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Ej255 Engine Cooling- With A/T


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I live in the desert and several times every summer my engine coolant temperature gets scary high (sometimes in excess of 230°F). When outside air temp >80°F engine and trans temps are usually fine. I have an automatic transmission with the oem radiator/trans cooler and an aux trans cooler installed in front of the AC condenser. I have tried cleaning the fins on every radiator up front with water and condenser cleaner numerous times and it barely made a difference (the rad is a relatively new denso unit).

 

I will soon be due for a coolant exchange and might as well just fix this perceived weakness now. Does anyone have a recommendation for a better radiator/trans cooler setup that will work in higher temp conditions?

 

I've scoured the search function pretty thoroughly and haven't found a satisfactory answer.

 

 

 

Any input appreciated and Happy New Years everyone!

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You could have air in the system or a blockage somewhere. I’ve heard radiator caps can also make a difference if it’s not working properly when the pressure exceeds the maximum.

 

If the coolant flush doesn’t help with your issues then I would look toward something mechanical failing such as a partially blocked heater core.

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I really doubt that there is air in the system. It only gets nasty when climbing a sustained grade for 10+ minutes regardless of calculated load, otherwise I could be driving the snot out of it and temps stay manageable.

 

Ac and heat work well and both rad caps are on proper and working, replaced last season while troubleshooting.

 

Forum member Bonbon had a similar story while climbing the rockies but his oem radiator is larger (m/t vs a/t). This seems more to me like a symptom of insufficient cooling capacity.

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I have a similar problem, which is made worse by the fact that I love in the foothills. If it is over 95° the car will get warmer than I like. His past summer I replaced the OE style radiator with an all aluminum Koyo which made it tolerable. This spring I will be adding an external oil cooler to help further.
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I had a similar issue with my OBXT with the AT trans. I never saw my cooling temp needle move unless I was heading up the canyon it would creep to just below the first line and then drop back down immediately after passing over the summit. I swapped my radiator out and refilled with Subaru super coolant and that seemed to help a ton. I found it happens only in low throttle boost situations. Eventually I’m going to swap in a Koyo aluminum radiator and an external trans cooler. But after emptying my old radiator completely and letting it sit overnight the weight difference between the new and old was considerable so I’m sure over time these units get some build up blocking cooling packages which doesn’t help.
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Could switch out the waterpump for the cast OEM style and make sure you use an oem thermostat along with oem radiator cap. If the A/T radiator isn't up to the task why not switch it out for the M/T or an aftermarket larger capacity and put a larger trans cooler on?
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If the A/T radiator isn't up to the task why not switch it out for the M/T or an aftermarket larger capacity and put a larger trans cooler on?

 

 

This really seems like the next step. I was hoping someone knew of a larger capacity oem style engine/trans cooler but this is probably what I'll end up doing.

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This really seems like the next step. I was hoping someone knew of a larger capacity oem style engine/trans cooler but this is probably what I'll end up doing.

 

I may not understand what you’re trying to say but why would you worry about transmission cooling when you have an engine cooling problem?

 

Either way, unless the radiator I had in my MT car was wrong I think it had the built in trans cooler. I’m actually surprised to hear that there might have been two different radiator sizes.

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Transmission loop through the radiator is more for temp equalization. In cold it brings it up to operating temp and while hot helps transfer that heat to atmosphere through the coolant.

 

I'm using the cast water pump and a second factory radiator, see no more than 210 over the Altamont grade. Usually 1 to 2 lb constant boost at 75 to 80 heading west bound.

 

The hardest grade for my car has been the I5 Grapevine, either direction you just need to back out of it and turn off the AC.

 

If you must, go with a bypass thermostat in addition to a external cooler with a Aluminum Radiator. This way you still have the ATF warming up in loop until it's up to temp and then routes more pressure through the cooler.

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I'm the original owner of a 05 5EAT LGT wagon with 127k miles. I have the exact problem, it started 3-4 years ago ( 5200 ft,only under load, 90+ degrees, inclines, I replaced the radiator & coolant this summer,still rises on these short 2-3 minute climbs. I can beat on it in the flats, 90-100 degrees I cannot get the temp to rise, crazy stuff.

 

I've been told it could be a head gasket, Blackstone oil analysis has come back clean too.

Probably need to have combustion leak test done!

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I'm using the cast water pump and a second factory radiator, see no more than 210 over the Altamont grade. Usually 1 to 2 lb constant boost at 75 to 80 heading west bound.

 

The hardest grade for my car has been the I5 Grapevine, either direction you just need to back out of it and turn off the AC.

 

 

I too am on my 2nd factory unit but unsure of the waterpump type that was installed. My temps climbing Grapevine have been 230+ on >1lb boost with no AC every time I hit it and while crawling up the pass. Last time I had to turn on the heat. I need to remedy this before the next time I go that way.

 

 

If you must, go with a bypass thermostat in addition to a external cooler with a Aluminum Radiator. This way you still have the ATF warming up in loop until it's up to temp and then routes more pressure through the cooler.

 

 

Thanks for that! I'm digging through the FSM but you wouldn't happen to know where I can find an AT fluid flow diagram would you?

 

 

 

I'm the original owner of a 05 5EAT LGT wagon with 127k miles. I have the exact problem, it started 3-4 years ago ( 5200 ft,only under load, 90+ degrees, inclines, I replaced the radiator & coolant this summer,still rises on these short 2-3 minute climbs. I can beat on it in the flats, 90-100 degrees I cannot get the temp to rise, crazy stuff.

 

I've been told it could be a head gasket, Blackstone oil analysis has come back clean too.

Probably need to have combustion leak test done!

 

 

In my case the car was doing this before my head gasket replacement and is still doing it afterwards. I believe this is a case of the oem radiator having insufficient cooling capacity for these demands.

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There was a heated (ba dum bump) discussion here a while back about ATF cooler sizes and how to fit them. Mainly in the nature of retaining the factory cooler ATF loop or not. Consensus was it's a good thing to keep even if there is another cooler loop added.

 

Let me see if I can find that discussion. As usual I'll just say Dave has been missed here (HexMod).

 

Edit: Here is the discussion. Understood this is a different discussion but the bypass loop option is about the only other thing we can do with a AT if the radiator is upgraded.

Using the bypass valve would at least give the car an opportunity to regulate added cooler need based on temp.

 

https://legacygt.com/forums/showthread.php/properly-plumb-your-5eat-transmission-cooler-221643.html?t=221643&highlight=ATF+Cooler

Edited by kzr750r1
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