The Ferrari Testarossa, along with its later 512 TR and F512M variants, are iconic cars of the 80s and 90s. Every kid my age wanted to be Sonny Crocket cruising around Miami in a white Testarossa. What we never saw, however, was Crocket having trouble starting his Testarossa. Every time he had to run from (or to) the drug dealers, the car started perfectly every time.

Those of us who own these wonderful cars know the real story: the Testarossa and 512 TR are notorious for their “hot start” problem. If you start your car when it hasn’t been running for a while, you’re probably fine. But if the engine is hot, or even still warm after being run recently, the heat soaks into the starter solenoid so that when you turn the key… it won’t start. In fact, it doesn’t even click. You get nothing. Fixing the Testarossa / 512 TR starter solenoid problem isn’t quite as easy as fixing a Sea-Doo starter solenoid, but it’s still doable even if you’re a first-time DIYer. And trust me… it’s way cheaper than dropping $2,391.56 on a new starter (yes that’s the real price, and no – you can’t just buy a new solenoid from Ferrari… you have to buy the entire starter assembly).

What Causes the Testarossa / 512 TR Hot Start Solenoid Problem?

Before attempting to fix the Testarossa / 512 TR hot start problem, it’s important to understand what causes it. The solenoid sits directly above the starter, just an inch or two to the left of the exact center of the TR engine bay (this image is a 512 TR, but the Testarossa location is the same):

Starter solenoid location on a 512 TR

Most TR owners agree that’s a terrible place for a starter solenoid, because it gets really hot right there. Inside the starter solenoid is a brass sleeve — and inside that is a snugly-fitting steel piston. That steel piston is designed to slide back and forth inside the brass sleeve to close the battery contacts and provide power to the starter motor when you turn the key. When the solenoid is cool, it works great. But when metal gets hot, it expands — and different metals expand at different rates. So when the solenoid is heat soaked, the steel piston inside the starter solenoid binds inside the brass sleeve and refuses to move… leaving you with a Ferrari 512 TR or Testarossa that won’t start.

Fixing the 512 TR / Testarossa Hot Start Problem

The trick to fixing the problem is reducing the friction between the steel piston and the brass sleeve, allowing the piston to move when heat causes them both to expand. You’ll need the following to do this fix:

• A brake cylinder hone tool ($15 on Amazon) and a drill.
• Some Blue Magic metal polish cream ($6 on Amazon) — this stuff is also great for keeping exhaust tips shiny!
• Some anti-seize lubricant ($7 on Amazon if you don’t already have some)
• A Dremel multi-tool ($37 on Amazon if you don’t already have one)
• A Phillips head screwdriver, a 13mm socket, and a 10mm wrench to remove the starter and solenoid.

Removing the Starter From the Engine Bay

Start by removing the starter assembly from the engine bay. Don’t worry, it’s easier than you think!

First, make sure you open the front bonnet and turn off the plastic battery disconnect knob on the passenger side (above the battery location).

Next, use a 10mm wrench to remove the two nuts (and their washers) holding the front of the coolant expansion tank in place shown here:

Remove the nuts holding the coolant expansion tank in place.

Use the 13mm socket to remove the three long bolts (with washers) that hold the starter to the large flywheel housing. Loosen all three first, then remove them the rest of the way by hand:

Remove these three bolts to free the starter.

There are two electrical connections to remove from the solenoid. First, disconnect the starter lead (it has a female spade connector that slides onto a male spade terminal) from back left side of the solenoid (you won’t need tools, it should just pull off). With the starter loose, it’s now easy to use the 13mm socket (or a 13mm wrench) to remove the nut and lock washer that hold the positive battery cable on the top threaded post of the solenoid.

With the starter unbolted and the solenoid disconnected, you should now be able to gently lift the coolant expansion tank upward and have enough room to slowly move the starter & solenoid assembly free.

Removing the Solenoid from the Starter

The solenoid is attached to the stop of the starter with three Philips-head screws:

Three Philips-head screws hold the solenoid onto the starter.

