Air in cooling system

First off, no I do not want to drag this dead horse out of the barn and start beating it again with and old stick. I’ve been battling a nascent overheating issue for the past few months, one that seems all too common and I’ve read literally hundreds of posts on it dating back at least 10 or 12 years on this site alone. The threads have another thing in common - they either come to no resolution or the perceived “corrections” are all over the map.

For my own saga I’ve replaced the pressure cap, thermostat and radiator. My fans work, I’ve done a vacuum leak test with no leakage detected and a block test with no combustion gases detected. The car runs fine when moving but will creep up when stopped and the fans will not contain the creep like they used to when I first got it.

I have followed the elaborate bleeding procedures written by Birdman and Verell with both heater cores open and FWIW my opinion is that if I fill the head tank until coolant comes out the bleeds it should be good but I am finding that there is a LOT of air trapped in the radiator after a drive, more than I think there should be.

So here’s my question: if I start the engine with the cap off of the tank and look inside I see a lot of air bubbles coming in through the manifold bleed hose. I figure that’s it’s purpose, to bleed the air out but it doesn’t seem to ever quit and it seems to me that when the thermostat opens that air is also getting pumped up to the radiator where it will get trapped.

But where is it coming from?

 

Yes both, holds vacuum and pressure rock steady.

Maybe some of you could conduct an observation for me. Open the pressure cap, start the engine and look in there with a flashlight. Tell me what you see.

 

If I don’t overfill the tank I will not expel any coolant unless I let it actually overheat and boil out.

Also I should state that I’m not interested in reengineering the system. If everything is right it should work perfectly well the way it came from the factory.

 

I haven’t but I’m thinking I might have to go there next. Or maybe I’m just jumping the gun, I’ve only had it out twice and the weather went bad. Maybe another bleed session or two is in order. Thing is I replaced all my main line coupler hoses and wanted to make sure I had no leaks so, it’s filled with distilled water right now because I didn’t want to deal with any mess and if I do get it sorted by bleeding I’ll have to drain it and start all over again!

 

I have those Andy, got them from Clark & Clark and I'm sorry to say that, at least in my case, they don't seem to do anything. I don't know why as many other people claim they work. Personally I'm not too keen on my system depending on a couple of 1/4 inch o-rings so I intend to put my original bleeder screws back in after drilling them to allow bleeding without complete removal.

As for Brian's suggestion that turbulence from the manifold bleed hose stream entering the top of the tank causes air to get pulled into the system I need to think about that a bit.

The way I understand the system is that the water pump pumps the coolant into the block which then exits through both heads into the crossover manifold. From there it has two paths, one to the thermostat and the other through the small bleed hose back to the expansion tank. At the thermostat it goes either back to the water pump or to the radiator or both depending on the temperature and position of the thermostat. The expansion tank is a "head" that stands above the entire system and the only flow into the system is to replace what came out through the bleed hose. So I don't know if the bubbles I'm seeing are coming from the system through the bleed hose or if they are just forming from the turbulence of the stream splashing into the tank. I have read at least one thread on this subject where a guy claims to have solved his problem by simply clamping off the flow from the bleed. Maybe even just reducing it would help. Another thread made vague mention of a tube that is required inside the horizontal expansion tanks (as opposed to the earlier vertical tanks) causing the outflow to exit below the surface rather than splash onto it but obviously I don't have one in my tank. I'm having trouble seeing how the air can get in that way but of all the reading I've done on this it seems that everybody always has some air trapped in the radiator and it's considered normal so it has to be getting in there someway.

Anyway, my system is bled right now (for the third time) so I'm going to give it another idle run up to temp in the garage and see if it has improved any. It used to be that it would climb to 195, the fans would kick on and then cycle to keep it there. That's what I'm hoping for. If it does that I don't care how many bubbles I see or how much air is trapped in the radiator, so long as it works.

