The 351 Windsor is a 5.8L small-block V8 engine produced by Ford from 1968 until 1997. It is one of Ford’s longest running and most successful engines to date. The 351W is part of the Windsor V8 engine family, an informal name given to the engines produced out of the Windsor, Ohio manufacturing plant. The Windsor family is a group of 90 degree OHV small-block V8 engines, produced from 1961 until 2002.
At 351 cubic inches, or 5.8L, the 351 Windsor is the largest V8 in the Windsor engine family. Over its nearly 30 year history, the 351W went through a number of revisions and improvements. While there are too many to list specifically, here are some of the more material changes throughout the years:
- Block casting was changed in 1975, the 1969-1974 versions are significantly stronger and therefore more desirable
- Deck height was increased in 1971 for a lower compression ratio
- The rear main seal was changed to a one-piece design in 1984
- Switch from speed density to MAF in 1994
- Lifters were added in 1994
- Carburetor replaced with fuel injection in 1988
Ford cars that use the 351 Windsor
- 1968-1974 Galaxie
- 1968-1970 Mustang
- 1969-1970 Mercury Cougar
- 1969-1991 Country Squire
- 1969-1970 Fairlane
- 1970-1976 Torino
- 1974-1976 Ford Elite
- 1975-1996 E-Series Vans
- 1977-1982 LTD / LTD II
- 1977-1979 Thunderbird
- 1979-1996 Ford Bronco
- 1979-1991 Crown Vic
- 1987-1997 Ford F150/F250/F350
- 1977-1979 Mercury Cougar Station Wagon
- 1978 & 1986-1991 Mercury Colony Park
- 1978-1982 Mercury Marquis
- 1986-1991 Mercury Grand Marquis
- 1980 Continental Mark VI
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.
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+)
A noteworthy disclaimer: many of these problems are problems because of how old these engines are nowadays. The engines themselves, blocks, internals, heads, etc. are very strong and virtually bulletproof.
1. 351W 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 only repair option is to replace the gaskets. Fortunately the gaskets are cheap and are somewhat easy to DIY if you know your way around an engine. If you are leaking coolant the most tell-tale symptom is frequently running low on coolant. Making sure your 351W stays topped off on coolant is extremely important for preventing overheating and serious engine damage.
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 – 351 Windsor
An exhaust manifold bolts up to the exhaust ports on the engine block. The manifold is responsible for collecting exhaust air and funneling it to the exhaust system where it is then released via the tail pipes. The 351W has two exhaust manifolds, each responsible for 4 cylinders.
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.
351W 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
351 Windsor Exhaust Manifold 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.
With that being said, a popular option is upgrading from cast iron manifolds to steel exhaust headers. Headers differ from exhaust manifolds in that there is a separate steel tube that bolts up to each cylinder where they eventually meet into one connector tube. Exhaust manifolds are one solid cast iron structure. Headers can increase power by 10-15hp so it is a common upgrade for performance enthusiasts, although it will require further exhaust system upgrades.
3. Gasket & Rear Main Seal Oil Leaks – Windsor 351
One generic common problem that I want to point out along with the rear main seal oil leaks, is general gasket oil leaks. The head gasket, water pump gasket, timing cover gasket, etc. etc. are all prone to deteriorating and leaking with age. That being said, any old 351W without a fresh rebuild or gasket repairs likely leaks oil or will at some point in the future. The gaskets generally do not last much beyond 150,000 miles, especially if they are originals.
On to the more specific problem, 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. 351W Broken Intake Manifold
Opposite the exhaust manifold is the intake manifold. The intake manifold is responsible for taking the air from the intake and sending it to each of the engines cylinders. The manifold is mounted on top of the block and the intake itself sits on top of the manifold where air is drawn in and then dispersed to each of the 8 cylinders.
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.
351 Windsor Vacuum Leak 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. 351W 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.