Coolant boiling on engine shutdown

[Jasonmc73]

This sounds very much like the cooling system/block surface finish problem that thousands of these engine had. Off to Mitsubishi.

If you put green coolant in with green coolant you’re fine. The gelling problem occurs when ethylene glycol coolant( green) is mixed with some GM coolants (orange)
Some other types shouldn’t be mixed, but they don’t gel. The best bet is don’t mix colours.

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Bubble bubble bubble, bubble bubble bubble, running hotter than normal?

A quick google search does suggest Mitsubishi wouldn't be surprised to see you.

[MuddyNL]

Hi,
I had my PB challenger serviced some months back and have to top up the coolant a couple of times when I had an overheat due to re-use of old hose clamps and a couple of different leaks found.

Problem:
When I turn the engine off the coolant starts to gurgle and boil into the overflow bottle..... I have never noticed this before/ is this normal. This has been happening for a couple of weeks plus now.

I used what was probably a different coolant to top it up, The coolant still looks good without apparent thickening (at the cap), Driving temperatures when warm are at 96 degrees. (If I can trust 'Torque Pro' preset PID)

Any ideas/ recommendations..
I have tried to look at how to flush the system/ coolant change but I cannot find where you drain the block.

Thank you in advance.

@kiwi downunder I had the exact same thing, i had a loose fit on the lid of the overflow bottle and an bad radiator cap. would boil over when i ever i turned the engine off. I fixed those and it was all good! hope it helps

[old Jack]

If the 96C indicated is correct then this is only just a bit higher than normal immediately after a hill climb. Not only can there be an incorrect reading on the setup of the external temperature gauge which is plugged into the OBD2 port but the coolant temperature sensor or the wiring loom or plug connections, for the dash gauge can be faulty and give a false output, and this is the signal that the OBD2 is reading.

I consulted for a forum member who's Challenger that was "overheating" and going into limp mode when climbing hills whilst towing, the car had been to the dealer service department many times and they blamed the lack of airflow caused by the Smartbar fitted and the position of the number plate. The dealer moved the number plate and the car still indicated an overheat situation, they then removed the Smartbar and the problem was still there, they then changed the radiator and the problem continued. The elderly owners was at their wits end as it was a 60km round trip to the dealer and every time they took the car in it was not fixed and every time they towed their 1800kg small caravan the engine went into limp mode. They were ready to sell the car when they contacted me. After some simple test I found that the engine coolant sensor was faulty, once this was replaced by the reluctant (embarrassed) dealer service department, the car no longer "overheated" or went into limp mode.

If the engine is overheating then you can expect to see steam and coolant exiting the overflow of the coolant expansion bottle when you have an indicated overheat. A simple thermometer test of coolant temperature can confirm the actual coolant temperature and be compared with the indicated coolant temperature.

The gurgling noise you can hear when the engine is shutdown is the hot coolant entering the coolant expansion bottle. Coolant expands by about 0.6% per 10C temperature increase so if the coolant starts off at 20C and is then operating at 90C that is a 70C increase so you will get about a 4.2% increase in coolant volume. There is 8.2 litres total coolant volume in the Challengers coolant system so 4.2% is 345ml, this is normal and can be seen by the coolant level rising and falling in the expansion bottle. When the engine cools down the radiator cap senses the pressure difference and opens, and this allows the coolant to be sucked back into the radiator. It is critical the hose between the radiator cap and the overflow bottle is not blocked, not cracked and is tight fitting, it must be vacuum tight otherwise not all the coolant will be sucked back into the radiator. A common mistake people make is to have the coolant level at the upper indicated level in the expansion bottle, this upper level is actually the hot level and the lower level is the cold level. If you top up the coolant to the hot level when the coolant is cold then there is not enough capacity in the expansion bottle for the coolant to expand once the engine is at operating temperature so it overflows out the expansion bottle!

If you have any air leaks in the cooling system then as the coolant cools, air can be sucked into the cooling system rather than coolant being sucked back into the radiator from the expansion bottle. If there is a coolant stain or crusty build up of coolant on any external part of the engine or cooling system then you have a potential air leak that needs to be fixed.
Once air is trapped in the cooling system it can cause coolant flow problems so it is important to remove all the air. This is best done with the front of the car slightly elevated, like on a set of car ramps, have the radiator cap off and run the engine until the thermostat is fully open and the coolant is circulating correctly, you want to measure a coolant temperature of 85C to 90C. It can take 10 or 15 minutes for all the air in the system to bleed out from the open radiator.

The engine block problem that causes the engines to over heat and be replaced under warranty is similar to a head gasket leaking into the combustion chambers. When the engine is running the combustion gases from inside the cylinders enters the cooling system, this not only aerates the coolant but also increases the cooling systems operating pressure so the radiator cap opens and the coolant is pushed into the expansion bottle. When the engine cools down air is sucked past the leaky head gasket or the faulty block face so the coolant is not sucked back into the radiator. Every time the engine goes through the heating on cooling cycle of the coolant, a small amount of coolant being pushed out of the expansion bottle overflow and eventually the engine is running on low coolant levels and this results in the engine overheating. If you are worried about this then a good radiator specialist can test for combustion gases in the coolant, alternatively there are some DIY test kits available from larger auto stores.

OJ.

[Giddyup]

If you mean they changed the coolant ratio and put a higher pressure cap on to fix a design flaw, then yes it has been addressed some years back (If you call that a fix), but I have since changed service agent (bad bad move) so coolant ratio could be wrong, I need to change it ASAP anyway, (as I have mixed coolants when I topped it up)

Mitsubishi never said it was a fix. They did it to make the bad engines fail so they could get weeded out. This is also why they did a stress test on the engine when they changed the cap. Have a think about it. Do you think running the coolant system at a higher pressure on an engine that was borderline would make it more or less likely to leak?

[DibbyDibbyDJ]

This sounds very much like the cooling system/block surface finish problem that thousands of these engine had. Off to Mitsubishi.

If you put green coolant in with green coolant you’re fine. The gelling problem occurs when ethylene glycol coolant( green) is mixed with some GM coolants (orange)
Some other types shouldn’t be mixed, but they don’t gel. The best bet is don’t mix colours.

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Not a good idea to mix coolants based on their colour as a rule. Mitsubishi coolant is premixed to specification, and you mix it with another "green" coolant that is not premixed or mixed to another spec you are weakening or concentrating the strength which can cause just as many problems.
Tthat is why when the ORIGINAL recall was done on these engines the coolant was flushed and replenished with the correct spec as well as the cap being replaced and the software update to ensure the overheat fault code is recorded.

[KevL]

Not a good idea to mix coolants based on their colour as a rule. Mitsubishi coolant is premixed to specification, and you mix it with another "green" coolant that is not premixed or mixed to another spec you are weakening or concentrating the strength which can cause just as many problems.
Tthat is why when the ORIGINAL recall was done on these engines the coolant was flushed and replenished with the correct spec as well as the cap being replaced and the software update to ensure the overheat fault code is recorded.

True, but mixing 2 different ethylene glycol (green) concentrations will only affect the ultimate boiling or freezing point, not make it gel which was what the op was concerned about.
The difference in freezing point and boiling between 33% and 50% isn’t great.
33% -18c 104C
50% -38c 109c
Also, as concentration increases, the coolants ability to transfer heat reduces.


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[old Jack]

This article provides an insight into different coolant types and has some good general info in regards to engine cooling systems.

https://www.chevyhardcore.com/tech-stories/fuel-cooling-ignition-tech/antifreeze-chemistry/

OJ.

[Kiwi downunder]

Just did another run home tonight, problem persists.
Yes I can see I still have a very mild coolant leak, back at the same place I found the original. Definitely coolant bubbling/ expansion into the bottle, with very small air bubbles formations on the surface with the pressure expansion.
Thus far I can see the coolant expand into the bottle and be sucked back out so all good there. Its just a case of where the air is getting in? or is it air trapped from my top up from weeks back? Exhaust gases not so sure as it only happens on my homeward journey (uphill working harder)

I will try to tighten up hose clamps further over the weekend once things have cooled off.
Not sure if I need to pull hose off to clean it first (Loose more fluid) or just tighten the clamp. Does the leaking coolant crystallise/ affect hose clamping?

