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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
Diagnosis & repair guide for leaky oil storage tank fill or vent pipe leakage

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.

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

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 SUPPLY 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 disassembling 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, people 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 (Bottini 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

Temporary oil tank fill or vent pipe leak measures (C) Daniel Friedman at InspectApedia.com

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

How to use epoxy to stop seepage at an oil tank fill or vent pipe

Gorilla expoxy used for oill tank leak repair cited & discussed at InspectApedia.comWatch out: this oil tank seepage-leak repair is suitable for sealing threaded fittings on an otherwise sound oil storage tank. If your oil tank is rusted, cracked, perforated, or leaking at the gauge or at a shutoff valve, an epoxy repair is not useful.

  1. Timing:

    Start your repair when there is no active seepage at the oil tank fill or vent line or other tank fitting.

    For fittings at the top of the tank this means waiting for your oil burner to use a few gallons of oil if in fact the oil tank was over-filled to its very top.
  2. Cleaning step A.

    Use a grease-cutting spray cleaner and paper towels or rags to clean off heating oil from the area of repair at the oil tank.

    In fact to reduce heating oil smells in the area, I prefer to clean off all of the accessible oil-wet areas on the oil tank.
  3. Cleaning step B.

    Use alcohol or lacquer thinner or a similar oil-free solvent-cleaner to complete cleaning the area of the toil tank top and surface to be sealed.

    I use a toothbrush to clean rust and oil debris from the exposed pipe threads and crevices around the fill or vent pipe where epoxy sealant is to be applied
  4. Cleaning step C.

    Wipe off debris and cleaner and let the surfaces dry fully. I use paper towels or a low-lint rag as I don't want to leave a lot of lint stuck to surfaces where it may interfere with good bonding of the epoxy.
  5. Apply sealant:

    Mix and apply any conventional two-part epoxy. Why epoxy to seal this oil tank seepage leak? I was not confident that a flexible sealant would remain in place.

    We used the Gorilla brand clear epoxy shown in the photo. But any clear epoxy product should work perfectly well on an indoor oil storage tank. If your oil tank is outdoors, choose an epoxy that is rated for outdoor weather exposure.

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

  1. Smooth the epoxy in place:

    Use a disposable bit of wood, cardboard, or even a screwdriver that you wipe clean of epoxy, smooth the epoxy in place.

    Take care that the adhesive/sealant is uniform, with no gaps or openings in the epoxy coating around the oil pipe and the surface of the tank. We extend the epoxy up about 1/4" on the pipe and out about 3/4" onto the oil tank surface.

    This sealant was completely effective against leaks at the oil tank fill and vent pipes in this location yet it remains easy to later remove the pipes should the oil tank later need to be moved or changed in any way.

    In fact this oil storage tank was later replaced completely, solving a problem of accumulated sludge and a completely specious and incorrect claim by an inspector that the tank was leaking. (It was not.).

    Those details are at OIL TANK REPLACEMENT PROCEDURE

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.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-12-16 by InspectApedia (Editor) - oil spraying out of the vent pipe during oil tank fill-up

@Judy,

What you describe - oil spraying out of the vent pipe during oil tank fill-up - is uncommon and usually means that the tank is being overfilled, OR the oil fill and vent piping are not connected in the required arrangement and spacing.

Help me out in helping you by providing some detail:

1. attach a photo of the oil tank fill and vent piping

2. Tell me where the oil is spraying from: the top of the vent pipe or at a lower fitting, indoors or outside, etc.

3. Tell me what your oil delivery company has said about this problem?

4. Is there actually oil on the ground from this spill? If so it needs to be removed.

On 2022-12-16 by Judy

When filling tank oil sprays out thee vent pipe. What’s wrong?

On 2022-12-15 by InspectApedia (Editor) - rag (or paper towels) wrapped at a couple of points is a good diagnostic idea

@Ellen Rollings,

The rag (or paper towels) wrapped at a couple of points is a good diagnostic idea.

Earlier I'd thought, too, that condensate might drip out at a leak point - that ought to be watery, with very little heating oil as there is basically never heating oil in the vent pipe itself - just fumes.

I diagnose this by careful cleaning and drying of all surfaces. Other forensic geniuses might dust a bit of baby powder around to (maybe) improve visibility of any leaks.

On 2022-12-15 by Ellen Rollings

@InspectApedia (Editor), thank you for this detailed answer! It’s definitely the vent pipe that is the pipe in question. I’d asked about how that one could leak oil and the explanation I was given at the time was that it was vapor that then condensed and must have leaked out of the joint that was not properly sealed with pipe dope.

I’d asked them at the time about the threads where the vent alarm connects to the tanks and they claimed those were fine. I’m going to do as you suggest and clean up the tank as best I can, and pay sharp attention at our next fill.

I may wrap a rag around that area as well, as that might help me determine if the oil is coming from above (as in a pipe) or below (from that fitting on the tank). Thanks again!!!

