The oil level indicator (dip stick) inside the oil filler tube of the Willys F-head engine, extends vertically down into the oil pan and will indicate the current level of oil in the pan. See the front cutaway view of the engine block (100K GIF).
As the oil level in the pan rises or falls, the oil is always taken from the top by the floating oil intake (100K JPEG), and is lifted through the oil float support tube by the oil pump (70K GIF). Incidentally, the Universal Jeep Service Manual (Section E63) comments, "Fluctuating oil pressure can usually be traced to an air leak between the oil float support and the crankcase."
Pat Mansfield asked on the CJ-3B Bulletin Board: "The dipstick from our '54 broke off, and the broken tip has been lost. Can anyone tell me the length of the dipstick, from where it attaches to the underside of the cap?"
Don Norris: "I measured two different dipsticks I have. From the inside of the cap to the tip is 25-3/8 inches long."
Chuck: "I went out to the garage to check out a couple of F-heads I've got out there.
"First of all, I assume we are talking about the F-head with the 14-1/4" tube and not the one with the 16-1/2" tube.
"Secondly, I also found the inside of the cap to the tip as 25-3/8 inches. However, that measurement could be a little misleading because there are a couple of places on the inside of the cap from which to reference your measurement. I found that there was a slight difference in the cap design on two of my dipsticks.
"Thirdly, what I found most interesting was the measurement from the tip back to the full mark. One measured 2-7/16" and the other measured 2-1/4". And the one that measures 2-7/16" from the tip to the full mark is a 'correct markings -- recent production' dipstick. The one that measures 2-1/4" from the tip to the full mark is a 'correct markings -- early production' dipstick. That is why I think maybe the reference point to measure the 25-3/8" from the inside of the cap may be more significant than one might think at first glance. I don't know how important 3/16" is on the oil level either."
Pat Mansfield: "Sorry I didn't give more detail -- yes, it's the F-head with the 14-1/4" tube. I'll go with the 25-3/8" length -- interesting about the different markings though. Hopefully the 3/16" difference isn't too critical.
Eric Lawson: "Measured from the inside of the cap, 58cm to the Full line, 59.5cm to the Add 1 quart line, 61cm to the Add 2 quart line, 64.5cm to the end of the dipstick. At 21.5 cm from the cap is a splash guard (a washer with four small holes in it). The splash guard prevents oil from moving past this point, but still allows air to flow into the crankcase. The splash guard is mounted at right angles to the dipstick and I don't think it is really needed.
"If you prefer inches: From the inside of the cap, 22-7/8 inchs to the full line, 23-3/8 inches to the Add 1 quart line, 24 inches to the Add 2 quarts line, 25-3/8 inch to the end of the end of the dipstick. The splash guard is 8-1/2 inches from the cap and is 1-1/8 inch in diameter."
Ken: "This note was found only in the 1965 Service Manual (SM 1002-R5) paragraph B-7:
"'Note: Models CJ-3B, CJ-5 and CJ-6 should be checked for correctly marked dip sticks. The correct marked dip stick measures 2-7/16" from the full mark to the lower end.'
"My dipsticks also measure out to 25-3/8" length from the cap rivet to tip. My dipsticks have the many marks associated with the earlier style. I currently don't know exactly when this style changed, probably in 1963, according to Bruce Agan's #678 Service Bulletin. My dipsticks measure 2-1/4" from tip to full. It appears the gauge is correct for the early dipsticks. My engine has just been rebuilt with 5 quarts of oil added. It has no old oil or sludge. The dipstick reads exactly full. The dipsticks in question would be the ones shown on the #678 Service Bulletin.
"I estimate that a 3/16" discrepancy is about 1/4 quart oil."
Service Bulletin No. 678; August 30, 1963
Thanks to Bruce Agan for the Service Bulletin, and Dane R. Marley for the photos of his M38A1 F-head. -- Derek Redmond
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