Hey guys. I'm new to this forum but would like any help I can get. A few weeks ago I took my 2000 jeep cherokee sport with a 4.0 engine in to have a motor blower resistor replaced I also had 4 brand new sensa trak shocks installed. A day or two later I noticed a massive coolant leak where I would lose all the coolant in my reservoir tank within 30 mins of driving. I went to a different shop and replaced the radiator, water pump, thermostat, and valve cover gasket because I had an oil leak. I just got my Jeep back two days ago. Yesterday I had parked at a store and went to start it and it idled extremely rough and stalled within 2 seconds. I started it again and it still idled rough and I noticed the oil pressure had dropped very low from what it usually is. It's usually around 50 at idle when cold and maybe 45 when warm but it had dropped to about 20 and only increased when I gave gas. The engine was warm already. I drove it some more and it was still rough and had low oil pressure around 30. Sorry for the long post. Oh, and I still leak coolant. It puddles on the ground in the very front of driver side headlight. Any advise would be extremely appreciated. Thanks everyone.

 

Take a look at your freeze plugs. Look on the drivers side right under the exhaust manifold on the block of your motor. It will orobably be easiest to see them from underneath. Make sure they aren't leaking.

Hopefully we aren't talking about a more serious issue here. Low oil pressure and loosing coolant from the resovoir usually points to a bad head gasket. How does the coolant look? Not milky and brown? Take the oil cap off the valve cover. Any milky slime?

(pics aren't working for me)

 

Check your oil dipstick for milky residue.

 

You MUST find and resolve that coolant leak immediately. Get underneath it with a warm engine, fully pressurized cooling system. Use a good light and you should be able to find it. Getting the vehicle on a hoist makes this a lot easier.

Has the engine ever overheated?

The oil pressure spec for the 4.0 is as follows.....what readings do you see for both of the below conditions?

*Not less than 13 psi with a HOT engine
*Between 37-75 psi OVER 1600 rpms.

 

When I checked yesterday the dipstick and oil were clean as was the cap. The coolant leaking on the ground is a neon yellow green color. Have not had any issues with thw engine over heating. I would go check some more now but its snowing pretty hard and we have a few inches on the ground.

 

UPDATE

I used a mechanical gauge yesterday and numbers were accurate and where they should be. Also coolant leak magically stopped. Havent lost any coolant from the reserve tank either. Only problem is my idleing stills seems slightly rough to me and my gauge still reads about 20-25 psi when engine has been and is hot at idle. It is starting to warm up and turn into spring weather so I think I will do an oil change using 10w30. The jeep has 126,000 miles but the engine only has about 65 or 70 thousand roughly. I was considering switching to synthetic. Is this a good idea?

 

Synthetic oil is fine if you want. Conventional works too. 5w30 is fine in the summer.

Sounds to me like your oil presdure sending unit took a dump, or the wiring was hacked up. Common failure actually

 

At hot idle the oil pressure should be 13 psi or so, your oil pressure seems fine.

I'm relatively new to the board as well and have done a lot of reading and people have really helped me understand oil. ideally I would go with a 0W30, they don't make one so 5W30 seems to be the best in reality.

My jeep will not be a high mileage jeep, probably only 6000 miles per year. Also it has alot of sludge in the oil like the po didn't know you could actually change oil instead of just add it. So I am going with a synthetic. It will help clean my engine well and the higher price isn't as big a factor as I'll likely only be changin spring and fall with a carquest blue oversize 85515(I think) filter. Due to some suggestion and some of the writeups on bobistheoilguy I' trying the Rotella T6 5W40.

Not definitive for certain but seemed like good choices for me

 

i personally think the rotella 10w30 synthetic blend is an excellent oil for the 4.0 along with a mopar or wix filter. there are no issues from switching to a synthetic blend or full synthetic oil atleast in my experience. any cel to go along with the rough idle? did it ever smooth out some? so you are not loosing coolant any more? im going to guess that the cap may not of been on the radiator all the way, or the hose from the radiator neck to the surge tank was not on all the way.

so the oil pressure qauge in the dash is showing different than what the mechanical gauge showed? if so you have a bad sending unit which is not uncommon.

 

igeeky1 i would never run 0w30 oil in a 4.0 the oil clearances in the 4.0 are too large for that thin of an oil. just as i wouldnt run 15w-40 or 20w-50 in the 4.0 because the oil wont flow like it should. 5w-30 or 10w30-40 is good for the 4.0

 

0w30 is the same thickness at operating temp as 10w30 dude... Thats what the 30 is.

Also: I think every large brand has a 0w30. I know Mobil and Shell certainly do. Its just not very common south of the tree line lol.

 

While this statement is correct, a sudden drop in oil pressure means something broke. I would be VERY surprised if his engine accumulated that much bearing wear while turned off in a parking lot. Lol

 

try it on yours and let me know how it works... in my opinion jeep designed the 4.0 for 5w-30 or 10w-30 for a reason... maybe in extreme cold weather it might be ok to run but not in the warmer climates. to thin for me.

 

I found this article djb383 steered me to very useful for understanding oil. http://www.supramania.com/aehaas/

 

Sorry, I must've misunderstood the op. I thought the bad readings were with dash gauge and electric sending unit. The new good numbers with a mechanical gauge.

I was making the assumption that sending unit was bad and was stating that the mechanical reading a 20psi hot idle sounded good.