Air in cooling system

I’m not convinced you have a problem. Why do you think you have air in the system? Do the water temperature and oil temperature gauges stay in the normal range as you drive? Does the car drive well? If so, relax.

It’s perfectly normal for your car to puke out a little engine coolant after a nice drive...obviously the coolant expands as it gets hot and the system is designed to allow any excess coolant to escape through the overflow tube. You probably had added a bit too much coolant when you topped up the tank.

Every once in a while, when the engine is cold, stick your finger down into the overflow tank...if you can just reach the antifreeze you’re good to go.

Find something else to worry about.

Good luck!
Alan
N.J.

 

Including the one under the plenum? I had a leak a few months ago that I traced to that clamp.

 

Air in the radiator is very common. A lot of people report seeing it. Some have resorted to fitting auto bleeders to deal with it.

I get it (but never huge amounts) & I have come to the conclusion that its caused either by a bit of cavitation in the water pump or possibly just the water splashing around in the expansion tank (there is a lot of flow in & out of there all the while the thing is running) & creating a few bubbles which get drawn into the system & accumulate in the rad.

So I'm also not convinced you definitely have a problem but if you want to chase it down some more then:

Puking out the overflow could be a sign of an aged / weak expansion tank cap. They are not that expensive, try a different one. Should be 1 bar I think. Could also be because you over-filled it a bit. It will get rid of excess that way.

If you really want to check that there are no underlying problems then you are going to need a couple of things: a cooling system pressure test kit & a block tester kit.

The latter is for everyone's worst nightmare i.e. combustion gases in the cooling system.

First step though is to bleed all the air out of the rad and the T'stat housing & then make a note of the level in the expansion tank (measure down from the rim). Then use the pressure test kit to pump it up to one bar and leave it overnight - 2 or 3 days if you like. If the pressure and the level drops during that time then start looking for puddles & if you find one then fix it & test again.

If the pressure has dropped & you can't find a puddle then you are on to looking at the integrity of the block & as to whether what you are dealing with are combustion gases.

At which point have look at your spark plugs - if you have coolant entering a cylinder then one or more of them may be a very different colour from the others. If they are all the same its not definitive because you can get situations where you get combustion gases entering the cooling system but NOT coolant flowing the other way.

After that, the next step is probably the block tester to see if you can detect any combustion gases in the expansion tank when the thing is running. To test that you probably want to drop the level in the tank so that there is almost nothing in there, then start the motor with the cap off , let it warm up & stick the block test on it & pray the fluid doesn't change colour!

If you do find you have got a leaking cylinder then its on to compression & leakdown tests to try & identify where it is so that you don't have to take both heads off unless you really have to.

 

I started a thread with this same title around three years or so ago. I went down the same rabbit hole - cap, thermostat, hoses, radiator, water pump and the situation continued to worsen until eventually the car began to overheat any time I got stuck in traffic. It turned out I had a blown head gasket but the general issue of "air in the cooling system" has been routinely discussed here for decades to where it's generally considered to be a "feature" of the 308.

What causes it? There are lots of theories on that and I have my own but without rehashing it all since it's all been said and discussed a hundred times. The bottom line is that an air pocket is going to get trapped at the top of the radiator which is going to displace some volume and raise the level in the expansion tank. If you keep bleeding this air pocket out after every drive and adjusting your expansion tank level for that condition you'll end up with too high a level during operation and you'll get overflow (spitting)

So the best thing to do is let it find it's own equilibrium. When you look in the tank on a cold engine it should be about half empty, down near the seam line. If the car is running fine in normal temperature ranges follow the advice above and don't worry about it.

 

I disagree. That indicates you either have too much coolant in the system (the expelling is normal, but the overfill isn't "normal"), or leak causing over-pressure.

 

I disagree with your disagreement...I clearly stated in the very next sentence that he probably added too much coolant.

As long as the car is running well and not overheating he should just move on with his life. If and when he suffers a blown head gasket or other catastrophic failure (God forbid) the car will let him know that in no uncertain terms.

Alan
N.J.

 

We're pretty much on the same page. I'm just saying it's not normal for the car to burp coolant all the time, after every long drive.

 

Agreed.

 

Yea, there were a number of changes that were made starting with the 328 and continuing through the 288 and F40 and two of them were to incorporate a bleed line from the radiator back to the expansion tank and the other was to relocate the engine bleed recirc line to the bottom of the expansion tank rather than the top. When I did my head gaskets I ran a hose through the center frame with the intention of running a radiator bleed line but I've never hooked it up to see if it would work. Another mod has been to insert a sort of stand pipe in the bleed return from the engine manifold so that it won't splash into the tank but will rather just fill in from the bottom like it does on the 328. The idea is that the splashing action tends to aerate the coolant mixture and draw that into the system where it ends up trapped at the top of the radiator. All of this is conjecture though nobody really knows. Beginning with the Testarossa and on to the 348 the radiator was moved to the back but I think that the "feature" of air in the system had been solved with the 328.

 

FWIW whenever I drain and refill the cooling system for whatever reason. Upon start up I open the heater valves. Place the front end on a slight incline. While running the motor I purge the front end. Then I place the back end on a slight incline. With the motor running purge the rear end. And I check the level in the overflow to make sure it’s at the right level once I’m done.

 

Not in my experience!

 

To the OP, did you install the correct type of rad cap? You want the one that has the little vacuum return valve spring-loaded to the rubber seal, NOT the one where the return valve hangs open. If you use the hang-open type, you will likely see coolant spit regularly from the overflow. This occurs because the system won't pressurize. IOW, your one bar cap will never actually see one bar and coolant will spit out when the volume expands due to heat. Spitting when the system is overfill is perfectly OK, and correct. In fact, I never worried about overfilling a bit because the system will take care of that on its own. BUT, the spitting that results from overfilling should only happen once - maybe twice, depending on how long the car was driven after overfilling he coolant.

With the wrong rad cap, after spitting regularly, the coolant level will eventually drop to below the correct level and overheating can result...even in a 328!

 

Afternoon Paul,
On the 328, water is sucked from the lower hose on the header tank and return is on the upper hose (splashes).

John.

 

You're right John, it was the F40 I was thinking of

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For those constantly checking for and bleeding air. I never do. The only time I take off the radiator cap is to change coolant. I used to use the bleeder when I filled them but don't even do that anymore.

 

Yup, after I did my head gaskets I would check after every drive and there would be a little pocket of air in the radiator that I would bleed out. The car ran fine, temps normal. So eventually I stopped doing that, haven't touched the radiator bleed screw in a couple of months. Car still runs fine, temps normal. It's like Schrödinger's Cat, there's only gonna be air in there if I look

 

I have a question for you about a 360 clutch job that was recently done on one of my cars. How can I contact you directly, if possible?

Thank you in advance!