help with overheating 79' 308 USA

I am not a mechanic and never had this problem on my 308 however, I did have this issue on my Fiat X19. It turned out that my overheating problem in that case was that the car was running to lean. Your car is carbureted I believe, therefore could this be a contributor to the problem?

 

We must always consider this: when the cars leaved the factory, they worked well. If they don't work well or give you a problem (leaks and so on), means there is something to fix somewhere.

It's obvious, but I heard several mechanics (here in Italy!) to tell me this: "It's due to the actual fuel, it's a problem the car had also when new, it's impossible to get rid of it" and so on. They were all bullsh@ts, of course.

Go on an find where the problem is: you already are on the correct way to find it out.

Ciao

 

When I fill my system after a service I jack the rear of the car up higher than the front and fill the system. I then bleed air from the to of the thermostat. I then lower the car and raise the front so its higher than the rear and fill to the required level while the radiator bleed screw is out. Once a stream of pure coolant is running out I install and tighten the bleed screw. I have no cooling issues with my car and it too is a carb car ('77). As mentioned before, I took five gallons of coolant out of the system and needed five gallons to refill it.

 

The reason why there's such fiddly issues with air in the coolant system is the placement of the heater cores. They sit higher then anything else. There's also the routing the heater hose takes from the engine to the front... Slight down then up over the fuel tank, then down into the frame rail, then up to the front fender then over to the distribution block, then it's spaghetti City to the cores and every which way before dumping back into the radiator hose. The jumble of hoses up front trap air.

In some, it's not a terrible amount and the air eventually purges.. In others it's a constant hassle. These are handbuilt cars and carry with them all kinds of little frustrations.

 

I've never seen a radiator core like this before - doesn't look like the best tube to fin contact, I can see through it quite clearly. I'm not saying this is your issue, but it can't help.

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There is another theory about this air in the radiator issue that does make a bit of sense and that is that because the bleed line from the manifold to the top of the expansion tank has no stand pipe the coolant cascades out and drops approximately 2 inches before hitting the surface of the level inside the tank. This causes the air at the top of the tank to get mixed with the coolant. The larger bubbles immediately rise to the surface but there are countless smaller air bubbles that effectively aerate the solution and this condition is enhanced when you have a 50% glycol mix (don't know about Evans) So the aerated coolant then enters the system and is carried forward to the radiator which, due to it's design, becomes a trap. The result is that the coolant level in the expansion tank has risen due to the displacement caused by the air that is trapped at the top of the radiator. The fact is: that air came from the top of the expansion tank so no "new" air was ever introduced to the system. You bleed the air out of the radiator and the expansion tank level returns to it's normal position.

You can observe this phenomenon by removing the cap and starting the engine cold then look into the tank and watch the flow, Rev the engine to a higher RPM and see how much disturbance is created. Some people have apparently solved this by putting a length of tubing into the tank from the bleed input nipple so that the introduced flow is directed to enter below the level in the tank, preventing any aeration. Others have simply blocked off the bleed line. I'm not sure if blocking off the line is a good solution because you are sealing off the expansion header and creating an air tight trap. Every other car I have has the plumbing to create a closed loop flow through the tank and I believe that is necessary for the system to work properly. Interestingly however is that the flow in the other systems all enter below the coolant level.

When I had my engine out I ran a quarter inch line through the center frame tube alongside the main coolant tubes with the intent of connecting it to the bleed on the radiator and the input at the top of the expansion tank. I have not yet connected it though as I will need to make a nipple for the radiator bleed and then tee into the expansion tank input line. I have a winter project lined up to do my suspension bushings and may hook that up at that time as well as fashion some sort of internal stand pipe or tube for the tank. Both of those modifications would actually mimic how the system was eventually set up on the 288 GTO and the F40. I believe the F40 was the last model built with a forward mounted radiator. Starting with the Testarossa and 348 the radiator was moved to the back where it has remained through all subsequent models..

 

I agree that post #34 makes sense and COULD be an explanation that supports the idea that air is brought into the system in the absence of any leaks/other issues. OTOH, I haven't seen any evidence of the problem in my 328. When I change coolant, I bleed per the Ferrari procedure - at the radiator and then bleed at the thermostat area. I don't raise/lower the front/rear of the car or re-bleed until the next coolant change. So I'm not sure why the action noted in the post would affect some cars and not others with the same cooling system. It's a mystery!

The only issue I had with the cooling system spitting on a regular basis was due to the incorrect type of radiator cap. Once I replaced it with the correct type, the only time it would spit was immediately after a coolant change when I had overfilled and the engine spit out the excess during/after the first drive. No spitting from that point on.

 

I second that. In fact, once correctly bleeded (especially the heater cores by a good drive with the heating on) and with the coolant exactly where the owner's manual says it should be: at the seam of the small overfill tank in the engine compartment (= 6 cm under the cap, as per the owner manual) the system sort of stabilises itself rapidly: then, it doesn't spit any excess of coolant and stay perfectly at the same level for months.

If it overspills, then either it has not been bleeded properly, or it has too much coolant. Really a no-brainer.

But I do think there are minor differences between the 328 cooling system, and those of the 308s bretheren. At least the front radiator is not fitted exactly at the same angle.

