Photograph of  an oil tank with seepage around the filler pipe and a too-small vent pipe. Leaky Oil Tank Filler or Vent Piping Repair Procedures
A diagnosis & repair guide for leaky oil storage tank fill or vent pipe leakage.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Oil tank leaks at the fill or vent piping:

This article discusses the causes of leaks at oil tank fill or vent piping, what the leak and other hazards are, and what to do about oil tank piping leaks.

We explain what to do about leaky oil tank vent or filler piping; oil tank piping sources of leaks and oil odors or smells.

We illustrate the places where both minor and more significant oil leaks can occur and we describe and illustrate how to repair those leaks using any of several methods ranging from trivial leak control (using a rag) to permanent leak repairs using an epoxy sealant or by re-making the pipe joints using an oil-resistant pipe thread joint sealant compound.

We give examples of stopgap and then permanent measures to control small oil tank fill and vent pipe leaks, permanent oil seepage leak repairs using epoxy, and proper oil tank piping repairs by re-making the pipe joints using a proper thread sealant.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Why Oil Storage Tank Piping Leaks & How to Fix Leaky Oil Storage Tank Filler or Vent Piping

Photograph of a seepage leak at an oil tank filler pipe, wrapped with a rag

This article discusses the causes & cures of leaks at the oil storage tank fill or vent pipes.

It is very common for there to be leakage around the oil filler pipe or vent pipe where they are connected to the top of an oil tank.

If the tank is buried these leaks may go undetected for some time, but on an above ground oil tank, inside or outside, the seepage is quickly visible and also can be smelled by most owners shortly after an oil delivery.

[Click to enlarge any image]

A separate article found at OIL LINE PIPING LEAKS discusses leaks in the smaller-diameter piping between the oil storage tank and the oil burner(s) it serves.

Article Series Contents

Diagnose the Causes of Oil Tank Fill or Vent Pipe Leaks

Photograph of severe seepage leaks at all top fittings of a heating oil storage tankHere are reasons for the leakage at the oil tank fill and vent piping or at the oil tank gauge.

Heating oil leak problems at oil tank fittings and pipe threads

The pipe threads (NPT) which are cut into an oil tank top tapping intended to accept the filler pipe or vent pipe are not precisely machined - they are a bit rough.

So are the threads on most large-diameter iron piping used to screw into the tapping.

Having installed a few of these, we can testify that it requires some very careful workmanship to make a leak-tight joint, combining cleaning of the threads, use of a high quality pipe dope rated for use on petroleum products, and turning the pipe into the tapping with sufficient force to seal it without damaging threads.

In sum, often the connection is simply not very tight.

Because dis-assembling and re-assembling oil tank fill and vent pipes can be a chore, especially where those pipes are partly buried or where they are cemented into a foundation wall, peoople often live with these oil tank seeps and leaks until the oil leaks become more than a small nuisance.

Below we describe in-place efforts to seal such leaks using a combination of cleaning and surface sealant epoxy.

Heating oil leak problems due to pressurized oil storage tank fill procedures

Heating oil deliver with an attentive operator (C) Daniel Friedman Bottini Fuel Wappingers Falls NYIn the mind of the installer, "What the hey, after all, the tank is just going to be at atmospheric pressure and filled by gravity from above, right?"

Wrong. Oil companies recognize that the time needed to complete an oil delivery is part of their profit or loss picture. Modern oil delivery trucks are designed to pump heating oil into the tank under pressure in order to speed the delivery process.

At a recent oil delivery we filmed and timed the oil tank fill process. The delivery driver (Bottinin Oil December 2017) pumped 225 gallons of heating oil into a nearly empty oil tank in a bit over four minutes. That was fill rate of about 50 gpm. Some delivery trucks pump oil at up to 70 gpm.

Photo: the Bottini oil delivery operator is demonstrating the correct and thoughtful way to fill an indoor or buried oil storage tank.

During oil tank filling the driver is listening to the tank whistle or tank alarm to avoid over-filling the tank - a common source of seepage and occasional heating oil or fuel oil spills. If the plumber or installer locates oil fill and vent pipes where they are difficult to access, don't expect such careful oil deliveries.

