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

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

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.

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.
Click to view attachment

Click to view attachment


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

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?

So that's 'no' then.

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.

published reference...

Impressive technical knowledge... I want to drink a beer with you guys!

Any time Rob! I think I owe you one already

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.

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

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.

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.

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.

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.

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

sent you a PM

You say the temps climb when at idle, if you idle up the engine to let's say 2000 - 2500 rpm and hold it there does it start to cool down? if so then you are not pumping/flowing enough water at idle speeds. I sort of see this effect with my V6, it doesn't over-heat at idle but will cool down a bit if the idle is brought up.

yes, this does happen. If i hold the rpm up it does start to cool down. maybe the thermostat isn't opening enough?

and mine will and does begin to overheat at idle if the rpm's are not brought up.

You must not be moving enough coolant if you need to idle the motor up. I tried the stock 02 wrx radiator in my 914 and it will not fit standing up inbetween the headlight boxes, course it's not a crossflow, it needs to be layed in at a angle that uses much more space. you are not making wrx power though so what you have may work. Are you sure the fans are turning the right direction? I think I read where the exhaust openings need to be 30% bigger than the inlet of the radiator. You can google it. If you use several 90 degree bends in the coolant lines you will get more restriction in the system and you will need bigger diameter lines to overcome the flow restriction. There is is a chance the thermostat is not seeing the bypass flow subys require to send the hot coolant to the thermostat to make it operate right. The stock suby has a heater, a oil warmer/cooler, and the reservoir bolted on the intake the third bypass to the thermostat thats what makes it open and close properly.

When it's idling open the hood and see if it cools ok.

I'm not sure how well you know subys but they do blow headgaskets pretty easy if they get hot very often.

I am running a 1996 era 2.5l N/A so, i was comparing my radiator size to that of a 1996-1998 legacy.

Yes, the fans are turning the correct direction. when the turn on, i can feel the air being pulled into the front trunk.

I do know about the headgasket issues, especially with the series motor. I actually do think this might be a possiblity because after driving it one day, i came back, let it sit for an hour, went and fired it up, and a big plume of white smoke came out the exhaust. Will a bad headgasket cause it to overheat at idle, and not while moving?

-Peter

(p.s. Mike (kg6dxn) stopped by yesterday in his sweet 914 -8 and we talked about cooling systems, we talked about different ways of getting the air out of the system, and finding a good high point to pull a vacuum from. Thanks Mike!!)

In my case, it'd idle all day just fine and overheat within 10 minutes on the road.
I'm not saying your scenario isn't possible, 'cause I donno - but I did have the Subie bad head gasket issue. Idle fine, overheat on the road...

You could try the the Bong method to get the air out and water in to teh cooling system the Bong is a tall pipe, maybe three feet, of PVC pipe, maybe 2 inches diameter, it is attached to the top of the filler hole via a rubber plumbing sleave with two hose clamps to make a tight seal to teh Bong. the bong can now be filled with coolant, becuase of teh tall sixe of teh bong, it will give the filler head pressure to help force air out.

this works great on a vanagon, which are well known for trapping air no need to jack up the van nor hybrid 914 with the bong.

the bong idea is compliments of the samba.


for my 914 Buick car, before I had the bong, I used a steep, very steep driveway to help get the radiator higher and got the air out, took several trys


give the bong idea a try, cheap and easy to make, and it does work very well on vanagons which have simular probelms with high spots trapping air.


good luck

I had the exact same problem in 2 of my sub conversions. And both turned out to be a stock subie thermostat that opened up a very small amount and very very very slowly. Take your stock subuaru thermostat out, go buy a cheap aftermarket one, boil some water in a big shallow cooking pan that is high enough to cover both thermostats completely in the water and watch the reaction time of both.

I guarantee the stock subaru thermostat has a slow reaction time and gets suck from time to time. Air bubbles are not that hard to burp.

Oh also the other thing I messed up with on my first subaru conversion is that I eliminated all recirculation lines except for to the turbo and back to the water pump inlet. This isn't sufficient and it causes extremely high temps when stopped combined with the slow opening thermostat.

