A lot to unpack here, but here we go.
I picked up a 99 4.0. First drive it ran at about 220 for 3 hours straight. I popped the cap to check coolant condition...while it was still a bit warm and it puked brown orange coolant everywhere. Afterward, I could hardly drive the thing without it overheating. (Assuming I had air in the system after topping off with water) This being a replacement for my 94, I knew we deal with cooling issues and opted to do a full cooling system upgrade, as well as replaced the head due to the fact that the original head had so much rust scale in the coolant passages, and I had an extra 99 head on hand.
New set up includes:
Mishimoto Aluminum Radiator
OE mechanical fan and Aux fan
FlowKooler High flow water pump
Mishimoto 180° thermostat
Mishimoto 19 psi Cap
Mishimoto Radiator and Heater Hoses
I flushed the cooling system probably 7 times using Prestone Cooling system cleaner until the water finally started draining clear, and there was almost no scale on the drain plug magnet. Compression is 155-165 on all cylinders. No smoke. Engine oil and Trans fluids are clean. The last Prestone flush I ran for a couple weeks, and it was running probably 190 pretty solid. I even towed our pop-up camper a couple hours away and had no issues. It did creep up to 220 on the way back, but I somewhat expected it to do so with the 2000# trailer.
All was well until I went to swap the flush mix for 50/50 coolant mix. First drive it got right up to 220 under easy driving conditions and has been doing so on short drives since. Long drives bring on a boil. I would park on incline, let it cool and make sure that if any coolant was slurped from overflow it was restored to "Full", but this never got better....leading me to believe air in the system wasn't the issue. Today, when trying to make a 45 min drive in 75° weather, the temp gauge would get to 180 and then slowly creep to 220-225 and hang there till it would lurch and the "check gauges" light would come on (I'm assuming this is a safety feature built into later models intended to catch peoples attention). I knew what we were in for, so I grabbed a few gallons of distilled water while it was cooling down.
I let the overflow drink, we drive 10 min it boils over again, repeat. We drive 25 min it boils over again, repeat. By this point a significant amount of coolant has been left behind and replaced with water. Now, we drive home 45 min and ride at 210 while on the move, 215 while at stop lights, and it recovers to 210 when we get moving again.
This is telling me that this jeep doesn't like 50/50 coolant if I'm following the trends.
I have tried other things. Different thermostats/no thermostat with 50/50, resulting in overheat. Mishimoto Electric fans/shroud, overheated with these but ran fine when OE fans were swapped back in (I'm about to test CFM on these, because they felt nothing like 950 cfm EACH). It just blows my mind because I've covered all the bases (pressure tested and checked for combusion gases) and put some good parts in, but my 94 was rock solid at ~185 most all the time with nothing more than an "HD" radiator from the parts store...and I could even get away with the aux fan being dead during weather like today.
This jeep has been my nightmare, and I feel a bit bonkers saying the only way I can get it to run cool is by running all, or mostly water. What the heck?!
Thoughts anyone?
I picked up a 99 4.0. First drive it ran at about 220 for 3 hours straight. I popped the cap to check coolant condition...while it was still a bit warm and it puked brown orange coolant everywhere. Afterward, I could hardly drive the thing without it overheating. (Assuming I had air in the system after topping off with water) This being a replacement for my 94, I knew we deal with cooling issues and opted to do a full cooling system upgrade, as well as replaced the head due to the fact that the original head had so much rust scale in the coolant passages, and I had an extra 99 head on hand.
New set up includes:
Mishimoto Aluminum Radiator
OE mechanical fan and Aux fan
FlowKooler High flow water pump
Mishimoto 180° thermostat
Mishimoto 19 psi Cap
Mishimoto Radiator and Heater Hoses
I flushed the cooling system probably 7 times using Prestone Cooling system cleaner until the water finally started draining clear, and there was almost no scale on the drain plug magnet. Compression is 155-165 on all cylinders. No smoke. Engine oil and Trans fluids are clean. The last Prestone flush I ran for a couple weeks, and it was running probably 190 pretty solid. I even towed our pop-up camper a couple hours away and had no issues. It did creep up to 220 on the way back, but I somewhat expected it to do so with the 2000# trailer.
All was well until I went to swap the flush mix for 50/50 coolant mix. First drive it got right up to 220 under easy driving conditions and has been doing so on short drives since. Long drives bring on a boil. I would park on incline, let it cool and make sure that if any coolant was slurped from overflow it was restored to "Full", but this never got better....leading me to believe air in the system wasn't the issue. Today, when trying to make a 45 min drive in 75° weather, the temp gauge would get to 180 and then slowly creep to 220-225 and hang there till it would lurch and the "check gauges" light would come on (I'm assuming this is a safety feature built into later models intended to catch peoples attention). I knew what we were in for, so I grabbed a few gallons of distilled water while it was cooling down.
I let the overflow drink, we drive 10 min it boils over again, repeat. We drive 25 min it boils over again, repeat. By this point a significant amount of coolant has been left behind and replaced with water. Now, we drive home 45 min and ride at 210 while on the move, 215 while at stop lights, and it recovers to 210 when we get moving again.
This is telling me that this jeep doesn't like 50/50 coolant if I'm following the trends.
I have tried other things. Different thermostats/no thermostat with 50/50, resulting in overheat. Mishimoto Electric fans/shroud, overheated with these but ran fine when OE fans were swapped back in (I'm about to test CFM on these, because they felt nothing like 950 cfm EACH). It just blows my mind because I've covered all the bases (pressure tested and checked for combusion gases) and put some good parts in, but my 94 was rock solid at ~185 most all the time with nothing more than an "HD" radiator from the parts store...and I could even get away with the aux fan being dead during weather like today.
This jeep has been my nightmare, and I feel a bit bonkers saying the only way I can get it to run cool is by running all, or mostly water. What the heck?!
Thoughts anyone?