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Originally Posted by roughinit2
Yesterday we took our 2007 FEH (4WD) up a fairly steep rough road (jeep trail) near Olathe, CO. It involved some steep inclines and probably gained ~1000 feet. Since the vehicle is essentially new (2 weeks old), I didn't want to go too far and we stopped halfway up and hopped on mountain bikes. We turned it off and got ready for our bike ride. Someone noticed some serious dripping under the car. Coolant was POURING out. This was not some minor drip, but a stream of coolant. I didn't think I hit anything and was concerned a hose fell off.
With the hood open, it was easy to tell it was the engine's coolant that was pouring out: the reservior was almost empty. When we released the cap, however, the tank filled halfway up and the dripping stopped! A quick inspection showed that all the hoses were intact. This was perplexing. There were no messages from the onboard computer.
We did get the vehicle back down and parked it over night. In the morning we filled the coolant back up to the line (50/50 per manual). In a few minutes what we put in was gone! So we added more. This time it stayed. Today we drove back to Colorado Springs and had no problems.
My questions to the group: has anyone seen this? Does anyone have a hypothesis for why it happened?
My guess is this: going slowly up the rocky road caused the engine to heat up. It was pretty steep and a lot of work to get up as far as we did. The increased heat and decreased ambient pressure (~7000 feet elev) causes pressure to build up in the coolent system. The pressure got so high, the coolant slipped out one of the hose seals. The coolant was doing its job (kept the engine cool) and thus the onboard computer didn't register it as a warning. When we opened the cap, the pressure equalized and backfilled the reservior. With things stable, the coolant system is now back in action.
Thanks for any thoughts. I need to decide whether to bring it in right away or if it fixed itself.
ryan
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Anti-freeze running onto the ground, coolant reservoir was empty, when the radiator cap was loosened slightly(??) coolant in radiator flowed into the reservoir.
It is not at all unusual for the coolant temperature to rise, sometimes dynamically so, when a HOT engine is shut down after a HARD pull wherein the coolant is already at or near the boiling point. Most systems have a thermostatic switch that keeps the radiator cooling fan running if the coolant temperature is elevated, even after the ignition key is removed. I can certainly understand why this might not be the case with the FEH/MMH, smallish 12 volt batttey and the DC-to-DC down converter would undoubtly be shut down.
As a rule if the coolant reached the point of boiling, or even only expanding dramatically due to the rise in altitude and high engine work load, the radiator's pressure relief/bypass cap would automatically open to allow the excess pressure/fluid to flow into the reservoir.
Once the reservoir overfills the reservoir's excess fill will get dumped onto the ground.
But your reservoir was empty....
The way it should work.
Heat exchangers, your radiator, are at their most efficient when the temperature differential between the outside air and the coolant is at its greatest. Water, "coolant", boils at 212F at sea level. So keep the coolant from boiling until its temperature reaches ~240F, take it below sea level by pressurizing the system.
As the coolant volume within the system, engine, radiator, etc, increases due to engine heat, the pressure will eventually increase enough to overcome the pressure bypass spring in the radiator cap and coolant will flow into the reservoir until the radiator coolant pressure is low enough.
This pressure bypassed radiator outflow will ALWAYS be into the bottom of the reservoir for reasons that will soon become obvious. The reservoir fill cap will be at the top and will typically be reasonably well sealed except for a fairly small "bleed" hole/orifice.
When the engine is shut down and now the coolant slowly cools to OAT a slight, very slight, vacuum will develop and that will result in syphoning, "pulling", the coolant from the reservoir back into the radiator. The inflow/outflow tube in the reservior must be at the bottom of the reservoir, immersed in any remaining coolant.
But your FEH maintained a vacuum, apparently a fairly srong vacuum, for an extended period with the reservoir practically empty.
How can that be.
Aha, a float valve within the reservoir.....
A float valve that closes the return path, syphon path, from the reservoir to the radiator, unless they is coolant in the reservoir to be "returned" to the radiator when the vacuum develops due to the coolant temperature declining.
So here's what happened to you.
The float valve in the coolant reservoir become stuck shut due to the lack of sufficient coolant. How many hest/cool cycles might it take for there to be so much vacuum in the radiator system that the float valve is forced so thoroughly closed that it STICKS closed.
Now you do an extraordinary, non-everyday thing, you tax the radiator beyond its normal, everyday, limits. Even more coolant is PUSHED out of the radiator. But where will it go, something has to give, right?
So much pressure is built up within the radiator and hoses downstream of the radiator that your coolant is FORCED out at the hose clamp interface area.
The next day the engine/radiator/coolant is at OAT and as a result of the STUCK float valve there is a HIGH vacuum within the engine/radiator coolant system. You add water to the reservoir, your "boat"(float) floats, the float valve opens as a result and the reservoir contents begin to be symphoned off into the radiator.
But what started this process..??
The coolant level may have been too low when you picked it up at the dealer and only the extraordinary circumstance resulted in a "failure". If you don't remember ever smelling anti-freeze during the previous two week I would guess that to be the case.
If you didn't smell anti-freeze at all during that timeframe then I would suggest returning your FEH to the dealer ASAP...NOW!
PS: The idea of a float valve in the reservoir is only a guess given your overall circumstance. I have never encountered one nor read of one but it seems to make some sense to have a float valve in the reservoir to prevent the system from "sucking" air once the coolant is exhausted. Let me know the outcome, please.