[fbd73]

Hi All,
I have a 1973 Firebird Formula 350. About 3 years ago I installed a 3 core aluminium radiator from Ledfoot Racing. We also installed twin electric fans and have had no overheating or cooling issues since.
Now to the problem. A couple of weeks ago, I took the car out for an afternoon cruise. No problems. 24 hours later I went into the garage and noticed a pool of coolant on the garage floor. On inspection it was coming from the water pump. I went to take off the radiator cap and coolant sprayed all over the inner and outer fenders. The cooling system still had pressure after 24 hours. I have never heard of that happening. I have since replaced the water pump but the system holding pressure has not been solved.

What are your thoughts as to why this could have occurred?

[gtospieg]

Is it possible you have a head gasket going bad and pumping presure into the system? I know it seems unlikely. I would think if it leaked in one direction it would "leak back" after shutdown....Unless the leak has to do with heat expansion that cools and stops the leak.

[fbd73]

Hi All,
Here is the latest.

I took the cap off (slowly) and released the pressure. I let the car sit overnight without the cap on. I did not start the car at all.
The next morning I put the cap back on. The next day I went to take the cap off and it had built up pressure, without even having started the car.

Next step.
My mechanic went to tighten the head bolts down (just a theory that it might be the problem) and had to stop as he found tiny broken springs in the top of the cylinder heads. They are the valve stem seal springs disintergrating. I have had the car towed back to the shop who overhauled the motor and they are in the process of replacing the valve stem seals and then will investigate the system holding pressure. By the way, it isn't just a small amount of pressure it is holding. If I removed the cap quickly or not carefully, it would spray all out over the fender.

[shermanator2]

Originally Posted by fbd73

Hi All,
I took the cap off (slowly) and released the pressure. I let the car sit overnight without the cap on. I did not start the car at all.
The next morning I put the cap back on. The next day I went to take the cap off and it had built up pressure, without even having started the car.
.

This is very interesting. We are now getting somewhere. Was the battery connected or disconnected when it built up pressure on its own? If it was connected, then once you get it back and the issue is still there, then try it with the battery disconnected.

I am not surprised that it had full pressure in it just like it was running and hot. You seen th have electrolysis or something else chemical going on here that is giving off a gas and pressures the system until the cap bleeds off just like when it is running.

[Chris65LeMans]

Originally Posted by fbd73

Next step.
My mechanic went to tighten the head bolts down (just a theory that it might be the problem)

I would think that this would have ruined the head gasket, too - if this was the problem.

Also - I'm not following the logic that bad valve seals could cause extra pressure in the cooling system.

[shermanator2]

Originally Posted by Chris65LeMans

I would think that this would have ruined the head gasket, too - if this was the problem.

Also - I'm not following the logic that bad valve seals could cause extra pressure in the cooling system.

I think that he was saying that the valve seal problem was a separate problem discovered when his mechanic was re-torquing the head bolts. The head bolts nor the valve seals can have anything to do with the cooling system pressurization issue.

[shermanator2]

Radiator cap. There is nothing else that is supposed bleed pressure out of the cooling system. The situation you describe is very strange though. Normally when the car gets warm, the thermal expansion increases the pressure until the cap vents at 15psi or whatever it is set for, then as the engine cools the pressure drops back to atmospheric or below. Was it very cold overnight between your afternoon cruise and noticing the puddle and was it then warm? If so maybe nothing is wrong. What kind of radiator cap is that?

[fbd73]

We are in the middle of our summer here so definitely warm on the cruise and also overnight. Here is a photo of the radiator cap I purchased when I bought the radiator. Sorry for the bad photo.

[fbd73]

Here is an update. I put the new radiator cap on (16lb) and took it for a drive. All went well. I let the car cool down for about 4 hours and then went to remove the radiator cap. It was still holding pressure.

[firechicken]

Originally Posted by fbd73

Here is an update. I put the new radiator cap on (16lb) and took it for a drive. All went well. I let the car cool down for about 4 hours and then went to remove the radiator cap. It was still holding pressure.

4 hrs cool down might not be enough.
Try letting it sit overnight with the new cap.
Is your recovery tank vented?

[fbd73]

Hi All.
An update.
The engine rebuilders replaced the valve stem seals with a better type so that will fix that problem.
While the car was there, I took a snapshot of the last suggestion about disconnecting the battery and gave it to the mechanic. He tried it and guess what, no pressure build up.
I got the car back on the weekend and tried it myself. I parked the car and let it sit for about 2 hours and then disconnected both battery terminals (I didn't think to do it immediately after parking it) and let the car sit for another couple of hours. There was still pressure there when I went to remove the cap but not a lot. I then checked it another couple of hours later and no pressure. I checked it this morning before I left for work and still no pressure build up.

So, if it is electrolysis, what can I do so that I don't have to disconnect the battery all the time?

Any thoughts?

[shermanator2]

Originally Posted by fbd73

So, if it is electrolysis, what can I do so that I don't have to disconnect the battery all the time?

Any thoughts?

It looks like you have an electric fan mounted to the radiator. If there is some electrical leakage from the positive side through the fan or fan thermostat into the radiator, and the radiator is not electrically bonded to the engine, then I could see this happening. Is the radiator in rubber mounts that electrically insulate it from the chassis? What is the electrical path from the fan and thermostat and whatever other fan controls you have back to ground? Do you have the ground straps from the engine to body installed?

You are looking for something in contact with the coolant that is at a different voltage than something else in contact with the coolant. If you have a multimeter, measure the DC voltage from the radiator to the engine block with the battery connected. It needs to be very close to zero.

A wire from the radiator to the engine may solve it, but if there is leakage current from the fan system, your battery may run down while the car is sitting.

[shermanator2]

OK, for a long shot, what chemicals do you have in your coolant?

[gtospieg]

Just an FYI...not a bad idea to disconnect the neg. terminal when the car is parked. I do this and run a battery tender.

[dataway]

Another long shot ... clogged overflow tube? Does the position of the overflow fitting on the radiator require a specific cap to intersect the overflow tube fitting properly?

If the cap seal doesn't lift enough to uncover the overflow opening it might retain pressure.

Just mentioning it because the wild card here is the radiator. The design of the filler neck is pretty important to make the cap work properly. The spring in the cap has to be compressed the right amount etc.

[fbd73]

I checked the overflow tube and it isn't clogged. When I bought the radiator, I bought the radiator cap with it, so hopefully it was the correct one. It has been working well for nearly 3 years. It is a Champion Radiator 3 core aluminium radiator bought through Ledfoot Racing.

[dataway]

I'd drive it a few times with the new cap and see if it's doing the same thing after that. With no coolant recovery system the radiator has to find it's happy place. Expelling enough coolant till it has the proper amount of air space in the radiator. I know systems with no coolant recovery like the right amount of air space in the radiator, not sure if Champion makes any recommendations in that respect.

[fbd73]

It does have an overflow bottle. One that I had custom made as shown in the photo.

[fbd73]

That is correct Sherminator. My mechanic found the broken valve stem seal springs when he went to tighten down the head bolts.

Here is the latest.
For the last few days I have had the battery terminals off and on and checked the radiator cap. There is still no pressure build up. I haven't started the car though. I will do that in the next hour or so and run it up to temperature and then do the whole process again to see if it builds up or retains pressure in the cooling system.

[fbd73]

An update.
I was working away for the last week and went to remove the radiator cap yesterday and there was still pressure behind it, to the point that some coolant sprayed out onto the inner fender and motor. That is after sitting for a week.
Also, the overflow tank is vented.