Is my dad's Jeep really having problems, or is it th gauges?

[noob5,000,000]

TL;DR, my dad's Jeep would often 'overheat', and the oil pressure would appear very low at idle when at operating temp, but could this actually be faulty gauges? Or could one be true and the other a gauge issue? Or both real problems?

Full Story:

Oil pressure issue:
The oil pressure gauge would drop to near zero when at idle, only when the engine was at operating temperature. You have to drop it into neutral and give it some throttle to keep the oil pressure up. I have a feeling that this is actually a real problem and not the gauge . BUT, it could be a sensor or gauge issue.

Engine temperature issue:
For quite a while now, the car has had issues with overheating. My dad replaced the water pump (which was very shot), but it continued to have problems. A new thermostat was also installed. My dad brought it into a shop to have them flush the cooling system, and it seemed okay for a while after that. The problem resurfaced recently, and we discovered that the shop broke off half of the flange the the thermostat housing. They used a large washer to clamp down on what was left of the flange and gooped RTV everywhere.

Today, we replaced the thermostat housing with a new one, along with a new thermostat. We also did a thorough system flush with Prestone cooling system cleaner, which seemed to actually dislodge some junk in the cooling system. We drove around for a while and the temperature seemed to be holding steady at just slightly over the middle mark in the gauge. But, I pulled into a parking spot and left it running and after a minute the gauge jumped all the way to overheat. It shot right up there, it didn't climb slowly. I shut it off for a few minutes and when I restarted it it was at normal operating temp. It jumped back up when I began driving again so I shut it off again.

Here's where it gets crazy. The temperature gauge actually came back down to normal temp while driving. It went up again and came down again, all while driving at neighborhood speeds (20-30 mph). I doubt an engine could heat up and cool down 50º in less than a second, which leads me to believe that I am being lied to. Anyone ever heard of this?

[4onthefloor]

My car has low oil pressure at idle when at operating temperature. I'm still not sure whether it's a legit. problem or just a mis-read from the cheapish gauge I bought.

It's usually best to troubleshoot it starting with the simplest fault, which in this case would be a wonky gauge.

[AHTOXA]

The oil pressure sensors are known to read badly on the XJs. I'd be more concerned with overheating.

[noob5,000,000]

The oil pressure sensors are known to read badly on the XJs.

I'll grab one (or a couple) next time I'm at the junkyard and see what happens.

As far as overheating, I'm really baffled by the fact that the gauge can go back and forth between normal and too hot as it pleases, in less time than it would actually take to get that heat or cool. It was really overheating in the past when the water pump was bad, it would occasionally steam and you could hear the coolant bubbling sometimes, but it's not doing any of that anymore, despite the gauge's readings.

I want to get an aftermarket temp gauge and see what's really going on.

[theholycow]

I'm really baffled by the fact that the gauge can go back and forth between normal and too hot as it pleases, in less time than it would actually take to get that heat or cool.

I had an oil pressure gauge that fluttered from its low limit to its high limit so fast it was a blur, like butterfly wings, in a dumptruck. I knew it had to be the gauge, how could oil pressure do that?

Then the engine died. I was wrong. I guess it must have been bubbles in the oil or something. Do NOT assume that a gauge is failing.

I want to get an aftermarket temp gauge and see what's really going on.

Do it. Get old-school mechanical gauges for testing when possible. If Harbor Freight has been unable to get rid of them, they may still have mechanical oil pressure gauge kits marked down to $2.50. Otherwise, buy at a more normal price (they have a test kit for $25) or get a loaner from a parts store. Whatever you do, don't let him drive another mile until you get some gauges on it.

[watkins]

Jeep has been known to have issues with coolant temp sensors

[noob5,000,000]

So, my plan is to replace both the coolant temp and oil pressure sensors, and install an aftermarket temp gauge. Luckily, my dad has another vehicle to use so we won;t be risking any damage in the meantime.

Thanks for the input so far.

[bk7794]

Could be a bad headgasket aswell. OR a bad radiator . Does the cooling fan come on? Seems like you have the cooling issue only when idling.

[Squint]

I had an oil pressure gauge that fluttered from its low limit to its high limit so fast it was a blur, like butterfly wings, in a dumptruck. I knew it had to be the gauge, how could oil pressure do that?

Then the engine died. I was wrong. I guess it must have been bubbles in the oil or something. Do NOT assume that a gauge is failing.

You need a spoiler tag or something in that story. I was like, oh, Cow is going to affirm what we're all thinking.. NOPE.

[Shadow]

Does the cooling fan come on? Seems like you have the cooling issue only when idling.

After quickly reading through the original post, that's what came to my mind right away. If the temp gauge goes up when the car is not moving and it goes down when the car is moving, that usually indicated an inoperable fan. The temperature can climb/drop quickly, but I'm not so sure it can drop as quickly as he was describing.

[noob5,000,000]

Does the cooling fan come on? Seems like you have the cooling issue only when idling.

After quickly reading through the original post, that's what came to my mind right away. If the temp gauge goes up when the car is not moving and it goes down when the car is moving, that usually indicated an inoperable fan. The temperature can climb/drop quickly, but I'm not so sure it can drop as quickly as he was describing.

Yes the fan does work. I'd also suspect the fan if the temp didn't go down and up while moving.

I'll also try bleeding the system really good again, any air bubbles could potentially give funky readings as they pass over the temp sensor probe.

[bk7794]

What kind of thermostat you put in it? I wonder if it is the wrong one. Like it opens at the wrong temperature.