One way to test if it's thermostat or non enough recirculation lines is to gut out the thermostat and run it gutted wide open but with the rim still there so it will seal.

Best setup was to run a new thermostat whichever brand but new, with one small hole in it to let some air pass buy but definitely small or else it will cool too much in the winter.

That will test if your front radiator is enough and if cruising at highway speeds it should run cold if now at 160 degrees all day in 70 to 80 degrees weather. That's what mine does with thermostat gutted.

So, your saying literally drill a hole in the thermostat to allow flow even when the thermostat is closed? I just want to make sure I understand this right before I go about drilling holes. Thanks budman.

This is what I was thinking too, I actually just called Kohlweiss to see if they had thermostats. I am kind of thinking this might be it because of the fact that I have now pulled vacuum several times from several ports in the system. And also that when revving the engine (forcing more water through the engine) it cools down. Off to kohlweiss to pick up the thermostat and gasket! Ill keep you guys posted.

-Peter

well, new thermostat installed. no change... well, id say maybe a 5 degree difference while driving, now around town I am probably steady at around 195-200 moving a littler faster it drops to around 185-190. stopped, it goes to about 215. my local shop said that they can sniff for hyrdocarbons at the radiator and determine if there is exhaust leaking into the cooling system. I will be doing this on tuesday morning.

One other note:

I have been reading online and on other forums and it seems that normal engine operating temperatures are between 180-220. But most of you guys say that you are running between 150-160 while driving. just curious what some thoughts are on this.


-Peter

having temp fluxuations is fairly common with a conversion car. Some go as far as removing the thermostat. Removing it will keep the tamps more consistant, instead of up/down. It will take longer to warm up in the winter if removed. Since everybody has a different cooling system, even with the same engine. It's hard to say exactly why you have a problem. I could be as simple as you needing a new water pump. There are electric in line pumps that can be fitted if flow is your problem.

Since your car does not overheat while moving, your problem is either flow or air. 90% of the time it will be air. When you have all the air out, the problem is flow. Here's where it gets tricky. You can have a problem with both too much and too little flow. Too little, the water does not get cooled fast enough and hot water is returned to the engine. Too much and the heat exchanging effect will not work and hot water will be returned to the engine. At this point, you should try removing the thermostat and see if it helps. This should increase flow. If the system cools down, your system has too little flow. If the temp goes up, you may have too much flow. At that point try to pinch the hose aome to restrict flow. I would suspect too little flow is your problem.

To cure to little flow... Remove thermostat... or... Inline Water pump... or... Smaller pully on the water pump... or... larger pulley on the crank. Also look for any natural restrictions in your hose, kinks, bends etc...

one question, how many return lines do you have that recirculate water around the engine when the thermostat is CLOSED?

What happened when you did the boiling test with thermostats ? old vs. new?

the basic design of the water pump housing on a subaru needs ALL these recirculation lines so the Tstat will open. It has cool water trying to enter the Thermostat from the inlet and hot water on the inside of the thermostat. If the hot water is NOT recirculating around the inside side, the thermostat will try to open and then close itself once cool water has entered.

With ALL recirculation lines intact, which i think on your N/A motor there are two inlets. The tstat will always have a hot supply of water to stay open if hot.



On my first conversion i was like, cool i will clean up the way the engine looks,etc. So i eliminated all these recirculation lines, heater ,etc. which was a major fault.

budman-

First, when i did the tstat test, the new thermostat opened much quicker than the old. However, once both were open, they looked like they had opened the same amount. so, despite realizing that the thermostat was fine, I installed the new one anyways.

re: recirculation lines
I guess my answer is that no, I do not have any return lines to the engine while the Tstat is closed. My expansion tank is connected to the heater return line (just on the inside of the thermostat) and then there is the incoming radiator line on the outside of the thermostat.

Basically, I fill the system via gravity through the expansion tank into the heater return line... then the fluid goes through the engine, out to the radiator, then back to the thermostat.

So, how would I setup the system to have a recirculation line? If I used the heater return line, say connected to a port at the top of the crossover pipe, where would I run my expansion tank?

I only know of 1 recirculation line, which is just on the inside of the heater return, which is where my expansion tank is currently hooked up. where is the second?

