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For the past few months, my F355 had been dogging me with temperature problems. Upon hearing this, a curious car guy could respond with the following typical questions:

Did it overheat?

Did it melt?

Did your kid put too many fingerprints on it?

Did you put too many miles on it? (i.e. over 10,000)


Actually, the car had been running too cool.

The coolant temperature is supposed to remain between 170F and 190F (77C - 82C) depending on my driving. At idle, it jumped around between 150F and 190F. At steady highway speed it stayed consistently lower than 150F, with occasional oil pressure spikes which worried me. Oil pressure is supposed to remain just under 70 psi at steady speed.

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The correlation between high speed and cold coolant told me that the thermostat had clocked out and was no longer closing properly. Too much coolant was being sent to the radiators by the thermostat sitting open. Driving the car hard and using the higher revs would probably not be good for long-term health since the oil viscosity is not optimal.

So, after reading various FerrariChat threads which mostly agreed that the original thermostat was:

  1. A ripoff at over $300, and
  2. Not very durable,

I ordered this thing from a shop in Arizona for less than $60 shipped:

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Despite its janky appearance (it actually looks worse than the bad one that we eventually fished out of my car), this thermostat is fairly well-received in the F355 crowd. Behr Thermot-Tronik Italia made this aftermarket unit for certain Italian cars (among them the Fiat X1/9, Ferrari 348 and F355). A crude stamping reading “4M 82" denotes the proper 82C threshold.

I failed to find any sort of part number or model number aside from the above text, so I have no idea whether Behr still makes these. The packing slip was not much more helpful, reading “NON O.E.M. THERMOSTAT”.

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Anyway, it was finally time to get my hands dirty on this car, in a mechanical way. With the help of an expert friend and fellow F355 enthusiast, we replaced the thermostat in just under two hours. It’s tucked all the way to the forward side of the engine (near the belts), buried deep under a bunch of other plumbing.

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  1. Let the car cool down for at least 1 hour. We did not do this, and in a later step I will explain why that was a bad move.
  2. Relieve coolant and fuel pressure (open gas cap and open coolant expansion tank cap)
  3. Remove rear bonnet. This is a 2-person job due to the unwieldy size. Total of 4 bolts.
  4. Remove the decorative central engine cover between the two intake manifolds. 2 of the screws are different from the other 4—sort all the screws, washers and bolts. Everything is metric.
  5. The fuel distribution hoses and 2-to-4 fuel distribution block are in the way (braided steel hoses—there are 6 total). Disconnecting them, we got random sprays in the face by residual pressurised fuel in the hoses. Lesson: Let the car cool down longer.
  6. The power steering fluid reservoir is in the way. Remove its mounting screws—a pain due to other hoses in the way. Remove its metal mounting bracket and tilt the tank rearwards:

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  1. Now we see the thermostat housing (below, red arrow). Remove the short but nearly 2" thick coolant hose feeding the thermostat housing (below, yellow arrow). The better half of a gallon of coolant will puke out. Cost of doing business.

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  1. Remove the thermostat upper housing, 3 nuts. Now the thermostat is exposed, as shown below. It’s flooded in coolant, so take it out carefully. Move the original rubber seal to the new thermostat.
  1. Re-assemble everything by going backwards.
  2. Replenish the lost coolant. Using the expansion tank opening and a pressure tester, test the car for leaks.
  3. Clean up the engine bay—by now, that fuel spray should have long evaporated. Start the car, and check for leaks.
  4. Re-assemble the engine bonnet before the engine bay gets too hot to bear.

Car runs like a charm now, with good temperature and steady oil pressure. Mission accomplished, right on time for the Lunar Year.