150. I'll let you know how it goes.
Heres the issue with the discoloration, obviously much of the problem comes from the accumulation of grit on the inside of the tank - this can be cleaned off with the coffee ground method, or really sloshing around anything that can abraid the inner surfaces of the tank. However, the root of the issue is that the plastic is degrading from the heat. polymers are very susceptible to unfavorable reaction kinetics between the molecules when exposed to heat and UV in particularl. It is through a similar process that they get brittle. but basically these side reactions which often result in chain scission. This causes a decrease in molecular weight, and a resulting decrease in toughness. (molecular weight of a polymer is the difference between the polyethylene used for garbage bags and that used for hip implants.) These side reactions also cause browning in the presence of oxygen and other chemicals.
Essentially the material itself is degrading from the inside out. I cut a piece out of my ballooning tank to show the cross section. See how it's more brown on the inside (right) than on the outside (left)? Disregard the white on the left side of the piece, that is chain crystallization due to when I broke the piece off.
So what are the issues with buying a used tank? it will get old (obviously). A new tank while still inherently full of these issues will last another 20 years.
What are the issues with adding a port to a nonturbo tank? ($135 instead of $285)
-it must hold pressure (15 psi)
-it must be able to withstand the force of a stuck hose being pulled off
-it must not expand or contract much more than polypropylene
-it must be thermally and chemically stable
This is what I have found:
With a 1-inch spade drill bit, this fitting will screw right into the side (or top) of the coolant tank.
The fitment is secure enough that it will not move no matter how much force I put on it, and just based on how tight it threaded in, will likely withstand the pressure by itself. When I put it on the new tank I will use Permatex ultra grey around the edges just to be safe.
The CTE of brass is 1.7-2.07x10^-5%/degC
The CTE of polypropylene is 1.22-1.8x10^-4 %/degC
different by a power of 10, but considering this will only experience a temperature swing of roughly 150degC, this is insignificant.
Brass is thermally stable up to 800degC, so no issues there, and is chemically stable in both water and ethylene glycol.
I'm going to buy the new tank and have it shipped to me within the week, and will be posting updates to the process as I go. Stay tuned, the car is currently out for a few more weeks with a burnt valve, so I won't get to test this new tank for a while for those of you who will be waiting around eating popcorn to see how this turns out.
05-11-2014, 01:19 PM
#2
Burning Brakes
That looks like a good way to save some money. In my experience, the brass hose barbs are sharp and grip hoses too tight, to the point where it's almost impossible to remove a hose without cutting it off. It might grip so tight that the brass barb might pull out of the tank and ruin it if you try to pull the hose off. To help with this issue I like to dull the barbs with a wire wheel, sanding wheel, or just file them down a little. There's still plenty of grip and it seals just fine with a regular hose clamp.
05-12-2014, 12:05 PM
#4
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I am assuming that you don't know that there is a check valve in the coolant connection that goes to the turbo coolant pump. So just adding a conection to an NA tank will not get you the same result.
BTW - if you still want to go that route I have used a straight thread AN fitting w/rubber Oring to adapt AN lines to coolant tanks, that works well.
BTW - if you still want to go that route I have used a straight thread AN fitting w/rubber Oring to adapt AN lines to coolant tanks, that works well.
05-13-2014, 06:40 PM
#5
Racer
Thread Starter
Hmm. Maybe the two tanks that I have had have had that piece taken out? As far as I can tell there's nothing in there. Which direction does the coolant flow through this port anyhow?
09-26-2014, 01:22 AM
#7
Three Wheelin'
Agreed, $285 is a lot for a piece of plastic, especially when considering the 951's role as a "budget" Porsche.
However, the damn things last 25-30 years!!! That seems like a pretty good value proposition to me. I don't have a degree in plastics, but whatever material the '80s 944 expansion tanks are made out of works very well. The same cannot be said of modern Boxster/996 or later Porsche expansion tanks, or any BMW or Audi tanks from the last 20 years or so.
I just replaced the original expansion tank of my 8/85 production date 951 late last year. It went 27 years and 155K miles, with 10K+ of those miles being on track. It wasn't even leaking, it was starting to bulge and I didn't trust it. The new shiny white tank really dresses up the engine compartment as well!
They also give you a LOT of warning before failure (discoloration/bulging). They don't fail suddenly and dump all of the coolant out as in many modern cars. Also 944 cooling systems don't run nearly as hot as those of modern engines, which helps.
However, the damn things last 25-30 years!!! That seems like a pretty good value proposition to me. I don't have a degree in plastics, but whatever material the '80s 944 expansion tanks are made out of works very well. The same cannot be said of modern Boxster/996 or later Porsche expansion tanks, or any BMW or Audi tanks from the last 20 years or so.
I just replaced the original expansion tank of my 8/85 production date 951 late last year. It went 27 years and 155K miles, with 10K+ of those miles being on track. It wasn't even leaking, it was starting to bulge and I didn't trust it. The new shiny white tank really dresses up the engine compartment as well!
They also give you a LOT of warning before failure (discoloration/bulging). They don't fail suddenly and dump all of the coolant out as in many modern cars. Also 944 cooling systems don't run nearly as hot as those of modern engines, which helps.
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09-26-2014, 06:38 PM
#9
RL Community Team
Rennlist Member
Rennlist Member
Could one put a tee on the NA tank's single port to create two ports? I'm sure the answer is no because the flow would be all wrong.
Maybe a tee can be added somewhere else, where the flow would work?
Maybe a tee can be added somewhere else, where the flow would work?
09-26-2014, 07:23 PM
#10
Intermediate
I have done this with a brass fitting from home depot. I even place a brass nut on the inside with a socket mounted on a l shaped Allen key. It worked for me except for the fact that the forward placed fitting on the na is placed further back then the tank for the turbo making the forward hose kink in order to line up with it.