NA radiator with Turbo engine, cap question

THAWA · Post by **THAWA** » Tue Mar 22, 2005 9:49 pm

So I'm just about to get started on this whole thing and I wanted to make sure I had everything I needed before I did. As has been explained before in other threads I'm going to use the turbo tank, and find a barbed fitting to go where the bleed screw is on my Na radiator. However what to do about the radiator cap on the radiator? One the newer turbo engines there is a cap on the radiator and on the expansion tank. The cap on the radiator is rated for a higher opening pressure. I assume that is to keep it as a sealed place in normal conditions, but will still work for bleeding the air, because if the top cap is opening as less of a pressure it should release the pressure before the lower cap gets close to its threshold. The newer engines have the caps rated at 108kPa for the expansion tank and 137kPa for the radiator. Our radiator caps are rated for 88kPa. So my question is, what pressure cap should I put on the radiator? Should I use a 108kPa, or a 137kPa? The increase of pressure between the 108 and the 137 is about the same as it would be between 88 and 108, so I'm thinking that might be the right descision. Then again it might be better to have a cap with a higher rating to prevent it from trying to open when I don't need it to. Of course I wonder though, does it even matter what pressure the radiator cap is at if the tank cap will be opening at 88 kPa anyway? I can't understand what situation there would be where the radiator cap and the tank cap would both open. Then I also wonder if I should go up in pressure some and use the 108 for the tank and 137 for the radiator. Honestly though I don't completely understand the reasoning behind using a higher pressure but I think it has something to do with the boiling point. Anyway, what are your guys thoughts on this? Should I do 88 and 108, 88 and 137, or 108 and 137?

evolutionmovement · Post by **evolutionmovement** » Tue Mar 22, 2005 11:46 pm

I'd go with the higher rated caps. Your cooling system is going to have more heat to absorb now and Subaru figured those pressures for the turbo so I'd go with it and not have to worry about it. Good to know the cap ratings, though. Thanks.

Steve

Post by **Legacy777** » Wed Mar 23, 2005 1:05 am

Hardy, can you explain the whole bleed screw thing, or point me to a thread that does?

I hadn't really heard about that.

I'm basically in the same boat as you. I have a relatively new n/a radiator, so I would like to use it.

As for the radiator cap, the cap's there to release air/pressure if there is any, and also allow the coolant a place to go as the temperature increases & decreases.

Pressure should be the same at both the radiator & coolant tank. Personally, I wouldn't increase the pressure in the system by putting higher caps on. It was designed to run at that pressure, and if you allow it to get higher then what it was designed for, you could get leaks or rupture something.

With water, as pressure increases, boiling point increases. This is the reason most systems are pressurized. It's possible that the newer systems are actually undersized when compared to ours if you were to run them at the same pressure.

As long as you're running a decent 50/50 mix, and water wetter wouldn't hurt, you should be fine. I was contemplating looking into NPG+
http://www.evanscooling.com/main25.htm

I was looking at the diagram for the cooling system for the turbo, and to be quite honest......I don't see why you couldn't eliminate the line that runs from the coolant tank to the resevoir. You already have a line that goes from the radiator to the resevoir. Just put a higher pressure cap on the coolant tank, then you do the radiator. That will ensure that the radiator cap always opens and vents into the resevoir.

Thoughts?

THAWA · Post by **THAWA** » Wed Mar 23, 2005 2:51 am

I forget the thread but basically you take one of these:

and put that where the bleed screw is. That would then go to the expansion tank.

I'm thinking the reason there is a radiator cap on the radiator of new turbos is to create a seal when in normal use. It doesn't have a nipple on the side of it like a regular radiator cap. So if it were the same pressure as the coolant tank it would open just like the coolant tank cap right? But if you make it a higher pressure you can keep the cap there and have it not open up on you when the coolant pressure is up. I'm pretty sure its only purpose to to bleed air out of the system when changing the coolant, like the na cars used to have a bleed screw.

That makes sense about the pressures, but I was under the impression the new turbo radiators were fairly large ones.

That NPG+ sounds cool, do you know if it's compatible with any cooling system?

I see that too, but I'm either going to have to cap the expansion tank nipple, or cap the radiator tank nipple and the radiator nipple sounds like a better idea. Or I could get one of the 91-94 overflow resivoir caps that have the extra nipple in the cap and connect that to the radiator nipple. Why would you want to have a higher pressure cap on the coolant tank than the radiator though? If you get air in the cooling system above the radiator it would get trapped there because the pressure wouldnt be enough to open the tank cap. Does that make sense?

Post by **Legacy777** » Wed Mar 23, 2005 3:40 am

Why bother putting the fitting on the bleed screw since the highest point is the coolant tank? The turbo setup doesn't have it.

yeah, you're right about the coolant caps.

Not sure why the new systems have a higher pressure then.....you got me.

I'm not super familar with the NPG+ stuff. I've just known about it from some other people doing engine build-ups. As I get closer to finishing things, I'll research the specifics more closely.