In fact most modern oil tank filler caps have a special fitting, often different from one oil company to the next, that permits the installer to "lock" the filler hose to the filler pipe during the fill-up procedure.

Usually an oil storage tank is filled right to its top during an oil delivery. This is because the way that the delivery driver knows that the tank is full is that s/he is (supposed to be) listening at the filler pipe. Tank fill or vent valves are (supposed to be) equipped with a whistling noisemaking device that indicates when the tank is full as the heating oil reaches the sounding device.

So if, unlike the driver in our photo above, the oil delivery pumper is not listening, say s/he went aside to smoke a cigarette or make a cell call, or if the tank top fittings are not absolutely tight, it is common to see some leakage around the tank top after a fill-up.

We discuss details of oil tank pressures created during the oil tank filling operation at OIL TANK PRESSURE.

Oil Tank Fill/Vent Pipe Leak Diagnosis

When and what should you do something about a leak at the top fittings of an oil tank?

Photograph of a small heating oil leak at a tank fire-o-matic safety valve at the tank bottom Photograph of copper piping used for an oil tank fill and vent pipe

How to Repair Seepage or Small Oil Tank Fill or Vent Pipe Leaks

Oil tank fill or vent pipe seepage leak stopgap repair (C) Daniel Friedman

Epoxy sealant stops seepage at oil tank fill and vent piping (C) Daniel Friedman Epoxy sealant stops seepage at oil tank fill and vent piping (C) Daniel Friedman

How to Repair a Significant Oil Fill or Vent Pipe Leak

Photograph of a basement heating oil storage tank leak onto the concrete floor

Oil tank with fill and vent pipes removed (C) Daniel Friedman Oil fill and vent caulking at house wall (C) Daniel Friedman

Above and continuing with more photographs below we illustrate an oil tank whose fill and vent piping has been removed to permit tank relocation and re-piping. That is a convenient time to take extra care that the oil piping connections are well sealed when they are re-made.

At above right we illustrate taking care to seal the oil vent or fill piping where it passes through the building wall, avoiding water entry, drafts, and insect damage by keeping these wall penetrations well-sealed.

Oil fill or vent pipe sealed at the building exterior wall prevents water, insects, drafts from entering the structure (C) Daniel Friedman

Shown at above left is the outside view of the oil fill or vent pipe - well-sealed at the building wall: we caulked on both sides of the exterior wall sheathing in this installation.

If a reader or product manufacturer has a sealant that is actually effective in this application, dealing with the rust, oil, surface shapes, and fill pressure, I'll be glad to report on that product here. It would indeed be less trouble than re-piping the tank. Make sure the new piping is properly sealed and secured. If heating oil has been dripped on the floor, ask your oil company to clean it up and deodorize the area.

Proper sealant stops leaks at an oil tank fill and vent pipe (C) Daniel Friedman\ Proper sealant stops leaks at an oil tank fill and vent pipe (C) Daniel Friedman\

Above we show re-made and properly-sealed oil fill and vent piping connections using an oil-resistant pipe joint thread compound. We have had good success sealing even the rough threaded pipe joints in large diameter oil tank fill and vent piping using "Brush-on/Blue Block", a pipe thread and gasket sealant compound provided by Hercules / Oatey Block pipe joint and gasket sealer.

An 8-ounce container retails for less than $7.00 U.S.D. and is available from your local plumber supplier or building supply store such as Davies Hardware in Poughkeepsie, NY or at Home Depot and Loews building suppliers.

A similar Oatey product, Oatey SCS 15707 Hercules Block Greenish-Blue Thread and Gasket Sealant is also effective for sealing oil tank fill and vent pipes. Oatey's Great Blue® pipe joint sealing compound is also rated for use with diesel fuel oil, gasoline and many other liquids.


Continue reading at OIL FILL / VENT PIPE RUST-CAUSED LEAKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see OIL TANK PRESSURE - what role does the fill-pressure play in oil storage tank leaks?

Or see these

Oil Tank Piping Leak Articles

Suggested citation for this web page

OIL FILL / VENT PIPE LEAKS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman