Coolant Escape from Overflow after shutdown - Any ideas?Monaco Wagon 383

[DJAstral]

Hi there, just wondering if anyone might be able to advise. Quite often when I switch off the engine, I get a small amount of coolant escape from the overflow pipe.

I have renewed the rad cap for the same type that was on it, a Stant Lev R Vent 16LB. But has made no difference. I wanted to renew the thermostat as well, but the bolts are seized solid & im scared I’ll break them off with too much force.

I checked the coolant level was about 1-1”1/4 below the filler neck and suspecting air in system ran it without the cap for about 1/2 hour until warmed up. I checked the temp with a thermometer & she was exactly right at all times, and dropped quickly as expected if I revved the engine lightly as the fan cooled it.

However, as soon as I shut the engine down, after a few seconds the coolant level rose up & chucked some out of the open filler neck.

Car runs very well & doesn’t seem to overheat, no coolant loss when driving/running & no water or visible fumes from the exhaust at all.
Pops a bit on the overrun when backing off the throttle from higher speeds but this might be due to the non-OEM open cherry bombs & Lake Side pipes. Engine itself very quiet. Full compression on all cylinders.

Any advice as always, would be gratefully received. Thanks.

 

[ceebuddy]

If you don't have a coolant recovery bottle the symptom you described is quite normal. After shutting down the engine, heat continues to build up in the engine block for a moment, causing steam bubbles which rise from the block/water pump into the radiator where momentarily this creates more than the usual 16 lbs pressure the radiator cap is designed for. This, in turn, causes the valve to open and release the steam/coolant mix into the overflow pipe. You may reduce the risk of this occurence by lowering the level of coolant in the radiator a bit, without sacrificing actual cooling capacity of the system. Just covering the ribs of the radiator net should be fine.

If your car continues to produce pee stains nevertheless, it might indeed be that the valve spring in your radiator cap is too weak (a new cap doesn't cost much)--or maybe your radiator is clogged so your engine is always running a little hotter than it should be.

You might consider attaching a 40 oz or 50 oz plastic bottle to the radiator yoke with wire ties, and in a position that when you route your overflow hose into that bottle the hose ends about an inch above the bottom of the bottle. Then fill that bottle about 1/3 with coolant. It will catch coolant pushed out of the overflow and allow it to be sucked back in when the system cools down. This might not be a real solution to the problem but prevents those coolant puddles under your car and keeps your form constantly checking and topping up coolant.

 

[DJAstral]

That is REALLY helpful! Thank you so much for that - I’ll give this a go today. I hadn’t considered adding this & am sure it will help.

Job done, coolant recovery bottle fitted to catch & return the max 1/4-1/2 cup of coolant that comes out as you suggest.

 

[Chrome58]

When you say that she doesn't seem to overheat, what makes you say that exactly ?

 

[DJAstral]

The temp gauge, feel of top of radiator , way it drives, visual & thermometer checks.

 

[Yeahrightgreer]

View attachment 261425
I wanted to renew the thermostat as well, but the bolts are seized solid & im scared I’ll break them off with too much force

If the bolts are seized, have you already checked that the coolant is clean? Usually siezed thermostat housings are from neglect and corrosion over the years. You can drain a little coolant from the petcock below the radiator, to see if the coolant is coming out clear. I would also wait till the engine is cold, and take off the upper radiator hose and look down into the thermostat for a visual inspection.

If it is damaged, stuck open, or corroded all to hell, I’d suggest an impact wrench to get the bolts out. If you don’t have one at the moment, a good breaker bar.

 

[DJAstral]

If the bolts are seized, have you already checked that the coolant is clean? Usually siezed thermostat housings are from neglect and corrosion over the years. You can drain a little coolant from the petcock below the radiator, to see if the coolant is coming out clear. I would also wait till the engine is cold, and take off the upper radiator hose and look down into the thermostat for a visual inspection.

If it is damaged, stuck open, or corroded all to hell, I’d suggest an impact wrench to get the bolts out. If you don’t have one at the moment, a good breaker bar.

Thanks for this, i’ll give that a go as I’m keen to change the thermostat.
Hopefully the bolts are as strong as they look & don’t snap the heads off when I try & force them to move.

 

[mr. fix it]

My 1st thoughts are that if this is a good operating & confirmed no overheating other than the after boil "Open" cooling system then you simply have too much coolant in the top of the radiator when it is cold.
Too much coolant during the after boil stage will cause what you are seeing.

There should be about 3/4"-1" from the rad cap opening for an open system when cold.

Too much water in the coolant mix will do this as well since water boils at a lower temp than the glycol coolant

If this continues to force coolant out then chances are you have pin hole head gasket leak which if the errant cylinder is in the "compression" stroke position will result in the same thing happening.
The forcing of the coolant will be 2 fold.
1) after boil
2) Compression stroke trying to force compressed air at a high temperature
3) Generally pin hole leaks are the hardest to find without removing the cylinder heads for a physical inspection.
Depending on the engine, if it has the original head gaskets then they are likely steel gaskets if i am not mistaken. (Anyone reading this please correct me if i am wrong on this point)

Some cooling system notes:

1) Open system rad caps are designed to vent air not coolant. This will happen in an overheat situation like extended idling in traffic...
2) Closed system caps are designed to vent coolant & then allow it back in during the cooling off stage.
3) If you add a overflow bottle then convert it to a closed system and be done with it. This will prevent the coolant from exiting.
4) You will know if you have a bad rad cap if you notice when the engine is stone cold that the rad hoses are collapsed.
this indicates the vent/pressure valve in the cap is not allowing air back into the system which in turn will cause a vacuum as the coolant cools off back to ambient temps

I hope this helps you out in your quest.

