There are all sorts of different engine oil dipsticks out there, and a trip to will reveal plenty of them. Some are stock replacements, some incorporate slick braided housings, while still others offer dipsticks that are locked and sealed within the tube.

Those latter designs are important.

(Image/Wayne Scraba)

Here’s why: The reason for the locking, sealed dipstick assembly is because it helps seal the crankcase. In many high performance or race applications (or even regular daily driver combinations), the dipstick can blow out due to excess crankcase pressure.

That pressure is commonly called “blow-by.”

What is Engine Blow-By?

Blow-by is really just combustion gasses that leak past the rings. It often contains unburned and partially burned fuel. As you can well imagine, this mix contaminates the oil and adds pressure to the crankcase. Excess crankcase pressure reduces cylinder vacuum on the intake stroke and simultaneously increases windage inside the oil pan.

There are a number of causes of blow-by. Some perfectly healthy engines (no matter what type, be it a Volkswagen flat four, motorcycle V-Twin, import four cylinder, North American V8, etc.) are affected by blow-by.

How Blow-By Relates to Your Dipstick

Causes and cures are beyond the scope of this article, but suffice to say if crankcase pressure is too high, it can blow the dipstick right out of the tube. Allowing the dipstick to blow out isn’t a great idea. While in some situations it’s relatively harmless, in other cases, it can mean hot, fuel-contaminated oil is sent spewing onto even hotter headers—and we all know what can happen next.

That’s why many race sanctioning bodies mandate locking, sealed dipsticks.

Sealed, locked dipsticks are most often fitted directly to the oil pan. Here, they fasten to the pan by way of a 1/4 inch NPT fitting. On opposite end, a compression fitting grips the dipstick tube and in turn, the nut holding the compression fitting in place locks into the 1/4 inch NPT fitting.

Things to Consider When Selecting a Dipstick

It’s easy enough to set up, but the big trick is fitting the tube into something like a car with large tube headers and raised exhaust ports. Factor in large diameter, sleeved ignition wire and tight spark plugs, and you can have a real fit dilemma.

With some locking dipstick setups, the tube is actually Teflon lined steel braided hose. It allows you to snake the tube in place rather easily. But there’s a word of caution: Do not allow the braided tube (hose) to come in contact with a header pipe. The heat will melt the Teflon liner. These types of dipsticks demand some air space between the tube and the header.

When it comes to metal tube dipsticks like the universal fit Moroso one shown in the photos below, it is possible to bend the tube. A common tubing bender does the job nicely. It may also be necessary to shorten the tube. In our sample build, it took two different cuts to get it right. (By the way, a small tubing cutter works well to cleanly slice open the tube.)

Once the new dipstick tube is in place, fill the pan with the required amount of oil, insert the dipstick, and check the level. At that point, you can mark the dipstick at the “full” level. Some folks place a little notch on the side of the dipstick at the full mark. Others simple scribe a very shallow line on the dipstick. Simple enough.

For a closer look, check out the photos:

Here’s the Moroso universal locking dipstick (part number MOR-25973). As you can see from this workbench shot, we’ve pre-assembled it and bent it slightly. (Image/Wayne Scraba)
This is the layout of the fittings used in the kit. There’s a 1/4 inch NPT fitting at the top, followed by a compression fitting “olive,” and then a compression nut. FYI, you cannot re-use the olive once it has been tightened. If you have to move it, you’ll have to replace the olive. (Image/Wayne Scraba)
The pipe threads will require sealant. No secret. This writer regularly uses this made-in-the-USA pipe thread sealant with Teflon from the folks at ARP. (Image/Wayne Scraba)
The NPT adapter fitting screws in the pan just like this. The pan in this photo is the one I wrote about a while back from the folks at Stef’s. (Image/Wayne Scraba)
So far so good, but as you can see there are several big obstacles in the way in our application. The 2.25 inch header tubes really complicate the tube placement. Note the spark plug access too. It’s fine with nothing else in the way, but adding a dipstick tube doesn’t help. (Image/Wayne Scraba)
In order to get the dipstick tube out of the way of the #2 header pipe, we bent it back slightly. With this set of custom headers, the #2 cylinder header pipe tucks in behind #4 pipe. (Image/Wayne Scraba)
The dipstick tube was too long at this point. As a result, it was shortened. In fact, we had to cut it twice to get it to the necessary length. A simple tubing cutter made short work of the tube. (Image/Wayne Scraba)
With the dipstick tube shortened, we can install it after the header pipes are in place—which is very important with our combination. (Image/Wayne Scraba)
We should point out that the tube was carefully deburred and cleaned after cutting. (Image/Wayne Scraba)
Next up, we test fit the assembly without the headers. This photo gives you an idea of the bend required for our application. (Image/Wayne Scraba)
Here’s a topside view of our dipstick assembly. Note the tube just touches the #4 header pipe. But there’s no Teflon to melt inside. If you refer to the picture at the top of this article, you’ll see we’ve positioned it so that it still allows access to the spark plug. It is still tight though and the adjacent header bolt will have to be replaced with a conventional 6-point fastener to allow for an open end wrench to reach it. (Image/Wayne Scraba)
This is the actual dipstick assembly found in the Moroso kit. The handle is a twist-lock affair while the actual cable design allows the dipstick to fit a number of tube bends. (Image/Wayne Scraba)
As noted in the text once you have the location and tube length nailed down, you can mark the end of the dipstick for your specific crankcase “full” location. (Image/Wayne Scraba)

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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.