coolant system: where does all the air come from?

You're checking the right things.

Remember that coolant is being constantly circulated thru the reservoir tank. If the tank gets too low, air can be sucked into the system.
"Regularly check the mixture level in the header tank WHEN THE ENGINE IS COLD.
The mixture level in the tank should never be 2.3" below the filler plug base' - Owner's Manual

If the level in the tank is too high, the tank will overflow when the engine warms up. (Probably know this).

Search the archives, believe I remember a problem where a tube inside the tank was corroded away letting air get sucked into the system.

 

I have the same problem, only worse....my car's cooling system is gulping air into it, and I can't keep it out. After about 50 miles, the system needs bled of air. If I don't, the car overheats. I've been bleeding air so much, that I've stripped the threads to the bleed screw opening and now the bleed screw won't tighten all the way - and a puddle of coolant is forming on the floor of my garage as I type this.

All this after I've replaced most all of the coolant hoses, replaced all of the hose clamps, redone the water pump/thermostat, rodded out the radiator, replaced the fans/fan thermo switch, and refinished the expansion tank.

To eliminate the possibility of the hose clamps being loose, I'm replacing the Ace Hardware Cheapo worm-drive hose clamps with ABA heavy-duty units for thick-walled hose (I have Gates Green Stripe, very thick and not easily clamped). I'll also be trying the Breeze High_Torque clamps to shut off any air from thermal expansion/contraction at the coolant hoses. We'll see what works there.

While ordering the hose clamps, I spoke to a vendor who has done several Major Services on 308s. I told him my problem, and he highly recommended that I look into having the head bolts re-torqued. This makes sense, as a friend had the same problem in his Testarossa with air in the cooling system - he fixed it by re-torquing the head bolts. This should be done during any major service (or a valve job), but for some reason it can get skipped. Anyone have an idea what the torque value is for head bolts on a 308?

 

Good point....I know that my 328 had the head bolts retorqued during the major service. I believe it is in the shop manual for the 308, Mondial and 328. I read in the 328 shop manual that they were switching head bolts to something that "shouldn't" require retorquing...and asking dealers to report back their findings on if any headbolts were loose upon major service...but no further mention was made. My technician said a couple of mine took up to 1/8 or 1/6th turn to reach proper torque, so they can still loosen.

I gentleman on the Ferrarilist had his headgasket go on his 328...he was having the car serviced at a independant Porsche shop for several years...they never knew to retorque the heads....

 

You can find the torque specs & a lot more at Steve Jenkens Private Ferrari Document collection web site:

http://ferrari.jenkins.org/books/

BTW, a lot of the material in the 308GT4 shop manual still applies to the 328.

The 328 & QV head torqueing is angle based to stretch the stud, thus putting it under controlled tension. In theory they shouldn't need retorqueing.

Suggest you have a sample of your coolant tested for combustion products. Will tell you if a head gasket is leaking exhaust into the coolant. If it is, then retorqueing is worth trying. If no exhaust in coolant, then look elsewhere.

 

When bleeding, Make sure the heater tap/s is/are set to HOT, and of course, that they actually work. Often the cables and/or taps are not working correctly.

Also, if your coolant mixture is too strong (over 40%), the surface tension of the thicker coolant can promote cavitation of the pump at extreme rpm's. But this is not a problem with correct coolant strength.

I haven't read Verells "How to bleed" post, But I will say that the engine should not be running of course, as I've seen people try to bleed while running before, and it can create more problems.

I sometimes connect my cooling system pressure tester (on TRossa/348/360/550), to help pump the water through, and so far I have never needed to bleed the thermostat housing on any Ferrari's, or had any problems with bleeding.

 

Because when you have air in the system, it recirculates it's water back to the top of the header tank from the pump. If that water has air in it, it just gets drawn back in again as aeriated water and pumped around all over again.

Let the car settle over a few hours for it to dis-aeriate (Is that a word?). Don't start it at all. Then fill and bleed on level ground until the bleed screw leaks nice clean coolant.

Keep the tank over half full at all times.

Maybe you have some problem with your water that's producing foam... soap in it or something?? Did you fill it from a soapy bucket??

 

It seems that with all the replacement parts, there is still a leak, somewhere.

I would use a pressure tester to find the leak, first.

Open the heater valves, top up the reservoir, and pump the tester to 15 psi.........and find the leak. Rather straight forward.........to me, anyway.

 

I don't run the engine while bleeding, Just open the reservoir cap & both temp levers to hot. Bleed radiator, then engine. Repeat a couple of times.

Seems to work faster when front wheels are elevated about a foot, but is not absolutely necessary.

Drive it awhile, let it cool down & repeat. Usually that's it for the driving season.

Pressure test is a good idea, but won't show head gasket leak as water goes into cylinder(s). Hard to detect with small leaks. Coolant test for exhaust gasket is needed for small head gasket leaks.