I have been chasing this for a while and figured I'd post here to see if anyone had experienced anything similar or had any ideas? '79 euro GTB. The background is that I was chasing endless radiator leaks with the original. Numerous visits to 2 different radiator shops, and unfortunately little pinhole leaks kept popping up at various places, so I decided to bite the bullet and replace it. Each time I pulled the radiator out to take it to a rad shop, I would experience this same phenomenon. I never got it solved because it would always spring another leak within a few drive cycles. So, replaced the radiator, and the hoses while I was at it with all of the coolant drained. I refilled in the normal way (gravity bleeding) fill from the tank until it comes out of the radiator bleed screw. Bled from the rad bleed screw and also I have the "bleeder" screw (drilled hole) on top of the thermostat housing. Each time I drive, start with coolant in the tank around the min level. Upon returning from drive, little bit of coolant comes out of the overflow hose (after the car is turned off and as it cools down). After the car is cool, I remove the cap and the level has RISEN in the tank by approx. 1.5-2”. Open the radiator bleed screw and a bunch of air comes out....some bubbly coolant....then a normal coolant stream. Check the tank and the level has gone back down. Go drive again....come back.....cool down....level has risen in tank....bleed air....level returns to normal......rinse and repeat. I lost count, but I have done at least 10-15 of these drive cycles and it continues to yield the same result. -Water temp is good while driving. Car does NOT run hot (always under 90c on the gauge). Fans cycle, etc. Everything behaves normally. -Before I started the job I ran the heat so the system was open and I wouldn't get air trapped in the heater core. -I have run with the heat on a couple of times just to see if that affects anything. it doesn't. (heat is hot). -No air or bubbles from the thermostat housing bleed screw. -Pressurize the system to 10-11psi and it holds pressure indefinitely. No leaks. -Cap tested good. I have even tried several different caps (correct .9 bar)...both new and old/used. And the cap is definitely doing its job because it will push excess out the overflow hose as necessary. If I fill the tank to the max level (or above), it will come out of the overflow hose when hot as expected. Usually you'd expect the car to vent a little bit of coolant out of this hose unit it reaches its "happy" place/level and then stop. Much appreciate any thoughts or ideas as I am really scratching my head on this one!
In normal operation an air pocket will always exist in the radiator top tank and has no detrimental effect on cooling. One filled, bled and stabilized I never bleed the system until the next cooling system service. Bleeding and topping up is just an unnecessary viscous cycle.
Went through the same issues, there are many discussions as what the cause of this is but ultimately the solution is to stop checking for air in the radiator and sleep well at night.
Re spitting from the overflow - other than being overfull initially and then finding its own level, I had a similar issue where it would spit after almost every ride and discovered I had fitted the incorrect rad cap. It was listed as being the proper one for the car but it wasn't. The correct cap has the little "vent disc" on the underside of the cap spring-loaded closed as opposed to "hanging" open. Here's a good diagram/explanation of the difference between the two types of caps: https://www.coolcatcorp.com/Radiator%20Caps/Radiatorcaps.html
This has to do with the design of the overflow tank and in particular the position of one of the return hose at the top of the tank (the small one). In normal operating conditions, you can experience a negative pressure (by comparison to the rest of the cooling system) in this hose which will result in air being sucked from the overflow tank (instead of returning coolant). This air will ultimately end in the radiator and will be trapped here. Some people have modified their overflow tank by adding an additional tube inside in order to continue this tube and lower the pick-up point/returning point of this hose and always suck coolant (and not air). Others have changed the position of this tube and put it lower on the overflow tank with the same intention. There is no such thing as a 308 with no air in the radiator (even the later models which had a revised design), but you can keep it to acceptable standards with the modifications described above.
Image Unavailable, Please Login Here is a picture of the modification, you can clearly see where the hose entrance was removed (on the top left) and relocated (at the bottom of the tank, where there is no air. According to the owner, it fixed all its air issues.
Nothing new. I regularly see people fix things that are not broken. The design had no faults. The understanding of how it works did.
This is all great and very interesting info. Thanks!! Good to know that the air pocket is normal, and that is a good point about the design of the tank/position of the return line.
I would not describe the air pocket as "normal" but rather as "acceptable" in normal operating conditions... If you don't have to rely too much on your radiator in the traffic to cool the car during long periods, then I assume it is totally fine to have some air trapped in the radiator. If sometimes you end up being caught in traffic when you return from a very nice weekend with your favorite car, it is not ideal to have a sub-optimal set-up. Air in a radiator will always be less efficient than coolant, so you definitely loose some cooling capacity due to the air pocket. In the whole history of cars, no engineer ever said "let's put some air bubbles in the radiator, this will be much more efficient..."
You really need a better understanding of how the cooling system works. Water in the top tank does not contribute to cooling. Water flowing through the tubes does. A few cubic inches of air trapped in the tank does not effect water flow. Air iis light, stays at the top away from the tubes, water is heavy and fills the tubes flowing downward as gravity requires. The air return hose going into the top of the reserve tank will allow air to return to the tank. The hose rerouted to the bottom of the tank defeats that capability. Of the thousands of 308s with that particular cooling system never had a cooling issue. A few might have but it was not a design issue. 308s until the QV came along never had cooling issues in any climate. The QVs did and is why the 328 had a complete cooling system redesign. Those still have an air pocket in the radiator.
