Well..may just be the sending unit

 

I bought a salvage engine for $1000 when I bought my jeep for a song because it has symptoms like yours. That was years ago and the salvage engine is still on the engine stand!
I prefer a guaranteed,hot tested salvage engine over a rebuild b/c it is 100% complete and ready for plug-n-play.

 

If it was me I would just drive it till it dies.Then when or if it dies I would just find a motor from a salvage yard thats got a warranty and slap it in there.The 4.0s are everywhere and easy to find.

 

Replacing an engine, and how you go about it, depends on a lot of things.

1. How much money are you willing to spend on it?

2. What is the level of your mechanical expertise/time/tools/place to work on it?

If I had an XJ with an 0331 head, and I intended to daily drive it and keep it until the end of the world, I would buy a Jasper engine with a 3-year warranty through a shop that guarantees their work for a reasonable amount of time. This option costs the most money but should have the most peace-of-mind.

Alternatively, I would have my short-block rebuilt and buy a brand new aftermarket head to put on it. Use the 0331 head for a boat anchor or a door stop because that's all they are good for. Under no circumstances would I attempt to have one rebuilt or reuse it.

If I had a Jeep with an 0331 head that had not cracked yet (to my knowledge) I would immediately drain all the green coolant from the system, totally power flush it at least 3 times with clear water, and refill with DexCool coolant.

If DexCool gets into the bearings, it will not eat them like green coolant does.

 

I would almost like to buy a junkyard one and go step by step rebuilding it myself (very little mechanical experience but good at learning) then have it sitting there ready to go when needed and have a local shop swap it in, no idea where to start though. Even if it took me a year or two I would love the learning experience.

 

If you go the salvage yard route, at the very least pull the spark plugs and rotate the engine over by hand (on the crankshaft bolt) to make sure it isn't locked up.

 

I guess you could attempt to rebuild the 4.0 as a learning experience, but you may find that to be exceptionally difficult with limited knowledge and, I assume, the tools and equipment for engine work. For a learning experience I would recommend tearing into small engines to learn the basic workings and how to deal with systems on a smaller and less expensive scale. Not trying to discourage you, but think about how much money and time you're willing to dump into something you may not be able to see through to the end.

 

What sounds like an exciting adventure can turn into an expensive, frustrating nightmare real quickly when working on engines in particular, and vehicles in general.

 

If you didn't already pick up a mechanical gauge then if I were you I would just replace the sending unit first in case that is bad.

It's not uncommon on many makes / models for those to go bad and give all kinds of false readings.

I really would pick up a mechanical gauge though, install it and monitor it. You could even pick up one of those dash mounted gauges cheap, run the hard line through your window temporarily just for troubleshooting.

 

Update..Thing has been idling around 15-20 sometimes higher PSI for the last 10 days (when I created this thread)

Been driving it 5 days a week to work with no issues or drops in pressure, always sits around 15 at idle and around 40PSI at 1600ish RPMs (give or take a bit)

Today half way to work I get pegged at 0PSI and check gauges light just like what happened whne I started this thread. PSI increases with RPMs..whats weird is that teh gauge will drop very gradually from say 30-10PSI, but from 10-0 is an immediate drop..not gradual at all..

Checked oil again..not milky..normal levels, no more knocks other than what I already had which is a slight either bottom end knock of flex plate knock

 

Until you verify with a test gauge we are running in circles

 

I'd pull the sender and at least clean the hole or just replace it. While it's out give the motor a quick start to blow the passage clear, might just have some gunk there given that it's an intermittent issue, it's unlikely to be a mechanical issue of a bearing or pump.

 

No don't do that unless you want a huge mess that he won't come out and clean up for you.

 

haha!


I know I know

 

I have now put 2 new senders in my 14 year old Jeep Cherokee Sport with 104K miles. It is such a cheap part to replace (and easy - even for me a non-mechanic) that I don't bother trying to clean out the old one. My symptoms were just as you describe.