Too much pressure in overflow tank

It's normal for there to be some pressure.

What temperature were you running? If normal it sounds like you might have a leak.

 

I'm pretty sure that overflow tank is to be empty when engine is cold & takes overflow from rad. as coolant expands and is drawn back into the rad.. as engine cools. If I'm not mistaken, the pressure cap is to be on the overflow tank & the plain 'rubber seal' cap on rad.. My experience w/overflow tank reactions (under normal conditions & properly operating pressure cap) is 'no hissing' unless engine is extremely hot. Only 10 min. drive and hissing pressure relief from overflow vent I think spells 'something's up'.

 

I can't tell from your profile what car you have but typically the "expansion tank" is meant to have some coolant in it even when cold (the actual level varies from car to car but is frequently an inch or so down from the neck). It is not an "overflow tank" in the true sense of the word, it is part of the cooling system that keeps the rest full. If you hear hissing it sounds like the pressure cap is leaking either from overheating or because it's faulty. It is also possible that you have a leaking head gasket. This could put pressure into the cooling system without overheating. It would be a good idea to pressure test the cap and see if that's the problem (just because it's new doesn't mean it isn't defective).

It is never a good idea to remove a pressure cap when the engine is hot. It is not surprising that some coolant was expelled.

 

The expansion tank if that is what you are refering to as the overflow tank should be at about 1" to 1 1/2" below thw filler neck when cold. There is no cap on the radiator itself.

 

Not sure but are you saying that it took you ten miles for you engine to warm up if so that's seems excessive and if you have a lot of pressure you might have a faulty thermostat that is stuck open hence the long warm up and pressure, if that is what you are saying.

 

Even if you don't work on your F yourself, you need to bleed the coolant system before you can determine if you really have a problem or not. It's not hard (when just doing it at the radiator fitting) -- it's about like checking the engine oil level or refueling. Your next step should be to bleed the system and ensure that you're at the right (cold) coolant level -- if you note abnormal behavior after that, then get the Mechanic involved.

Also checking the bleeding status occasionally can give useful information too -- i.e., if you have to put in a couple of quarts in every week, that's a flaw that probably should be investigated with some priority; if you have to put in a 1/2 quart or less every month, not such a critical problem IMO. But, it needs to be rechecked more than "never" -- even if you are only losing a very small amount each week, it adds up, and "higher pressures/more coolant coming out" is a sign that you're just very low on coolant level (i.e., portions of the cylinder heads/upper areas are starting to be unwetted).

 

I hope your luck runs better than mine. My 328 had the same symptoms that ,unfortunately, resulted in engine removal and cylinder head replacement. I bought an engine block test kit that prooved the head gaskets were leaking. To add insult to injury the heads were warped past spec. for milling. I should have the car back any day now. After going an entire driving season without it I plan to drive it this winter (weather and road conditions permitting).

 

You may need to pressure test the systme with the right testor. You should make sure mechanically that you have the right cap. The cap needs to be the right pressure and the right internal length from the top on the radiator neck to the bottom of the radiator seat in the neck. Italian cars are not always the same standard dimensions as the typical STANT cap from NAPA eventhough you can get the caps to contain the radiator fluid. Too mjuch pressure in the overflow is a dead give away for either wrong internal cap length or improper preload on the cap spring fron wrong internal length.

 

After more than 30 years reading books and manuals, over 10 years of chatting on various Ferrari sites, and owning two 308's, the one for nearly 4 years now, it came as a great surprise recently to notice the expansion tank on both cars has the hot and cold fluid levels clearly stamped into the metal below the cap.

 

Paul I thought everyone could see this when you look in the tank. Don't know about the FI cars but the carb tank is visible . I guess we still make some assumptions.

 

As "2NA" indicated it's not just an expansion tank. It is really a recirculation tank, a point to check coolant level and add coolant and allows for expansion of the coolant. Coolant does not just get forced into the tank as it heats up and sucked back out when it cools down. The coolant circulates in and out of the tank. In through the top hose and out through the bottom hose when the engine is running. Of course as the coolant heats up (expands) the average level in the tank goes up also but it's still constantly going through the tank while the water pump turns. This applies to the 328 but I'm sure the 308 is the same.