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XJ Im buying today. Thoughts?

S

saybye

NAXJA Forum User
Location
Soddy Daisy TN
Yesterday after work I went to look at a 93 2 door sport auto with 185k on the clock. Its been sitting for about 4 months, with the occasional start it up and let it run in the driveway every now and then; the owner got a DUI and license revoked blah blah blah.

Anyways, he had it running when I got there which always kinda sketches me out a little. Not expecting much I gave it a look over, drove it around the block, etc. The engine has the normal valve noise these 4.0's usually make, but it did smoke a little.

Not much smoke it any at idle, but once on the gas pedal it did. Not a thick white haze, but enough that its noticeable. I'm buying this thing today, gonna throw some 31's under it and use it to hunt out of and occasionally drive to work and around on the farm.

How much life does a 4.0 have left in it after it begins to smoke? Can I add some thicker weight oil and possibly slow the smoking down or maybe even stop it?

If I wasn't getting the thing for so cheap I wouldn't even waste the time but at the price I cant pass it up...
 
Some 10w-40 should help with the smoke and be better for the engine in general.

What alarmed me about your post was that he had it running when you got there. I had a dealer do the same to me. Make sure to give it a couple starts on your own so you know what your really dealing with. I know the XJ I was looking at had a dirty NSS and was a PITA to start. It's a simple enough issue to fix, but it would have been nice to know before buying the Jeep.

I'm sure someone with more engine knowledge will chime in about the smoke issue. Good luck and enjoy the Jeep!
 
10w-40? The 4.0 was designed for 5w-30, so the only thing changing it would do is make the engine work harder to pump it.

The smoking is probably the rings, but could just be valve seals, which are easy to replace. Definitely hear it start up cold though before throwing any money down. These engines last a ****load of miles, but only if they were maintained properly. Check the dipstick and the bottom of the valve cover cap for white sludge also - that means a blown head
 
I was under the impression that running a thicker/heavier weight oil was better for older/high mileage engines. But I am still on the noob side of things, so any clarification on this would be great and appreciated. Not trying to hijack...
 
Hopkins said:
I was under the impression that running a thicker/heavier weight oil was better for older/high mileage engines. But I am still on the noob side of things, so any clarification on this would be great and appreciated. Not trying to hijack...
Click to expand...

Pretty sure that's the idea, atleast that's the way I understand it.
 
Hopkins said:
I was under the impression that running a thicker/heavier weight oil was better for older/high mileage engines. But I am still on the noob side of things, so any clarification on this would be great and appreciated. Not trying to hijack...
Click to expand...

it's exactly the opposite. While it is true that a heavier weight oil will in theory cut down on the amount that leaks out of seals and such due to the increased viscosity, the engine will have to work harder to pump the thicker oil (If a seal leaks, fix the leak!). Relate an engine to your body - over time the arteries/oil passages get partially clogged with buildups of carbon and sludge, decreasing the size. Increasing the viscosity (resistance to flow) of the oil will only hurt the lubrication of the engine. FLOW is what lubricates the engine, not pressure. Additionally the higher the first number in the oil weight (ie. 5W-xx, 10W-xx), the more it'll thicken after turning off the engine, and since 90% of engine wear occurs right at startup, you want the oil to pump to the engine parts as quickly as possible, so again a thinner oil will provide benefits.

If you're up to it read this - it'll tell you everything you ever wanted to know about oil and more: http://www.bobistheoilguy.com/motor-oil-101/
 
dukie564 said:
10w-40? The 4.0 was designed for 5w-30, so the only thing changing it would do is make the engine work harder to pump it.

The smoking is probably the rings, but could just be valve seals, which are easy to replace. Definitely hear it start up cold though before throwing any money down. These engines last a ****load of miles, but only if they were maintained properly. Check the dipstick and the bottom of the valve cover cap for white sludge also - that means a blown head
Click to expand...

5w-30 is for maximum ambient temperatures below 60F, down to around -20.
10w-30 and/or 10w-40 is for ambient temperatures between 120 F and 0 F.
20w-40 and/or 20w-50 is for ambient temperatures above 120 F and 32 F.
At least this is what my 87 owners manual says.

Most of the reason they recommend a thinner oil is for the fleet gas mileage numbers trying to make the EPA happy.