PS: thanks for all the info team, I appreciate it all!

[littleriver]

Just did another run home tonight, problem persists.
Yes I can see I still have a very mild coolant leak, back at the same place I found the original. Definitely coolant bubbling/ expansion into the bottle, with very small air bubbles formations on the surface with the pressure expansion.
Thus far I can see the coolant expand into the bottle and be sucked back out so all good there. Its just a case of where the air is getting in? or is it air trapped from my top up from weeks back? Exhaust gases not so sure as it only happens on my homeward journey (uphill working harder)

I will try to tighten up hose clamps further over the weekend once things have cooled off.
Not sure if I need to pull hose off to clean it first (Loose more fluid) or just tighten the clamp. Does the leaking coolant crystallise/ affect hose clamping?

PS: thanks for all the info team, I appreciate it all!

I may have missed it .. but have you been to get a combustion gas analyser test done yet ??? ....



...

[Kiwi downunder]

I may have missed it .. but have you been to get a combustion gas analyser test done yet ??? ....



...

No not yet, but I may have found the issue, ref next quote....

[Kiwi downunder]

Radiator cap

OK, big problem guys and gals (Maybe small?)
I took the radiator cap off to prep to run the engine to get any air that may be in the system with the small coolant leak I found.

I then notice a small metal retaining clip left behind in the seat of the cap socket????
My radiator cap looked like it had broken away, but what had?

So after driving to Australian motors to get a new one..... no stock.....

long story (Low and behold I now have one)
It looks like the original 127kPa cap has broken away and a part fallen into the coolant system...
This could become a issue on its own! all pending the coolant direction flow. Any ideas on that team.

I have taken pics of the broken cap and the new replacement/ and it looks like a different material plastic vs fibre glass.

So can you tell me were the part could become lodged based on coolant flow please.

Maybe all PB owners need to seriously look at changing there radiator caps soon! (Quoted $65-** from MMA)

[Kingbrown]

The coolant returns to the engine (ie to the thermostat and water pump connection) via the bottom radiator hose. So the top hose where the radiator cap is situated is the hot feed water to the radiator.

Radiator is a cross-flow design where the tanks are at the sides.
Hence your missing/broken part will have most likely ended up in the feed tank.

Comparing yours to my 127kPa cap, your missing part looks like a miniature version of the jumper/washer out of a household tap.

The round seat for the valve is also missing from Kiwi's broken cap.
This seat appears to be fused to the underlying plastic during manufacture.

These pieces would be too big to get through the passages of the radiator so they will most likely be trapped in the feed tank (passenger side of the radiator).

I wouldn't be too concerned about it personally.

But it does explain the bubbling of coolant at shutdown.

[Kingbrown]

Photo that shows the part that's broken off of Kiwi's radiator cap.

[Kingbrown]

Here's an hypothetical for the boffins:

What would happen if the valve became stuck to the seat during operation and then the engine cooled down ?
A vacuum would be drawn on the valve with some force, . . . . but how much ?

Atmospheric pressure being exerted on the cooling system = 101 kPa (kN/m2)

Diameter of valve = 15mm. Hence area = 177mm2.

Force = Pressure x Area. Thus:
F = 101000 N/m2 x 0.000177 m2 = 17.9 N.

Equivalent mass is m = F/g = 17.9/9.81 = 1.8 kg.

That's a lot of weight for a little piece of plastic (the valve seat) to hang onto !!

Purely conjecture of course . . . ..

[old Jack]

Here's an hypothetical for the boffins:

What would happen if the valve became stuck to the seat during operation and then the engine cooled down ?
A vacuum would be drawn on the valve with some force, . . . . but how much ?
.

Trick question?

The radiator hoses would collapse under the vacuum so the force on the seat would be less.

OJ.