WhatĚs the difference between 4.0 and 4.2 oil dipsticks? - JeepForum.com
  • 1 Post By jeepwhore
  • 1 Post By Fourtrail
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post #1 of 4 Old 03-01-2018, 12:43 PM Thread Starter
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1983 CJ7 
Join Date: May 2017
Location: Las Cruces
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Whatís the difference between 4.0 and 4.2 oil dipsticks?

Hey fellow jeepers!

When I replaced the seals in the bottom end of the 258 in my 1983 cj7 and installed the stud girdle, I noticed that the 4.0 oil pan I had snagged at the junk yard had a larger sump than my original 258 pan. The 4.0 sump went all the way to the rear of the block whereas the 4.2 pan was a recess at the rear. I ended up installing the 4.0 pan when I buttoned everything up figuring the extra capacity couldn't hurt. I kept the 258 dipstick (long style) and figured the oil level would be the same distance below the crank as the old pan. It took about 7qts total (6in pan+1 in filter) to fill the engine. Iíve driven it this way for about 1000 miles with no issues: no frothing on the dipstick or changing oil pressure.

So long as the dipstick is stock, the level should be the same regardless of the pan, right? Should I change to a 4.0 dipstick? Does anyone have a 4.0 dipstick and tube to measure?

When in doubt, throttle out!
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post #2 of 4 Old 03-01-2018, 04:20 PM
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1984 CJ7 
Join Date: Jun 2006
Location: Kamloops
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The 4L dipstick is about 4" shorter than the 4.2 dipstick. I have a 4L stick and tube in my 4.2 with a 4.2 oil pan and with the recommended amount of fluid it shows about 1" higher than the full mark.
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'84 CJ-17: 17" stretch, locked Toy axles, 5.5" lift, FI, AX15, D300 w/twin sticks, boatsides & junk.
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post #3 of 4 Old 03-01-2018, 05:05 PM
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1974 CJ6 
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Did you also change the pump/pickup to the one from the 4.0? If not, then stay with the level from the factory 4.2 dipstick knowing that you are not pulling oil from the same place as the 4.0 and it's associated oil level. If you did change the pump/pickup then you can use the 4.0 dipstick and tube.

I would stay with the 4.2 oil level as you said, it is factory and below the level of the crank. The extra capacity is nice to have to keep things cool and go longer between changes.
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post #4 of 4 Old 03-01-2018, 10:04 PM Thread Starter
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1983 CJ7 
Join Date: May 2017
Location: Las Cruces
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Fourtrail and jeepwhore thanks for putting my mind at ease! I did put in a new HV pump with the 4.0 pickup so it is pulling from the bottom of the sump. Iíll leave it with the 4.2 dipstick for now. With these long 258 dipsticks getting harder to find, Iíll definitely keep that info on the 4.0 dipstick in mind in case I have to replace it
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