cooling issues..., fine when driving, spikes when stopped. Options

[malaga_red75]

subaru JDM EJ25 DOHC

So, got my conversion finally road worthy and have noticed that while I am driving around, the car stays at around 200 F. when i stop, or let it idle in my garage... the temp slowly climbs and doesnt stop (i shut it off around 230 F). I am assuming this is an issue with my fans.

I am running a front mounted radiator, using 2 push-style fans. A few things that i think may be wrong...

-There is no shroud around the fans... just the shroud that seals the radiator to the front (since they are push fans, they are mounted on the front side of the radiator, in between the radiator and the nose of the car)

- there is about a 1 1/2" gap between the fans and the radiator (this was just the way that ended up working for mounting the fans)

anyways, i am pretty sure that the cooling system is working (no kinked lines, thermostat working, fans do turn on) as indicated by driving and the temp staying cool, there is just something not working when i stop moving. let me know what you guys think.

-Peter

[BarberDave]

(IMG:style_emoticons/default/smilie_pokal.gif)

1st. Are you useing the same size radiator as in the Subby ?

If you are, it's not getting enought air thro it at idle,

fit a shroud,be sure all the air goes thru the radaitor,

use Water Wetter ,it works!

2 ed Try bigger fans, I would check fans to see whether there is a difference

In air flow if you use them as pullers. ( other side of radaitor. )

Good luck ,let us know Dave (IMG:style_emoticons/default/slap.gif)

[Mike Bellis]

First, you should pull the air not push. Second, i bet you have small pockets of air in your system. I would recommend you seal the system and pull a vacuum at the high point. This will force all the air to the vacuum.

When I do mine, I clamp off overflow tube on the expansion tank near the engine. Pull vacuum on the front for a few minutes. Take the overflow tube in the engine bay and put it in a bottle of water. Un-clamp the tube and the water will displace the air. Do this several times and all the air will be gone.

Mine runs at 150-160 on the freeway, 180-190 stoped.

[malaga_red75]

Dave,
I do have a shroud that feeds all the air through the radiator... there is just not a shroud that feeds all the air from the fans, which sounds like it may be the problem.





My radiator is not from the subaru, but has the same core dimensions as the subaru.

I will have to get all the air out as well. what did you use for a vacuum?

-Peter

[ArtechnikA]

First, you should pull the air not push.

Reference, please - 'cause everybody else in the world says it's easier to push a fluid than suck it...

[Mike Bellis]

First, you should pull the air not push.

Reference, please - 'cause everybody else in the world says it's easier to push a fluid than suck it...

Air from any fan modulates. It may feel like just air blowing but as the blade cuts through the air, the air modulates.

When you try to force air into a radiator, the surface design of the radiator will reflect the forced air molecules back on itself. This causes turbulence even before any air gets through the radiator. This action reduces the efficiency of the fan.

Fans react more to output turbulance than input turbulance. The energy is the motion of air molecules moving in space. If I pull air from the back side of the radiator, there is no more turbulance than if I run the fan in free air. The efficiency of the fan increases. Air will be pulled through the radiator at a greater rate than if I try to push it.

Have you ever tried to push a rope?

[ArtechnikA]

Reference, please - 'cause everybody else in the world says it's easier to push a fluid than suck it...

When you try to force air into a radiator, the surface design of the radiator will reflect the forced air molecules back on itself. This causes turbulence even before any air gets through the radiator. This action reduces the efficiency of the fan.

So that's 'no' then.

[Mike Bellis]

Fluid dynamics is different. Pushing or pulling fluid is dependent on priming the pump head. Most pump do not pull very good vacuum. If you place the pump closer to the source liquid, the pump will prime easier. No matter where you install the pump, it is pushing. If it's a fuel pump, it pushes fuel out the outlet. The inlet is the vacuum side. The fuel molecule has more mass and specific gravity than air. comparing a fan and a liquid pump is not a good comparison.

Liquid pumps will always work better closer to the source and pushing.

Fans will work better closer to the source and pulling.

If the radiator were the fuel tank, both would effectivly be installed in the same place, sending their energy the same direction.

[ArtechnikA]

published reference...

[EdwardBlume]

Impressive technical knowledge... I want to drink a beer with you guys! (IMG:style_emoticons/default/beer.gif) (IMG:style_emoticons/default/w00t.gif)

[Mike Bellis]

Impressive technical knowledge... I want to drink a beer with you guys! (IMG:style_emoticons/default/beer.gif) (IMG:style_emoticons/default/w00t.gif)

Any time Rob! I think I owe you one already (IMG:style_emoticons/default/beerchug.gif)

[DBCooper]

published reference...

That's hard to do because you can find published results supporting either or both, depending on how they're set up. There's an awful lot of research about fan cooling of electronics, for example, where there isn't any restriction on how things can be configured, push or pull. Those results are published and could be cited (let me know if you want a list) but they really aren't applicable for what we do.

For our cars the difference is often what's viable and what's not, and not what's theoretically better. In our cases, for example, we get forced air movement whenever the car is in motion and using a lot of energy, when the fan isn't needed at all. You COULD put the fan in front in push mode, but with the shroud that's required to make it cool efficiently at rest that would mean the shroud, along with the fan blades themselves, would be blocking some of the radiator's surface area and slowing down airflow. Or you could run without a shroud, like the Cobra replicas, but only at the risk of not having enough cooling capacity at rest or in stop-and-go traffic. So as a practical matter it makes more sense to pull the air from behind the main air flow, so air can pass through the full radiator surface unimpeded when in movement and only then be funneled through the fans. When the car's at rest you don't have all the cooling air originating from the round fan opening in the front of the shroud, in a pusher application, then being dispersed at much lower pressures through the larger radiator surface.

