The 5 Most Common Ford 351 Windsor Engine Problems

The 5.8L small-block 351 Windsor was a staple of Ford’s trucks and muscle cars of the 60s, 70s, and 80s, even 90’s. While the engine went through numerous design changes over the years the main engine design remained in-tact. These engines are known to be nearly bulletproof.

Despite their bulletproof reputation, they do suffer from a number of common engine problems. A few of the most prevalent include timing cover leaks, cracked exhaust manifolds, rear main seal leaks, intake manifold bolts, and block issues. In this guide we’re going to dig into each problem in depth and discuss overall 351 Windsor reliability. And we’ll even cover some differences between the very similar 351 Cleveland at the bottom of this article.

Ford 351 Windsor Common Engine Problems

• Timing cover coolant leaks
• Cracked exhaust manifolds
• Rear main seal oil leaks and gasket leaks
• Broken intake manifold bolts
• Weaker blocks (1975+)

1. Timing Cover Coolant Leaks

The timing chain on the 351 Windsor is protected by a cover which protects the timing chain and sprockets from dirt, mud, and grime. The timing cover bolts to the front of the block and is sealed in place with a gasket.

Over time, as is normal with gaskets, the timing cover gasket begins to deteriorate and cause leaks. When the gasket leaks, engine coolant will leak around the timing cover. Additionally, the gaskets near the water pump are known to cause coolant leaks as well which will also result in coolant leaking around the timing cover.

The 351W’s don’t take extra heat well which is the most common cause of catastrophic engine failure.

Coolant Leak Symptoms

• Excess coolant consumption
• Leaking coolant around the timing cover or water pump
• Engine overheating
• Occasionally no leaks are noticeable but a smell of burning coolant is

2. Cracked Exhaust Manifolds

The exhaust manifolds on the 351 Windsor are made of cast iron. When cast iron is heat up it expands, and it contracts when it cools down. Engine heat cycles, or the engine warming up and cooling down constantly, create a lot of stress on the cast iron as it is constantly expanding and contracting. Over time the heat cycles and constant engine vibration lead to the manifolds cracking which causes an exhaust leak. Outside of the negative environmental impact of exhaust leaks, it can lead to various performance issues such as a loss of power or acceleration.

The OEM manifolds on the 351W are known to crack around the 120,000 mile mark. Unfortunately there isn’t much in the way of preventative maintenance outside of replacing the manifolds ahead of time or upgrading to performance manifolds.

Cracked Exhaust Manifold Symptoms

• Loud engine/exhaust noise from cab
• Smell of exhaust gases from inside cab
• Loss of power and acceleration
• Poor fuel economy

Replacement Options

Due to the number of 351W’s produced there should be plenty used parts available. Replacing the manifolds with used/junk yard manifolds is common as the parts are generally easy to find and cheap to replace. However, the downside is that any set of OEM manifolds is likely to crack again. A popular option is upgrading from cast iron manifolds to steel exhaust headers.

3. Rear Main Seal Oil Leaks

The rear main seal is prone to developing oil leaks. The rear main seal is located at the back of the engine where the crankshaft meets the transmission. The small circular seal is responsible for keeping oil from leaking out the back of the engine.

When the 351W isn’t driven frequently the seal can dry out and form cracks that cause oil to leak out. While letting the car sit for a while can cause this, it is also prone to happen on frequently driven cars as the seal is a small rubber part that is prone to deterioration as is common with any seal or gasket.

Unfortunately replacing the rear main seal is a rather cumbersome project. The part is only a few bucks but it requires extensive amounts of labor to be able to get to the seal which makes it an expensive repair bill if you aren’t capable of DIY’ing the project.

Rear Main Seal Oil Leak Symptoms

• Oil leaking under transmission/back of engine
• Quick oil consumption (frequent refills needed)

4. Broken Intake Manifold Bolts

On the 351 Windsor the manifold bolts are prone to breaking. Because the bolts mount to the block they are prone to high temperatures and experience the same heat cycles from the engine. The effects from heat cycles combined with the constant vibration they receive causes them to break off.