 

Ran two tests this morning just idling in the garage. There are 4 marks on the gauge 140, 2nd, 195, 3rd and 250. At about 2 minutes the needle hit the second mark, warm up light went out and idle dropped to 1100. Temp continued to rise to 195 then dropped back to second mark which I assume means the thermostat opened. It did a few cycles like this with decreasing swing until it settled at the 195 mark. From there it crept very slowly up until a needle width over 195 when the fans kicked on. At that point it continued to rise and fans kept running until I shut it off at the 20 minute mark with the needle halfway between 195 and the 3rd mark.

After it cooled I removed the cap and saw the tank was completely full. I bled the air out of the radiator and it dropped back to about half full (where I started) So a lot of air in the rad which was completely bled when I started.

I repeated the same test with a house fan blowing into the nose. Same results except the temp creep after the fans kicked on was very slow, I quit when it was only a couple of needles width past 195. Again lots of air in radiator.

Tomorrow I’m going to repeat the same test but pinch off the heater core hose where it goes into the head. Then maybe try with manifold bleed hose pinched off. There has to be a source for this air somewhere. I know people are going to suggest head gasket and I’m not ruling it out but I have done block tests multiple times with negative results for combustion gases in the coolant. Plus if it were a head gasket I don’t think I’d be able to romp on it and drive around all day with no problem. It’s only when I stop that it does this.

Anyway, I’m not giving up until I solve it. I need to study the heater core circuit and get a better understanding of how it works.

 

I put in an aluminum radiator that I got from Nick’s Forza Ferrari. I also installed a pair of new Spal fans that are shrouded and directly touching the front of the A/C condenser. Also note: these symptoms began with the OEM radiator and fans in place so they didn’t start with the new installation, it is a pre-existing condition. While working through it I looked in the top tank of my old rad with a boroscope and saw a good deal of scale and debris so I opted for a new radiator and decided to upgrade the fans as well.

 

I think the first step is to isolate that whole sector by clamping off the hoses at the engine and where it tee’s into the main line by the steering rack to see if that does anything. If it does then I’ll dig into it further, if not I’ll have to look elsewhere.

I’ll publish what I did with the fans once I get the whole thing working, don’t want to point anyone down this road until I’m convinced it’s all adequate. Very simple install though, they even mount right to the original fan saddle clamps with no modifications other than a couple holes drilled for mounting bolts. The shrouds are integral.

 

dougelam - thanks for chiming in. I'm not ruling out head gasket but, as I said, there are literally hundreds of posts going back more than a decade or two that describe these exact symptoms that were determined to be from other causes. So I need to work through all of those possibilities before I consider tearing my engine apart. I'm trying to do that methodically like a forensic scientist at a crime scene. I've had blown head gaskets in my life before as well but a couple of things that give me hope - multiple block tests have failed to detect any combustion gas in the coolant and it seems I can drive all day flat out with no problem as long as I don't stop. I think if it were a blown head gasket it would overheat at all times and would be worse when I'm spooling it up to 7,000 rpm but still I'm not saying it's impossible. If it is I'm prepared to deal with it.

Tony - New thermostat came from Superformance. It did not have a bleed hole, I drilled one same size and location as on original.

Hal - I understand the distilled water issue but as I stated earlier these symptoms were occurring prior to all of this work with 50/50 glycol and a 1.1 bar cap. I have only run with the cap off for a minute on cold start to observe the flow into the tank through the bleed line and have always shut down when I see that the fans are not stopping the rise over the 195 mark so never got anywhere near 240. Also, even if the water were to boil at a local spot it would create steam which would then condense back into water when it got to the radiator or any other spot that is below the boiling point such as the crossover manifold where the gauge sensor is located. I don't think it could create air. I'm pretty sure the air has to be coming from an external source. Whether that's the heater circuit, the water pump, the head gasket I don't know yet. The distilled water just makes it easier for me to drain and refill and conduct tests, it's only temporary.

Thanks to everyone for the feedback, wish me luck in finding this.