The gauge itself may be bad, sensor may be fine.

 

Could a bad egr valve make it run hot?

 

Get this, I turn my overdrive off and it doesn't run hot.

 

This may sound stupid, but check you lower radiator hose for internal collapse. It does happen. Not often, but it does.

 

Do you have a trans cooler? I don't know much about the Grands, but if it's setup similar to an XJ (trans lines run into the radiator) your transmission could be overheating. If you don't have an external transmission cooler it might be worth installing.

 

The lower hose is fine. Already checked it. I don't have a tranny cooler. The lines go into the radiator. I think I'm gonna get an external cooler.

 

Most ZJs with the tow package came with a tranny cooler. 3 of my i6 Grands had them and my V8 has it, might be able to get it cheap at a pull yard.

 

Too lower a couple degrees add some hood vents, but with your situation prob wont do to much. But an idea.

 

Forgot to mention I already added 3 hood vents.

 

With your overdrive off your averaging a higher rpm, hense faster coolant flow... Sounds like you have a restriction. definitely check your hoses. Have you flushed it yet?

 

Here's an off-the-wall idea. Is your drivebelt routed properly? If the waterpump is spinning in reverse, it won't give much flow.

As I said, It's an oddball idea.

 

Your injectors may be a little clogged causing it to run a little lean. This would make it run hot under a load. When I had my '97 V8ZJ, it did the same thing in the Tenn mountains. I had some injection system cleaner ran through it, and what a difference it made. More power, and no more climbing temps when climbing those grades.
Before doing it, the idle was smooth, and power was good, so I didn't know if it would help, but I tried it anyway. I was glad I did.
Might not be your issue but it sure did help with mine.

Another thought: My son bought my ZJ and now he wants to replace the injectors w/some newer ones w/a better spray pattern. I've read threads where people use the 784's or 789's in their 4.0L, and wondered if anyone's done it with their V8 ZJ? If so, what were the results?

 

I have Ford Racing 24 lb/hr injectors in my 5.2. Just a little more flow than stock and the 4 pintle spray pattern. Work great, and all 8 brand new were only $120.

 

Thanks for that info. I appreciate it.

 

brand new or cleaned and tested? $15 per injector is one hell of a deal if they are new.