Thanks budman, I know you know your subaru stuff. especially cooling, living in AZ.

-Peter

IMO a blown head gasket would be much worse under load and show the least troublesome with no load (Idle, coast etc). If your not getting enough flow at idle, bring the rpm up to 2k. I would assume you have done this, you sound like you have done your homework ! I have found most often with cooling problems that have you scratching your head end up to be a radiator issue..

I have thought about this too, and realized that my radiator might be to small. although I am running a engine from a 96 era subaru, I am making about 40 more HP due to the EMS stinger. I am thinking that I may need a new, bigger one. but I don't want to do this until I sort out any other issues, because well, re designing the front shroud is a little more time intensive than some other fixes.

-peter

Peter YOU NAILED IT! congrats! Get that recirculation line back and your problems will be SOLVED!!

There should of been two tubes that go to the stock subaru heater core when it was in the stock subaru car. These are at the rear drivers side of the engine when you have the subie in the 914. Just put those back, put a loop so basically you loop the coolant back to the thermostat. Whatever way you get the top manifold on the engine (hot water) to loop back and feel to the inside engine side of the thermostat is the route. You can T into this line for your expansion tank. When flowing it will just run past your T in the line and back to the water pump. The T in the line will be good for filling and expansion to the overflow etc.

here is a stolen pic from STI progress thread. shows the route of a turbo recirculation lines. You just need the one the runs from the manifold top and back down the top of the block, through the front area of the engine and to the water pump.

Cool, I think I understand. I actually removed on of the pipes, but the other one (the one that comes directly off the crossover pipe) will work just fine. I will get a T fitting, and basically run from there down to the tstat and have it T off up to the expansion tank.

But will this help after the tstat is open? Or are you saying that because there is no circulation, it is constantly trying to open then close then open...etc.?

-peter

budman, i got your message, i might call you tomorrow, but i think i got it figured out.

well, I think (fingers crossed) that the cooling system is finally working properly.

As budman mentioned, I did not have any return lines to the thermostat while it was closed. So today, I bought a T valve and some more lines and ran a return line from the heater output on top of the crossover pipe down to the thermostat where it Tee'd off to my expansion tank. Took it for a test drive and the temp stayed at or below 180 the entire time. When I came to a stop, it rested at 185, and thats only with one fan pulling right now (i broke the other one, idiot mistake). so THANKYOU budman for the answer. Thanks to Mike as well for coming down and helping me get the air out of my system.

Hopefully this will be it and I wont have to burp the system again.

-Peter

Awesome! Now put that thing back together and drive it like you stole it.h

SWEET! cool, anxious to see now where your temps stay at during idle and cruising around with both your fans working and that radiator. I bet your fine!

Once you are positive the system works perfect ( a few weeks worth), the thermostat with the holes isnt really needed. Mine is Stock Aftermarket with no holes in AZ. After 3 Subaru stock ones sticking during my various engine swaps, only cheap Autozone ones for me.

so, as the ultimate test for my cooling system, I brought my car to school with me ( Chico) where the days temps are in the 90's and sometimes into tripple digits. I drove it yesterday and while driving the temp is about 178ish... and when I stop it goes to 190. So I think when I get my second fan in there it will drop to around 185.

-Peter

Awesome!

SWEET!

I guess you also don't have the oil filter cooler/heater bypass lines on the na motor? subaru designed the suby to mainly be a snow car and the idea of the bypass was a lot of trouble to design but it is for more consistent cooling and heating year round. The ideal street car motor temp is to keep the oil and motor about 200 degrees, as quick as possible, that keeps the moisture boiled off the oil and keeps the oil at it's designed viscosity to get everywhere as fast as possible and to keep the motor parts at their correct tolerances to prevent cold start wear and tear. At 20 degrees oil gets real thick and slow so the bypass lines kept the warm coolant around the motor until it warmed up, and out of the radiator, including warming the oil filter.

The importance of bypass lines on subys has been discussed since subys first were put in other street cars. Outback my not use bypass lines on sandrails though.

Donno about conversions...
My EJ25D had one, and our 3,0 six has one.
When used with a block heater in the winter, the oil comes up to temp in a flash. Nice.