On 2022-12-14 by InspectApedia (Editor) - tank alarm is not installed on the oil fill pipe

@Ellen Rollings,

Proper installation position of union fitting on oil tank fill or vent piping

When installing a union on iron pipe it is common practice to install towards the external thread side of the union, but it makes absolutely no difference in the performance of a union.

If a plumbing union fitting leaks at the point of connection to the threaded iron pipe, then either the threads were mis-cut or damaged or the union was not properly sealed with pipe thread sealant.

If a plumbing union fitting leaks not at its threaded connections but at the mating faces between the two halves of the union, then those tapered compression-fit surfaces may have been dirty or gouged.

Now, if your photos show the tank alarm or as you put it, tank whistle, that device is normally installed on the VENT pipe that is allowing air out of the oil tank as it is being filled.

The tank alarm is not installed on the oil fill pipe.

Therefore there is not normally any oil passing through the oil tank vent piping nor the vent alarm or "tank whistle".

In some instances one *might*, find condensation inside of vent piping and that might leak out of a leaky plumbing fitting, but finding heating oil leaking out of a plumbing vent suggests that either the piping is improper or the tank is being over-filled.

If in your close inspection after an oil tank fill-up you find a rivulet track of heating oil below the vent fitting, follow it carefully by eye and touch up the oil tank and find the point of its origin. The most likely exit point would be at the threading of the tank whistle in your photo to the top of the oil tank itself. These fitting threads are large, sometimes a bit coarse in cut, and can be tricky to seal thoroughly.

If the leak is from a point higher up the vent piping then we need to review how the tank is being filled, as I've explained above.

See

OIL TANK GAUGE & VENT ALARM INSTALL / REPLACE

On 2022-12-14 by Ellen Rollings

Oil tank fittings (C) InspectApedia.com Ellen R@InspectApedia-911, I think that’s why I’m confused. According to the gauge, it hasn’t been overfilled. And when the tech fixed the issue originally, he said the leak was from one of the fittings higher up on the pipe, which he fixed.

Could the seal on that joint have deteriorated over the course of a year? I’m including a photo of the fitting that had originally been installed upside down, which they fixed and resealed last October.

On 2022-12-14 by InspectApedia-911 (mod)

@Ellen Rollings,

If you're sure that that was a new leak then you've answered your question for yourself.

However it's a bit odd for the oil to leak out at the very top of the tank like that unless the tank is being overfilled.

On 2022-12-13 by Ellen Rollings

@InspectApedia (Editor), thank you! I neglected to mention that the impetus for the post was that we had a fill today, and I found a fresh drip on the underside that had followed the path of the previous one in the photo. I’m certain it was new as I check after every fill. So something is amiss, it’s not a major issue and definitely coming from the vent pipe, not the fill.

On 2022-12-13 by InspectApedia (Editor) - drips from oil tank fittings

@Ellen Rollings,

It looks like blue Leak-Lok was used at the tank fittings - the right stuff.

I think I see the same dribble mark in all of the photos..

I would clean the tank top thoroughly - any household spray cleaner - dry it off, and then you'll be able to know if there is any sign of new leakage.

On 2022-12-13 by Ellen Rollings

Oil tank fittings (C) InspectApedia.com Ellen RWe replaced our oil tank last October, and the piping was initially problematic. Our oil company sent their best guy out who discovered one fitting hadn’t been died at all, and one fitting had been installed upside down.

He disassembled the whole vent pipe and resealed all the joints/connections (and put the upside down connector in correctly).

What prompted the call back was I noticed some drips that started from the top of the tank and ran all the way down the sides. Not ideal for a brand new tank.

The problem seemed solved, as I checked each fill-up and hadn’t noticed any new drips…until today.

Is it possible a seal has deteriorated in a year, or could something else be afoot?

I’m attaching photos from last year, and one from today. I don’t see any real changes to the path of the drip (it’s the drips around the red whistle fitting in the left of the photos) but I’d be grateful for any ideas you experts may have. Thank you!

 

On 2022-08-19 by InspectApedia-911 (mod) - dual-tank installation venting requirements

@Jb,

Typically even in a dual-tank installation only a single vent pipe carries air to the building exterior, perhaps in your case out of the downstream of the two oil tanks.

In that case the vent alarm would, as you'll see at

OIL TANK GAUGE & ALARM INSTALL / REPLACE

be installed where the vent pipe connects to the oil tank top.

Also see DUAL OIL TANKS - PIPING

where you'll find the illustration below, showing that the vent alarm or tank whistle is at the exiting vent pipe. Note the GREEN vent pipe


On 2022-08-19 by Jb

@InspectApedia-911, I was a bit confusing on my description. Here is a picture [no photo submitted] from your website that is how it is piped. I just didn't know where to install the alarm.

