Toyota FJ Cruiser Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
671 Posts
Discussion Starter #1
Anyone with an AT install an electric cooling fan in front of the radiator or install a seperat transmission cooler? Been on a few beach trips where the AT transmission oil temp HI light came on. Thinking about installing something to help keep the transmission oil cooler to avoid damage from hight temps.
 

·
Premium Member
Joined
·
18,479 Posts
The light actually came on when I was playing in a lot of snow. I had snow up to my axles when this happened. Do you think the coolers would help? :) I stopped as soon as it happened, but was surprised to see the light given I was practically dragging the bottom side through the snow.
 

·
Registered
Joined
·
656 Posts
I haven't done that much dragging in the snow and never had the Hi temp light come on. In my case it was more breaking a trail through hard spring snow in low range. Air temperature was high but I wasn't pushing snow with the bumper. Mostly undercarriage and gas tank.
Is it possible that snow had accumulated enough to block air flow in front of the cooler? Was your engine temp OK or was it climbing too? I've read on this forum where enough mud can accumulate to cause the engine to heat up, maybe that was something similar here.
An auxiliary cooler for the auto's is never a bad idea.
 

·
Premium Member
Joined
·
8,285 Posts
Anything that stresses the torque converter (mostly slipping it a lot) will elevate the ATF temperature. I got my light to come on running (and stalling on) super-steep Wipeout Hill in Moab in moderate temperatures in the fall. The stock "cooler" is more of a regulator than a cooler, since the radiator runs near the thermostat temperature of 190-210 degrees. An external cooler will exchange a lot more heat because it is exchanging with ambient air temperature not radiator temperature.
 

·
Premium Member
Joined
·
18,479 Posts
My engine temperature was OK, only the trans light came on.
 

·
Registered
Joined
·
5,495 Posts
If nothing else you are also adding fluid capacity with a trans cooler. Just that in itself will help cool things down as well. If I had an AT this would have been one of my first mods. :cheers:
 

·
Premium Member
Joined
·
8,285 Posts
My engine temperature was OK, only the trans light came on.
yep, that's the problem of putting the stock transmission "cooler" in the engine radiator - it can never cool the ATF more than the difference between the ATF temperature and the radiator, which runs a little below the thermostat temperature of 210 degrees. With an aftermarket heat exchanger, you have a much greater delta T available between the ATF temperature and ambient air temperature.
 

·
Premium Member
Joined
·
18,479 Posts
yep, that's the problem of putting the stock transmission "cooler" in the engine radiator - it can never cool the ATF more than the difference between the ATF temperature and the radiator, which runs a little below the thermostat temperature of 210 degrees. With an aftermarket heat exchanger, you have a much greater delta T available between the ATF temperature and ambient air temperature.
Do you have any links? I'm not understanding how one cooler (radiator type) differes from an "exchanger". Is it more or less a heatsink desgin that will also hold more oil?
 

·
Premium Member
Joined
·
8,285 Posts
Do you have any links? I'm not understanding how one cooler (radiator type) differes from an "exchanger". Is it more or less a heatsink desgin that will also hold more oil?
I think the terminology is getting us mixed up Tony. A radiator is just a specific kind of heat exchanger. In the context of automotive applications, to cool the engine, crankcase oil, ATF, power steering fluid, or whatever you need a fluid medium to transfer the heat away from whatever it is you're trying to cool, and something with a lot of surface area away from the item to be cooled, so that the heat can be exchanged or bled-off into the surrounding air. For automotive applications, that heat exchanger is always something with fins soldered to the fluid tubes, to give it more surface area to shed heat into the atmosphere. For any of these to work, there must be a temperature difference between the item to be cooled and the surrounding air. The greater that difference in temperature is, the more efficient the heat exchanger will be and the more cooling capacity it will have. Fortunately, all the things we want to cool in a truck are usually much warmer than the surrounding air, so the various heat exchangers have enough temperature difference to work.

