ATV Oil Leaking From Exhaust Manifold (3 Reasons why)

Oil leaking from an ATV manifold isn’t a good sign, and you already know that. But the fault could be something simple.

Top 3 reasons Oil is leaking from an ATV exhaust manifold, include:

  1. Crankcase over full
  2. Blown head-gasket
  3. Oil stem valve seal failure

In this post you’ll learn the most common reasons oil leaks from your atv exhaust manifold and what you can do to fix it.

Oil Level

I’ll start with an overfull oil level, since this is the easiest to check and the simplest to fix.

Over filling your oil is easy to do but can cause some unexpected problems.
The correct oil level in your engine is very important.

Too much will cause the piston at BTD (Bottom Dead Centre) to displace the excess oil to wherever it will flow.

You’ll find an engine with too much oil, will develop oil leaks around the pan, dipstick, breather pipe, crank seal, exhaust, head-gasket and anywhere else it can push it.

If this turns out to be your problem, it’s an easy fix, unless of course you’ve damaged some seals.


Allow the engine cool and check the oil level, if it’s too full, and you suspect you over filled it, you’ve found your problem. Just drain off the excess oil and ride on, but do check for further oil leaks.

However, there’s another possibility for the over full oil level – a faulty carburettor float needle.

The float needle controls gas flow from the tank to the carburettor, when it fails, it allows gas fill their cylinder which leaks past the rings and into the crankcase.

To test for this condition, smell the oil, if it stinks of gas, you’ve likely found the source of your high oil level.

To fix this you’ll need to remove the carburettor fuel bowl, test and replace the needle, seal and seat. It won’t hurt to also check your float level and adjust if necessary.

Blown Head-gasket

A blown head-gasket can happen for various reasons, excessive blow by, too much oil, old age, loose head bolts, engine running too hot etc.

Depending on where your head-gasket blows, oil can be drawn into the combustion chamber and blown out the exhaust valve where it leaks from the exhaust manifold.

This however is usually accompanied by plooms of smoke, if you do have a lot of smoke, you’ll also need to consider failed rings.

A leak-down test is the best way to check a cylinder issue.

Worn Oil Stem Seal

Oil stem valve seals are nylon seals that fit over the valve stems and sit on top of the valve guides. The seal to designed to fit tightly around the valve stem and prevents oil escaping into the exhaust manifold.

Trouble is, as the seals age they become hard, oil then sneaks past the seal, where on the exhaust side, it escapes directly into the exhaust manifold.

Your seals may not be worn, they may be damaged. Your valves move up and down inside a valve guide. Wear and tear on an guides can cause them to simply wear out. This creates excessive valve lateral play and the valve damages the seal.

How to check valve guides and valve seals? You have two options. Remove the exhaust system and check the route the oil takes to the manifold. Or, remove the valve covers and check the condition of the seals and check for valve stem play.

Replacing the valve stem seals is possible without removing the cylinder head, but you’ll need to know a few hacks.

John Cunningham

John Cunningham is an certified mechanic and writer on I’ve been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of ATV ownership, from maintenance, repair to troubleshooting.

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