FrankGRUN

I've searched the threads here and on NAXJA and seen some similar problem descriptions but no clear solutions. Therefore, I hope to access the experience present here.

I have a '96 XJ Country 4Dr with 4.0L six, 4.5 inch lift, AX4 automatic, Dana 30 with Aussie Locker in the front, Dana 44 with posi-traction in the rear, solid Rusty bumper front and rear, brush guard in the front with KC spot lights and winch. The cooling system is stock with a clean-out and checkup by the local radiator shop, who pronounced the cooling system in excellent shape about 2,800 miles ago. I have a stock but new 195F thermostat, new heavy duty fan clutch, cold air intake, 99+intake manifold, 4-hole injectors, headers, new high flow water pump, 200+ amp alternator and 3.55 gears. I monitor the engine with an Ultra-guage along with the standard instrument panel gauges.

My problem is overheating on longer 1000+ foot elevation grades at 55 to 70 mph. Around town, long term idling, low speed off-roading in Death Valley and nominal highway cruising the engine runs between 204F and 214F with or without AC on. When I run up a long grade, starting at 60 mph and just under 2,000 rpm, the temperature climbs slowly up to 230-235F (2.2 mile long grade - temp climbs to 235 in about 2 miles). Over the whole climb, the transmission is seeking back and forth between 4th and 3rd. If I lock the trans in 3rd and hold the rpm to 2,000, the temperature will drop to 225 and hold steady. If I keep it in third and accelerate to 3000 rpm the temperature will go up to 235, at which point I will back off.

I just ran up the grade out of Bishop, CA on 395 at 70 mph in 4th, not watching the gauges, when suddenly antifreeze was spraying on the windshield. The gauge read 245F and I shut it down. Had to let it cool, then add two gallons of coolant and restarted with no apparent problem. Idle fine, low speed fine. I then tackled the grade again, this time at 55 and crested at 232F - no boil-over.

Checked the system with my mechanic. No hydrocarbons in coolant, no significant back-pressure in the exhaust system, no loose belts. His conclusion: I have two problems:

1. Running 33x12.5x15's with 3.55 gears puts a high load on both the engine and the transmission. The additional heating of the transmission pushes the cooling system over the edge and I have boil-over!
2. The winch, brush guard and KC Hi-lights are seriously blocking airflow at higher speeds, depriving the radiator of the amount of cooling air needed. He suggests this blockage reduces the cooling system margin, which then goes south with transmission heating and engine load from pulling the 33's with 3.55 gears.

His solution is to first re-gear the differentials to either the stock torque equivalent for the 33's of 4.11 or the often recommended 4.56. The 4.56 gears would have some hit on mileage but would put lots of torque on the ground. Then, he suggested going to a separate transmission oil cooler mounted in front of the radiator or with a fan and mounted elsewhere on the chassis. He also suggested a booster fan mounted to the front of the radiator to increase the airflow at at speed in high load conditions.

After reading so many threads about overheating problems, I'm inclined to re-gear to reduce the engine and transmission load and add a B&M super cooler (70274) transmission oil cooler with a Upgr8 12" electric pusher fan (2500 cfm) mounted to the radiator. However, I'm certain that many forum members have encountered this problem if its truly related to winch etc blockage of airflow and at the same time running 33's with stock gears.

Anxiously awaiting any insights and better suggestions as well as comments.

docmedpros

I would definitely go with a stand alone tranny cooler for the AW4, that helped me loads. As far as objects obstruction the flow, do your best to get as much air to that radiator

FrankGRUN

I've now checked into the under grill area more thoroughly and found that there is an auxiliary transmission cooler mounted in front of the radiator. it appears to be the factory auxiliary cooler supplied with the towing package. Looking at the radiator, the AC condenser is mounted directly in front of the radiator covering about 75% of the radiator inlet area. The tranny cooler is mounted in front of the AC condenser and covers about 75% or so of the width of the AC unit but extends about 1.5 inches above it. All in all, the tranny cooler really blocks the cooling radiator and is aligned right in front of the mechanical fan. The factory aux tranny cooler is an 8-pass tube and fin and should provide about 18,800 BTU of cooling. It is plumbed after the trans cooler line in the radiator heat exchanger. I'm going to remove the factory aux cooler and replace it with a fan assisted 25-row plate and fin cooler that I will mount front of the front crossmember and behind the shield of the front Rusty's bumper. This cooler is rated at 45,000 BTU cooling and the two 6"x4" openings in the crossmember should serve to vent the effective chamber formed by the cooler/fan package. I will regear to 4.56 this week and test for temp profiles before doing the cooler change.

All comments welcome.

macgyver35

In my opinion, your gearing is your biggest issue. 33's on stock gears make for a lot of additional strain, and thus heat.

I live in Texas and with an Or-Fab winch bumper with bull bar and an 18" LED light bar mounted on top of the bull bar, and my temps stay at 210 even in 100-105 degree heat with the AC on.

I've got 3.55's with a rear Spartan locker, but I'm running 235/75-15's, or roughly a 29"-30" tire.

You've already increased the strain by using stock gearing, and every few degrees of additional uphill grade just magnifies that strain exponentially.

I would go with 4.56's if I were you. I'm not sure where you heard 4.11's for 33's. I've been on this forum for a long time, and the general consensus (as well as the gearing math that has been posted) show you use 4.10's for 31 inch tires. 4.56 are recommended for 32"-33", and 4.88 are recommended for 33"-35".

FrankGRUN

I agree, it seems the primary problem is gearing! Today, I ran the Jeep in its 3.55 gear current configuration, but locked the transmission in 3rd (1:1 transmission ratio), up several different grades into the mountains around Lake Tahoe. This was the equivalent of a a axle gear ratio of 4.43. I ran the engine at speeds from 2500 to 3500 rpm and all times my UltraGauge display indicated an engine temperature of 204F. Downhill, the temperature fell to 197F. Ambient temperature was 62F.

I will go ahead with the fan assisted oil cooler between the front bumper and the crossmember, adding a temperature control for the fan set at 170F on and 160F off. Before todays test, I was concerned about the cooling capacity of the system and was going to mount the fan/cooler between the transmission and the radiator. Now, I intend to use the more traditional approach of between the radiator heat exchanger and the trans. I will also add a transmission temperature gauge to the port on the trans for monitoring.

After regearing, I will install the Extreme Triple Threat Fan system with shroud that I have had sitting in the garage unmounted. I had sent a note to this completely unresponsive company asking for a price to upgrade to their current fan controller (I purchased my set in March of 2013). They ignored me as many of you have said was your experience as well. I will use a reputable digital fan controller from Hayden instead of the one they supplied, together with 80-amp relays.

Finally, I will add the engine splash shield as a quick computer model shows that it will act as an air dam block at low speeds to effectively direct air flow through the radiator and block hot air from the engine compartment from being drawn into the front of the cooling system.