blowing air bubbles in overflow tank

[lismo]

Hi all,

Im hoping someone can help me as to what my problem could be.

In the span of about 8 months, my water pump went, next was the heater core then my head gasket. I remembered that i could hear like air bubbles being blown up through my overflow tank, it never overflowed,first it started of to be just every now and then when it got hot and just got worse blowing more and more bubbles.

About 3 weeks ago i had my radiator recored as i thought it was the source of all my problems. I got a bigger core with 20% more cooling than the original.

I thought that would be the end of the air bubbles. But they are back.

Is it normal for it to do that???

Has anyone else experienced this problem???

[Grant]

My car used to do that in the heat of the summer, the water was actually boiling in the overflow reservoir, and sounded like a kettle boiling...

Sorry, not sure of the cause though sorry.

[elbee111]

I believe that any bubbles in your cooling system is not good.

My understanding is that it would mean gasses from a combustion chamber getting into the cooling system, via the head gasket or a crack in the head.

Do you get these bubbles when the engine is started and running dead cold with the radiator cap off ? If so, it will be as above.

Or... If you have an overheating problem that gurgles into the overflow it could be as simple as a tired radiator cap not keeping enough pressure.

Hoping for the best.

El Bee

[psybic]

210RWKW on 12psi on stock turbo... did you achieve this some serious timing advance?

Sounds like its getting way hot.

Yeah, bubbles means exhaust gas getting thru head gasket, should get a chemical test done on the fluid in the radiator, they can tell whether there are any exhaust gases in there or not. NRMA dude can do it.

[Jordan]

Now when this was happening to me in my skyline I was stumped, I couldnt work out how the water was getting from the radiator to the overflow, and back again

If you look at a standard radiator cap, it says 90 somewhere on the top. That number is the pressure in Kpa that the radiator cap is set to allow pressure to escape down to the overflow tube to the overflow tank. This is a one way thing and kinda works like a pressure relief valve. In fact thats exactly what it is, a valve.

Now the if you look closely at the bottom of the radiator cap, there is a small return valve and piston that you can hook your fingernails around and pull downwards on a spring. This bit is the exact opposite of the outgoing pressure relief valve, it allows liquid to pass back under vacuum.

If you look at the Overflow bottle, it has a vent at the top that allows it to release gas into the atmosphere. After driving around and the engine is cooling down and the pressure in the radiator drops it will go from positive pressure to a vacuum. What happens is that this vacuum will suck what liquid is left from the overflow bottle back into the radiator so that it is ready for the next time you take it out for a drive. In practice the radiator is never empty, and it never has air introduced into the system. Everything is hunky-dory.

Ok, now heres what it really means.

While your driving around, and you notice the overflow bottle is bubbling away, its not the bottle itself boiling, its just passing the superheated steam (which has increased the pressure in the radiator to 90+kpa) from the tube at the bottom of the tank. Since most of the water is probably been pushed into the overflow valve already then all you are getting is the leftover pressurised gas escaping from the top of the radiator tank thru the cap.

So the bubbling is coming from the radiator, duh. But is it doing it because of a bad pressure spring in the cap? Pressure coming into the cooling system from engine combustion? or the water is leaking out from somewhere, introducing air (sucked in via vacuum thru the cap from the vented overflow bottle which has already been sucked dry) and letting the engine overheat and boil, creating more steam. This last one was only realised by me after refilling my empty overflow bottle from water containers I had to keep in the back of the car.

Take it to a mechanic to test and check it for you. They can also clip something over the radiator and pressure test the whole system for leaks, and testing the valves in the radiator cap also. It could be something simple.

[elbee111]

Ah whatever.

The easiest thing is to check the radiator just after the engine is started (and still cold). If you get bubbles it is coming from a combustion chamber.

El Bee

[lismo]

It only gets the bubbles when it is hot and i have been driving around for a while. I only hear it when the engine is off and it only gurgles just a little bit. It dosnt do it at all when it is cold.

When the head gasket was stuffed i took it to get a simple test (where they put that thing in the top of your radiator and it turns green or something) and it didnt change colour so we thought it wasnt the head gasket. My uncle who works at nissan took the engine apart and the head gasket was well gone. It was replaced about 4 months ago with a metal head gasket and im pretty sure the head was tested to see if there were any cracks.

