Renix overheating

Well I got the head gasket replacement finshed on the 89, and found it trying to run at 230 F. At first I thought the thermostat was bad, as the E-fan did not turn on. I checked the radiator outlet temperature and it was only 165 F at first, and the thermostat outlet was 230 F (used an IR gauge to verify). I know the mechanical fan clutch is weak, but the E-fan was not coming on even with a new radiator E-fan switch.

So I thought the thermostat was not letting enough water (coolant) flow, or maybe the water pump was bad, but after a while the e-fan finally came on, and stayed on. The radiator outlet, return temperature to the engine finallly climbed to 210 F (took 30 minutes at idle) with the radiator inlet reaching 235 F even with the Efan running the whole time. Increasing the engine rpms helped early on, but later it made no difference, so it became clear that the radiator was not transferring enough heat to the cooling air efficiently enough, and this means the radiator is partly scaled up.

I shopped for a new radiator on line, found one for $93, called to check on delivery and they delivered it in 1 hour to my house, for a total of $102 (plus sales tax), and it even had a bag of thank you for the order CANDY attached! 1-800-radiator, radiator.com

And get this, it has a lifetime warranty on the radiator! 2 row, brass/copper core with plastic end tanks, like the one I bought 4 years ago for my 87 XJ, which is still working perfectly to this day.

You gotta know that it's well worth replacing the fan clutch if you already know it's bad... It does make a world of difference even with the new radiator. Sounds like you gotta great deal on the new rad! Good luck.

I had the same problem with a 88 MJ 3 or 4 years ago when I changed the head gasket for a customer . Turned out it was just a little air trapped in the head . I had to jack up the rear and pull out the temp sender in the head and let the air out 2 or 3 times .

Got a new clutch at Autozone, for only $35. Top quality, OEM style with the fins and spring on the front side. It's going in with the radiator.

I forgot to mention that during the first hour of running the engine after the rebuild, I got lots of foaming in the renix bottle with the engine at 2 to 3,000 rpm in the last 15 minutes. After it cooled down the bottle went from nearly full before start up to nearly empty, 1/4 full after it cooled down. I ran the heater the first 15 minutes, so the heater core should have been flodded by then.

Since I did not have that problem with my other 87 renix (which got a new radiator 4 years ago), I assume that most of that air come from the radiator, namely partially blocked flow tubes with trapped air in them! THe system did not overpressure or leak, and the coolant in the bottle droped as I said, so I am pretty sure the raidator had trapped air slowly bleading out of it.

So my point is that people that have air in the renix coolant systems purging problems, may have had this same problem of partly blocked horizonatal tubes holding on to the air for quite some time!

Think of an exit tube blocked but the inlet tube open (horizontal layout), and the tube full of air, it would take a long time for the air to bleed out becuase it would need to travel upstream first.

Also, the way the horizontal flow is set up with the radiator inlet at the top, there is no way to flush trash out of the inlet side tank (which is where trash would accumulate) unless you pulled the radiator out and back flushed it with the inlet tank on the ground leaned toward the inlet nipple, and the outlet on tap with a garden hose dumping water in the outlet tank side.