Hey fella's just wanted to share a little info on the much hyped ford 5.0 coyote engines. As a mechanic I get the opportunity to see the bad side of many of our beloved cars, and lately i've seen a lot of the new stangs. It is no secret to those in the know that the last few generations of ford engines have suffered from piston reliability issues. Starting with the 5.8/351 back in the late 80's. It is not uncommon to find the ring lands broken on motors with over 100k miles due to the pcv system causing overly lean conditions in certain cylinders. Fast forward to the 90's and the 4.6 and 5.4 motors suffer very similar problems, especially with mileage over 80k. 5.4's that are started cold and immediately rev'd and driven away will break the ring lands and spit the rings, plug, and coil out the top. 4.6's just seem to burn copious amounts of oil.

Now on too the new engines. Had a customer come in several weeks ago with a new 5.0 stang. Beautiful black on black car, lowered, with the ususual I/E mods. He was also running a sct tuner with there out of the box 93octane performance tune. Car was smoking very heavily at idle, and he complained of lack of power. The car is still under warranty, but obviously the dealers suck ass so he came to see us for a little check up. Well after a quick drive and compression test, the bad news was 2 cylinders showing over 10% leakdown and one with about 30%. He decided to take the car to ford, as the warranty would not cover us tearing into the motor. Long story short, they disassembled the motor to find bad rings on 4 cylinders and one cracked piston. The of course voided his warranty because of the tuner, and presented him with a 12,000.00$ estimate for a complete new engine and 900$ labor for the teardown and inspection of the original motor. After two weeks of argueing with them, they released the car at no charge, and he had it towed to us for the rebuild. We are gonna hone the cylinders and replace the pistons and rings, saving him about 6,000$ in expense.

As for the motor, it is absolute shit. The pistons and rods are CHEAP CAST JUNK. I'm amazed that ford would build an engine with such inferior parts. If you buy one of the cars, DO NOT attempt to install blowers, turbo's, or nitrous without first rebuilding the motor with quality internals. You will inevitably have a catastrophic failure in short order. We took the stock pistons and rods to our local machine shop/engine builder and he started laughing histerically when he examined them. I also contacted a friend a the local ford dealer,and he told me they had seen several failures of the pistons already. The problem is the castings, they are extremely poor quality. The piston that failed in our motor shows zero signs of trauma on the surface, but a large section between the upper and lower rings simply cracked and fell apart, taking the rings with it. You can see looking at it closely that there are small air bubbles in the aluminum. Anyway, i'm not ford bashing here, between myself and my brothers, we've owned 6 different stangs in the past 15 years, and I was hoping for good things from the new models. Not gonna happen though. My advice would be to save your money for the Boss, or gt500 versions with forged internals, as the standard 5.0 is a turd. Oh and don't mod a car thats not paid off. Our customer is not a happy man as he still owe's 30k on a car with bad pistons and NO warranty. I'll get some detailed pics of the pistons up on tues so you can see what i'm talking about.

I should add the car has 22k miles and the owner admitted to driving it hard. Still no reason for pistons to fail as they did though.

 

Two thoughts:

1) Who's to say that the "tune" the owner had on the car wasn't the issue? The coyote engines are already tuned to run quite lean to begin with.

2) There may or may not be something wrong with the design or manufacturing quality of the 5.0 pistons. But the fact that the pistons are cast is not a sign of a low quality part. Virtually every car comes with cast pistons and rods. Cast pistons, while more brittle are typically lighter than forged.

Andrew

 

I think the story about a modified 5.0 falling apart is only valid in that it is a great warning about ensuring you have a quality tune on any car you change.

He did mention the dealer said they'd had the same problem on a number of cars, though, and that's an interesting tidbit of information.

 

OP, do you have a reference for this? Sorry it's not the first time you have been critical of something without a lot of strong supporting evidence.

 

When I get the pictures of the pistons up you'll see what i'm talking about. Very poor quality. I'm stating that from my 17 years experience as a mechanic and ford owner, my machinist experience as a professional engine builder, and my ford tech friends statement as a ford trained technition that the motor is a F-cking piece of crap. It runs beautifully, smoothly, and makes good power. Its just built of shit. If you mod it, you will break it. I'm critical of things that suck ass. This motor sucks ass. When its rebuilt with quality parts, like the forged version found in other cars, it will be great. In its base form, its weak sauce. Mod it with caution.

 

BTW, which piston failed? Cylinder #8??

Andrew

 

Oh I don't doubt that you were able to identify a failed piston. However, you have proudly announced that we should all avoid this motor like the plague. OK, since I wasn't looking to get a Mustang anyway this doesn't really change my buying plans. However, what makes the engine junk? Based on my web search conducted after your post it appears the motor doesn't have a lot of excess strength. That is a trade off you make for a 5L V8 with that kind of power yet at a low price point and with low weight. What I haven't seen in the posts was some sort of clear proof that this is a big problem for stock motors. Perhaps this is like the crank failures the '99 Miatas had. I've read more than a few posts claiming no one should buy a '99 Miata because they have crank failures. Perhaps, because you are in the trenches and see this you don't have a great grasp of the number of motors out there and the number that are stock yet having problems.

Now if you wanted to say that it's a bad motor to mod, unlike say a 2JZ, because it has little excess strength then I would say you have a fair claim. However you have said it's no good. This is just as stupid as the thread where you and others were bitching about a Saturn part that by all accounts works perfectly.

 

PLEASE let this thread be like that one!

 

LOL

 

TIL: When you run random boltons, and some crappy pre-boxed tune and the engine blows up; it's clearly a bad engine.