3.5L Ecoboost Common Problems

Last Modified : Apr 3, 2021

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 in horsepower, the addition of a secondary low-pressure fuel system, and some design changes to fix the timing chain issues.

As the chain expands, the tensioner arm has to extend more to pull the chain tight. The further this expansion occurs the more out of sync the camshafts will become with the crankshaft. The reason for this is simple; as the tensioner expands to pull the chain tighter causes the camshaft gears to turn counter-clockwise, or retard the cam timing.

Eventually, the tensioner will reach a physical maximum stop point. A fully extended chain tensioner will cause the chain to bend backwards on itself 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

This is a common failure on the 2nd generation 3.5L Ecoboost on 2017 to 2021. Ford successully fixed the timing chain issue but now has VCT units wearing out prematurely. Symptoms of a bad VCT unit can manifest itself has a startup rattle in best case,a rattle when accelerating, or a constant rattle in worser cases.

Easy to diagnose. Ford released a new service message to cover the condition, TSB 20-2315, resulting in the replacement of all 4 of the VCT units. 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.

UPDATE 04/12/2021 Ford is saying not to do the reprogramming as mentioned in above TSB because it causes shifting concerns!

Ignore the message at the bottom of the TSB, you can do this yourself!

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 be a much cheaper repair for a leaky hose.

The degas bottle hose tends to be a reoccuring one. The degas bottle itself can easily crack if the engine has been overheated due to previous leaks causing low coolant condions.

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