Overheating problem has me stumped....

I have a Mondial t (same prob as if a 348) with an overheating problem. 2 Weeks ago I flushed the whole system, a full drain, then water flush X 3 until no more color coolant came out. I replaced the coolant with red long life coolant mixed 60/40 (water to coolant). Car is summer would rarelay go over two fifths of the scale, and in winter about one quarter. I normally cover 50% of the radiator to make sure it heats up properly to avoid the ECU going in cold engine enrichment. With the mask I get summer type coolant temps.

3 days ago I was stuck in traffic on an upwards incline, when after about 10 minutes of standstill traffic I went totally to overheat. Once I go nose down, then it cools again. The fan did not kick in, though if I unplug the sensor wire and short it the fans do work, though do not drop the temperature below the 1/2 mark (90 deg. C).

What the hell can it be?

1) not the thermostat as after the engine warms up the radiator gets hot - so there is circulation
2) not the pump as I can see circulation in the header tank that varies in synch with the rpm
3) no air bubbles as I bled the system at the radiator and the pump housing, and when filled the cabin heater is at full hot (and very hot when running)
4) it is MUCH worse when pointing up an incline
5) fan comes on when temp reads a bit higher (about 8-10 deg C) than the 85 deg. specified for the fan heater, then as it continues to overheat the fans go off...
6) having the cabin heater engaged seems to drop the temperature
7) when it overheats and the fans come on, I could swear the radiator is not so hot

Point 6 I think is due as the cabin heater shorts the radiator with the piping closest to the coolant temp sensor.

What are the thermostat failure modes? I thought the failsafe design would make them fail in the open position to ensure there is no chance of an overheat. As far as I know it has never been changed...

Does anyone know the diameter of the coolant hoses and a non Ferrari thermostat that can be bought in the UK?

Marco

 

On the T' everything is south of the filler...
Only bleeds are on the single radiator at the front bumper, and on the pump output housing - see why this defies all reason?

Marco

 

The thermostat was broken. The metal bracket was split on one side, and it would sometime close/open properly and some other times jam itself. Now where can I get one of these?

M

 

Had no time as I wanted to get it going ASAP...

Basically there is a "bridge" on top of the thermostat, that a pin acts on to push the valve down when it gets hot. This "bridge" is also the retainer for the brass bracket below. Looking at the oxidation on the broken interface, it went in two phases, cracking from the right to the left.

I rebuilt the thermostat, by grinding more brass material so to be able to fit it in the slot, then on the other side I bent it sideways effectively putting the whole assembly back together. A key thing was to take a bit off the main spring as the assembly would be 3 mm shorter, thereby increasing the spring tension.

For good measure I put a dollop of high tension solder on the protruding brass to ensure it will not break off again.

On the incline issue, I guess, if the valve was merely rolling around in the casing, I found that if tilted backwards it would be pushed up by the pump pressure, in effect activating the bypass, but if tilted forward, it would jam itself in the hole and leave it partially open. Give that it is winter, I guess this was just good enough to keep things cool.

Incidentally, I also found out that thermoswitches for the fans, will disengage if the temperature exceeds 30-35 degrees C above their activation temperature!!! This was the case with bot my thermoswitches. On the Mondial T they are fitted at the bottom of the radiator, so air gaps cannot isolate them...

Enclosed are two pics, thanks Lusso64.

Marco
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The failure mode for the thermostat is in the bypass position. Either if the top part breaks off (brass does not handle the tension cycles that well - steel would have been better F-guys!!!), then the lever is lost, or if the actuator toes not engage, will cause the spring to close the thermostat gap and lock it into bypass position.

So instead of opting to have it go into radiator mode - they will force us to stop motoring.

Marco