Renix Engine Coolant System Updates

[CBJeeper]

I have issues with my 1990 Wagoneer overheating as I climb grades when in warm weather despite a recent coolant system flush and fill. The previous owner was diligent in maintaining this Jeep, but I do not have a full history of what had been serviced. I decided that the best approach would be to start by replacing all the heater hoses. The radiator hoses and water pump look to be recently replaced, so I am going to assume that they are OK for now. The heater hoses look darned good, but are likely original and I want fresh. I also installed a new Gates 195 degree t-stat and drilled a hole at 12:00 o'clock. Felpro gasket. This is all complete. I ran the Jeep today and let it idle until hot. My temp gauge showed roughly 225 F when I finally shut off the engine. The aux electric fan never kicked on. Now, I can tell you that the electric fan absolutley kicks on when I turn on the AC. My first question- Does the electric fan operate autonomously from the radiator temp switch when running the AC? If you were going to start replacing parts, would you start with the gauge temperature sending unit (it looks original) or go for the fan switch on the radiator? I am leaning toward the gauge sending unit. When I do climb grades and show temperatures of as high as 265 degrees, I do not seem to be boiling over. When I drive around town on a moderate day, the gauge shows between 195 and 220. Sometimes this is arbitrary. If still running hot on grades, I will likely install a new fan clutch (OEM replacement). The clutch feels good, but appears to be original.

 

[Saudade]

So a few things.

Check and make sure there's no build up of crud between the radiator and the condenser that would block airflow. It's also possible your radiator is internally blocked.

The fan switch in the radiator is on the cooler side. Hot coolant returns to the radiator, passes through it until it reaches the other side where the switch is located. The switch is supposed to close/open around 190F. Your temp gauge sending unit is on the back of the head. Even more confusing, the CTS is in the engine block. So 3 temperature "sensors" in 3 different places each doing something independently. The gauge (if you have the full cluster) and CTS are variable resistors. The radiator one is Open/Closed.

There is a diode (small orange block) near the air cleaner (in front) that directs power to the fan relay. One leg comes from the AC circuit, the other from the radiator switch. If you disconnect the switch, then jump the terminals on the harness side (key on, AC off), the fan should come on. If not, check for 12v at the yellow wire on the main harness side.

If your XJ is really hot(!), you can also test for continuity on the switch side. The diodes prevent back-feeding power to the other side. So if the fan comes on due to temp, it doesn't feed to the AC clutch.

 

[CBJeeper]

So a few things.

Check and make sure there's no build up of crud between the radiator and the condenser that would block airflow. It's also possible your radiator is internally blocked.

The fan switch in the radiator is on the cooler side. Hot coolant returns to the radiator, passes through it until it reaches the other side where the switch is located. The switch is supposed to close/open around 190F. Your temp gauge sending unit is on the back of the head. Even more confusing, the CTS is in the engine block. So 3 temperature "sensors" in 3 different places each doing something independently. The gauge (if you have the full cluster) and CTS are variable resistors. The radiator one is Open/Closed.

There is a diode (small orange block) near the air cleaner (in front) that directs power to the fan relay. One leg comes from the AC circuit, the other from the radiator switch. If you disconnect the switch, then jump the terminals on the harness side (key on, AC off), the fan should come on. If not, check for 12v at the yellow wire on the main harness side.

If your XJ is really hot(!), you can also test for continuity on the switch side. The diodes prevent back-feeding power to the other side. So if the fan comes on due to temp, it doesn't feed to the AC clutch.

Which radiator did you end up installing?

 

[Saudade]

I got the OSC 78 from Rock Auto.

Here's my thread:

Cooling System "Refresh"

I've had a very small leak in my radiator for some time now. It's so slight, there's no coolant on the ground and it takes about 500 miles or so (mostly short distance drives) to require topping off the tank. So it's not been a priority until now. As I prep for my biannual smog test, I decide...

naxja.org

 

[Fred]

One, all XJ cooling systems need to be burped multiple times. Two, my 90 with a cheap two row aluminum open system radiator runs very cool. It's a bored 4.1, milled 11-1 HO ported HO head with a Hesco cam and water pump, bored T-body, Mopar headers, 2.5 inch exhaust on 35's, 4.11's, stick, full roll cage and lot's of added steel, and lives at 6k feet where the air is thin. I've had a flowkooler pump which worked well, the Hesco pump is amazing.

 

[Saudade]

The pic below shows the orange diode. This is between the airbox and the drivers side inner fender. The big harness leads to the headlights. The small one, with the connector showing, is the radiator temp switch. The other one leads to the fan. The yellow wire to the switch brings 12v with the key on. The Grey/T is the other side and goes to the diode.

I recall the center wire on the diode brings 12v to the fan relay, and the one on the left (in my pic) comes from the clutch circuit.