Coolant overflowing from the expansion tank.

[nowthenkia]

I've just been thinking about this a bit more. If it were a blocked radiator and boiling the water, I would expect to have seen some steam, right? None of these bubbles look like steam to me, and I get the bubbles immediately when I start my engine from cold. Also, my car is not overheating, according to the temperature gauge.

[nowthenkia]

So, to summarise the symptoms:

1. Bubbles in my expansion tank
2. Bubbles where my radiator cap is (once removed), immediately as I start my engine from cold. (The bubble do not appear to be steam.)
3. Coolant overflowing from the expansion tank. I lose about 1 litre in 10 miles of driving when the car is warm.
4. No coolant overflows when the car is stationary with the engine running, even if I rev it up high.
5. The bubbles have not registered as combustion gases using the test kit.
6. No overheating, according to the temperature gauge.
7. Compression tests have given 300psi-310psi on all 4 cylinders.
8. When applying 5bar compressed air to the cylinders, no bubbles appeared in the coolant.
9. No steam from the exhaust.
10. No trouble starting in the morning.
11. The car runs perfectly normally. Acceleration and power are normal. Fuel efficiency is normal.

[Conglomerate]

Just a suggestion, replace your radiator cap.
Also check for the notorious leaking pipes traveling to rear heater.

Suggest you travel over some dusty roads, then inspect underside of vehicle for any wet/muddy spots around tubing...
As it may be a slow leak that only opens up when hot..

[nowthenkia]

Thanks for your suggestions.
I have already changed my radiator cap, but this can't be the cause of the bubbles. They appear before they arrive at the cap.
I have already short-circuited the rear heater pipes beyond the front section.
I'll be very lucky to find a dusty road at this time of year. I notice you are from Australia - plenty of dust. But, to be honest, I know where I am losing water. The question is where I am admitting gas into the coolant system.

[GottaCruise]

Greetings,

Using blue-colored paper "shop" towels are also really handy for detecting leaks from the coolant system - the towel turns a dark blue, when liquid is on it..

SCOTT Shop Towels, Roll, 10 2/5 x 11, Blue, 55/Roll, 30/Carton: Amazon.co.uk: Car & Motorbike

SCOTT Shop Towels, Roll, 10 2/5 x 11, Blue, 55/Roll, 30/Carton: Amazon.co.uk: Car & Motorbike

--
I would carefully inspect all hoses, even a -small seal leak- will emit lots of coolant when the vehicle gets hot / to temperature.

Any soft hoses should be scrutinized and/or replaced,

Any rusted clamps should be replaced w/ new hardware,

in addition to removing the hoses & inspecting the connector ends, making sure there is no material inside the mating portion of the hose that may be acting as a leak path,

and using fine-grit sandpaper and/or fine steel wool to clean up any scale/corrosion on the mating surfaces as needed,

The coolant drain in the bottom of the radiator should be inspected: if tight, I would release a small amount of coolant to lubricate the rubber seal around the drain plug, and re-tighten (hand-tight / firm only),

* You should be using the recommended 50/50 mix of anti-freeze and distilled water recommended for your Sedona ..

If cleaning up hose connections & Q/A'ing -> re-tightening the radiator drain plug doesn't solve it, then I would consider & investigate the radiator, and water pump, as possible causes next..

--
I hope this helps,

Regards,
GottaCruise

[nowthenkia]

Thank you for your suggestions
How can air be admitted into the water system when the water system is under pressure?
Thank you

[GottaCruise]

Originally Posted by nowthenkia

Thank you for your suggestions
How can air be admitted into the water system when the water system is under pressure?
Thank you

You are losing coolant under pressure - air is being sucked back in to equalize the system / the displaced coolant,

Suggest you re-check the thermostat first, pull the thermostat, heat some water to > the opening temp., and place the thermostat in the hot water to make sure it is opening fully and evenly.

Gloves are recommended, kitchen tongs are handy to remove the thermostat and check it..

When cool, reinstall, making sure the metal (spring) portion of the thermostat is in the direction of the heat source (motor).. The thermostat s/b marked w/ direction of coolant flow, the spring portion that opens the thermostat should be pointing towards the motor.


You have (2) radiator caps (old and new), compare the Open PSI and make sure it matches what the system is rated for..

** Re-check the radiator, get a flow test done like Dr. Bob suggested,

** Purchase an InfraRed (IR) thermometer so you can more accurately determine:

The temp. at the thermostat outlet (where the top radiator hose connects to the motor),

The temp at the top radiator hose inlet,

The temp at the bottom radiator hose outlet.

--
You stated above the heater core was disconnected, where the (2) hoses going to the heater core (plugged) or properly (bypassed) ?

** If plugged and NOT bypassed, you may have omitted coolant from the engine, install a proper bypass using some hose connectors and a length of heater hose ASAP..

After you have verified the thermostat / that the system / hoses are hooked up or bypassed properly, place a piece of carboard under the vehicle, and run the vehicle until hot, this may take up to 1 hour or more.. Use the IR thermometer to closely monitor the temp at the thermostat outlet, DO NOT RELY ON THE TEMP GAUGE ON THE DASHBOARD.. Shut off, let cool some, and check the carboard for any coolant -> start tracing to find the leak.


--
Does your vehicle have an electric fan? Is it working properly?
--
If equipped w/ a diagnostic port, consider purchasing a scanner so you can see the real-time value of the engine coolant temp. sensor and compare the value against the IR thermometer reading at the thermostat housing..

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Make sure you are purging all air out of the system when refilling coolant, this involves running the motor with the radiator cap off until hot / thermostat open, and topping off the coolant level in the radiator.. Shut the vehicle off, Make sure the overflow/expansion tank is filled to the MIN level, and squeeze the top radiator hose (wearing gloves/hand protection) to "burp" the system / force any trapped air into the radiator.. Top off w/ coolant as needed.

--
If the vehicle is overheating after (x) miles of driving, warm up the vehicle, drive 1/2 that distance, park, let the motor / cooling system cool down, and check the expansion tank level / and the radiator level.. Top off and try again.. (See above, trapped air in system),

If there is an air purge valve at the thermostat housiing, open it slowly to release any trapped air, close, and top off the radiator and expansion tank to the MIN level w/ coolant,

If no joy above..

*If the flow test on the radiator is good, consider the water pump suspect..

*If you do not have a service manual, consider getting one: I wouldn't be working on my vehicle without one.

--
Regards,
GottaCruise

[Dr Bob]

You could also use a fluorescent dye + UV light to check for leaks:

What types of fluorescent dyes should be used? | tracer

This sort of problem with the cooling system is usually associated with a fairly "dead" engine. You are lucky that everything apart from the radiator etc. appears to be OK (so far). Hope you get it tracked down before summer. Keep us informed.

[nowthenkia]

Thanks for your suggestions - a lot to test.
I would still like to have explained how any of these possible faults would explain why I only lose coolant while it is moving. The other tricky one to tie in is that the garage could not detect any CO2.

[Conglomerate]

do another coolant system pressure test
Gottacruise is correct.
Especially given your earlier hose clip fix.

Air gets sucked back into the system as cools down.This then rises and bubbles out as engine warms/pumps coolant. That air forces coolant out into expansion bottle in spurts.

you never indicated earlier that already replaced pressure cap,
nor that bubbles were visible at radiator fill point when cool.

check for dusty, blistered hoses (they delaminate), or strong glycol smell when hot engine, any loose hose joints onto pipes or fittings..
loose engine welch plugs can do it is well, but uncommon.
I reinforce the statement that it takes very little fluid loss to cause lots of bubbles.

Do another radiator pressure test