Those screws might have some Lock-Tite holding them in place, so there might be a bit of resistance at first. Once all three screws are removed, the outer housing solenoid should separate easily from the starter like this (I actually took these shots during re-assembly, but they still provide the needed visuals):

Solenoid housing removed from starter.

If the interior solenoid spring in the above photo falls out while you’re removing it, that’s OK. Just put it aside for later. The steel piston portion of the solenoid will now be “sticking out” of the starter like this:

Steel piston in place.

There’s another spring behind the piston that helps hold the “tail” of the piston on the starter motor lever (look at one of the pictures below to see what that tail looks like), and you have to “unhook” that tail by pushing it inward and wiggling the tail end upwards. It might take a couple tries, but you’ll get it. When the piston comes out, remove the retaining spring assembly and set it aside. This photo shows the starter motor lever on a Testarossa starter:

The starter lever on a Testarossa starter. This is where the “tail” of the solenoid piston hooks.

When the piston is free, put aside the starter and bring the entire solenoid assembly somewhere you can work on it (workshop, bench, etc.).

Grinding and Polishing the Solenoid

Here’s what my solenoid looked like before I did this fix:

Bosch starter solenoid.

If you look carefully, you can pick out the Bosch part number: 0 331 303 032. And what’s strange about that is that I’ve got a 1992 512 TR, yet that’s the part number for solenoid that fits on the the earlier Testarossa starter! Turns out the Ferrari factory used some Testarossa parts when assembling my 512 TR. Ferrari aficionados won’t be surprised by that. Before the more computerized assembly lines currently in use at the factory in Maranello, that kind of stuff happened all the time. These are hand-built cars, and so every now and then you’re going to get something “custom” like that. 🙂

Here’s what the brass sleeve inside my solenoid looked like before the fix:

Inside my solenoid sleeve.

Now grab your brake cylinder hone. Its course stones are designed to grind and smooth out the inside of a brake cylinder, but it’s also perfectly sized for a Testarossa solenoid:

A brake cylinder hone fits perfectly in the Testarossa solenoid.

Attach your brake cylinder hone to a drill, and gently insert it into the solenoid’s brass sleeve:

Don’t push it down too far or you’ll damage the stones.

Before you run the drill, get a feel for just how deep into the sleeve you can insert the hone before it bottoms out. If it bottoms out while you’re running the drill, it could chip the top of the hone’s stones (it likely won’t damage the solenoid, but will make the hone less effective).

When you’re ready, run the drill on high speed and hone the inside of the solenoid sleeve, moving the tool up and down slowly to cover the entire surface of the sleeve. Feel free to stop and inspect your work from time to time. After 45 seconds or so, it should look shiny and feel pretty smooth. You can hone it longer if you like, but I wouldn’t go for more than a couple of minutes max. Even if you go longer, it’s unlikely that you’ll take off too much material, but better safe than sorry. It should look like this when you’re done:

Solenoid sleeve after honing.

If you have a can of compressed air or an air compressor, it’s not a bad idea to blow out any metal or stone shavings left inside the piston when you’re done honing.

Now it’s time to bust out the Dremel and the metal polish creme to smooth the steel piston . Using a white cloth buffing wheel attachment on your Dremel (don’t use a polishing or grinding attachment), apply a small amount of metal polish to the wheel and polish the outer surface of the steel piston . Be sure to polish the tapered edge on the bottom, too. Start with the low speed to spread the polish around (it will turn dark grey as it works) and then increase up to medium speed on your Dremel to see a mirror-finish appear. If you never go full speed, and only use a cloth buffing wheel, you won’t actually remove any metal; you’ll just polish the metal that’s there. When you’re all done, wipe it down and inspect your work. It should be nice and shiny! There’s no harm in polishing all of it, if you want it to be pretty:

A nicely polished solenoid piston.

Great job! Now it’s time to start putting things back together!

Re-Assembling the Starter Solenoid

Test fit your honed sleeve and polished piston. There should be a lot less friction than before and it should slide in and out easily:

Much less friction after your fix.

Get your anti-seize lube (they sell individual packets at most auto parts stores) and head back out to the car:

A few dabs of anti-seize might come in handy.

