external trans cooler: Series or parallel ?
 

Moving right along on this important topic!

I read that the earlier SVX stock coolers had some screen in them that would cause them to clog and prevent adequate ATF flow.

Do the later ones (my 1997) have that same potential problem or did they get rid of that screen at some point?

Depending on and with the feedback from ths post, I'm thinking about putting my external cooler in parallel with the stock one.

Or do I just go in series with the stock one?

Pros and cons appreciated!!

Thanks and Happy Holidays to all!

97s don't have the screen.

lots of opinions on parallel vice series. I run mine in series, thru the radiator first, then to a plate & fin cooler between the radiator and the A/C condenser.

I put mine in parallel: rationale – if the stock cooler in the radiator were to clog the transmission would still get cooling through the external cooler.

Bill

ALSVX:

What year is yours?

Do you have that potentially clogable screen in your stock cooler?

Without the screen ( as Lee says mine does not have ) how prone is it to a clog?

Mine runs parallel but this spring I'm changing it to serial. I'm not sure about this but it seems that splitting the fluid may reduce the pressure it may need to run efficiantly through the radiators.

I've had mine running parallel for a year and a half with no issue. The transmission runs reasonably cool.

Mike

One additional thing that most do is add a transmisson filter as well as the cooler. This not only helps keep the lines and screens from clogging, but give you an easy place to put a temerature gauge sensor.

Water has a better ability to cool the fluid than air flow, so that is why most use the radiator first, and then go to the add on cooler aferwards for additonal cooling. JMHO :)

both
 

put a 3-way valve near the cooler in the radiator. In the summer, run the external cooler only. In the winter, either run both or just the factory cooler to make the fluid warm up a bit faster.

Good Point.

I see that when the trans is cold it shifts a bit harsh (1-2), but smooth when warm.

That makes sense now.

I have my cooler installed by itself, bypassing the stock cooler entirely.

This is the first mention that I've seen of any kinf of 'screen' built into the stock cooler - and I have been here for awhile I suspect that you're confusing the external ATF filter, which was not installed on '92 SVXs. Maybe not. I've been wrong before. If I am and somebody can elaborate, I'd appreciate it.

My reason for bypassing the stock cooler was ATF flow rate. I wanted more efficient cooling, to be sure, but I didn't want the fluid to flow more slowly.

Nobody knows what setup works best for lowering the ATF temps in the SVX because nobody's tested them. Once I install my new transmission, I want to install a temperature gauge as well. I want to hook up the coolers in all four configurations and see which keeps the fluid the coolest.

If I actually get around to it, I'll let you guys know what I find.

gschabel,

You asked...

****ALSVX: What year is yours? Do you have that potentially clogable screen in your stock cooler? Without the screen ( as Lee says mine does not have ) how prone is it to a clog?****

I have two, a 94 L and a 96 LSi. Both are set up with external coolers in parallel.

I, like Mr. Pockets didn’t know there was a screen to clog? If there’s a screen, where is it? You would have to be able to replace or clean it, wouldn't you??? Now I’m paranoid…

Bill

I believe it was Harvey, at least he was the latest to, mention the inclusion of a brass mesh inside of the stock cooler in the radiator. The mesh is like an extremely coarse steel wool and helps dissapate heat. Unfortunately it also helps snag the larger pieces of friction material from the torque convertor that make their way downstream, thereby clogging the cooler and depriving the rear (if I remember correctly) clutch of lubrication.

I think most of those that have opted for a paralell installation have done so in case the cooler should happen to completely clog. Not the most efficient method, considering temperature and pressure drops, but it does allow for a bypass route.

BTW - there is also a screen in the transmission pan, serving as a filter. Rarely do tranny screens clog (those with real filters do, however), in my experience anyway, for whatever that's worth. I'm unsure if Subaru recommends a specific service interval for it, but I'd probably do mine around every 50k, mainly to see what's collecting in the pan.

Part of the concern with using the stock cooler was the high temperature that the coolant bath is at. Even if the 94-97's don't have the mesh in the cooler, they can still cool the tranny fluid no lower than the coolant temp which I recall being around 200 degrees.

I have bypassed the stock cooler and only run an aftermarket. Sometimes in the dead of winter, the torque converter doesn't lock up on the freeway, but at least its staying cool.

Doug

Parallel seems to be winning at the moment!

Perhaps I will install some bypass / shut off valve for those very cold days, or hot ones!

Sounds like the best cooling in hot weather would be to run JUST the aftermarket cooler and bypass the stock one. Do we all agree on that?

Someone mentioned pressure. Would parallel decrease pressure below needed flow psi?

Beav:

What is the recommended service replacement on the stock external filter they added in the later years? I believe that it is a canister type.

Thanks!

When you think of the temp of the engine coolant in the radiator don't forget that the A/T cooler is at the very bottom, the coolest point in the system. If you want to keep the engine below a certain temperature you need to supply it with coolant significantly cooler than the target temperature. It should be cooler than the fluid exiting the transmission, making the auxiliary cooler the icing on the cake.

I don't think they ever issued a service interval on the campaign filter. As cheap as it is I'd change it at 30k - 50k intervals. However, I don't use one, so... ;) BTW, the external 'campaign' filter was only for '92 & '93, I think, as all problems with the transmission were corrected by the '94 model year (supposedly and as far as Subaru was concerned.)

Regarding pressure drop, every item added to the system can cause a pressure drop. How much of a drop is an engineer's question. I suspect a series would fare better, but I'm not an engineer. How about it guys, strictly from a pressure drop point of view?