A radiator uses water (and anti-freeze) as a fluid medium to transfer heat away from the engine, to the radiator, and there to be exchanged with the air. The stock thermostat in the FJC opens at 180 degrees F, so the radiator is open to flow above that engine temperature, and will exchange engine heat with the atmosphere, through the air moving across the fins on the radiator. If the air temperature is relatively low, then the delta-T between the hot engine water and the air is great and the radiator works efficiently. If the air temperature is hot like in Death Valley or the southern Arizona summer, then you have a lot less delta-T to work with and the radiator is not nearly so efficient. That difference in temperature (delta-T) is extremely important in a radiator.

The other common kind of heat exchanger in an automotive application is just some tubes with cooling fins soldered on the tubes, inserted somewhere in the oil/fluid line. These use the fluid being cooled itself as the fluid medium for heat exchange, and exchange heat directly with the atmosphere instead of using water as an intermediate heat transfer step. Examples are power steering fluid coolers and auxiliary engine oil and ATF coolers.

So the reason why an auxiliary ATF cooler will do a better job than the stock cooler in the radiator is just the greater delta-T between the temperature of the hot ATF in the transmission and the air, versus the temperature of the ATF and the radiator. The radiator is already close to 180 degrees to begin with before you ever start trying to shed heat from the ATF into it, while the ambient air temperature is going to be quite a bit less than 180 degrees no matter where you are. The ATF temperature is supposed to be between 115 and 130 degrees F, so if the radiator runs above that temperature, it is not going to take any heat out of the ATF until the ATF gets hotter than the radiator. In fact, it will transfer heat into the ATF if the radiator is hotter than the ATF. That's why I said that the stock ATF "cooling" system in the radiator is more of a temperature regulator than a cooler.

Sorry for the lengthy explanation - does that make more sense now, or am I not understanding your question?
 

·
Registered
Joined
·
671 Posts
Discussion Starter #11
So you think a seperate ATF cooler would be more efficient than an electric fan in front of the stock radiator. Would installing both be overkill?
 

·
Premium Member
Joined
·
8,285 Posts
So you think a seperate ATF cooler would be more efficient than an electric fan in front of the stock radiator.
In my opinion, yes. As long as you put the separate ATF cooler in a place where it will get plenty of fresh air flow.


Would installing both be overkill?
Again IMO, yes. A second (electric) radiator fan would help the radiator efficiency especially at low speed, crawling and idling - but because of the thermostat, the radiator is always going to be "cooling" at something close to 180 degrees no matter how many fans are blowing through it. You'll get a lot more actual ATF cooling with just an aux. cooler.
 

·
Premium Member
Joined
·
18,479 Posts
Thanks. I guess I just had the confusion of where the ATF cooler may be located.
 

·
Registered
Joined
·
90 Posts
Modern automatic transmissions are ran into the radiator for a reason, to keep the fluid at a constant viscosity that the transmission can pump. Ideally the tranny fluid should be at 200 deg F. to be at Ideal viscosity. Adding a cooler is fine but you should always keep the radiator cooler in the loop, preferably on the return side of any added cooler. Over cooling transmission fluid can cause as much damage to a transmission as over heating it.
 

·
Registered
Joined
·
671 Posts
Discussion Starter #15
In my opinion, yes. As long as you put the separate ATF cooler in a place where it will get plenty of fresh air flow.




Again IMO, yes. A second (electric) radiator fan would help the radiator efficiency especially at low speed, crawling and idling - but because of the thermostat, the radiator is always going to be "cooling" at something close to 180 degrees no matter how many fans are blowing through it. You'll get a lot more actual ATF cooling with just an aux. cooler.
Thanks for all the input. Thinking I'll go for a cooler. Hoping I can find one small enough to fit in the limited space yet affective. I've had the AT temp light come on enough and know I'll continue to expose my FJ to more situations that it will come on. I wish I could figure out a way to bypass it when I knew it was not needed.
 

·
Premium Member
Joined
·
8,285 Posts
Thanks for all the input. Thinking I'll go for a cooler. Hoping I can find one small enough to fit in the limited space yet affective. I've had the AT temp light come on enough and know I'll continue to expose my FJ to more situations that it will come on. I wish I could figure out a way to bypass it when I knew it was not needed.
Just do what Fedaykin said and leave the stock radiator loop in the line; that will regulate it and keep it from getting too cool, but the aux. cooler will still dump extra heat if it gets above the radiator temp.
 
1 - 16 of 16 Posts
Top