extrashaky

No, the cooling system seems to have extra capacity built in, because the oil temp will stay the same throughout that coolant temp range. My understanding is that the motor is actually built to run better at 220°, but the A/C works better at 195°. So it has this oddly large "normal" range of temps that would scare most people if they saw it happen on a gauge.

They could have given us a real gauge and made a note in the owner's manual that the behavior is normal, but we've seen time and time again on the community message boards that people get the cars, jump in and start driving without ever reading the manuals. There are numerous weird quirks about the car that are explained in the owner's manual, yet they are considered mysterious "hidden features" in the community because nobody reads it.

So I think they're probably doing the right thing for the overwhelming majority of their customers. Think about right here in our own community. There are still XJ owners who are convinced that 210° is too hot, and they do stupid things like bypass the factory wiring on their electric fans and install 160° thermostats because they think they know better than the AMC and Chrysler engineers how hot the 4.0L should run. Put those people in a Subie with an even wider range of normal temperatures and let them actually see a real gauge, and you'd have people ripping it apart trying to "fix" it.

Bugout4x4

I see your point, and unfortunately you are right about this. I guess at some point human nature comes into play. lol

dave1123

Before computer controlled fuel injection and clean emission standards, 180* was considered normal for any engine and people began to worry if it went higher. Now 210* to 220* is normal to help burn fuel more efficiently. The problem is at 240* aluminum pistons begin to deform and at 260* begin to transfer metal to the cylinder walls, oil begins to carbonize and gaskets begin it melt. Coolant pressures were increased to 18-20 psi to increase the boiling point so engines could run at these higher temps.

It's people's minds that haven't kept up with this.

One thing I forgot to mention. With carburetor float bowls open to atmospheric pressure, 190* was about maximum before fuel would boil in the float bowls.

Bugout4x4

Or in the lines on the way to the carb. Now days you mention vapor lock and it blows over without a clue. lol

dave1123

Fuel will still boil in the fuel rails, but at a much higher temp and when being delivered at a high pressure, it will only create a stumble as it passes thru the injectors. It's after shutdown that it causes starting problems. It never creates pumping problems because the pump is submerged in cold fuel.

Keith333

This was the first problem I encountered with my 2000 GC 4.0L a few years ago. If I recall correctly, oil pressure gauge would be fine on cold start-up but once the engine was up to operating temperature the gauge would begin to drop to zero at idle (red lights, etc.). Then, like you mention, it would jump back to normal on take off.

Mine was a relatively easy fix - replace the wiring harness going to the oil pressure sensor.

The next time your at a red light and your pressure starts to drop, hold hard on the brake and gently rev the engine above the 700 or so idle rpm and see if your pressure rises back. Also, the next time you have an opportunity to safely get out and pop the hood, leave the engine running and jiggle the harness wires. That was ultimately what I did to diagnose mine, I jiggled the wires at idle and the gauge rose to normal.

I hope your problem and solution are as easy a fix as mine was. Got my harness at NAPA (surprised they had one in stock) for under $20.