What causes the coolant to overflow my overflow reservoir after idling for an extended period and after a drive? My 560SL always has a coolant puddle under the area where the overflow tube releases coolant.

When the car is cool, the coolant level is at the midway point in the reservoir. When the level is less than that the coolant light comes on when the car corners.

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1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)

Either there is air trapped in the system causing it to overheat, or there is a blown head gasket or block/head crack that is allowing pressure into the cooling system.

Are there bubbles in the reservoir?

Good luck,

It could also be that the overflow tank cap has gone bad or has debris in the gasket area. Try a new cap first. Also check all hose connections. You may have a loose hose or a cracked hose. Also check the fluid level sensor. It may have developed a leak and needs a new gasket where it installs in the tank.
If its non of these then I'm afraid that Larry is right.
If you think its a blown head gasket or a cracked block a local shop can do a die test on the overflow tank fluid and see if hydrocarbons ( exhaust gasses) are in the antifreeze. If so then you do have engine problems.
Check the tank fixtures first. I had this happen to my tank. It was a loose hose.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Almost certainly a bad cap unless you also have an overheating problem idling.

Replace the cap -- I had a coolant loss problem in the TE after highway running bad enough to cause the low coolant light to come on. New cap fixed it.

Also verify that the visco clutch is working, and that the aux fan comes on, although you should also be running rather warm to get coolant loss out of a good cap.

If a new cap doesn't fix it, look for a leaking hose or cracked tank.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Be it a cap leak or some other sort of leak issue, if your system isn't holding pressure sufficiently, you WILL notice the effect at the temp gauge.

If it is happening at idle or after shutting the engine off, I would point the fault to the reservoir cap...


...also make sure the cap is on SECURELY!!! I only had mine on 1/2 turn and dealt with the exact same issue for about a week before I realized the cap wasn't screwed on tight!

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

[QUOTE]Originally posted by psfred
[B]Almost certainly a bad cap unless you also have an overheating problem idling.
Also verify that the visco clutch is working, and that the aux fan comes on, although you should also be running rather warm to get coolant loss out of a good cap.

Hi Psfred,
I have a 260E, 1988 euro, I have the feeling that mine is engaging at higher temperature than it should.
Do you know how to check the visco clutch
Thanks in advance

The recommendations above are excellent, start simple and move to the bigger items. Radiator cap is cheap and can make a huge difference.

Something I wanted to add.....check your thermostat to insure it's working properly. If not it may be reading normal temps at the interior gauge when in reality your car may be overheating. Overheating can also be caused by a blocked radiator and or wrong coolant ratios or wrong coolant altogether.

Good luck.

__________________
Afshin

Current:
02 C32 AMG

Previous:
92 500E
84 190E 2.3 5 Spd

Cheap and cheerful visco clutch checks:

First, sound. Should roar when first started as the fan is dragging, sound will vanish in a few seconds as the fluid pumps out.

Second: on startup, you shoudn't be able to hold the fan stationary with some folded newspaper or a flyswatter. DO NOT HOLD THE FAN BY HAND! If you can easily prevent it rotating, the clutch is bad (no fluid in it).

Third: when engine gets up to 90C or so, the fan should engage, producing considerable air movement and noise. May be a turbinelike whine or just the sound of rushing air, but will be noticalble. If the engine is shut off at this temp, the fan MUST stop within one revolution when the the engine stops -- takes two people to check. If it spins more than that, it's bad, replace (or refill) the visco clutch.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!