Spun Main Bearing
JK Super Freak
Joined: Feb 2009
Posts: 1,488
Likes: 1
From: Sydney, Australia
Cold engines produce quite a bit of moisture until they warm up (thus all the steam & water coming out of the exhaust for the first 10 minutes or so after you start it up from cold). So if you only travel a short distance before shutting it down again, some of this water vapour in the crank case doesn't have a chance to evaporate & can build up. Then the first time you take it for a longer trip on the highway and allow the motor to warm up properly and the oil to reach full operating temperature, the moisture in the oil will evaporate quickly and suddenly your oil level can be quite low.
In older cars with carburettors the problem was worse as unburnt fuel would also contaminate the oil, leading not only to quicker breakdown of the oil itself but also add to the false dipstick read problem. In the past , after several weeks of short-distance city driving in winter, I've seen my dipstick level drop by a quart after only an hour on the freeway due to this issue. At first I thought the motor was shot & suddenly burning oil due to the freeway speeds, but then I noticed the oil level remained constant after the initial drop for the rest of the 800 mile trip, & a mechanic later explained the reason why to me.
JK Jedi Master
Joined: Feb 2008
Posts: 12,907
Likes: 185
From: Maine
One thing to remember also if you find your oil level suddenly dropping is that if your vehicle use is short, low speed trips of a few miles (ie; short commute to work) moisture can build up quickly in the crankcase and dilute the oil over time, giving a false reading. So even though the vehicle is using oil (as we all know JKs do), there may not be a corresponding drop in the dipstick level.
Cold engines produce quite a bit of moisture until they warm up (thus all the steam & water coming out of the exhaust for the first 10 minutes or so after you start it up from cold). So if you only travel a short distance before shutting it down again, some of this water vapour in the crank case doesn't have a chance to evaporate & can build up. Then the first time you take it for a longer trip on the highway and allow the motor to warm up properly and the oil to reach full operating temperature, the moisture in the oil will evaporate quickly and suddenly your oil level can be quite low.
In older cars with carburettors the problem was worse as unburnt fuel would also contaminate the oil, leading not only to quicker breakdown of the oil itself but also add to the false dipstick read problem. In the past , after several weeks of short-distance city driving in winter, I've seen my dipstick level drop by a quart after only an hour on the freeway due to this issue. At first I thought the motor was shot & suddenly burning oil due to the freeway speeds, but then I noticed the oil level remained constant after the initial drop for the rest of the 800 mile trip, & a mechanic later explained the reason why to me.
Cold engines produce quite a bit of moisture until they warm up (thus all the steam & water coming out of the exhaust for the first 10 minutes or so after you start it up from cold). So if you only travel a short distance before shutting it down again, some of this water vapour in the crank case doesn't have a chance to evaporate & can build up. Then the first time you take it for a longer trip on the highway and allow the motor to warm up properly and the oil to reach full operating temperature, the moisture in the oil will evaporate quickly and suddenly your oil level can be quite low.
In older cars with carburettors the problem was worse as unburnt fuel would also contaminate the oil, leading not only to quicker breakdown of the oil itself but also add to the false dipstick read problem. In the past , after several weeks of short-distance city driving in winter, I've seen my dipstick level drop by a quart after only an hour on the freeway due to this issue. At first I thought the motor was shot & suddenly burning oil due to the freeway speeds, but then I noticed the oil level remained constant after the initial drop for the rest of the 800 mile trip, & a mechanic later explained the reason why to me.
Thread Starter
JK Enthusiast
Joined: May 2009
Posts: 121
Likes: 0
From: Hunstville, AL
Thanks guys!
Lots of great info being posted on this thread. 
Hopefully, somebody out there will learn more about their vehicle from some of you 'seasoned' veterans ( I guess my 40 yr old self could be considered one of those as well).
Anthony
Hopefully, somebody out there will learn more about their vehicle from some of you 'seasoned' veterans ( I guess my 40 yr old self could be considered one of those as well).
Anthony
JK Enthusiast
Joined: Mar 2007
Posts: 370
Likes: 0
From: Bristow, Virginia
OK, engine replaced---check!
New brakes--check!
Oxygen sensors replaced--check!
Catalyst replaced--check! (just a couple hundred road miles and I can finally register the thing again with the DMV!)
Differential leaking--uncheck!
Gotta do that this weekend, good deal that there are such great writeups on this forum for that. They wanted almost $400 for a differential check/refill at the dealer. I figure that I can do that one myself...
The light is definitely brighter on this end of the tunnel!!!
New brakes--check!
Oxygen sensors replaced--check!
Catalyst replaced--check! (just a couple hundred road miles and I can finally register the thing again with the DMV!)
Differential leaking--uncheck!
Gotta do that this weekend, good deal that there are such great writeups on this forum for that. They wanted almost $400 for a differential check/refill at the dealer. I figure that I can do that one myself...The light is definitely brighter on this end of the tunnel!!!
