Coolant

[Jonty]

Hi all

I’ve noticed a few times that I’m getting a small amount of coolant coming out my overflow when I park up. I’m not losing any material amount of coolant and I’m not needing to top up. I’m also not overheating and the fans work correctly. I have my water pump done a couple of months ago. Anyway I opened the overflow cap and there’s plenty of bubbles in there. I ran it for a bit in this video. It doesn’t appear to be “boiling” but should I be worried about a head gasket?

https://youtu.be/LYyB6d9Gx8c

[Jonty]

Also my radiator cap is fairly new from DGo. When I get the engine up to temp just before the fan come on is when I notice the overflow leaking slightly. If I lift the release valve on the cap it will spew coolant.

[Jonathan]

It's too full. Aim for about halfway up that reservoir. You can peer in and see the backside of the weld that holds that front bracket on... use that as a guide. It expands when it is hot, so assess the level when it is cold.

[Jonty]

Thanks Jonathan

I checked this morning when cold. Even after a dump of 100mls or so when I lifted the relief valve when hot it’s still over half full so will take a bit more out and get it below that weld mark thanks. The thing that concerned me was all the bubbles. Is this normal?

[Jonathan]

I wouldn't consider bubbles normal, no. How or why they are there though... It could be just the coolant getting mixed/agitated more than usual because the tiny little return line would be coming in under that level you showed. I would get the level down first, monitor for bubbles and then reevaluate.

Keep in mind what you are doing by removing that cap while the system is still hot and under pressure. By the system getting to just under 15 psi, it is effectively raising the boiling point. If we were talking just plain water, it would boil at atmospheric pressure at 212 deg F. Raise the pressure though and the boiling point goes up. You determine that kind of thing looking at what they call steam tables. Well, a stationary engineer operating a boiler would. We won't be. What I'm getting at is if you have a coolant temperature higher than what it would normally boil at while under no pressure, the second you take the cap off, you're bringing it back to atmospheric pressure and that coolant will flash to steam immediately. And you can get a lot of steam for a small amount of liquid water.

So I might recommend you wait for the system to be cold and then suck the necessary amount of coolant out using a turkey baster or something similar. A little less hectic doing it cold than hot. I used to work as an engineer in nuclear and we had some very large reactors and turbines there. The reactors were approximately 3 million horsepower of thermal energy and the intent was to make steam out of as much of it as possible. You do not want that kind of system breaking open to atmosphere. Not at 1,500 psi and 310 deg C. It would be lights out to anyone in the building in an instant if that ever happened.

[Jonty]

Great advice thanks Jonathan. Yes the return line was under the level so it might be just as a result of coolant being stirred up. I’ll suck some out and then then what happens. If I’m still getting bubbles I’ll try one of those test kits for exhaust gas in the coolant

[Jonty]

Hi Jonathan

Emptied it below half and took it for a drive and it’s still leaking plenty of coolant in a foamy state. I think I’m down a head gasket

[Jonathan]

Hi Jonathan

Emptied it below half and took it for a drive and it’s still leaking plenty of coolant in a foamy state. I think I’m down a head gasket

Sorry to hear that. Time for that exhaust gas testing in the coolant you mentioned.

[David T]

I agree, time to test for combustion gases in the coolant. If you have a coolant system pressure tester, one quick test is to see if the pressure builds up fast. Just put the tester on the system, pump it up to about 5 psi and watch it with the motor running. If it climbs quickly, you probably have a bad head gasket. Can't tell you which side but best to both sides anyway.

[Jonty]

Hi all

Well bit of an update on this. The car passed the gas test and ordered a full compression and leak down test and all passed. The mech actually said it had amazing compression (160-154 across the the board). They are now really baffled as they are convinced it’s not the head gasket. They are at a bit of a loss but are wondering if it could be a contaminant in the coolant (sounds unlikely) or there is a small leak somewhere. They did full system pressure test and it was fine and there were no leaks. Really baffled