Quote: "There is a reason lower water hoses are made of a stiff reenforced material while you can get away with using the thinner more flexible hoses on the return line."

Upper and lower hoses are the same thickness and have the same reinforcements.

The upper hose is actually under more stress because it is carrying hotter water back to the radiator. Hotter water is more corrosive over time.

 

I did a bit of looking into the temperature indicator/warning (dummy) light - it doesn't come on when I turn the ignition (the battery and oil pressure does) - is it supposed to? I pulled the "instrument cluster) to check the bulb and, unfortunately, that's not the issue. I tried cleaning the connections and checked the fuses under the dash (drivers side) to no avail. All other lights in the cluster (dahsboard, etc) are working properly. Thoughts?

 

For the XJ, only the OEM lower hoses are reinforced, and only because the reinforcement was required for part of the installation process at the factory. Aftermarket lower hoses for the XJ are not reinforced because the reinforcement is not needed unless you install a high-flow water pump.

 

Yes, all of the dash lights r supposed to momentarily light up when the motor is started, then turn off after the motor starts and runs a few seconds. It's a dash indicator/bulb check feature. If the bulb is good, it could be bad electrical somewhere between the light and temp sending unit....maybe even the temp sending unit, for that matter.

 

The water pump is NOT a positive displacement pump....I believe the oil pump is.

 

Right on - that will be the next thing I check. How would one go about determining where the problem is? I assume some sort of multi-meter check, but any hints as to where to test and what to be looking for? If anyone has any idea of the stock wire colors to trace, that'd be super helpful too (I've run across quite a few disconnected connectors along the way).

Also, considering I don't have a temperature gauge (just the dummy light) would I have a temp gauge sending unit (rear of the block on drivers side)? I haven't looked yet, but I'm wondering if I should be looking to determine if that is faulty or if I should be looking at the coolant temperature sending unit (on the thermostat housing)?

 

Switch your non-functioning light with a known good one from your cluster. See if it works then.

If it doesn't, replace the sending unit. It is unlikely, though not impossible, that the problem is between the sending unit and cluster.

 

I switched out the bulb - no dice. I then replaced the temperature sending unit (the old one had a crack in the plastic housing) and...still nothing. So it seems the trouble lies somewhere in between. Any thoughts on how / what to test out next?

Would a bad coolant temperature sensor (the one threaded into the thermostat housing) be a possible cause? I'm not sure which sensor is piped into the dummy light....