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Discussion Starter #1
How much pressure do you guys have in your overflows 1. 5 hours after a drive. My tank seems to have enough pressure and if i let the car cool off overnight i have a couple ounces of coolant on ground at front of the engine. If i loosen cap and relieve pressure no leak next morning. Any thoughts?

Coolant is about 7 cm below cap or 2 cm above the bottom of the tank when cold next day.

Also when i relieve the pressure i can hear the tank gurggle.
 

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Good question: Coolant on the ground after a run can mean several things.

1) Technically, the tank is of the expansion variety versus a simple overflow. The tank "pressure cap" is a critical component for the cooling system to function correctly. Nominal cooling system pressure is typically below 0.9-1.0 bar. Both the temperature and pressure in the tank do rise slightly when the engine is first turned off. The first thing I would be testing is the cap itself as these are a very high failure rate component. As they fail, the release pressure drops to the point where they hold little to no pressure.

2) Coolant level too high. Do nothing if all else is correct and she will seek her own level.

3) Excessive air in the cooling system.

Noises when cracking the cap whilst still under pressure is normal.
 

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If you have coolant on the ground at the front of the engine I would check to see if you can see any dipping from the edge of the under tray. If you do then you most likely have a leak up front which could indicate that the water pump is on the way out, or it could be a loose clamp. Leakage from the over flow of the expansion tank should be near the back of the engine on the right sire where the overflow hose dumps it.


Based on my experience I would say you can expect some pressure in the expansion tank 1 1/2 hours after a drive but the coolant should have cooled down enough so that slowing opening the cap allows the pressure to be released without resulting in flash boiling. Agree, a little gurgle may he heard depending on how hot the coolant still is.
 

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Discussion Starter #5
Was talking with my shop superintendant and he thinks it might be vacume. As the coolant cools off it want to contract and pull vacume. Maybe i am mistaking pressure for vacume.

Thanks Dave he also said to check the cap. Any real way to test it though?

I definately might have air in the system because i did replace the thermostat gasket because it was leaking.

I will check wsm and see where i should bleed it.
 

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Snap On makes an adapter for both the cap and the tank to test pressures (to be used with their cooling system tester.) This is an essential shop tool, without a doubt. The bleeder is on the thermostat housing, although most of the time bleeding is a non-issue. I presumed and perhaps wrongfully so, that the coolant was leaking from the tank overflow. I would follow John's lead and pull the underbody panels and determine the precise leak source. I've seen far too many F355 with bad water pumps that leak under pressure. And then the fun really begins, as the engine is coming out...
 

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Was talking with my shop superintendant and he thinks it might be vacume. As the coolant cools off it want to contract and pull vacume. Maybe i am mistaking pressure for vacume.

Thanks Dave he also said to check the cap. Any real way to test it though?

I definately might have air in the system because i did replace the thermostat gasket because it was leaking.

I will check wsm and see where i should bleed it.

I doubt you have a vacuum in the coolant system. The cap is a 1 way valve which allows the system to suck air back into it should it vent under pressure. Also, a vacuum would not result in a coolant leak.
 

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Discussion Starter #8
Another good common sense answer thanks John kinda came to the same conclusion. I wonder why though it would not leak right away after i shut the car down versus somewhere between 2 and 10 hours. I know it does not leak before two hours cause no coolant but next morning coolant on floor.

Dave has a good point it could be the water pump and i gues i will have to take the friggin thing apart again. Took it apart three times in july because it was obvious it was the thermostat leaking so first time tightened thermostat. Leak stopped for a week, then came back. Second time saw the leak came back mind you leaked less so ordered two seals and put it back together so i could drive it until seal came in. Third time replaced seal.

Keep you all posted on the fourth.

Do water pumps usually start to leak just before failure? Have a 1400 mile trip. Coming up so want to minimize my risk.

Thanks all
 

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Discussion Starter #11
I changed all hoses but did not replace water pump but that was 5 years in november so its due again. All the hises are scuderia rampart but 1 hose came internally damaged. I just replaced it a month ago. It was not leaking but when i took it apart and found the leak at the thermostate i noticed one of the hoses had a,split and would have failed.

The water pump i inspected but did not rebuild it looked and felt good.

Does it nit seem odd to anyone that it only leaks after i shut it off and after 2 hours maybe even four hours.
 

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I changed all hoses but did not replace water pump but that was 5 years in november so its due again. All the hises are scuderia rampart but 1 hose came internally damaged. I just replaced it a month ago. It was not leaking but when i took it apart and found the leak at the thermostate i noticed one of the hoses had a,split and would have failed.

The water pump i inspected but did not rebuild it looked and felt good.

Does it nit seem odd to anyone that it only leaks after i shut it off and after 2 hours maybe even four hours.


First, I would check to see that the hose clamps are tight if you haven't already. Second, if you have a small leak the coolant may evaporate before it hits the ground or get blown away when driving. If it's from the front of the engine, as I said before, it will run down onto the front under tray and may pool there before sufficient coolant accumulates to drip off the edge onto the floor, thus the delay of a couple of hours before you notice coolant under the car.


You need to get the under tray off and inspect things.
 

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Discussion Starter #13
You bet I will check under tray first it's easier to get off than all the top stuff. Thanks
 

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Discussion Starter #14
Chechked the front of the engine with a flashlight after removing the undertray and could find no visible source probably because the leak is too small. This weekend i will remove the undertray again and this time let it idle up to temp then shut it off and see if i can see a drip. The undertray was wet along the edge slightly when removing it.

Will keep you posted. Thanks all who have helped.
 

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Discussion Starter #15
This was a leaky hose clamp from. The water pump to the main pipe. Slightly wet after engine cooled off.
I might add this clamp was tight just not tight enough.
 
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