I don't want to argue anything, but whether pusher or puller is more efficient really depends on how the thing's configured.

For the original question I'd also guess there are air pockets that need to be exorcised. My car has a turbo motor with a very small opening in the front, and I've only heard the fans twice in use, both times in mid-summer after I'd come to a stop after thrashing it through the mountains. Renegade Chevy radiator, but it seems that all in all the Subaru motors are pretty efficient.

[malaga_red75]

So, I re-did the cooling system, bringing the fans to the other side and pulling the air. While I was doing this I also pulled the engine/tranny and fixed my tranny leak (a input shaft seal leak). I just finished putting the engine back in and connecting all the lines.

So, tomorrow I will be filling the system back up with coolant (and water wetter, thanks barberdave).

Can anyone give me a little more detail of how to get all the air out of the system.

-what did you use as a vacuum?
-where did you pull the air out?

I am using a pressurized burp tank system, i.e. there is no cap on the radiator. the pressurized cap is on the burp tank. The burp tank has an air bleed nipple, as well as the radiator. there is also a nipple on the crossover pipe, which I think might be the highest point in the system. Thanks!!!

sorry for the crappy cell phone pic, couldn't find my camera.

peter

[Mike Bellis]

I use a vacuum pump from harbor freight $70 and an air tank $35 that is converted for use as a vessel. Any velles will work so long as it keeps water out of the pump and does not cruch under vacuum. On my V8, I have a high point petcock in the front of the car. I have an expansion tank in the rear. If you do not have a high prtcock, try this...

You will need a clamp, visegrips will work. Fill the system with water and water wetter. once full, seal the system and pull a vacuum. At your expansion tank, use the vacuum to pull on the overflow tube. Use clear tubing to the vacuum pump. If the system is sealed, you should get very little water in your tube. Pull vacuum for a few minutes and clamp the overflow tube. Get a gallon of water ready and put the overflow tube into it. Un-clamp the tube, water should be drawn into the system. repeat the vacuum process and water fill process. after this is done several times you will get the air out. This will work even if the front is totaly sealed. Air will be drawn to the vacuum.

[Mike Bellis]

published reference...

I'm not sure what you mean here. I give this advice based on my experience with several modified cars. Including two 914 V8's and a VW Bus Rotary. if you would like to test my theory, go blow an a radiator. Not kidding. Put your lips on it and blow, you will feel the resistance. Now Suck on it, You will feel less resistance.

[Mike Bellis]

So, I re-did the cooling system, bringing the fans to the other side and pulling the air. While I was doing this I also pulled the engine/tranny and fixed my tranny leak (a input shaft seal leak). I just finished putting the engine back in and connecting all the lines.

So, tomorrow I will be filling the system back up with coolant (and water wetter, thanks barberdave).

Can anyone give me a little more detail of how to get all the air out of the system.

-what did you use as a vacuum?
-where did you pull the air out?

I am using a pressurized burp tank system, i.e. there is no cap on the radiator. the pressurized cap is on the burp tank. The burp tank has an air bleed nipple, as well as the radiator. there is also a nipple on the crossover pipe, which I think might be the highest point in the system. Thanks!!!

sorry for the crappy cell phone pic, couldn't find my camera.

peter

Looking at your picture, You may also want to consider making your fender outlet holes bigger. Your outlet surface area should be much larger than the inlet. This will help create a nagative pressure zone in the fender well. This will draw more air through the radiator.

[malaga_red75]

Looking at your picture, You may also want to consider making your fender outlet holes bigger. Your outlet surface area should be much larger than the inlet. This will help create a nagative pressure zone in the fender well. This will draw more air through the radiator.

ok, i will get to this tomorrow. Is there any ratio of the surface area of the radiator to the size of the outlet holes?

I will also add mesh material to not get rocks kicked up in there.

peter

[Mike Bellis]

Looking at your picture, You may also want to consider making your fender outlet holes bigger. Your outlet surface area should be much larger than the inlet. This will help create a nagative pressure zone in the fender well. This will draw more air through the radiator.

ok, i will get to this tomorrow. Is there any ratio of the surface area of the radiator to the size of the outlet holes?

I will also add mesh material to not get rocks kicked up in there.

peter

First figure out your surface area in/out. My outlets are 2-3 times your size. Very big. I'm not a math wiz so I won't try to calculate. Just make sure the oulet is noticably larger. This will make the inlet a high pressure zone and the outlet a low pressure zone. This will create natural confection to the low pressure zone. My setup is very similar to your latest picture. My radiator is slightly larger and tilted back. the top is shrouded like yours. My car runs at 150-160 on the freeway and 180-190 in traffic. My fans turn on at 180. I think maybe I run too cool sometimes. In the hot summer days, the car runs at 180 on the freeway.

[malaga_red75]

ok, i will make my holes bigger then take some measurements and publish them here. my fans turn on at 190. I am running an EMS stinger, so my guess is that I should be able to control when the fans turn on/off.

[malaga_red75]

So, yesterday I tried getting all the air out of the system. I indeed do have a air bleed nipple on the radiator in the front and I just jacked the front end up a little bit to make it the highest point in the system. I pulled a vacuum and followed your steps. I then took it for a drive. It helped, but the car still tends to slowly climb when Im stopped after driving. I am going to try again today with the vacuum and see if it will help.

any other ideas of maybe why it is overheating? cooling systems are really NOT my expertise, so I am kind of in the dark here. Thanks guys.

peter