When I had my engine out I ran a 1/4 inch hose through the center frame channel alongside the coolant pipes with the idea of connecting an air bleed return line from the top of the radiator to the top of the expansion tank. Don't know if it would work as I never hooked it up but it seems that every other car I have has such a connecting bleed line in the circuit.
You know, it is ok to accept that Ferrari made some error… nobody blame them for that! It was the seventies and they were still a small company. But you cannot pretend that this is normal to have air trapped in the radiator of car… This is the exact demonstration that the system was poorly designed. Let’s say that 30% of your radiator is filled with air… well, you are loosing 30% of your cooling capacity, as 30% of the air travelling through the exterior of the radiator will not perform its role of extracting heat from the coolant. What you describe is correct, assuming you have only one high point in the system and the air can actually flow back to this high point (i.e. the expansion tank)… The real issue with the 308 is that you have two high points (one at the front and one at the back) and only one expansion tank at the back. So the top of the radiator acts as an expansion tank for the front, which is far from normal. Ideally, you should have a second expansion tank at the front (and if you really want to, maybe an additional overflow tank at the back to capture any overflow from the expansion tank) for the circuit to be bullet proof. With respect to the QV, this is mostly due to the addition of all the anti-pollution systems in the US which cause the car to run hotter than other 308. For such cars, the cooling system always works at its limits, which are already quite low. The cooling system of European QVs work perfectly fine in all temperatures. Interestingly, all the modifications I have seen to 308 cooling systems in Europe were on carbureted cars. And I have seen a lot of such modifications… all very different with various results. Bottom line, 1) does the 308 cooling system works? Yes, globally. 2) Is the 308 cooling system optimal, no, definitely not.
"But you cannot pretend that this is normal to have air trapped in the radiator of car… This is the exact demonstration that the system was poorly designed." For decades, down flow radiators (which were the norm in the U.S. until the roughly the late 60's) operated correctly and well and by design with an air pocket in the top tank. As Rifledriver observed, as long as the cooling tubes are always full of coolant, you will get the maximum cooling that particular radiator can provide. So I would say it's perfectly normal to have air trapped in the radiator of a car if it has a down flow radiator, as long as the amount of trapped air is less than approximately 50% of the the volume of the top tank. Cross flows are another story as they have no built in header tank. Perhaps it is theoretically better to have a full top tank in the 308 radiator, but I find my 1977 car cools very well with its totally stock system with it's persistent air bubble up front.
Install a radiator bleed vent on the bleed port of the radiator and you will never have air in the radiator. They are designed to bleed air from hot water radiant heat systems. https://www.amazon.com/gp/product/B003QSJLL2/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1 Image Unavailable, Please Login Image Unavailable, Please Login
As did the thousands of 308s built from 1975 to 1983. But a one has a cooling problem and oh no Ferrari did it wrong and it needs to be reengineered. Defines dumb.
I tried one of those on my Euro 308 QV quite a few years ago - then took it off after a few months, when I noticed it had broken and was seeping coolant. In retrospect, I should have thought it through better - they ARE designed to bleed air from hot water radiant heat systems, but they are NOT designed for the vibration and movement of an automotive installation. After that trial, and reading more of the discussions here, I just accepted that there will always be an air bubble at the top of the radiator, accepted that my cold level in the reservoir is lower than prescribed because I have a larger radiator (greater volume of coolant, greater expansion volume, cold level is lower for the same hot level), and have no worries now. Rifledriver is absolutely right. (shouldn't be a surprise to anyone!) If I were to change anything, I'd perhaps like a larger capacity reservoir, but it's not necessary. Gordon
The only thing I can add ( sympathetic to Brian’s line of thought ie there’s nowt wrong with it ) is after a drain; + fill or other intervention. I do after warming up park it up hill and open the air vent on the rad .I do this the first 3-4 trips out .Burp it . Next day when cold open the expansion tank ( in the engine compartment) and top up as required. when it’s 1/2 full stop this air venting malarkey and leave it well alone . It’s been charged around the Alps in August up / down mountains passes and kept its cool . If you think about it Moderna gets pretty hot as does southern Italy in the summer …..and you can be sat in traffic. So it’s fit for purpose there’s no doubt about that .
I bleed mine every 5 years when I change the coolant. About once a year when I change oil I open the cap to be sure its still full. They work right just the way Ferrari made them. Panteras had a garbage cooling system from the start. Owners have been trying fixes since they were new cars. 308s did not.
fwiw have a coolant overflow bottle installed on my 308QV after seeing this recomended on fchat a few years ago . Works great I no longer have air come out when I crack the radiator bleeder .The expansion tank is full to the radiator cap with coolant and I just keep a eye on the overflow bottle level.
Actually the expansion tank is the high point. With the level of coolant above the half way point in the tank and with the cap off and car level if you open the bleed on the radiator the air will bleed out and you'll get coolant flow. Another thought experiment I had , which I never tried, was to swap the coolant pipe connections where they enter the center frame tube to make the radiator flow bottom to top and forcing any air back to the expansion tank. That would probably cause the fans to run constantly since the sensor would then be at the inlet side and there may be some other fluid flow physics that I'm not aware of but it's hard to believe that after all these years someone hasn't accidentally hooked it up backwards at least once. So it was just something that I wondered about.