Re-attach the retaining spring to the “tail” portion of your steel piston, then re-insert it into the starter body and latch it back onto the starter motor lever. Again, it might take a few tries, but you’ll get it. Use your finger to smear a small amount of the anti-seize lubricant to the polished outer surface of the piston so that it has just a light coating. Don’t use too much, or it could prevent the piston from moving inside the sleeve, which ruins the point of this process (if you use too much and the solenoid doesn’t move, just disassemble, wipe some off the piston and try again).

Finish mounting the solenoid to the starter by inserting the long spring into the middle of the piston (don’t forget this part!), then slide the housing over it. Re-secure the housing with the three Philips-head screws (some Loc-Tite on the threads isn’t a bad idea). Your starter and solenoid are ready to re-install!

Re-installing the Starter and Testing Things Out

I find it’s easier to re-attach the battery cable to the top solenoid post before moving the starter back into position, so rest the starter on the engine block while you use a 13mm wrench or socket to tighten down the lock washer and nut that holds the cable to the solenoid. Then lift the coolant expansion tank gently and move the starter back into place. Re-insert the three long bolts (don’t forget the washers) and hand-tighten them all as much as possible before torquing them down with the 13mm socket. Make them snug, but don’t over-do it.

Re-connect the female spade connected on the back left side of the solenoid.

Re-attach the washers and nuts on the coolant expansion tank, then double-check to make sure you have no “extra parts” left over, or any tools left in the engine bay.

Turn on the battery disconnect, say a prayer to the ghost of Enzo… and start the car.

If your 12 cylinders roar to life, you’ll know you didn’t mess anything up. But to truly test out the fix, you’ll need a passenger and a hammer as insurance. Drive the car until it gets hot. Go on the freeway and push it hard (obey all speed limits… cough cough… of course) and give the solenoid a chance to really get heat soaked.

Park the car somewhere safe (on a downhill decline would be best, so you can just bump-start the car in second gear using gravity, if needed) and shut it the ignition. Count to 10, then try to start it. If it works, congratulations! You just fixed your hot start problem!

But if it doesn’t work, don’t panic – you’re not stranded. If you can’t bump-start the car on a decline, open the engine bay and have your passenger gently tap repeatedly on the solenoid with the hammer (make sure you show them where it is so they don’t hammer something else accidentally) while you turn the key to start the car. Keep holding the key in the start position as they tap (it shouldn’t take more than 5-6 good taps). The tapping will jar the piston loose so that you can start the car and get back home.

Tweak your fix by repeating the honing steps and taking off some more material in the brass sleeve. In some extreme cases, I’ve actually heard of some owners that cut a relief channel in the sleeve. But chances are you won’t have to do any of that, and hopefully this fix worked for you on the first try.

Congratulations – you just saved yourself a couple thousand dollars, and kept the original part in the car (which is important if you ever take it to a Concours).

Alternative Fixes

If originality isn’t important to you, there are a few companies out there that make replacement solenoids that can be used in place of the original Bosch units. Ferrari themselves switched over to Denso solenoids part way through the 512 TR production run.

The original Testarossa Bosch solenoid was Ferrari part 120967 and Bosch part 0 331 303 032. It can be replaced by WAI part nbumber 66-9131, Ace Electric part number 7-851, or ZM part number ZM-576.

The original 512 TR Bosch solenoid didn’t have a Ferrari part number (you have to buy the entire starter), but the Bosch part number for the solenoid was 0 331 303 033. It can be replaced by WAI part number 66-9146, Ace Electric 7-745, or O’Reilly part number BWD S5402.

Just make sure that before you order a solenoid, read the original Bosch part number on your existing solenoid… in case you got a “custom” job from the factory, too. 🙂

I actually tried the TR version of the WAI replacement for my solenoid, and it fit perfectly. It even worked fine for a while, but the problem returned. I decided to go back to the original solenoid and use this fix, and look forward to many years of trouble-free starts ahead of me. I hope the same for you!

As always, I welcome your questions, comments, and feedback!

My baby – a 1992 512 TR.