I always open the oil filler cap and see if smoke comes out, put my hand over it and ev the engine and see how much blow by pressure it builds. Sometimes the CV system just needs cleaning and the crankcase pressures go way down. It may be rings, it may be something simple.
 
dukie564 said:
it's exactly the opposite. While it is true that a heavier weight oil will in theory cut down on the amount that leaks out of seals and such due to the increased viscosity, the engine will have to work harder to pump the thicker oil (If a seal leaks, fix the leak!). Relate an engine to your body - over time the arteries/oil passages get partially clogged with buildups of carbon and sludge, decreasing the size. Increasing the viscosity (resistance to flow) of the oil will only hurt the lubrication of the engine. FLOW is what lubricates the engine, not pressure. Additionally the higher the first number in the oil weight (ie. 5W-xx, 10W-xx), the more it'll thicken after turning off the engine, and since 90% of engine wear occurs right at startup, you want the oil to pump to the engine parts as quickly as possible, so again a thinner oil will provide benefits.

If you're up to it read this - it'll tell you everything you ever wanted to know about oil and more: http://www.bobistheoilguy.com/motor-oil-101/
Click to expand...

that's a good write up, thanks for sharing it!
 
dukie564 said:
The 4.0 was designed for 5w-30
Click to expand...

while the later ChryCo engines recommend thinner oils, the original '87/'88 owners manuals call for a 10W-40 or 20W-50 depending on average temperature the engine will see before the next oil change. I don't think a 10W-40 is going to stress the oiling system in our tractor motor very much.

C.A.F.E. standards seem to have as much play in recommended oils as anything else these days-- thinner oils allow that extra tenth of a mile per gallon that many manufacturers need to keep their fleet above the cutoff point.

edit- 8Mud--you beat me to the point
 
8Mud said:
5w-30 is for maximum ambient temperatures below 60F, down to around -20.
10w-30 and/or 10w-40 is for ambient temperatures between 120 F and 0 F.
20w-40 and/or 20w-50 is for ambient temperatures above 120 F and 32 F.
At least this is what my 87 owners manual says.
.
Click to expand...

Oil technology has progressed far past what was available in 1987. Ambient temperature no longer has any weight in the choice of oil (unless it's an air cooled engine) - it's now based on operating temperature. Meaning regardless of what temperature it is outside, a properly running (cooling) engine should always be at the same operating temperature

This is far more accurate:
oil_chart.jpg
 
So lets say it is the rings... is this something I should be super worried about and possibly not buy the jeep? Or is this something that will get worse over time and I could get a year or so out of the motor?
 
i wouldn't be super worried about it. If it's running smooth and has good power it's likely something other than the rings. 180k isn't that high for these engines - most get up to the high 200s or low 300s before they require rebuild/replacement.

Mine has 282,000 on it right now - I had a smoking issue a few months back, replaced the valve seals and smoking has stopped.

That said, you NEED to hear/see it run when it's cold before you buy it. Many issues disappear or become less evident when the engine is up to temp.
 
Check out the exhaust pipe, wipe your finger in there and smell it. See how much pressure you have coming out of the oil filler cap hole. If it is blowing smoke rings out of the oil filler hole, I'd pass. You might even want to pull a few plugs and have a look see. Bad rings can really gum up a set of plugs.

It may not be oil smoke, could be excess fuel or even coolant.

31's are gonna rub a lot without a lift.
 
Last edited:
8Mud said:
Check out the exhaust pipe, wipe your finger in there and smell it. See how much pressure you have coming out of the oil filler cap hole. If it is blowing smoke rings out of the oil filler hole, I'd pass. You might even want to pull a few plugs and have a look see. Bad rings can really gum up a set of plugs.

It may not be oil smoke, could be excess fuel or even coolant.

31's are gonna rub a lot without a lift.
Click to expand...

gonna buy the 2" budget lift. ill post some pics this afternoon after I buy it
 
dukie564 said:
Oil technology has progressed far past what was available in 1987. Ambient temperature no longer has any weight in the choice of oil (unless it's an air cooled engine) - it's now based on operating temperature. Meaning regardless of what temperature it is outside, a properly running (cooling) engine should always be at the same operating temperature

This is far more accurate:
oil_chart.jpg
Click to expand...

Re-read your post. You argue for "Operating Temperature".

Then go and post an OAT vs oil weight chart and say it's more accurate.

The "ambient" or "outside air temp" around the engine at minimum is what determines the low end of a Multi-viscosity oil weight.

In the old days of single viscosity oils, we litterally changed oil viscosity by season.

-Ron
 
Most of the 4.0s I've seen that smoked it ended up being valve seals. Not much of a problem just more of an annoyance. Keep the oil topped up and it should go 300k easy. I'd be more worried about why it was running when you got there.
 
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