F355 Coolant Rust and Fluid loss.

Ever since i have owned my F355 I have always had an issue with rust in the coolant expansion tank, which has puzzled me because AFAIK the block is aluminium, so from where its coming from I/m not sure...?

I have also had an issue with pressure buildup ( overflow cap leak) and loss of coolant on long drives, which I had chalked down to leaking radiators that were noted at the last major, and was a major PITA as I would find unsightly rusted fluid surrounding my expansion tank..I also changed my header tank cap to a new one.. no change..

Suspecting the rust was coming from the header tank, I removed it and cleaned out the rust it, and unblocked both nipples, but it was still happening. I also did a combustion chamber leak test on the coolant fluid.. all was OK.

Unfortunately I was unable to pressure test the coolant system as I don't have the correct coolant expansion tank plug for the F355, however I can confirm that both radiator fans come on and work properly. The leaking radiators was noted at the last major some years ago..

As far as the rust goes.. I am wondering if there is any benefit to doing a coolant system flush on the F355 using something like thermocure, as I want a pristine system before hoking up my new radiators and topping up with distilled water/coolant.?

As far as the pressure buildup/coolant cap overflow goes.. Is this normal for the vehicle..?
Whilst doing the combustion chamber leak test I noticed a fairly constant stream of air bubbles visible in the filler neck, which did not settle with time as expected..

I also noticed that the whole fluid level rises periodically ( at idle with the coolant cap off) and you get spill off of fluid even when the coolant level is no way near the top of the header tank..

Is this a common issue with this vehicle..?



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From a cold start.
After 9 min of idle only.. ( no revving) , with the expansion tank cap off, I see the water level starting to rise as the thermostat opens.
What follows is a constant trickle of air bubbles and a rising water level that overflows every so often resulting in water loss into the engine bay.
You can see the rust in the water in the video..

Rust has been diluted a bit because I topped up the expansion tank for the demonstration..
When I first observed the rust it was twice as concentrated as in the video..
NB: HEVC video extension required to play MP4 video..

Leak in radiators is very small, but present ij both radiators as noted with last major..
Its so small no fluid is left on the garage floor overnight.


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