Someone please educate me. Wierd oil symptoms.
Thread Starter
CF Veteran
Joined: Oct 2009
Posts: 2,867
Likes: 16
From: Fauquier County, Virginia
Year: 1991
Model: Cherokee
Engine: I-6 4.0 HO
1991JeepMan, I'd just drive your Jeep and keep logging anytime you add oil. You may be overly concerned here. I had an older XJ that burned some oil and I kept a small notebook in the glove compartment and noted in there whenever I added. That way, I could see how I was doing, the progression of oil consumption, and if I needed to be more concerned about it.
Oil consumption on older high mileage engines is not a death sentence. I've seen 4.0 engines run for tens of thousands of miles with moderate oil consumption.
As long as you are sure you have a clean CCV system, drive it. If you want a data point (and I love data points) run a compression test on all cylinders. It isn't difficult and is a good "snapshot in time" of the internal condition of the engine. The spec. compression for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders. If you don't have a compression gauge, they can be rented from many big box parts stores. Run the test dry, then add a teaspoon of oil to each cylinder and re-run it (wet compression test). SEARCH the web for interpreting these results but in general, if the compression is low in any cylinder and comes UP with the addition of oil, you have worn piston rings.
And skip the oil additives. Mobil 1 full synthetic is a fine oil; you certainly need nothing more. You aren't getting any value out of the additives here. And adding them and not adding them introduces a "variable" that gets in the way of logging your TRUE oil consumption.
Oil consumption on older high mileage engines is not a death sentence. I've seen 4.0 engines run for tens of thousands of miles with moderate oil consumption.
As long as you are sure you have a clean CCV system, drive it. If you want a data point (and I love data points) run a compression test on all cylinders. It isn't difficult and is a good "snapshot in time" of the internal condition of the engine. The spec. compression for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders. If you don't have a compression gauge, they can be rented from many big box parts stores. Run the test dry, then add a teaspoon of oil to each cylinder and re-run it (wet compression test). SEARCH the web for interpreting these results but in general, if the compression is low in any cylinder and comes UP with the addition of oil, you have worn piston rings.
And skip the oil additives. Mobil 1 full synthetic is a fine oil; you certainly need nothing more. You aren't getting any value out of the additives here. And adding them and not adding them introduces a "variable" that gets in the way of logging your TRUE oil consumption.
Senior Member
Joined: Apr 2011
Posts: 813
Likes: 1
From: Lansing, MI
Year: 2000
Model: Cherokee
Engine: 4.0
I'm not sure about the 4.0, but I know a lot of race car builders here at the shop who recommend dumping an extra quart in SBC engines, because 5 quarts is just what's recommended - they can actually handle more.
The reason I'm saying this is because I don't think having slightly more oil than recommended is going to hurt anything... but maybe the 4.0 is very strict on how much oil you can fit in it.
The reason I'm saying this is because I don't think having slightly more oil than recommended is going to hurt anything... but maybe the 4.0 is very strict on how much oil you can fit in it.
Seasoned Member
Joined: Dec 2011
Posts: 372
Likes: 1
From: Springfield, MA
Year: 1993
Model: Cherokee
Engine: 4.0
I dont think i've ever met a jeep I6 that didnt have oil disappearing out of the engine somewhere. Jeeps lose oil, its a fact. I have rebuilt jeep engines and even with a full gasket set, it still finds a way to get out somewhere. If you're in the safe zone and you have good pressure, i'd say dont worry about it. The only issue it will every cause is your valve cover seeping out down to the crankshaft position sensor and shorting it out. Oh and don't ever use cheap (fram) oil filters, i've had one with a bad flow back valve and it killed my rear bearings. might wanna also trying adding lucas oil or engine restore during your next oil change.
CF Veteran
Joined: Apr 2009
Posts: 4,734
Likes: 12
Year: 2015, 2012
Model: Grand Cherokee (WK2)
Engine: 3.6L
You don't need any additives. Waste of money.
If you are changing synthetic sooner than 7500 miles, you are wasting money and time.
Yes, by all means use a good oil filter. Cheap insurance.
For every gallon of gasoline burned, you also burn a gallon of water. That is the visible vapor you see on cold morning start-up, until the system warms up to temperature.
Forgive me for saying so, but it seems you might be over-worrying about this. It doesn't sound to me like that there is much to worry about. Just check your oil about every other tankful or so and you'll be fine.
If you are changing synthetic sooner than 7500 miles, you are wasting money and time.
Yes, by all means use a good oil filter. Cheap insurance.
For every gallon of gasoline burned, you also burn a gallon of water. That is the visible vapor you see on cold morning start-up, until the system warms up to temperature.
Forgive me for saying so, but it seems you might be over-worrying about this. It doesn't sound to me like that there is much to worry about. Just check your oil about every other tankful or so and you'll be fine.
Thread Starter
CF Veteran
Joined: Oct 2009
Posts: 2,867
Likes: 16
From: Fauquier County, Virginia
Year: 1991
Model: Cherokee
Engine: I-6 4.0 HO
You don't need any additives. Waste of money.
If you are changing synthetic sooner than 7500 miles, you are wasting money and time.
Yes, by all means use a good oil filter. Cheap insurance.
For every gallon of gasoline burned, you also burn a gallon of water. That is the visible vapor you see on cold morning start-up, until the system warms up to temperature.
Forgive me for saying so, but it seems you might be over-worrying about this. It doesn't sound to me like that there is much to worry about. Just check your oil about every other tankful or so and you'll be fine.
If you are changing synthetic sooner than 7500 miles, you are wasting money and time.
Yes, by all means use a good oil filter. Cheap insurance.
For every gallon of gasoline burned, you also burn a gallon of water. That is the visible vapor you see on cold morning start-up, until the system warms up to temperature.
Forgive me for saying so, but it seems you might be over-worrying about this. It doesn't sound to me like that there is much to worry about. Just check your oil about every other tankful or so and you'll be fine.
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