On 2022-08-18 by InspectApedia-911 (mod) - Usually there's just a single tank fill alarm

@Jb,

Usually there's just a single tank fill alarm.

But your description is a bit confusing. With the fill splitting ahead of two tanks and the vent merging from the two tanks, I am baffled as to how an oil tank delivery driver will know when both tanks are filled; there could be trouble as it's quite possible, depending on how the oil is piped both into and out of those tanks, that one tank is emptied before the other;

Is this a brand new installation?

Can you post a sketch and some photos?

one image per comment but as many comments and photos as you need.

On 2022-08-18 by Jb

Does a whistle alarm have to go in both oil tanks if the tanks are twinned together with one fill pipe splitting then going to each tank and the vent comes out of each tank and joins together and goes into one pipe going outside.

On 2021-10-22 by inspectapedia.com.moderator

@SG,
Thank you so much for the helpful follow up and feedback. It will help other readers.

On 2021-10-22 by SG

@inspectapedia.com.moderator, Just wanted to report back for anyone else who might come upon this page that after following your instructions and method my tank has had no weeping or spread from the fill valve. Just had the tank filled and it's still clean on the outside. Thanks again!

On 2021-06-09 by inspectapedia.com.moderator

@ SG

Thanks for the nice note back; we're glad to help; your questions help us see where we need to add or clarify information.

Working together makes us smarter.

On 2021-06-09 by SG

@mak.church,
Thank you! I really appreciate you taking the time to add that information- hoping it works as well for me as it did for you, but either way you saved me lots of time and second guessing trying to figure out if what I'm trying to do makes sense!

On 2021-06-07 by mak.church (mod)

@SG,
Thank you for the helpful question; we have added details about using repair epoxy on an oil tank now found in the article above. You may need to clear or refresh your browser cache to see the updated page. We welcome your further photos, comments, questions.

On 2021-06-07 by SG

Can you tell me what sort of epoxy sealant you used for the minor leak at the fill valve? I've got a stain that's starting to spread, had tank inspected said it was fine and that it might have been overfilled...but it does keep getting larger after each fill up. Would like to try and manage it without needing to dig up and redo any piping.

On 2021-02-14 by danjoefriedman (mod)

Gene

Forgive me but there must be some part of your question and piping problem that I do not understand. I don't understand how the work could be done correctly but have many leaks. In general if there's a leak in plumbing connections it's because either they were cross-threaded or we didn't use the proper sealant.

But of course since I can't see your installation there could be a different problem. I'm really sorry I wish I could be more helpful but from just your text I can't possibly tell you how to fix a single leak much less a multimillion-dollar job. You're welcome to post more details or photos of the situation and perhaps I can make a more useful comment.

On 2021-02-14 by Gene

I have many leaks on a diesel fuel system for a generator.... We used viega megapress fittings and black iron pipe but had many leaks i did the installation myself and know it was done correctly.... Has anyone else had problems with liquid fuel leaks. I have used this system hundreds of times in pressures many orders of magnitude higher with no problems..... Help please this is a multi million dollar job..... And im stuck.

On 2021-06-09 by inspectapedia.com.moderator

@gil collins,

You'll find the NY Oil Piping code (and New York's and NYC's adoption of the model codes) at

OIL TANK REGULATIONS

On 2019-10-04 by gil collins

need to find the code for the vent line for my oil tank NYS code

On 2021-06-09 by inspectapedia.com.moderator

@Douglas Ihlenfeld,

agree that the fill and vent should drain back to the oil tank.

My OPINION is that at each oil tank fill-up the pooled oil in the mis-pitched line is mixed with incoming new heating oil and pushed into the tank, so the chances of an accumulation of water or sludge that blocks the line are probably low.

If you want the installer to correct the error you can cite the model code

CHAPTER 13 FUEL-OIL PIPING AND STORAGE

1305.7.6 Pitch.

Normal vent pipes shall drain toward the tank. The normal vent pipes shall have no sags or traps where liquid can collect.

- source: NYC Mechanical code, adopted version of the model IMC.


A copy that you can print if needed is here as a free PDF download

https://inspectapedia.com/oiltanks/UMC-Chapter-13-Fuel-Oil-Piping-Storage-2008.pdf

Source: OIL TANK REGULATIONS

On 2017-12-05 by Douglas Ihlenfeld

Question, A recent install on new fuel oil tank. The contractor installed both the fuel and vent pipes pitched away from oil tank. Both pipe runs average ten feet. There is plenty of fuel sitting in pipe after first fill up. I live in PA . What about the weather? Oil left in pipe, doesn’t good.

Question:

(July 6, 2014) lee said:
I have a two line fuel oil furnace I can change to a single the one line is leaking is there a good product u can pump in like with a caulking gun ? I believe the leak is just below the top of the cement floor '

Reply:

this question was answered when you posted it on other articles, Lee. Please post in just one place.


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