3.5L Ecoboost Common Problems
The Ford 3.5L Ecoboost engine is a marvelous design, out performing the ledgendary Coyote while being the premiere engine in the F150 and Expedition line-up, as well as being used in more performance oriented vehicles like the Taurus Sho, Police Interceptor, and Raptor. But even such a well established engine has had several reoccuring issues.
This list of common problems with the 3.5L Ecoboost engine will include both generations. The second generation came with several improvements like more horsepower, the addition of a secondary low-pressure fuel system, and some design changes to fix the timing chain issues.
For consistancy, I will be refering to generation 1 being 2011 - 2016, and generation 2 as 2017 - 2021. Some early build 2016's will have the first generation, and some late builds could have the second generation.
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3.5L Ecoboost Stretched Timing Chain
One of the most common issues on the first generation 3.5L Ecoboost 2011 - 2016 is a phenomenon of a stretching metal timing chain. The truth of the matter is that the chain does not stretch, as elasticity is not a property of metal, but that each chain link developes wear. This small amount of wear over several of the tiny chain links causes the chain to grow in length. Symptoms can include check engine light, rattle on startup, and eventual engine failure. Replacing the timing chain on a 3.5L Ecoboost is managable.
The chain has a tendency to wear because of the routing. Since the engine uses one primary chain, it loops around a camshaft, then down to the waterpump on FWD (idler on F150), then back up to the other camshaft, then all the way back down to the crankshaft sprocket. This routing causes the chain to have a working angle sweep twice the length of most other Ford products, essentially the chain has to bend forward and backwards on itself. The 2nd generation fixes this issue by using two primary chains like the modular 5.4 or 5.0, effectively reducing the working sweep.
As the chain expands, the tensioner arm will expand more to keep the chain tight. This expansion causes the camshafts to become more out of sycn with the crankshaft. The reason for this is simple; as the tensioner expands to pull the chain tighter it causes the camshaft gears to turn counter-clockwise retarding the cam timing.
Eventually, the tensioner will reach a physical maximum stop. A fully extended chain tensioner will cause the chain to bend backwards on itself a bit again between the tensioner arm and the crankshaft pulley. Any further expansion of the chain creates sloppiness on the crank sprocket. Turning the engine backwards at this point will usualy cause the chain to slip teeth. This can occur on engine shut down due to compression kickback.
3.5L Ecoboost VCT Phasers
The 2nd generation 3.5L Ecoboost on 2017 - 2021 fixed the chain wear issue, however they introduced VCT cam phaser issues. Symptoms of a bad VCT phaser can manifest itself has a startup rattle, a rattle when accelerating, or a constant rattle in worse cases.
Easy to diagnose. Ford really made a mess of the situation. Firstly, they released a recall 21B10 that makes the dealer offer reprogramming designed to reduce or eliminate the noise. This reprogramming can cause an severe low RPM engine shudder, so then recall 21N08 gets opened allowing to reprogramming it back to stock if you develope a shudder. Finally after 21B10 gets claimed, 21N03 opens up to allow for replacement of all four VCT phasers, but only as a pro-rated charge depending on milage.
Unfortunately, if your vehicle is already out of powertrain warranty or extended coverages you may have purchased you will have to pay for the repair yourself. I'll make sure to create a write-up for this process as well.
3.5L Ecoboost Coolant Leaks
Some common coolant leak points include the lines that feed the turbochargers, as well as the crossover hoses at the front of the engine. Really any of the hoses at the front of the engine using a quick connector type hose with a locking clip in it. These hoses have replaceable O-rings in it that could result in a much cheaper repair for a leaky hose vs a replacement coolant hose.
The degas bottle hose tends to be a reoccuring leak. The degas bottle itself can easily crack if the engine has been overheated due to previous leaks causing low coolant condions. Water pump leaks are also fairly common.
3.5L Ecoboost Oil Leaks
Just like it's little brother the 2.7L Ecoboost, the 3.5L Ecoboosts with the plastic oil pans have a history of leaking due to improper RTV bonding. It will require the oil pan to be replaced and fresh RTV installed. The aluminum pan types do not seem to suffer from the same high probibility of leaks. The first generation also suffers from leaks from the front cover, generally located just near the AC compressor. Removal of the front cover and fresh RTV sealant will do the trick on those.
A few other notable oil leaks is the rear vacuum pump gasket. Oftentimes the oil will leak directly down onto the hot downpipe exhaust coming off the turbo and give a burning oil smell. Usually, replacing the gasket on the vacuum pump will fix the issue, but sometimes the issue will be the valve cover gasket itself or even the seal at the rear camshaft bearing cap. The bearing cap is sealed with a permatex red sealant that is more akin to threadlocker.
Overall Review of the 3.5L Ecoboost
Like most of the Ecoboost line-up, the 3.5L Ecoboost has impressive output considering the size of the engine. I suppose you can thank the turbochargers for that. There were some growing pains, especially in the early years of throwing pistons through the side of the block, but they have become a pretty well-rounded reliable engine. My personal truck, a 2015, has 152k miles on the clock and at this moment is still cruising right along.