You're right, since the coolant tank is the highest point, that'd probably be the best spot to put vent line. However if you bleed the system well, and don't get your temps above the boiling point, you shouldn't really have any air in the system. Especially if you do decide to use the NPG+ coolant.

The reason I wanted to use the vent line on the radiator is because it cleaned things up a little bit more.

vrg3 · Post by **vrg3** » Wed Mar 23, 2005 4:19 am

The simplest way to go is to leave the burp screw where it is.

Connect the burp fitting on the filler tank to the nipple on the neck of the radiator's cap with 5/16" fuel hose. Then rip out the small lower rubber gasket of the radiator's cap.

This will effectively render the radiator's cap inert, providing a path for air trapped at the top of the driver's side of the radiator to travel into the filler tank to be burped out. You can burp the passenger side using the screw as usual.

THAWA · Post by **THAWA** » Wed Mar 23, 2005 4:35 am

The Turbo setup does have a fitting on the right side of the radiator, where the NA setup has the bleed screw. It flows right to the expansion tank.

Connecting the radiator to the expansion tank through the nipples would get rid of the overflow tank right? Why not connect from the pipe that the turbo radiator usually goes to?

vrg3 · Post by **vrg3** » Wed Mar 23, 2005 4:46 am

THAWA wrote:The Turbo setup does have a fitting on the right side of the radiator, where the NA setup has the bleed screw. It flows right to the expansion tank.

Yes, that's correct.

Connecting the radiator to the expansion tank through the nipples would get rid of the overflow tank right?

No, you still keep the expansion tank -- it connects to the nipple on the filler tank's cap.

Why not connect from the pipe that the turbo radiator usually goes to?

I don't understand.

THAWA · Post by **THAWA** » Wed Mar 23, 2005 4:52 am

What are you considering the burp fitting?

vrg3 · Post by **vrg3** » Wed Mar 23, 2005 4:55 am

The burp fitting on the radiator is whatever is in the upper passenger side corner of the radiator. On a turbo it's a hose barb, and on a non-turbo it's a threaded hole plugged by the burp screw.

The burp fitting on the turbo's filler tank is the 7.5mm nipple on the back of the tank that has a built-in check valve only permitting flow into the tank.

THAWA · Post by **THAWA** » Wed Mar 23, 2005 7:03 am

Okay, I see what you're saying.

mhrallyteam · Post by **mhrallyteam** » Wed Mar 23, 2005 2:22 pm

What i did :

Installed STI rad cap on remote coolant tank.

Removed pressure relief system in radiator cap and leave it there.

Thats it

Post by **Legacy777** » Wed Mar 23, 2005 3:25 pm

Vikash,

You said, "Connect the burp fitting on the filler tank to the nipple on the neck of the radiator's cap with 5/16" fuel hose. Then rip out the small lower rubber gasket of the radiator's cap."

So you're saying connect the burp screw/fitting on the pass. side of the radiator to the filler neck nipple on the radiator?

vrg3 · Post by **vrg3** » Wed Mar 23, 2005 3:32 pm

mhrallyteam - Which cap did you remove the pressure relief from? The STi one on the tank or the regular one on the radiator? It seems to me that to go the two-cap route you'd want to put the STi cap on the radiator and use a regular cap on the filler tank, leave both caps intact, and tee their overflow fittings together to go into the overflow tank.

Josh - No... I'm saying to leave the burp screw on the radiator alone. I'm saying to connect the filler neck nipple on the radiator to the small nipple on the back of the filler tank (after removing the lower gasket of the cap on the radiator).

Post by **Legacy777** » Wed Mar 23, 2005 3:38 pm

What does the small nipple on the back of the filler tank normally connect to?

THAWA · Post by **THAWA** » Wed Mar 23, 2005 3:51 pm

The fitting on the right side of the radiator. Follow the tube on your engine backwards from the expansion tank, it will have a rubber tube which leads to a plastic pipe that crosses the intake manifold, or maybe it's metal, which leads to another rubber tube, which goes right to the radiator.

vrg3 · Post by **vrg3** » Wed Mar 23, 2005 5:39 pm

Right. It's a metal pipe and two rubber hoses connecting it to the barb at the burp area of the radiator.

Project_Legacy · Post by **Project_Legacy** » Sun Mar 27, 2005 7:30 am

dang. pictures would say a thousand words rite now. haha.

thats a lot of useful info that i will need as well. but i dont quite follow it all. heheh i guess ill figure it out if i keep reading it over and over.

vrg3 · Post by **vrg3** » Mon Mar 28, 2005 10:04 am

Here we go:

http://www.graphics.cornell.edu/~v/pics ... ooling.png

That shows most of the turbo-specific stuff in the cooling system.

THAWA · Post by **THAWA** » Mon Mar 28, 2005 4:22 pm

For clarifications sake, I was incorrect about the new turbo radiators. The radiator cap does have a bleed line like an NA radiator, it tees into the line coming from the expansion tank and flows to the overflow tank.

Project_Legacy · Post by **Project_Legacy** » Wed Mar 30, 2005 7:52 am

thanks for the pic vrg3. very helpful.

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NA radiator with Turbo engine, cap question

NA radiator with Turbo engine, cap question