Please post your results

 

[mrfury68]

Before you try impacting or breaker bar-ing those bolts, try applying some heat to them. Patience is key when dealing with seized bolts. Good luck.

 

[DJAstral]

Before you try impacting or breaker bar-ing those bolts, try applying some heat to them. Patience is key when dealing with seized bolts. Good luck.

Great, will do thanks.

 

[ceebuddy]

1) Open system rad caps are designed to vent air not coolant. This will happen in an overheat situation like extended idling in traffic...
2) Closed system caps are designed to vent coolant & then allow it back in during the cooling off stage.

Even the orignial radiator caps for the non-coolant-recovery-system cars (coolant recovery tanks came around 1973, IIRC) actually feature two valves: One pressure valve which opens up if the system pressure exceeds a certain value and a vacuum valve that allows air or coolant do be drawn back upon cooling down to ambient temperatures.

 

[DJAstral]

My 1st thoughts are that if this is a good operating & confirmed no overheating other than the after boil "Open" cooling system then you simply have too much coolant in the top of the radiator when it is cold.
Too much coolant during the after boil stage will cause what you are seeing.

There should be about 3/4"-1" from the rad cap opening for an open system when cold.

Too much water in the coolant mix will do this as well since water boils at a lower temp than the glycol coolant

If this continues to force coolant out then chances are you have pin hole head gasket leak which if the errant cylinder is in the "compression" stroke position will result in the same thing happening.
The forcing of the coolant will be 2 fold.
1) after boil
2) Compression stroke trying to force compressed air at a high temperature
3) Generally pin hole leaks are the hardest to find without removing the cylinder heads for a physical inspection.
Depending on the engine, if it has the original head gaskets then they are likely steel gaskets if i am not mistaken. (Anyone reading this please correct me if i am wrong on this point)

Some cooling system notes:

1) Open system rad caps are designed to vent air not coolant. This will happen in an overheat situation like extended idling in traffic...
2) Closed system caps are designed to vent coolant & then allow it back in during the cooling off stage.
3) If you add a overflow bottle then convert it to a closed system and be done with it. This will prevent the coolant from exiting.
4) You will know if you have a bad rad cap if you notice when the engine is stone cold that the rad hoses are collapsed.
this indicates the vent/pressure valve in the cap is not allowing air back into the system which in turn will cause a vacuum as the coolant cools off back to ambient temps

I hope this helps you out in your quest.

Please post your results

I’ve checked the coolant level & believe it to be correct as you suggest, thank you.
The brass seating where the rubber of the rad cap meets the radiator filler neck is a bit uneven on one side which may not making s proper seat though.... may post pics but am at work until late now in my other car.

I’ve added a diy coolant return bottle at the end of the overflow pipe as Ceebuddy kindly suggested. Not sure if you need to make the drilled cap I made airtight or breathable though.

If I ever need to get head gaskets changed.... is this a big job on a standard & base ‘67 383? I see the gaskets are reasonably priced but not sure what to allow for labour/time? I don’t want to go down this route unless I’m 100% convinced this is the cause of the problem, which I’m not at the moment - preferring to try the return bottle and new thermostat first before having to go to my local garage to strip the engine down.
Many thanks for your kind advice.

 

[ceebuddy]

I suggest not to use an airtight cap. You need to allow air to go in and out of the bottle to compensate for changes in coolant levels in the bottle as the system "works". If you don't like the idea of having an open bottle with the possibility of dirt falling into it and contaminating your coolant, at least drill a small breather hole into the lid of the bottle.

 

[DJAstral]

Thanks Ceebuddy, that’s what I’ve done

 

[mr. fix it]

Actually, the closed systems have vented overflow bottles either integral to the bottle or an addition hose mounted in the cap itself to act as a breather for expansion & contraction

 

[DJAstral]

Thanks for that, very reassuring.

 

[413]

Common for the threads to be eaten away right under the bolt head. If that happens they will break easily when trying to remove. So apply heat to the iron housing where the bolt threads are. Don’t heat the water neck, it won’t do anything. You need alot of heat so use an oxy acetelyne torch. A propane torch is not hot enough.

 

[Snotty]

It's normal. Installing something like what I have here is very helpful.

 

[TxDon]

Get rid of the lever rad cap and buy a good 16 lb VENTED cap plus a coolant recovery bottle. (NOT just an overflow) Run the hose from the rad to the bottle and fill the rad all the way to the top plus about an inch inside the bottle. No more puking, larger coolant capacity.

 

[Davea Lux]

I found that with most of these older Mopar's it was pretty normal for them to pee small amounts of coolant. Usually after they do it a few times they will stabilize the coolant level and stop doing territory marking. If you are worried about a head gasket leak, Auto Zone and most other major parts houses have a hydrocarbon tester to check for head gasket leaks and the tester is usually free to use.

Dave