The radiator has a bigger new core and with it i got a new radiator cap. There is no leaks and the cooling system is not losing any coolant.

I will take it back to the guys who did my radiator and tell them whats going on and see if they can do some tests for me.

Thankyou everyone for taking the time to reply to me.

[lismo]

psybic: the car has been doing this before it had 210rwkw. the water pump, heater core and head gasket have all been replaced by new ones and i just had the radiator replaced by a bigger core with 20% more cooling than previously.

When i had the test done your referring to, my head gasket was blown but still that test did not work and i have no idea why.

The cars timing is not advanced at all.

Before i got 210rwkw, my car previously had 160rwkw. I acheived 210rwkw buy getting a microtech lts 12 and getting someone in brisbane who really knows microtechs to tune it. So buy just adding a computer i gained a massive 50rwkw. I was told microtechs are better then apexi pfc cause you can do a couple more things with them. And now i believe it.

[elbee111]

Does your car actually overheat ?

How high do you go on the standard temp guage ?

[lismo]

It dosnt seem to be over heating......the temp gauge is right in the middle and thats where it always seems to stay when its running normal. the only time i saw it hot was when i had the other problems. I have just bought a more accurate temp gauge that displays the actual temperature.

[elbee111]

Right in the middle is where mine sits as well.

Do you ever have to top up the reservoir ?

[lismo]

no i dont have to top it up, hardly ever actually.

[elbee111]

See Jordan's explanation of how the radiator cap allows coolant out to reservoir and back in.

You may be noticing this in operation as the coolant temperature actually goes up for a short while after you stop the car.

As I understand it, the cap holds closed till the proper pressure is reached and then opens to allow a small amount of coolant to go into the reservoir.

The movement of the coolant would happen in one or more "gloops" to the reservoir that may appear to be air but isn't. :Oops:

It is just coolant that has been forced out by expansion and pressure. This goes back into the radiator as it cools.

Hope that makes sense and I hope that this is the case. Might be wise to get it checked and confirm this.

El Bee

[Jax]

Ist, what 'Jordan ' said abt radiator caps is right. 2 nd., there is a fair chance there's nothing the matter. 3 all these things can be checked from outside. PRESSURE Check..In place of radiator cap, goes a guage, which seals where the cap seals. It has a hand pump attached. Pump up to required pressure, and watch guage. If it holds the pressure, without the guage dropping, it's OK. Any Radiator Repairer can do this.

If there is a leak, then by various tests, you can isolate where it is, e.g., if you had a leak from #1 cylinded head gasket, into the water jacket, if, with the radiator cap off, and putting compressed air, via a screw-in fitting into the spark plug thread of #1 cylinder then air bubbles would be evident, looking into the radiator. And so on. There is no need for guesswork.

There's prob nothing the matter with yours, but you would be surprised how many heating problems are eventually traced back to the radiator cap. Whenever in doubt, renew the cap FIRST, rather than last. I's quick and relativly cheap to try. ALWAYS fit the Proper recommended cap.. NEVER fit a cap with a lower pressure rating than original equipment.

Good luck, it's prob OK

[Jordan]

I had a leak in the engine somewhere that I didnt get fixed for 2 months. I was carrying 8 litres or water around with me in the back seat and I had to keep pulling over and filling it up. (I could tell when it was empty because the engine started to heat up and the guage started rising).

I thought it was one of the welsh plugs, but it ended up being a 10cm bit of hose right in the back of the engine down near the starter motor.

[lismo]

When i had the radiator recored i got a new cap with it so i dont think the cap is the problem. But yeah i will go and get it tested by the guys who did my core.

Thanks so much peoples for your time in replying and your very helpful comments.

Its very much appriciated......THANKYOU.

liz

[boostn32]

bubbles in the radiator means u have a blown head gasket or cracked head, get a gas test done on your coolant in the radiator, this will tell u if u have a blown gasket or cracked head

[ferni]

Mine did the same thing a month or two ago, not sure why, came home cooled engine down, turned off engine, heard bubbling, popped bonnet - radiator sounded like it was boiling.. let it cool down for 45mins, (boiling stopped after 5mins or so) open radiator cap - no oil/bubbles there....

Cap i had was an aftermarket one that came with the car 1.3bar replaced it with a stock 0.9bar... haven't heard it since, dunno if its because of radiator cap.. but not complaining... also temp guage never raised off its normal place in the middle.