When the manifold bolts break, intake air starts to leak out, also known as a vacuum leak. This can throw off the air to fuel ratios of the engine and lead to numerous performance issues such as a loss of power, lack of acceleration, cylinder misfires, etc.

Fortunately, fixing this issue is as simple as replacing the manifold bolts. While you are at it it is worthwhile to inspect the manifold gasket to ensure it is intact and not leaking itself.

Symptoms

• Cylinder misfires
• Lean/rich AFRs
• Lack of power and acceleration
• Bad fuel economy
• Stuttering or hesitation under acceleration
• Rough idling
• Increased engine noise

5. Weak Cylinder Blocks

While this isn’t necessarily a problem, it is something I wanted to point out for performance enthusiasts. The 1969-1971 blocks are considered the strongest produced. 1972-1974 were strong as well, albeit slightly less strong that the previous ones.

In 1975 Ford changed the block castings to produce a lighter weight block. To do so Ford essentially decreased the amount of metal used in the block, making various components of the block thinner vs. the older models which were thicker and had more metal support.

While there are people pushing more power on the stock blocks, the newer blocks appear to be reliable up until the ~650whp mark. We have seen claims of the stock block running 750-850whp. The older blocks appear to be capable of handling power levels closer to the 1000whp levels.

While this isn’t necessarily a problem, 351W’s are commonly modified engines in today’s world. Be cautious of the power levels you are shooting for and the capabilities of the block that you have.

Ford 351 Windsor Reliability

Ford’s 351W engines are virtually bulletproof. The blocks, even on the 1975+ models, are very stout and will not give any problems until serious power is added. The rods, pistons, and other internal components are rock solid as well.

Overall, the 351 Windsor is a tough engine and is built to take a beating. While the block, internals, head, and other major components are rock solid, keep in mind these are getting to be old engines. Oil leaks, coolant leaks, work gaskets and seals, water pumps, etc. are all prone to failure given the age of these engines. Both the intake and exhaust manifolds tend to run into some minor issues due to age. Otherwise there aren’t too many engine specific issues you will run into with these engines.

Proper maintenance is always the key. Heat is the biggest killer of the 351W engine so preventing coolant leaks and engine overheating is paramount to reliability. If you are going to modify the 351 make sure you have an adequate cooling system to prevent excess engine heat.

With proper maintenance and care the major components of the 351W engine shouldn’t have an issue surpassing the 300,000 mile mark.

351 Windsor vs. 351 Cleveland

From 1969 until 1982, Ford produced a 5.8L, 351 cubic inch V8 called the 351 Cleveland. The Cleveland title was given due to its manufacturing location of Cleveland, Ohio. Despite both being 5.8L V8’s, the 351 Windsor and 351 Cleveland are actually from different engine families. Commonly referred to as the 351W and 351C, the 351C was part of Ford’s “335” engine family.

The 351 Cleveland was born when Ford realized that demand for the 351 Windsor was greater than their production capacity in the Windsor plant. Therefore, they decided to begin producing the 351’s in the Cleveland plant as well. However, Ford also decided to upgrade the Cleveland built 351’s with a new cylinder head design for improved performance. Two new head designs were built, one similar to the 351W but with larger valves and ports, and one with large ports and canted exhaust and intake valves.

To make things slightly more confusing, the 351 Cleveland had numerous different engine codes. From 1970 to 1974 Ford produced H, M, R, and Q versions of the 351C which were primarily performance oriented versions of the traditional 351C.

Performance enthusiasts commonly swap the heads of a 351 Cleveland onto the block of a 351 Windsor, creating a 351 Clevor. The Windsor blocks were known to be stronger while the Cleveland heads had more flow and therefore more performance potential.

If you like to know more about common engine problems of Ford 351 Cleveland, then you are at right place.