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Engine and tranny overheating...sometimes...

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Chrisja77

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Discussion starter · #1 ·
I'll start off with a little background on the rig. It is a 95 YJ that has a powertrain from a mid 90's Z71 swapped in (TB 350, 700R4, 241) running D60's and 42's. It also has an aluminum radiator and the tranny is not plumbed into the radiator. It has 2 aux coolers stacked on top of each other with a shroud around them and an electric fan blowing up through them. The tranny coolers are under the rear of the tub close to the front of the rear axle. When driving on the trail or around town the engine and tranny temp stay between 190 and 210 all day long...pretty good. When you hit highway speeds of over 45 for any extended time, the tranny will start to overheat. I have autometer gauges in it and 250 is as high as they go...I stop when it gets close to there. You can stop the tranny from overheating by shifting into 3rd and leaving it there, but then the engine tries to overheat. I'm assuming because of the additional RPM's, but it's still not that bad...under 3,000. When you slow down, the engine will start to cool down but the only way to get the tranny to cool off is to stop and let it chill out. What am I overlooking or where do I need to start looking?

tranny coolers:

Image
 
#2 · (Edited)
The air is being pushed so fast at higher speeds that the fan cannot suck the air upward and cool the tranny. Angle it! And that location is kinda scary to me, hopefully you never break a rear u-joint.
How do you have the coolers stacked? Which one is closet to the fan, supply from tranny or return to tranny? It might seem like a dumb question but one could actually counteract the other.

And for engine heat, are the fenderwells still in original form?
 
Discussion starter · #3 ·
rockbuggy84 said:
The air is being pushed so fast at higher speeds that the fan cannot suck the air upward and cool the tranny. Angle it! And that location is kinda scary to me, hopefully you never break a rear u-joint.
How do you have the coolers stacked? Which one is closet to the fan, supply from tranny or return from tranny? It might seem like a dumb question but one could actually counteract the other.
Click to expand...


They are ran where the supply from the tranny is on the top and then it goes to the lower one. I haven't even thought about the angle, but it makes sense when you mention it. I'll see about angling them towards the front. I don't guess it will take much of an angle to make a difference. Also hadn't thought about location much.:homer: I guess I need to go back to the drawing board on this one, huh? :D

Also, one of my friends mentioned a manual lockup for the torque converter. I am running 5.13 gears and he is thinking that I'm not turning enough RPM's at highway speed for the torque converter to lock itself up.
 
#6 ·
I would try dropping the back of the cooler at least 1-2" and see if that makes a difference. Also do you have the computer hooked up through the brakes system etc? Or is it a stand alone system? The reason I ask is if you are hooked the computer through the brake switch driving down the highway barely tapping the pedal will tell the computer you trying to slow and the converter will unlock and rpms will jump a little. An easy way to verify its locking up.
 
Discussion starter · #7 ·
rockbuggy84 said:
I would try dropping the back of the cooler at least 1-2" and see if that makes a difference. Also do you have the computer hooked up through the brakes system etc? Or is it a stand alone system? The reason I ask is if you are hooked the computer through the brake switch driving down the highway barely tapping the pedal will tell the computer you trying to slow and the converter will unlock and rpms will jump a little. An easy way to verify its locking up.
Click to expand...


I didn't do the swap, so I'm not 100% if the computer is hooked up, but I would say no because when I tap the brakes nothing happens. I had a 98TJ with the 3speed auto before, it had the lockup torque converter, so I know what you are talking about. This one doesn't do that.
 
#11 ·
Your electic fan move X amount of airflow, we will say 500cfm(just a made up #) And the air at 65 mph is we will say 1000cfm (once again i am giving these for examples) the fan is going to fight the 1000 cfm because it wants to run at 500. This is why we have fan clutches and the old style solid mount would flex at high rpm and loose their pitch.
 
Discussion starter · #13 ·
Makes sense. I'll get a switch wired up inside so I can kill the fan and try it that way. I'm gone for work, it's gonna be a couple of weeks before I get home to try it out, but that could be at least one easy fix...maybe 2 if angling and moving the trans cooler works also. Any suggestions on where to move the coolers to? I don't want them in front of the radiator for obvious reasons, and now you've made me nervous about where they are at! LOL Also, you haven't mentioned it, so I'm assuming they are correct, but they are plumbed correct, right?

Appreciate the help!
 
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rockbuggy84
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