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Coolant cap under pressure always?

May 06, 2014, 12:39:28 am

Is this normal? Seems odd, at least different than my car, but so us the engine!

Engine totally cold, loosened coolant tank cap on the black metal cube reservoir tank and coolant spewed out until I tightened the cap back up.  I assumed it would not be under pressure when the engine us cold.  Not sure how the clear plastic tank works as a reservoir if constant pressure in the metal rank.

Should it do this?  If not, what are consequences and does that mean the cap is bad?

Mike

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Re: Coolant cap under pressure always?

Reply #1 – May 06, 2014, 02:02:03 am

Not under pressure, its just that the tank is full, opening the cap does allow some to escape. Would not worry.
Dave M

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Re: Coolant cap under pressure always?

Reply #2 – May 06, 2014, 06:53:42 am

Like Dave said, some will come out as it is full. If you have heat in there still some will come out under a bit of pressure.  If you are not leaking when the engine is running, then the cap is fine.  I changed mine a year ago just to be certain. 

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Reply #3 – May 06, 2014, 08:14:38 am

thanks, was about to leave, checking things and swoosh, out came fluid.  The plastic tank was about empty, that was strange.  So I added to it. Then I thought, why not add to the black metal tank.....now I know why, blew out coolant.  Cap hard to get off so I concluded that was pressure.

Thanks again...

mike

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Reply #4 – May 06, 2014, 08:22:24 am

Mike, got the same thing. Nothing in the plastic, black cube full.

I thoughts the plastic tank says cool level, hot level?

If John S, Dave M says let it be DW say do what they say

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Reply #5 – May 06, 2014, 08:46:12 am

I am totally with you.....if John and Dave says it ok, so be it.  No better source.  But I just cannot get my head around that white plastic tank going empty and no leak from it.  No drips on the concrete pad where park. 

So in this latest filling the plastic back to "cold", I did so and then decided I would take the metal reservoir cap off.  That was a mistake!

thanks all,

mike

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Reply #6 – May 06, 2014, 09:35:01 am

Mike, Not a mistake, good to know and the plastic tank getting low is not a panic either, I have to add about a quart every 4-5,000 miles.  Was worse before Mike @ MOT had me pour about 4 bottles of Barr's Leak Liquid in the metal tank, much less usage since.  Talk to Mike Rodgers at MOT.
Dave M

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Reply #7 – May 06, 2014, 11:10:07 am

You might have a small leak. First check the Aquahot and see if it is coming from one of the elbows. Then look at the radiator. The bottle should not go down below the cold mark much. I add maybe a cup or two every six moths to a year. I think it blows out the overflow when it gets hot and I am climbing. I filled it up too much that time and it did. So if you have nothing in the bottle, I would suspect a small leak. Bars leak is a good first thing to try.

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Reply #8 – May 06, 2014, 10:09:40 pm

I noticed that my plastic tank was low this winter after the cold weather, filled and drove and low again, then saw several hose connections leaking. Tightened all clamps and refilled and now all ok. seems like cold weather causes hose clamps to loosen up and leak.

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Reply #9 – May 06, 2014, 10:20:02 pm

Yes winter seems to cause that and my water pump started weeping one year so I had it changed out. 

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Reply #10 – May 06, 2014, 10:25:21 pm

Another couple of things to check if the level doesn't change in your plastic overflow - condition of radiator cap and overflow hose.  Not just the big engine ones but generator and AquaHot (if you have it).

We replaced our AH cap and hose 1 1/2 years ago and found the hose had cracking at one end.  Also found our generator radiator overflow hose had issues and replaced it at that time.  This year when we inspected the generator radiator cap we found its gasket had developed some cracks and have since replaced it.

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Reply #11 – May 07, 2014, 12:41:34 am

Fill the semi-clear tank with the proper (for your engine) 50-50 coolant to the applicable line when it gets low. The metal tank has a sight glass on most with a low coolant sensor installed just below that. It is connected to the ECU and if the coolant level goes down below the sensor, it will not let the engine start or will shut it down if running on many of our Foretravels. Lots of little places for coolant to seep out so good to check the tank when you stick the oil.

Pierce

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