Rgds

 

I too have never had a bleed issue with my car. No topping up between coolant changes and no spitting out either. The cooling system shouldn't manufacture air if its filled and sealed.

 

Yes I want to apologize for the length of post #34 but to summarize the main point was that air was not being "manufactured" but rather simply moved and that the radiator becomes a trap because of the unique feature that omits a bleed-back line to the expansion tank. Take a look at every other car you own. Granted the radiator is not located at the opposite end of the chassis like the 308 but there is always a bleed line from the radiator back to the expansion tank. The 308 does not have that.

As to why this phenomenon seems to affect some but not all well, I think it does. It is only if you obsess over the fact that there is a trapped air pocket at the top of your radiator is it noticed because aside from that everything works normally. The "spitting" only occurs when the tank is initially overfilled. There were a great number of changes made to the system on the 328, not just the angle of the radiator and even on the 308 with the original unshrouded fans the system is, for the most part, completely adequate.

Now of course, in my particular case, I had a blown head gasket so even though the symptoms were similar to identical it was in fact "manufacturing" air so I had a condition that simply couldn't be ignored as it progressively worsened to the point where the car became unusable.

 

If the system is bled, where is the air coming from?

 

As I explained earlier, it is the air that is at the top of the expansion tank that, through the process of aeration, gets mixed into the solution and circulated and then becomes trapped in the radiator. So it is air that was already in the system after it was sealed by putting the cap on.

Also I'd add that this is one of a number of theories (relevant to the 308, not the 328) but it's the one that makes the most sense to me.

 

So you are saying that essentially the air above the coolant in the reservoir (at most 40 cubic inches of air, is going to circulate and deposit itself at the top of the radiator. Okay but what does that cause? The upper radiator tank is so large it would maybe, at best, "trap" a layer of air a half inch in height at the top of the radiator. I'm not of the opinion this will impede flow or cause an overheat. If the air were to gather at the water pump impellor then there would be an issue, but that won't happen if its trapped or even if it is released into the flow of coolant. If I were to open the top bleed screw on my radiator right now - four weeks since the last coolant change and bleed procedure - I can assure you I would possibly get a cubic inch of air at best.

 

I think the 308's expansion tank was about the same size from the first GT4 to the last QV, But the tank changed orientation. The QV has the tank horizontally mounted and some previous 308s (carbs? Euro? Dry sump?) have them vertically mounted. To kcbapilot's theory on aeration, this might be an important difference. Could the vertical tank help air at the top of the tank stay there?

 

I think I've said this already but it "causes" certain people to become obsessed about that air pocket. They will bleed it out, add coolant to the tank, experience coolant spitting out of the overflow, check the radiator, bleed it out and repeat endlessly.

After I bought my 308 I drove it everywhere. I put 10,000 miles on it in the first year. But after that I began to notice it would get hot if I got stuck in traffic. It would get up to 195 and the fans would come on but it wouldn't cool back down and the fans would keep running in a vain attempt to stop the rise in temperature.
I started reading all about it here and everywhere else I could find. I flushed and bled like you wouldn't believe. I replaced the radiator cap, the thermostat, all of the coolant hoses, the radiator, the water pump. So yea, I've been down this road and yea, I've probably read every post in every thread on fchat that has been written about it over the past 20 years.

Well, in my case, I had a blown head gasket. So that's what sent me down the rabbit hole of checking for air in the radiator. I have an excuse.

So to summarize yea, I agree with everything you said.

 

Minoru-San, prior of making intrusive tests on the engine would suggest to try a simple work-around ( already described in this Forum). To prevent coolant wiping ( line 6) and air being sucked into the tank when the engine gets cold (line 8) place a simple 2l plastic bottle below the expansion tank and put the drain hose inside ( almost to touch the base). Would suggest to cut to measure a new drain hose to preserve the stock one. Bleed the system as usual, fill coolant from the cap till the upper limit of the tank and close the cap. Drive as usual for at least 30 miles and forget the issue. When the coolant gets hot will purge politely via the drain hose into the bottle ( no spill in the garage); when the engine gets cold the system ( assuming there are no air leaks) will suck the coolant from the bottle ( which will act as expansion tank). If it works well also for you, just fabricate a nice aluminum ( or strong plastic ) tank to substitute the plastic bottle and end of story

 

Sorry to hear you had to deal with a head gasket. That job separates the men from the boys not only in complexity and difficulty but in the "while it's apart" syndrome working at full effect.

If the coolant reservoir cap is in good working condition and the neck of the reservoir also is in good condition, the two work together to seal the system (no revelation here; just cooling 101). Hot coolant expands and if there is too much in the system, the cap allows the excess to escape (usually on the garage floor or at Cars and Coffee events whereby people point and snicker at what "surely" is a major issue with that Ferrari).

Once the this purge has taken place there is no more excess coolant. The engine then cools and everything goes back to normal until we owners see the puddle on the ground. For lots of different reasons ranging from concern there is no more coolant in the system (its been leaking since I left the house), to simple curiosity as to how far down in the tank this new "ideal" coolant level is, the result is the same. We open the cap, a sucking sound occurs, and we now have added air into the system that wasn't there before. Congratulations.