Being a Dipstick

In an August 2013 article, I was left with a mystery. Why did the rear engine require so much less crankcase oil than the front engine to reach the dipstick half-full mark?

At the time, I'd assumed there was something lodged in the rear crankcase but didn't investigate further. Some three years or so later, while preparing to clean out the rear engine's oil sump, the actual reason has become apparent.

Take a look at the following photo with the two dipstick heads highlighted.

A new slant on dipsticks

Although the photo is taken from slightly above the level of the dipstick heads, it is clear that the far one is not only at an angle but considerably lower than the nearer one, about 3" in fact. I'd not taken any notice of this before and assumed that the dipsticks told the truth. When I checked the two dipsticks together, I found they were identical in length and markings. Thus the lower one dipped 3" further into its oil bath registering full rather in advance of actual fullness!

This answers the mystery of the differing oil requirements for each engine. What worries me is how long has it been like this and why are the two engines different?

Of course, the rear engine will have been running with two fewer gallons of crankcase oil than the front one. Hmm...

At some time in the future, the rear dipstick will need fixing. In the meantime, yet another mystery has also been solved.

In this photo, there is a drain cock to let water out of the sump and another highlighted in the top right.

Extra drain cock, top right

I'd wondered what this extra drain cock was for but now I know. Examining the front engine's dipstick for where the oil level would actually be in the sump, it is clear that this drain cock would let out any oil above the full dipstick level. Thus it is an alternative way of checking for sufficient oil without a dipstick.

The rear engine had a blanking plug instead of a drain cock so I swapped the two. The rear engine oil level can now be checked using the drain cock while the front engine's dipstick can still be relied upon.

The mystery has been solved but why the two engines are not identical remains an unknown.